XTM-12 AMP Speaker problem

R!f@@

Joined Apr 2, 2009
9,750
Then this is getting weird.
With the cables removed there is nothing to load the supply except the zener diodes which you tested OK.
This test can be performed in two ways.
One is to test the two diodes circled in the circuit for short circuit. Which you said you did.

Second is a bit tricky. Mess up and you will destroy the IC's.

So first step one.
As in post #39 you need to remove all the cables except Power cable. This method isolates the board from every other PCB. Except power cable which supplies only the power to this PCB.

Step two is to desolder all the 3 IC's again. We need to remove them for as the 3rd step is the dangerous one.
Remove IC's and do the test in post#37. If V4 and V5 does not change proceed to step 3. If IC's are faulty, removing them will provide V4 and V5 values. They should come close to ±15V or so. If V4 and V5 rises you have a faulty OPAMP. Not the 16 pin one. 16pin one is OK since you are getting 5V at V3. But 16 pin should be desoldered also

Step three.
This step is if V4 & V5 is still close to 0V.
Remember this test needs the IC's removed and the board isolated from others.
Then remove the two diodes I circled. And power up to see if V4 & V5 is at ±31V.
If V4 & V5 is same as V1 & V2 then you have a faulty Zener diode.

Note. Do not connect the rest of the circuit or solder the IC's with zener diodes desoldered. Do this and another component might blow
 

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