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Another m-4 question???

bob06

bob06

Addicted Member
Started working on the second M-4 the one with the crooked transformer. I have power to both sides. Adjusted every thing to specs except for the DC offset. I have no relays kicking in. Replaced all the fuses and still nothing. It seems that this M-4 has been dropped. Would that knock out both relays? If not what might be my problem? :scratch2:
 
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bob06 said:
Why don't I have MV's at the boards? Any Idea's? :tears:
Click to expand...

OK. Where did you find the adjustment procedure? There is a mistake in the service manual. It tells you to measure DC offset at the wrong test points.
Here is a corrected procedure.
http://www.audiokarma.org/forums/showpost.php?p=1273240&postcount=3
Once you get the DC offset dialed in it my come out of protection.Otherwise you may have a problem with to much DC voltage at the speaker outs,a power supply issue or protect circuit problem.

When you made the + 65vdc adjustment did you happen to also check the -65vdc pins as well?
 
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avionic said:
OK. Where did you find the adjustment procedure? There is a mistake in the service manual. It tells you to measure DC offset at the wrong test points.
Here is a corrected procedure.
http://www.audiokarma.org/forums/showpost.php?p=1273240&postcount=3
Once you get the DC offset dialed in it my come out of protection.Otherwise you may have a problem with to much DC voltage at the speaker outs,a power supply issue or protect circuit problem.

When you made the + 65vdc adjustment did you happen to also check the -65vdc pins as well?
Click to expand...

Hi Dave Yes I have the right adjustment procedure for DC offset. But I did not check - 65vdc. I will check that.
 
bob06 said:
Why don't I have MV's at the boards? Any Idea's? :tears:
Click to expand...

+/- 80vdc power supply problem perhaps.Betting a cracked solder connection or a cracked PC board trace.

Look for problems around F602/603, D604, C613/614.
 
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Now the left channel meter light is on if that means anything. If all else fails theres always a BFH. :D
 
bob06 said:
When i check -65 the right channel reads 13.2v and the left is -00.8. :scratch2:
Click to expand...

Ooooh--disreguard last post.Check solder connections on the large filter caps,D601/602 and surrounding circuit board for hairline cracks.
 
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Possibly.....at least one of them. Measure the voltage on them.Should be roughly +65 and -65vdc on them.
 
avionic said:
Possibly.....at least one of them. Measure the voltage on them.Should be roughly +65 and -65vdc on them.
Click to expand...

There both at 63v. I'll keep looking. I took everything apart and still dont see any cracks in the board. I resoldered a few joints that look iffy but still nothing. I'm not good enough at this to be able to find and fix problems. So my lesson of the day, is to buy stuff that is all ready working.:D
 
Well your losing the -63 volts somewhere between the power supply caps and the pre-drive sheets--broken wire,cracked PC trace or solder connection -bad connector socket/pins-solder connection on said socket/pins..Should be fairly easy to follow the schematic and locate the open circuit. Use your meter to probe for voltage along the path. And check continuity/resistance between components and connections within the path (with unit de-energized of course).
 
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Thanks Dave I will check everything out tomorrow. Because now it's time for me to relax and have a few cocktails. :beer:
 
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