Re: [softrock40] SDR40 v6.1 TX/RX stopped working
- ----- Original Message -----From: ian mcphedranSent: Wednesday, August 01, 2007 9:51 AMSubject: Re: [softrock40] SDR40 v6.1 TX/RX stopped workingHi Tony, I have removed Q9 again. The 5V line is 4.32V, U4 is running hot, and the input current at 12.5V is 107mA.Q9 collector pad reads 3.63V, base pad reads 0V as of course does the emitter.Nothing else appears to be hot to my touch. I looked up the data sheet on the 78L05 which says it has an inbuilt thermal cut out and a voltage cut out too (If I remember correctly, yes my memory isn't so good these days) and is "practically indestrucible" !So where this current is going is a puzzle.Ian
Tony Parks <raparks@ctcisp. com> wrote:Hi Ian,If Q9 was pulled from the circuit does the 5v line still have a high current load? Also with Q9 pulled, what voltages to you read on Q9's base and collector pads?Do you have any external loads on the S12v output from the RXTXv6.1 board?73,Tony KB9YIGHi, I have replaced Q9 and no improvement resulted. It is running hot too and the '5V' rail is 4.1V.I'm still searching for the fault that's taking all that 110mA on the 5v line.Thanks for your interestIan GM3GTQ
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>U8 86 FAt 2:44 am ((PDT)) Thu Aug 2, 2007, in Digest 1865 Tony Parks wrote:
>U8 pin 7 reads 4.2V
>Sure looks like U8 is a problem.Perhaps, but output near the +ve rail could be:
a) inputs driven to output saturation
b) output pulled high externally (i.e. by a pins 7-8 short)
c) device failure which also emulates (a) or (b).
Both (b) and (c) can explain the U8 heating
but only (c) is that device's fault.
(There's no source for the heating current in case (a).)
Meanwhile, none of these explain why:
d) Q9 ran hot and
e) Q9 replacement ran hot
This doesn't seem to be in a related part of the circuit,
so was Ian just unlucky with two rogue 2N3904?
[BTW, my apologies for saying that Q9 collector pad voltage
3.63V with Q9 removed seemed too low. I recalculated as
3.64V - within the DVM last digit uncertainty.
(Vcc-Q8vbe) * R40/(R35+R40) + Q8vbe =
(4.32-0.65) * 22.1/(4.99+22.1) + 0.65 = 3.64V ]
>Let me know what components you need to restore your boardI continue to admire your outstanding support for this project;
>and I will send them right away at no cost.
"May Great Leader Tony live ten thousand years!"