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Old 14th May 2013, 12:46 AM   #81
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Ok, rare strait forward question: what should the voltage be coming out of Q1? I did a quick comparison of the two boards, and was able to trace back a difference between the two to Q1, with the working board having just under 20v leaving, and the other zero. I replaced q1 on the non working board, and now get just under23v leaving it, which leads to a consistent 3v difference from then on between the two boards. Can someone tell me which is correct? Thanks as always.
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Old 14th May 2013, 01:26 AM   #82
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Per Wayne's voltage diagram, it should be around 20.2v.
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File Type: pdf Pearl II voltages.pdf (67.0 KB, 41 views)
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Old 14th May 2013, 02:11 AM   #83
6L6 is offline 6L6  United States
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Quote:
Originally Posted by jhsjhs99 View Post
I replaced q1 on the non working board, and now get just under23v leaving it, which leads to a consistent 3v difference from then on between the two boards.
About 20V there is correct.

There are 13 voltages on the schematic - are all thirteen of them 3 volts higher? Check the 0 volt points first, the top of R13 and the top of R17
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Old 18th May 2013, 06:35 PM   #84
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Hi Folks,

It took a while to get the two boards stabilized, but now that seems to be the case, so I checked voltage. What follows is Wayne/pcb #1/ pcb#2
Input R9: 20.2/22.6/19.7 (two boards noticably different, can't see why)
Output R9: 10.1/7.2/7.6 (two boards similar, but noticeably different from Wayne)
Output Q3: 9.4/7.1/7.5 (ditto)
Input R24: .01-.04/.06/.06
Drop across R6: 1.5/1.5/1.5
Output R6: 21/20.4/20.3
Input R13: 0/0/0
Input Q10: -23/-22.5/-22.6
Input R27: -22.3/-21.9/-22
Output Q11: -23/-22.5/-22.6
Input R17: 0/0/0

I am getting +- 23.6 at the output of the resistors at the regulators.

So, the area that is most different is around Q1 and Q3, and inconsistently so. PCB #1 has voltage two high going into Q1, but they both have voltage too low leaving.

Any thoughts? Thanks again for your time. If there is anything I can do to clarify, let me know.
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Old 18th May 2013, 08:19 PM   #85
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Quote:
Originally Posted by jhsjhs99 View Post
Hi Folks,


Input R9: 20.2/22.6/19.7 (two boards noticably different, can't see why)
Is R5 correct on the board with 22.6?

Quote:
Originally Posted by jhsjhs99 View Post
Output R9: 10.1/7.2/7.6 (two boards similar, but noticeably different from Wayne)
My readings were similar to yours until I bumped up R21-R24 to 20 ohms, on advice from Salas.
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Old 19th May 2013, 12:08 AM   #86
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I checked r5, it is fine, but I do think that is where the problem is. There is minimal voltage drop across it on the problem pcb. Possibly the solder for q1? It looks ok, but barring other ideas I may resolder q1.
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Old 19th May 2013, 12:40 AM   #87
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Maybe Q1 is no good. Any spare ZTX450s?
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Old 19th May 2013, 12:55 AM   #88
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Just tried! No change. Odd.
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Old 19th May 2013, 06:14 PM   #89
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Ok, progress--tested around r7, something was obviously wrong (got same voltage both sides), replaced it, and that sorted the first voltage anomaly noted above--now I am getting around 19.6 v out of q1 on both boards. I will try 20 ohm resistors as suggested when I get them (hello, mouser).

One odd thing--I tested the r7 I pulled from the board after replacing it, and it tested out ok. The problem must have been the solder, I guess? I don't know.
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Old 19th May 2013, 11:31 PM   #90
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Big ground plane on the Pearl 2 - a little extra solder juice is needed, especially on the ground side of the big caps.
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