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Old 20th January 2002, 10:21 AM   #21
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Join Date: Nov 2000

Happy to see, your first channel is running.

Q2 could be a problem. Test it by removing Q1 and Q2 from the board and do the matching trick again as I already explained. Check the Vgs.

If they are OK put them back in and try to see what is happening at the drain resistors.
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Old 20th January 2002, 04:59 PM   #22
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i removed/tested Q1 &2 and both are fine. i get 4 volts out of Q3 but only 3.27 across r114???????
everything in the chain checks out, what gives??

and q5 (which i have changed out 4 times!) shows only .17 volts?????

all the components around it check out

what gives?????
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Old 20th January 2002, 06:15 PM   #23
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Can you tell me what voltage is accross R40?

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Old 20th January 2002, 06:42 PM   #24
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i get 0 volts across r40. somehow i'm not turning on the input mosfets Q1&2. maybe my ground has shifted yielding a lower voltage from the inputs, but i don't know how to fix that.

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Old 20th January 2002, 08:41 PM   #25
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3.27 on R14 means current is going through Q1. If Q1 and Q2 are OK out of circuit, I would say both are conducting.
0 Volts accross R40 is no conduction for the output devices at all.
If all your wiring or PCB is OK(please triple check!!), I am afraid only one thing is left. Q6, Q7, and Q8 are blown. To make sure, take them out and measure them using the well known method.
If your at it, do the same for Q18,Q19,Q20.
In the case the FETS measure OK, there must be a wiring fault. But since you checked this more then once, I doubt that there is.

As a last option you could take the whole thing apart, removing all components from the PCB. Then check all traces with an ohm meter. Re-populate the board, testing each component before putting it in.

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Old 20th January 2002, 10:06 PM   #26
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i seem to be working backwards. i now get no current flow in the problem channel and full + rail voltage at the outputs. i'm confused cuz both channels are grounded the same but one works fine and the other is not??? are my channel references mixed up? before, when i got smaller than nominal voltages in the problem channel, my ground was from the -input to signal ground and to earth. but this isn't how it's supposed to be is it? my output mosfets are fine and the wiring checks out. i'm sooo confused!!

my grounding scheme is as follows:

from -in to earth ground

tranny/caps to chassis

left and right channel grounds to star point then connected to the tranny/cap ground point.

is that right?

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Old 20th January 2002, 10:27 PM   #27
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For now I do not see any real grounding issues.

If I were in your shoes, first thing I would do now is test one channel at the time.

If your "working" channel keeps on working when it is alone on the PS (i.e. other channel completly disconnected), I would disconnect this and put it aside. Then reconnect the "problem channel" and start doing your measurements.

This way you will not run the small risk of destroying the working channel when your testing/measuring.

I hope I'm not offending you when I say, take your time.
Copy the schematics (paper), take your measurements and write down the measured voltages near each node. Then compare.

If you cannot find the problem, simply redo the channel as I stated in my previous post.

I know this is a little bit of a pain, but sometimes starting over yields faster results then trying to debug a faulty circuit.

I will check tomorrow, to see your results.

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Old 23rd January 2002, 04:18 AM   #28
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thanks to all for the patience and time!!!!
i wanted to end this thread with good news, so here goes...

i have decided to reload the channel that is giving me problems. i found a bad 9610 and decided that since one channel is up, and the power supply is behaving well, that i'll start over.

i know that my posts regarding this project have been trying to most of the people on this forum, but, let me tell ya, i sure have learned alot about electrical circuits. at first, i barely understood what a transistor was, but now, i still barely know what a transistor is, but at least i'm a little more comfortable with diy projects.

i'm a geologist by trade but way back took, and barely passed, an ac circuit class and have lamented the fact that it was so difficult. if i only had had this forum back then

i'm sure that this project will work out and, again, thanks to all that took the time to help me with this,

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