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Laser 310 failure

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  • alesmukler
    Hi! I m have a problem with a Laser 310. It show at screen garbled characters. I thought that could it be a RAM issue then I remove all chips replacing them
    Message 1 of 25 , May 18, 2016

    Hi!

        I'm have a problem with a Laser 310. It show at screen garbled characters. I thought that could it be a RAM issue then I remove all chips replacing them with new ones with socket. The screen was the same. I check out ok the Z80 in a ZX Spectrum, the Static Ram by replacing them with same result. Also, I burned a EPROM 27c128 thinking about a ROM failure (I could read OK the ROM chip with a Eprom burner!). The 6847 works well because I check this in a TRS-80 COCO-2. 


    Could it be this behaviour due any of the two  custom chips fail? Perhaps any capacitor dry? Thanks for any clue!!!!


    Alejandro


  • Gerardus
    Classic symptom of a custom chip failure unfortunately. They are no longer available, so repair is very difficult.
    Message 2 of 25 , May 19, 2016

      Classic symptom of a custom chip failure unfortunately.

      They are no longer available, so repair is very difficult.





      On 19/05/2016 3:18 AM, alesmukler@... [vzemu] wrote:


      Hi!

          I'm have a problem with a Laser 310. It show at screen garbled characters. I thought that could it be a RAM issue then I remove all chips replacing them with new ones with socket. The screen was the same. I check out ok the Z80 in a ZX Spectrum, the Static Ram by replacing them with same result. Also, I burned a EPROM 27c128 thinking about a ROM failure (I could read OK the ROM chip with a Eprom burner!). The 6847 works well because I check this in a TRS-80 COCO-2. 


      Could it be this behaviour due any of the two  custom chips fail? Perhaps any capacitor dry? Thanks for any clue!!!!


      Alejandro





    • Dave Maunder
      ... Heh! I was just writing out a reply at the same time ! I ve personally never seen garbage like that before; it looks like just the character generator is
      Message 3 of 25 , May 19, 2016


        Classic symptom of a custom chip failure unfortunately.

        They are no longer available, so repair is very difficult.



        Heh!  I was just writing out a reply at the same time !

        I've personally never seen garbage like that before; it looks like just the character generator is stuffed - since it is attempting to produce VIDEO TECHNOLOGY / BASIC and READY.
        Every VZ that I have destroyed always ends up with random characters completely covering the screen.
        Deffo the GA003 and / or GA004 chip.





      • Leslie Milburn
        From: Dave Maunder dave.maunder@gmail.com [vzemu] To: vzemu@yahoogroups.com Sent: Thursday, May 19, 2016 10:04 PM Subject: Re: [vzemu] Laser 310 failure ...
        Message 4 of 25 , May 19, 2016
          From: Dave Maunder dave.maunder@... [vzemu]
          To: vzemu@yahoogroups.com
          Sent: Thursday, May 19, 2016 10:04 PM
          Subject: Re: [vzemu] Laser 310 failure

          >> Classic symptom of a custom chip failure unfortunately.
          >> They are no longer available, so repair is very difficult.



          > Heh! I was just writing out a reply at the same time !

          > I've personally never seen garbage like that before; it looks like just
          > the character generator is stuffed - since it is attempting to produce
          > VIDEO TECHNOLOGY / BASIC and READY.
          > Every VZ that I have destroyed always ends up with random characters
          > completely covering the screen.
          > Deffo the GA003 and / or GA004 chip.

          Except they are not random characters if you look closely. I have seen this
          happen twice before and both were due to a fault with the internal ribbon
          cables, but I cannot remember if this was on a VZ200 or VZ300.

          Noting that this is all from memory and I have not opened a VZ in well over
          10 years: there is a small ribbon cable going from the motherboard to the
          small daughter board - this causes garbage on the video display. The other
          is the ribbon cable going from the motherboard to the keyboard which is a
          memory mapped device as well.

          I would look there first and replace the ribbon cables before assuming a
          custom chip has gone south. In fact, unless you have been hit by a large
          voltage surge I find it hard to believe the chips are faulty.

          The reason why the ribbon cables cause this sort of problem is because a lot
          of the workings of the VZ are memory mapped and so the ribbon cables are
          carrying address line data across them, and if these break then the wrong
          data and/or addresses are being sent around the system. I found this out by
          accident well back in '91 ish when I was wiring in a new keyboard.

          So, do not give up hope yet.
          Leslie.
        • alesmukler
          I try the MC6847 (char generator) in a TRS-80 COCO-2 and works fine.Perhaps I need to try the COCO s MC6847 into the LASER. When I power up the machine the
          Message 5 of 25 , May 19, 2016
            I try the MC6847 (char generator) in a TRS-80 COCO-2 and works fine.Perhaps I need to try the COCO's' MC6847 into the LASER. When I power up the machine the message is always the same:

            DIDEM DEAHLMLMEI?
            @AAIA D , ?? ???

            ??
            @EADI?

            instead of:

            VIDEO TECHNOLOGY 
            BASIC V2.0

            READY





          • alesmukler
            Thats true! there aren t random chars! I took a VZ Emulator and compare both ASCII values of each character in the regular message vs my Laser message: VIDEO
            Message 6 of 25 , May 19, 2016
            Thats true! there aren't random chars! I took a VZ Emulator and compare both ASCII values of each character in the regular message vs my Laser message:


            VIDEO TECHNOLOGY 
            BASIC V2.0

            READY


            VS


            DIDEM DEAHLMLMEI?
            @AAIA D , ?? ???

            ??
            @EADI?


            V=86   D=68   
            I=73   I=73  
            D=68  D=68  
            E=69         E=69  
            O=79 M=77   
            T=84  D=86
            E=69  E=68 
            C=67  A=65 
            H=72  H=72
            N=78         L=76   
            O=79 M=77 
            L=76  L=76 
            O=79 M=77 
            G=71 E=69  
            Y=89         I=73 

            B=66       @=64  
            A=65        A=65  
            S=83        A=65  
            I=73        I =73  
            C=67       A=65  
             =32    =32  
            V=86       D=86  
            2=50         =32  
            .=46         ,=44 
            0=48         =32  


            Most of the characters differs in 1 or 2 ASC value. 


            Besides, I couln't see the ribbon cable that you say. Only the keyboard cable. Could it be the keyboard causing some kind of trouble? 

          • Gerardus
            The VZ300 doesn t have the ribbon cable. The symptom is a classic custom logic failure I m afraid. I probably still have a couple of custom chips here that
            Message 7 of 25 , May 19, 2016

              The VZ300 doesn't have the ribbon cable. The symptom is a classic custom logic failure I'm afraid.

              I probably still have a couple of custom chips here that display that exact fault.

              The VZ300 custom logic does nothing more than replicate the VZ200 circuitry within a 40 pin chip so if you have the patience and know-how you could replicate the circuitry and plug it into the 40 pin socket. I've done it but don't recommend it.

              Type this in:

              10 PRINT "I AM FLAKEY";

              20 GOTO 10

              RUN


              You will probably see that the program runs fine even if the display is a mess so from the computers point of view everything is ok, the issue is with the way it is making it to the screen.

              See the troubleshooting guide http://users.on.net/~clockmeister/VZ300/VZ300-tech-ref-man.pdf too.

              What you might try if you haven't already is to replace the video memory though that is unlikely to be the problem in my experience. If you like I will dig out my bits and pieces and replicate your exact fault (if I still have the dud custom chips) on the weekend.



              On 20/05/2016 12:54 AM, alesmukler@... [vzemu] wrote:


              Thats true! there aren't random chars! I took a VZ Emulator and compare both ASCII values of each character in the regular message vs my Laser message:


              VIDEO TECHNOLOGY 
              BASIC V2.0

              READY


              VS


              DIDEM DEAHLMLMEI?
              @AAIA D , ?? ???

              ??
              @EADI?


              V=86   D=68   
              I=73   I=73  
              D=68  D=68  
              E=69         E=69  
              O=79 M=77   
              T=84  D=86
              E=69  E=68 
              C=67  A=65 
              H=72  H=72
              N=78         L=76   
              O=79 M=77 
              L=76  L=76 
              O=79 M=77 
              G=71 E=69  
              Y=89         I=73 

              B=66       @=64  
              A=65        A=65  
              S=83        A=65  
              I=73        I =73  
              C=67       A=65  
               =32    =32  
              V=86       D=86  
              2=50         =32  
              .=46         ,=44 
              0=48         =32  


              Most of the characters differs in 1 or 2 ASC value. 


              Besides, I couln't see the ribbon cable that you say. Only the keyboard cable. Could it be the keyboard causing some kind of trouble? 




            • Leslie Milburn
              I cannot agree with others at this early stage of the investigation that this is a custom chip failure - it could well be the case. But given that the computer
              Message 8 of 25 , May 19, 2016
                
                I cannot agree with others at this early stage of the investigation that this is a custom chip failure - it could well be the case. But given that the computer is not fully functional right now, there is nothing to lose by poking around a bit and perhaps we will all learn something new.
                 
                First of all, if the startup message appears incorrectly the same way every time then we have a clue to look towards the data lines. If however the message changes each time, there may still be a pattern to the problem. What it does tell us is that the address lines appear to be fine because the message is positioned correctly each time, so my attention now turns to the data lines.
                 
                Considering this as a code breaking exercise - we know the clear text message and we have the output message. And so what you did below is the next step but I would have converted the values to binary not decimal.
                 
                A very quick check of a few of the values seem to indicate that D1 and D4 look to be incorrect, with D4 perhaps floating at times. If the message output does change then we might be able to identify floating versus wrong/inverted values. The key is to consider the complete output as a whole and not character by character.
                 
                Also, you should also check the good outputs, such as the characters I,D,E,A, H & L (from what I can see) against the keyboard matrix documented in the technical manual. Is there pattern there ?
                 
                 
                So, it could be a simple as dry joint issues, coca cola spilt inside the keyboard (I doubt it here), a broken cable, or chip failure - an oscilloscope would be handy to help with this. Sometimes light pressure on the motherboard can be a help because if there is a joint failure the output will change as you press and then revert when you release. But be careful, light pressure only.
                 
                 
                Of course, if you have another VZ300 (or a parts bin) you could always grab the GA chips from there any plug them in to rule them in or out up front. Worse case scenario, you can use the VZ200 circuit diagram and replace the need for the custom chips with the trusty VZ200 LS chips etc. It is only a few chips from memory.
                 
                 
                And Yes, the Keyboard cable is one of the ribbon cables I was talking about. It looks like the other one is VZ200 only. So, it depends upon how brave you are I guess if you want to go near that cable - your call, but I think you may be able to leave it for now. Does moving the keyboard and thus the cable change the output at all ?
                 
                If you had more equipment (like a spare VZ) then you could write a small program to check the keyboard and display a character to say OK or not OK. You could display an "A" for Ok, and an "E" for not ok because they appear to display correctly on screen each time.
                 
                You could also type the A-Z one by one and see what is displayed on screen and note the binary differences, that could help. Also (from memory) the VZ keyboard is driven via one of the custom chips in the 300, so this test would then be a test of that chip.
                 
                 
                Anyway, just some ideas before giving up and not a bad project if you have the time - as a reward you may well fix it.
                Leslie.
                 
                ----- Original Message -----
                Sent: Friday, May 20, 2016 2:54 AM
                Subject: Re: [vzemu] Laser 310 failure [1 Attachment]

                Thats true! there aren't random chars! I took a VZ Emulator and compare both ASCII values of each character in the regular message vs my Laser message:


                VIDEO TECHNOLOGY 
                BASIC V2.0

                READY


                VS


                DIDEM DEAHLMLMEI?
                @AAIA D , ?? ???

                ??
                @EADI?


                V=86   D=68   
                I=73   I=73  
                D=68  D=68  
                E=69         E=69  
                O=79 M=77   
                T=84  D=86
                E=69  E=68 
                C=67  A=65 
                H=72  H=72
                N=78         L=76   
                O=79 M=77 
                L=76  L=76 
                O=79 M=77 
                G=71 E=69  
                Y=89         I=73 

                B=66       @=64  
                A=65        A=65  
                S=83        A=65  
                I=73        I =73  
                C=67       A=65  
                 =32    =32  
                V=86       D=86  
                2=50         =32  
                .=46         ,=44 
                0=48         =32  


                Most of the characters differs in 1 or 2 ASC value. 


                Besides, I couln't see the ribbon cable that you say. Only the keyboard cable. Could it be the keyboard causing some kind of trouble? 

              • cdb4w
                I sent this reply via email but it has not come through yet, so I am posting it directly within Yahoo - sorry for he double post in advance (when Yahoo finally
                Message 9 of 25 , May 19, 2016
                  I sent this reply via email but it has not come through yet, so I am posting it directly within Yahoo - sorry for he double post in advance (when Yahoo finally gets around to it, that is).
                  ----------------------------------------------------------

                  I cannot agree with others at this early stage of the investigation that this is a custom chip failure - it could well be the case. But given that the computer is not fully functional right now, there is nothing to lose by poking around a bit and perhaps we will all learn something new.
                   
                  First of all, if the startup message appears incorrectly the same way every time then we have a clue to look towards the data lines. If however the message changes each time, there may still be a pattern to the problem. What it does tell us is that the address lines appear to be fine because the message is positioned correctly each time, so my attention now turns to the data lines.
                   
                  Considering this as a code breaking exercise - we know the clear text message and we have the output message. And so what you did below is the next step but I would have converted the values to binary not decimal.
                   
                  A very quick check of a few of the values seem to indicate that D1 and D4 look to be incorrect, with D4 perhaps floating at times. If the message output does change then we might be able to identify floating versus wrong/inverted values. The key is to consider the complete output as a whole and not character by character.
                   
                  Also, you should also check the good outputs, such as the characters I,D,E,A, H & L (from what I can see) against the keyboard matrix documented in the technical manual. Is there pattern there ?
                   
                   
                  So, it could be a simple as dry joint issues, coca cola spilt inside the keyboard (I doubt it here), a broken cable, or chip failure - an oscilloscope would be handy to help with this. Sometimes light pressure on the motherboard can be a help because if there is a joint failure the output will change as you press and then revert when you release. But be careful, light pressure only.
                   
                   
                  Of course, if you have another VZ300 (or a parts bin) you could always grab the GA chips from there any plug them in to rule them in or out up front. Worse case scenario, you can use the VZ200 circuit diagram and replace the need for the custom chips with the trusty VZ200 LS chips etc. It is only a few chips from memory.
                   
                   
                  And Yes, the Keyboard cable is one of the ribbon cables I was talking about. It looks like the other one is VZ200 only. So, it depends upon how brave you are I guess if you want to go near that cable - your call, but I think you may be able to leave it for now. Does moving the keyboard and thus the cable change the output at all ?
                   
                  If you had more equipment (like a spare VZ) then you could write a small program to check the keyboard and display a character to say OK or not OK. You could display an "A" for Ok, and an "E" for not ok because they appear to display correctly on screen each time.
                   
                  You could also type the A-Z one by one and see what is displayed on screen and note the binary differences, that could help. Also (from memory) the VZ keyboard is driven via one of the custom chips in the 300, so this test would then be a test of that chip.
                   
                   
                  Anyway, just some ideas before giving up and not a bad project if you have the time - as a reward you may well fix it.
                  Leslie.
                • alesmukler
                  I like this analysis; I ll follow the D1 and D4 lines; perhaps I find something to solve the problem. I forgot to say that when I touch any key after the
                  Message 10 of 25 , May 19, 2016
                  I like this analysis; I'll follow the D1 and D4 lines; perhaps I find something to solve the problem. I forgot to say that when I touch any key after the scrambled message, the computer hangs showing the screen that I'm attaching.

                  Thanks! 

                • Leslie Milburn
                  ... From: alesmukler@gmail.com [vzemu] To: vzemu@yahoogroups.com Sent: Friday, May 20, 2016 2:29 PM Subject: Re: [vzemu] Laser 310 failure [1 Attachment] ...
                  Message 11 of 25 , May 20, 2016
                    ----- Original Message -----
                    From: alesmukler@... [vzemu]
                    To: vzemu@yahoogroups.com
                    Sent: Friday, May 20, 2016 2:29 PM
                    Subject: Re: [vzemu] Laser 310 failure [1 Attachment]

                    > I forgot to say that when I touch any key after the scrambled message, the
                    > computer hangs showing the screen that I'm attaching.

                    Ok, with that additional information it could well be a problem with the
                    keyboard or its ribbon cable or I am afraid the custom chips. Its hard to
                    tell, because touching a key also triggers the interrupt routine and if
                    there is a data line problem then the VZ will misbehave - its a tough one.

                    What I did with my VZ keyboard was remove the ribbon cable and solder molex
                    (?) pins to the motherboard and a side connector on the back of the keyboard
                    itself, then I made a new ribbon connector which can be easily replaced next
                    time around (never needed to yet).

                    It sounds like you are confident with this sort of thing and if so, its an
                    easily accessible thing to change and you could then eliminate the keyboard
                    itself as the source of the problem. So if it were me I would cut the ribbon
                    cable and remove it completely so see if that is causing issues.

                    You can also leave the keyboard unplugged/disconnected while
                    troubleshooting the motherboard.

                    If you do have a parts bin it might be worth swapping the custom chips
                    sooner rather than later as it could save a lot of effort.
                    Leslie.
                  • Leslie Milburn
                    ... Actually thinking about it further, what if you just press say the shift key or the ctrl key (any non printable actually), does that cause the screen to
                    Message 12 of 25 , May 20, 2016
                      >> I forgot to say that when I touch any key after the scrambled message,
                      >> the
                      >> computer hangs showing the screen that I'm attaching.
                      >
                      > Ok, with that additional information it could well be a problem with the
                      > keyboard or its ribbon cable or I am afraid the custom chips. Its hard to
                      > tell, because touching a key also triggers the interrupt routine and if
                      > there is a data line problem then the VZ will misbehave - its a tough one.
                      >

                      Actually thinking about it further, what if you just press say the shift key
                      or the ctrl key (any non printable actually), does that cause the screen to
                      corrupt like your second image or not ?
                    • Gerardus
                      ... 74LS245/74LS174 failure within the custom chip. The 74LS245 section gets warm so is usually the common failure point, certainly that s the part I ve had to
                      Message 13 of 25 , May 20, 2016
                        On 20/05/2016 12:29 PM, alesmukler@... [vzemu] wrote:
                        >
                        >
                        > I like this analysis; I'll follow the D1 and D4 lines; perhaps I find
                        > something to solve the problem. I forgot to say that when I touch any
                        > key after the scrambled message, the computer hangs showing the screen
                        > that I'm attaching.
                        >
                        > Thanks!
                        >
                        >

                        74LS245/74LS174 failure within the custom chip.

                        The 74LS245 section gets warm so is usually the common failure point,
                        certainly that's the part I've had to replicate using 74 series logic.
                        Having come across this very problem on a number of occasions I made
                        board(s) that replicates two of the custom chips (GA003 and GA004). I
                        desolder the custom chip(s), solder in a socket and then plug in the
                        board to verify the failure.

                        See here: https://groups.yahoo.com/neo/groups/vzemu/photos/albums/1543299856

                        The VDP is in graphics mode in your shot. If you still hear the key beep
                        then it's not locked up, if not then the 74LS174 contained within the
                        custom logic has also locked up. If you load a small looping program
                        PRINT as I posted before you may still see the top third of that screen
                        changing as the program scrolls.

                        There was a chap selling some VZ300 custom logic on an Amiga forum quite
                        some time ago. He may still have them.
                        http://www.amibay.com/showthread.php?59864-Load-of-mixed-IC-s-part-3
                      • alesmukler
                        It hang up with any key pressed!
                        Message 14 of 25 , May 20, 2016
                          It hang up with any key pressed!
                        • alesmukler
                          Nice work!!! Have you any schematics of the custom chips? Thanks!
                          Message 15 of 25 , May 20, 2016
                            Nice work!!! Have you any schematics of the custom chips?

                            Thanks!
                          • Leslie Milburn
                            ... Refer to the VZ200 circuit diagram in the Technical Manual, its an easy compare with the VZ300 circuit to see what parts you need (not that many). But the
                            Message 16 of 25 , May 20, 2016
                              > Nice work!!! Have you any schematics of the custom chips?

                              Refer to the VZ200 circuit diagram in the Technical Manual, its an easy
                              compare with the VZ300 circuit to see what parts you need (not that many).

                              But the plug in replacement board Gerardus did is a great idea. If you look
                              at his last post he did provide a link to a photo gallery:
                              https://groups.yahoo.com/neo/groups/vzemu/photos/albums/1543299856 (in case
                              you missed it) - all that is missing is a board layout and circuit diagram
                              and away you go, but it's not too hard to work out.

                              Leslie.
                            • Gerardus
                              ... Note that this board does enough to enable functionality but doesn t do any of the PAL timing so the output is basically NTSC. The PAL timing circuitry
                              Message 17 of 25 , May 20, 2016
                                On 21/05/2016 9:47 AM, 'Leslie Milburn' vzemu@... [vzemu] wrote:
                                >> Nice work!!! Have you any schematics of the custom chips?
                                > Refer to the VZ200 circuit diagram in the Technical Manual, its an easy
                                > compare with the VZ300 circuit to see what parts you need (not that many).
                                >
                                > But the plug in replacement board Gerardus did is a great idea. If you look
                                > at his last post he did provide a link to a photo gallery:
                                > https://groups.yahoo.com/neo/groups/vzemu/photos/albums/1543299856 (in case
                                > you missed it) - all that is missing is a board layout and circuit diagram
                                > and away you go, but it's not too hard to work out.
                                >
                                >

                                Note that this board does enough to enable functionality but doesn't do
                                any of the PAL timing so the output is basically NTSC.
                                The PAL timing circuitry alone increases the chip count considerably
                                (LS390 x 2, LS393, LS123, LS86, LS21, LS02, LS00) so it's not quite as
                                simple if you want to replicate the custom logic in full.

                                I've been meaning to do a schematic but finding time is an issue at present.
                              • Gerardus
                                Just a quick followup: The chip at U14 contains the 74LS245, 74LS244, 74LS174, 74LS32 U13 74LS139 (and also shares the 74LS32 above IIRC) Some of the pins are
                                Message 18 of 25 , May 22, 2016
                                  Just a quick followup:

                                  The chip at U14 contains the 74LS245, 74LS244, 74LS174, 74LS32

                                  U13 74LS139 (and also shares the 74LS32 above IIRC)

                                  Some of the pins are for I/O between the custom logic. I also used some
                                  diode/resistor combinations for gates I didn't have at hand so I might
                                  have missed a chip. U13 also contains all the PAL timing IC's which I
                                  didn't bother with, hence that one is easy to replicate if you just opt
                                  for basic functionality. U13 is simple enough to do on a perfboard and
                                  using header pins can be trimmed to approx size of the 40 pin DIL chip
                                  and plugged into the socket fitted after removing the chip as I did to
                                  get one VZ300 going again.

                                  Anyway, I hope this is helpful.









                                  On 21/05/2016 10:18 AM, Gerardus swancity@... [vzemu] wrote:
                                  >
                                  > On 21/05/2016 9:47 AM, 'Leslie Milburn' vzemu@... [vzemu] wrote:
                                  >>> Nice work!!! Have you any schematics of the custom chips?
                                  >> Refer to the VZ200 circuit diagram in the Technical Manual, its an easy
                                  >> compare with the VZ300 circuit to see what parts you need (not that many).
                                  >>
                                  >> But the plug in replacement board Gerardus did is a great idea. If you look
                                  >> at his last post he did provide a link to a photo gallery:
                                  >> https://groups.yahoo.com/neo/groups/vzemu/photos/albums/1543299856 (in case
                                  >> you missed it) - all that is missing is a board layout and circuit diagram
                                  >> and away you go, but it's not too hard to work out.
                                  >>
                                  >>
                                  > Note that this board does enough to enable functionality but doesn't do
                                  > any of the PAL timing so the output is basically NTSC.
                                  > The PAL timing circuitry alone increases the chip count considerably
                                  > (LS390 x 2, LS393, LS123, LS86, LS21, LS02, LS00) so it's not quite as
                                  > simple if you want to replicate the custom logic in full.
                                  >
                                  > I've been meaning to do a schematic but finding time is an issue at present.
                                  >
                                  >
                                  >
                                  >
                                  > ------------------------------------
                                  > Posted by: Gerardus <swancity@...>
                                  > ------------------------------------
                                  >
                                  >
                                  > ------------------------------------
                                  >
                                  > Yahoo Groups Links
                                  >
                                  >
                                  >
                                  >
                                • alesmukler
                                  Thanks Gerardus for these tips. I m viewing the VZ200 schematics and I can see: 74LS245 74LS174 74LS123 74LS139 But I can t figure the 74LS244! Thanks!
                                  Message 19 of 25 , Jun 1, 2016
                                    Thanks Gerardus for these tips. I'm viewing the VZ200 schematics and I can see: 

                                    74LS245
                                    74LS174
                                    74LS123
                                    74LS139

                                    But I can't figure the 74LS244! 

                                    Thanks!
                                    Alejandro
                                  • Gerardus
                                    U12, keyboard buffer.
                                    Message 20 of 25 , Jun 1, 2016
                                      U12, keyboard buffer.

                                      On 2/06/2016 1:53 AM, alesmukler@... [vzemu] wrote:


                                      Thanks Gerardus for these tips. I'm viewing the VZ200 schematics and I can see: 

                                      74LS245
                                      74LS174
                                      74LS123
                                      74LS139

                                      But I can't figure the 74LS244! 

                                      Thanks!
                                      Alejandro



                                    • alesmukler
                                      Hi Gerardus, I m back again with this machine trying to bring again to life. Have you the schematic of the PCB that replace the GA00X chips? Thanks!
                                      Message 21 of 25 , Jun 16, 2017
                                        Hi Gerardus, I'm back again with this machine trying to bring again to life. Have you the schematic of the PCB that replace the GA00X chips?


                                        Thanks!
                                      • Dave Maunder
                                        His site for this: http://users.on.net/~clockmeister/Junkbox_VZ/ And became famous on hackaday:
                                        Message 22 of 25 , Jun 16, 2017
                                          His site for this:



                                          Sent from my VZ gizmoid.
                                          On 17 Jun 2017, at 6:19 am, alesmukler@... [vzemu] <vzemu@yahoogroups.com> wrote:

                                          Hi Gerardus, I'm back again with this machine trying to bring again to life. Have you the schematic of the PCB that replace the GA00X chips?


                                          Thanks!
                                        • Gerardus
                                          Hi and thanks for the intro Dave, I had my 15 minutes of fame and my life is now complete :-) I forget, have you determined which chip has failed? What are the
                                          Message 23 of 25 , Jun 16, 2017
                                            Hi and thanks for the intro Dave, I had my 15 minutes of fame and my
                                            life is now complete :-)

                                            I forget, have you determined which chip has failed? What are the
                                            symptoms and are you sure it's a custom chip that has failed and not ROM
                                            or RAM?
                                            I'm don't have a schematic perse but I have been messing with a VZ300
                                            just lately (replaced 8x4116 DRAM with two 4464 DRAMs, German SHRG hack
                                            and some other misc stuff) and might be able to help using my notes.


                                            On 17/06/2017 4:19 AM, alesmukler@... [vzemu] wrote:
                                            > Hi Gerardus, I'm back again with this machine trying to bring again to life. Have you the schematic of the PCB that replace the GA00X chips?
                                            >
                                            >
                                            >
                                            > Thanks!
                                          • alesmukler
                                            Gerardus, My Laser 310 display several characters on the startup screen. Later, it get freeze when I type a key. There are some pictures that I
                                            Message 24 of 25 , Jul 28, 2017
                                              Gerardus,
                                                              My Laser 310 display several characters on the startup screen. Later, it get freeze when I type a key. There are some pictures that I uploaded: 


                                              and 


                                              The RAM chips are ok. I put them into sockets. The Z80 and the video chip (I the micro into a ZX Spectrum the and video chip with a Radio Shack Coco 2) are working. 

                                              So I believe that the Custom chips were failing


                                              Thanks!
                                            • Gerardus
                                              ... Both photos are a classic symptom of a failed GA004 as it contains the 74LS174, 74LS244 and 74LS245 (see VZ200 schematic for details). In fact that chip
                                              Message 25 of 25 , Jul 29, 2017
                                                On 29/07/2017 11:59 AM, alesmukler@... [vzemu] wrote:
                                                > Gerardus, My Laser 310 display several characters on the startup screen. Later, it get freeze when I type a key. There are some pictures that I uploaded:
                                                >
                                                >
                                                > https://groups.yahoo.com/neo/groups/vzemu/photos/photostream/lightbox/1610353572?orderBy=mtime&sortOrder=desc&photoFilter=ALL#zax/1610353572 https://groups.yahoo.com/neo/groups/vzemu/photos/photostream/lightbox/1610353572?orderBy=mtime&sortOrder=desc&photoFilter=ALL#zax/1610353572
                                                >
                                                >
                                                >
                                                > and
                                                >
                                                >
                                                > https://groups.yahoo.com/neo/groups/vzemu/photos/photostream/lightbox/1345421639#zax/1345421639 https://groups.yahoo.com/neo/groups/vzemu/photos/photostream/lightbox/1345421639#zax/1345421639
                                                >
                                                >

                                                Both photos are a classic symptom of a failed GA004 as it contains the
                                                74LS174, 74LS244 and 74LS245 (see VZ200 schematic for details). In fact
                                                that chip pretty much always fails with those exact same symptoms.



                                                >
                                                > The RAM chips are ok. I put them into sockets. The Z80 and the video chip (I the micro into a ZX Spectrum the and video chip with a Radio Shack Coco 2) are working.
                                                >
                                                >
                                                > So I believe that the Custom chips were failing
                                                >
                                                >
                                                >
                                                >
                                                > Thanks!
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