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Re: dec drive issue - does not seem to be hardware caused - any similar experiences?

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  • johansea
    Gday ???? If its only one direction not playing, then its more than likely a burnt out Mosfet in the motor drive circuit. (Circuit diags can be found in the
    Message 1 of 14 , Oct 1, 2010
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      Gday ????

      If its only one direction not playing, then its more than likely a burnt out Mosfet in the motor drive circuit.
      (Circuit diags can be found in the files section of this group)
      I doubt very much that the firmware has anything to do with it.
      To check quickly,
      There are two 8pin chips on the motor board in the fork arm
      ( Q1 and Q2 ), and these make up a H-Bridge supply for the motor.
      Look very closely at these ( use a mag glass if reqd ) and see if there are any burn marks or "pimples" in the surface of one of the chips. If so, thats your problem.
      Many people have replaced these quite successfully,
      but you need access to someone who can competently work with surface mount components.

      Andrew Johansen Melbourne Australia

      --- In LX200GPS@yahoogroups.com, "kyuubi777" <kyuubi777@...> wrote:
      >
      > I just recently purchased a UHTC GPS lx200 8" off ebay. I've tested it several times with the wireless autostar ii handbox I bought for it. At first, whenever I'd try to align it it would stop moving the RA drive and report "motor failure" in the handbox. I noticed that the tube of the scope was moving further to the floor with every attempt. With that observation noted, after a few tries of this I skipped over auto align. I got myself into the mode where the handbox is reading out the angles of view and you can slew by using the four arrow keys. I slewed the RA drive clockwise and conterclockwise two full rotations to be sure. This was fine. Next I tried slewing downwards. No problem. I tried slewing upwards, and I got no response. Dead silence. Using the manual adjustment knob I was able to make the scope body move upwards. I am not one to generally be afraid of cracking open machines to check out the guts and make adjustments or repairs myself. So, I opened the Dec drive bay to check out the motor assembly and the controller board. Everything looked fine (the board looked brand new with no evidence of heat induced damage). My suspicions were confirmed that it was a newer model (new gps style + cheap foam packaging) because it had brass gears.
      >
      > Long story over. Is it possible that the error is in the programming (os 3.01 shows up on the controller when it starts) and that and upgrade will fix this issue? Or is this a hardware fault? I had a suspicion that a lead might have come unsoldered, but it didn't appear to be the case when I opened her up. Whatever the issue is, I think it has to do with the current not being able to be reversed. But this is my first scope, so I am asking for any ideas as to what I should try in order to fix this. (I really hate the idea of sending it to meade)
      >
      > on a side note, is there someplace that sells components to these scopes - I've read that meade stopped doing that but I didn't know if there was a third party vendor out there somewhere)
      >
      > All replies will be greatly appreciated. Thank you
      >
      > I posted this on the 4m forum but I figured I should ask around. Idk if some of you guys are more hands on with your scopes. I've seen builds where people have modded their scopes (spectacularly) with homemade devices- so I don't want to be flummoxed by a small error in my scope.
      >
    • kyuubi777
      Hello there Andrew, thank you for the response. I ve read about those but at first glance they looked fine. I ll check them out again later. I m not
      Message 2 of 14 , Oct 1, 2010
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        Hello there Andrew, thank you for the response. I've read about those but at first glance they looked fine. I'll check them out again later. I'm not experienced at messing with controller board circuitry... maybe I should just check out the files section so I don't look like a moron asking this, but are these Mosfet chips available for purchase through regular means and where might I find them?
        -
        Mark Sibole answered my post on the 4m forum, but to be honest your response was a lot more detailed than his and even if it isn't the chip (which I now highly suspect it is) your info at least gave me something I could use as a base to investigate. I kind of got the feeling he gives out basic troubleshooting answers on a reg basis. Sorry, I tend to ramble some times but I'm trying to express my gratitude for a competent response to my issue.

        Thank you.
        -Bryn R.
      • johansea
        Gday Bryn ... I suspect so, as lots of users have reported getting them, but i cant find any old posts with a supplier yet. Also, where are you ( generally )
        Message 3 of 14 , Oct 1, 2010
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          Gday Bryn

          --- In LX200GPS@yahoogroups.com, "kyuubi777" <kyuubi777@...> wrote:

          > are these Mosfet chips available for purchase through regular
          > means and where might I find them?

          I suspect so, as lots of users have reported getting them,
          but i cant find any old posts with a supplier yet.
          Also, where are you ( generally ) as that may affect what you can get.

          The same chips are used in the ETXs, LX90s and some of the other Meade scopes, and its mainly those type of scopes that burn out.
          The chips are marked 4936 and 4947 ( and may have an SI prefix )
          These are from Siliconix/Vishay

          If the chips look OK, then you need to look at the switching transistors Q7 and Q8. If you have access to a CRO, it wont take long to see where the signal is breaking down.

          Another option to pursue may be a member of this site, Ron Sampson, who does some board repairs.
          If its only the H-Bridge drive chips that are dead,
          he can probably fix that fairly easily.
          Just search the site for Sampson for details.

          Andrew Johansen Melbourne Australia
        • Ray Schmidt
          RS Components have the Si4936 and Farnell have Si4936 & Si4947. Ray ... [Non-text portions of this message have been removed]
          Message 4 of 14 , Oct 1, 2010
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            RS Components have the Si4936 and Farnell have Si4936 & Si4947.

            Ray


            On 2/10/2010 8:35 AM, johansea wrote:
            >
            > Gday Bryn
            >
            > --- In LX200GPS@yahoogroups.com <mailto:LX200GPS%40yahoogroups.com>,
            > "kyuubi777" <kyuubi777@...> wrote:
            >
            > > are these Mosfet chips available for purchase through regular
            > > means and where might I find them?
            >
            > I suspect so, as lots of users have reported getting them,
            > but i cant find any old posts with a supplier yet.
            > Also, where are you ( generally ) as that may affect what you can get.
            >
            > The same chips are used in the ETXs, LX90s and some of the other Meade
            > scopes, and its mainly those type of scopes that burn out.
            > The chips are marked 4936 and 4947 ( and may have an SI prefix )
            > These are from Siliconix/Vishay
            >
            > If the chips look OK, then you need to look at the switching
            > transistors Q7 and Q8. If you have access to a CRO, it wont take long
            > to see where the signal is breaking down.
            >
            > Another option to pursue may be a member of this site, Ron Sampson,
            > who does some board repairs.
            > If its only the H-Bridge drive chips that are dead,
            > he can probably fix that fairly easily.
            > Just search the site for Sampson for details.
            >
            > Andrew Johansen Melbourne Australia
            >
            >


            [Non-text portions of this message have been removed]
          • george
            I had the same problem on my LX200GS 10 , successfully replaced the MOSFET (which I took out of an old Meade motor box I found at a garage sale), ran it for a
            Message 5 of 14 , Oct 1, 2010
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              I had the same problem on my LX200GS 10", successfully replaced the MOSFET (which I took out of an old Meade motor box I found at a garage sale), ran it for a few days, and then experienced the same problem again. Turns out the resistor leading to the MOSFET was also fried, so I replaced that as well with a non-surface mount type and it has been working fine ever since.

              --- In LX200GPS@yahoogroups.com, "johansea" <johansea@...> wrote:
              >
              > Gday Bryn
              >
              > --- In LX200GPS@yahoogroups.com, "kyuubi777" <kyuubi777@> wrote:
              >
              > > are these Mosfet chips available for purchase through regular
              > > means and where might I find them?
              >
              > I suspect so, as lots of users have reported getting them,
              > but i cant find any old posts with a supplier yet.
              > Also, where are you ( generally ) as that may affect what you can get.
              >
              > The same chips are used in the ETXs, LX90s and some of the other Meade scopes, and its mainly those type of scopes that burn out.
              > The chips are marked 4936 and 4947 ( and may have an SI prefix )
              > These are from Siliconix/Vishay
              >
              > If the chips look OK, then you need to look at the switching transistors Q7 and Q8. If you have access to a CRO, it wont take long to see where the signal is breaking down.
              >
              > Another option to pursue may be a member of this site, Ron Sampson, who does some board repairs.
              > If its only the H-Bridge drive chips that are dead,
              > he can probably fix that fairly easily.
              > Just search the site for Sampson for details.
              >
              > Andrew Johansen Melbourne Australia
              >
            • kyuubi777
              ... Oh my god, thank you Andrew and Ray. I would have never found out about these mosfets and those sites would have evaded me indefinitely. I m unfortunately
              Message 6 of 14 , Oct 1, 2010
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                --- In LX200GPS@yahoogroups.com, Ray Schmidt <rayschmidt@...> wrote:
                >
                > RS Components have the Si4936 and Farnell have Si4936 & Si4947.
                >
                > Ray
                >
                >
                > On 2/10/2010 8:35 AM, johansea wrote:
                > >
                > > Gday Bryn
                > >
                > > --- In LX200GPS@yahoogroups.com <mailto:LX200GPS%40yahoogroups.com>,
                > > "kyuubi777" <kyuubi777@> wrote:
                > >
                > > > are these Mosfet chips available for purchase through regular
                > > > means and where might I find them?
                > >
                > > I suspect so, as lots of users have reported getting them,
                > > but i cant find any old posts with a supplier yet.
                > > Also, where are you ( generally ) as that may affect what you can get.
                > >
                > > The same chips are used in the ETXs, LX90s and some of the other Meade
                > > scopes, and its mainly those type of scopes that burn out.
                > > The chips are marked 4936 and 4947 ( and may have an SI prefix )
                > > These are from Siliconix/Vishay
                > >
                > > If the chips look OK, then you need to look at the switching
                > > transistors Q7 and Q8. If you have access to a CRO, it wont take long
                > > to see where the signal is breaking down.
                > >
                > > Another option to pursue may be a member of this site, Ron Sampson,
                > > who does some board repairs.
                > > If its only the H-Bridge drive chips that are dead,
                > > he can probably fix that fairly easily.
                > > Just search the site for Sampson for details.
                > >
                > > Andrew Johansen Melbourne Australia
                > >
                > >
                >
                >
                > [Non-text portions of this message have been removed]
                >

                Oh my god, thank you Andrew and Ray. I would have never found out about these mosfets and those sites would have evaded me indefinitely.

                I'm unfortunately in the states (Washington state) so that second site won't work for me. I'll go look over the schematics I downloaded from this group right now and try to make some sense of these mosfets and the direction in which the motor turns.

                That bit about the etx scopes was a godsend. If worst comes to worst I'll just purchase one for 100-200usd used, steal the chip out of it, and make a mount where the scope ota can be piggybacked on my lx200.

                And I'll check out this Ron Sampson as well. Chances are it'll be a few pence cheaper to send him the board than to use Dr. Clay's service. :)
              • John Mahony
                ... I hope you didn t use the dec manual knob with the scope powered up. You can damage the scope doing that. -John
                Message 7 of 14 , Oct 2, 2010
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                  ----- Original Message ----

                  > From: kyuubi777 <kyuubi777@...>
                  >
                  > I just recently purchased a UHTC GPS lx200 8" off ebay.
                  >... Next I tried slewing downwards. No problem. I tried slewing upwards, and
                  >I got no response. Dead
                  >
                  > silence. Using the manual adjustment knob I was able to make the scope body
                  >move upwards.
                  >

                  I hope you didn't use the dec manual knob with the scope powered up. You can
                  damage the scope doing that.

                  -John
                • kyuubi777
                  ... How is that so? The knob engages the two gears that drive the worm gear.. I did use it when the scope was on and the dec angles adjusted with the movement
                  Message 8 of 14 , Oct 2, 2010
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                    --- In LX200GPS@yahoogroups.com, John Mahony <jmmahony@...> wrote:
                    >
                    > ----- Original Message ----
                    >
                    > > From: kyuubi777 <kyuubi777@...>
                    > >
                    > > I just recently purchased a UHTC GPS lx200 8" off ebay.
                    > >... Next I tried slewing downwards. No problem. I tried slewing upwards, and
                    > >I got no response. Dead
                    > >
                    > > silence. Using the manual adjustment knob I was able to make the scope body
                    > >move upwards.
                    > >
                    >
                    > I hope you didn't use the dec manual knob with the scope powered up. You can
                    > damage the scope doing that.
                    >
                    > -John
                    >

                    How is that so? The knob engages the two gears that drive the worm gear.. I did use it when the scope was on and the dec angles adjusted with the movement accordingly... or did you think I was talking about the clutch adjustment knob? I didn't loosen the clutch and move the body around or anything. I thought it was there for making minute adjustments to the pitch of the scope for centering objects. If you can't use it when the scope is on, then what is it for?

                    -Bryn
                  • Ian Roberts
                    The CPU puts out two signals on two pins, Motor Dir A and Dir B and an Enable Motor logic. Between those outputs and the motor(s) are numerous components and
                    Message 9 of 14 , Oct 3, 2010
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                      The CPU puts out two signals on two pins, Motor Dir A and Dir B and an Enable Motor logic.
                      Between those outputs and the motor(s) are numerous components and pieces of wire with connectors.
                      Unless one of the 4 the high power pass transistors show obvious visual failure symptoms don't rush into assuming one or the other has failed. Rather follow the entire drive path with an oscilloscope, right up to the motor, which will test the motor itself, with the hand box instructing the scope to move.

                      If a component has failed, try and establish why. Could be balance or drag problems, or the previous owner fancied Meade's much advertised Arctic slew speed, which will probably increase dissipation on all components 

                      Good luck,
                      Ian.


                      --- On Sat, 10/2/10, kyuubi777 <kyuubi777@...> wrote:

                      From: kyuubi777 <kyuubi777@...>
                      Subject: [LX200GPS] Re: dec drive issue - does not seem to be hardware caused - any similar experiences?
                      To: LX200GPS@yahoogroups.com
                      Date: Saturday, October 2, 2010, 8:49 AM







                       













                      --- In LX200GPS@yahoogroups.com, Ray Schmidt <rayschmidt@...> wrote:

                      >

                      > RS Components have the Si4936 and Farnell have Si4936 & Si4947.

                      >

                      > Ray

                      >

                      >

                      > On 2/10/2010 8:35 AM, johansea wrote:

                      > >

                      > > Gday Bryn

                      > >

                      > > --- In LX200GPS@yahoogroups.com <mailto:LX200GPS%40yahoogroups.com>,

                      > > "kyuubi777" <kyuubi777@> wrote:

                      > >

                      > > > are these Mosfet chips available for purchase through regular

                      > > > means and where might I find them?

                      > >

                      > > I suspect so, as lots of users have reported getting them,

                      > > but i cant find any old posts with a supplier yet.

                      > > Also, where are you ( generally ) as that may affect what you can get.

                      > >

                      > > The same chips are used in the ETXs, LX90s and some of the other Meade

                      > > scopes, and its mainly those type of scopes that burn out.

                      > > The chips are marked 4936 and 4947 ( and may have an SI prefix )

                      > > These are from Siliconix/Vishay

                      > >

                      > > If the chips look OK, then you need to look at the switching

                      > > transistors Q7 and Q8. If you have access to a CRO, it wont take long

                      > > to see where the signal is breaking down.

                      > >

                      > > Another option to pursue may be a member of this site, Ron Sampson,

                      > > who does some board repairs.

                      > > If its only the H-Bridge drive chips that are dead,

                      > > he can probably fix that fairly easily.

                      > > Just search the site for Sampson for details.

                      > >

                      > > Andrew Johansen Melbourne Australia

                      > >

                      > >

                      >

                      >

                      > [Non-text portions of this message have been removed]

                      >



                      Oh my god, thank you Andrew and Ray. I would have never found out about these mosfets and those sites would have evaded me indefinitely.



                      I'm unfortunately in the states (Washington state) so that second site won't work for me. I'll go look over the schematics I downloaded from this group right now and try to make some sense of these mosfets and the direction in which the motor turns.



                      That bit about the etx scopes was a godsend. If worst comes to worst I'll just purchase one for 100-200usd used, steal the chip out of it, and make a mount where the scope ota can be piggybacked on my lx200.



                      And I'll check out this Ron Sampson as well. Chances are it'll be a few pence cheaper to send him the board than to use Dr. Clay's service. :)

























                      [Non-text portions of this message have been removed]
                    • johansea
                      Gday Bryn When actually tracking , the scope attempts to keep on target. If you use the DEC slomo control to manually move the axis, the firmware detects that
                      Message 10 of 14 , Oct 3, 2010
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                        Gday Bryn

                        When actually "tracking", the scope attempts to keep on target.
                        If you use the DEC slomo control to manually move the axis,
                        the firmware detects that it needs to reposition the axis,
                        and issues a slew command to do so ( no beg yr pardons )
                        If you have a firm grip on the slomo knob when this happens,
                        and have plastic transfer gears,
                        this can result in teeth stripping off the transfer gear.

                        Andrew Johansen Melbourne Australia

                        --- In LX200GPS@yahoogroups.com, "kyuubi777" <kyuubi777@...> wrote:
                        >
                        >
                        >
                        > --- In LX200GPS@yahoogroups.com, John Mahony <jmmahony@> wrote:
                        > >
                        > > ----- Original Message ----
                        > >
                        > > > From: kyuubi777 <kyuubi777@>
                        > > >
                        > > > I just recently purchased a UHTC GPS lx200 8" off ebay.
                        > > >... Next I tried slewing downwards. No problem. I tried slewing upwards, and
                        > > >I got no response. Dead
                        > > >
                        > > > silence. Using the manual adjustment knob I was able to make the scope body
                        > > >move upwards.
                        > > >
                        > >
                        > > I hope you didn't use the dec manual knob with the scope powered up. You can
                        > > damage the scope doing that.
                        > >
                        > > -John
                        > >
                        >
                        > How is that so? The knob engages the two gears that drive the worm gear.. I did use it when the scope was on and the dec angles adjusted with the movement accordingly... or did you think I was talking about the clutch adjustment knob? I didn't loosen the clutch and move the body around or anything. I thought it was there for making minute adjustments to the pitch of the scope for centering objects. If you can't use it when the scope is on, then what is it for?
                        >
                        > -Bryn
                        >
                      • kyuubi777
                        ... Ahh. Gotchya. So If I m doing the two star alignment it s fine then. I didn t have it tracking at the time so it should be ok. Whew, that scared me. :)
                        Message 11 of 14 , Oct 3, 2010
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                          --- In LX200GPS@yahoogroups.com, "johansea" <johansea@...> wrote:
                          >
                          > Gday Bryn
                          >
                          > When actually "tracking", the scope attempts to keep on target.
                          > If you use the DEC slomo control to manually move the axis,
                          > the firmware detects that it needs to reposition the axis,
                          > and issues a slew command to do so ( no beg yr pardons )
                          > If you have a firm grip on the slomo knob when this happens,
                          > and have plastic transfer gears,
                          > this can result in teeth stripping off the transfer gear.
                          >
                          > Andrew Johansen Melbourne Australia
                          >

                          Ahh. Gotchya. So If I'm doing the two star alignment it's fine then. I didn't have it tracking at the time so it should be ok. Whew, that scared me. :) Good to know, good to know.

                          -Bryn
                        • John Mahony
                          The computer regulates the motor position, so if you use the dec knob when the scope is powered up, you re fighting the electronics. The manual warns not to
                          Message 12 of 14 , Oct 3, 2010
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                            The computer regulates the motor position, so if you use the dec knob when the
                            scope is powered up, you're fighting the electronics. The manual warns not to
                            use this knob when the scope is powered up.

                            But note in the manual (in the last online version I downloaded, anyway), there
                            a serious error regarding this. There's a large picture of the scope on p6
                            showing the parts. The dec knob is labelled part# 16, and the following pages
                            cover the parts one at a time. For the dec knob it says "In order for this
                            control to operate properly, power must be off." That's correct, but there's a
                            sidebar tip next to it:
                            -----------------------------------------------------
                            Important Note:
                            After the telescope is aligned (see page 18), the Dec. slow motion control may
                            be used and the telescope will remain in alignment. However, if the R.A. slow
                            motion control is used after the telescope has been aligned, alignment will be
                            lost and the telescope will need to be realigned.
                            ----------------------------------------------------------
                            That first part is wrong.

                            -John





                            ----- Original Message ----
                            > From: kyuubi777 <kyuubi777@...>
                            >
                            > --- In LX200GPS@yahoogroups.com, John Mahony <jmmahony@...> wrote:
                            > >
                            > > ----- Original Message ----
                            > >
                            > > > From: kyuubi777 <kyuubi777@...>
                            > > >
                            > > > I just recently purchased a UHTC GPS lx200 8" off ebay.
                            > > >... Next I tried slewing downwards. No problem. I tried slewing
                            >upwards, and
                            >
                            > > >I got no response. Dead
                            > > >
                            > > > silence. Using the manual adjustment knob I was able to make the scope
                            >body
                            >
                            > > >move upwards.
                            > > >
                            > >
                            > > I hope you didn't use the dec manual knob with the scope powered up. You
                            >can
                            >
                            > > damage the scope doing that.
                            > >
                            > > -John
                            > >
                            >
                            > How is that so? The knob engages the two gears that drive the worm gear.. I
                            >did use it when the scope was on and the dec angles adjusted with the movement
                            >accordingly... or did you think I was talking about the clutch adjustment knob?
                            >I didn't loosen the clutch and move the body around or anything. I thought it
                            >was there for making minute adjustments to the pitch of the scope for centering
                            >objects. If you can't use it when the scope is on, then what is it for?
                            >
                            >
                            > -Bryn
                            >
                            >
                            >
                            >
                            > ------------------------------------
                            >
                            > Yahoo! Groups Links
                            >
                            >
                            >
                            >
                          • johansea
                            Gday John ... Not strictly true. ;-) You can do minor adjusts with the slomo knob, ( just dont hold it too tightly when trying ). Ie, As the slomo mechanism
                            Message 13 of 14 , Oct 3, 2010
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                              Gday John

                              --- In LX200GPS@yahoogroups.com, John Mahony <jmmahony@...> wrote:

                              > For the dec knob it says "In order for this
                              > control to operate properly, power must be off."
                              > That's correct, but there's a sidebar tip next to it:
                              > -----------------------------------------------------
                              > Important Note:
                              > After the telescope is aligned (see page 18),
                              > the Dec. slow motion control may
                              > be used and the telescope will remain in alignment.
                              > However, if the R.A. slow motion control is used
                              > after the telescope has been aligned, alignment will be
                              > lost and the telescope will need to be realigned.
                              > ----------------------------------------------------------
                              > That first part is wrong.

                              Not strictly true. ;-)
                              You can do "minor" adjusts with the slomo knob,
                              ( just dont hold it too tightly when trying ).
                              Ie, As the slomo mechanism is directly moving the motor
                              ( and hence encoder ), the scope still knows where it is.
                              I havent ever bothered to see how far you can move the slomo
                              ( when tracking ), before it annoys the scope :-)
                              but its not too far.

                              Andrew Johansen Melbourne Australia
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