XTM-12 AMP Speaker problem

Dodgydave

Joined Jun 22, 2012
10,050
From what I can gather, he gets 23V on the top of the 68ohms resistor ( nearest side to the pots) and zero on the other side, so the resistor has full supply across it, meaning the is a short circuit possibly across the zener or other silcon device.
 

Thread Starter

notnulled

Joined Jan 9, 2016
19
that's what I did

If I turn the board counter clockwise the potentiometers are on my left side. So i put ground where you pointed.
Right after powering ON if I measure I get 23 and it decreases very fast to 0
right side the same decreases very fast and remains at 0.1 Volt
The same thing for all of them, the right side is always 0.1 volt.
So every resistors shows voltage only after directly power on and starts decreasing very fast.
If I leave it on for 20 30 second and measure again then I get just 0 left side and 0.1 right side from the resistors.
 

R!f@@

Joined Apr 2, 2009
9,750
That is not possible.
All zener's dropping what they suppose to and the total supply across the resistors ...no way
OP's making a mistake
 

Thread Starter

notnulled

Joined Jan 9, 2016
19
If I measure the positive and the negative side of the resistors then I get 29.6 Volt for the first, 29.6 for second and 26 for the 3rd.
I have checked the 3 zeners and none of them are shorted.
 

R!f@@

Joined Apr 2, 2009
9,750
That is funny.
Wait a minute. I think I made a boo boo.
Need some time to check your boards.
In the mean time if you haven't attached resized image of the Power Amp board, can you do that.
Same way as you have attached the pictures of the preamp board (volume cntrl board).

Both side of this one
DSC_1848_zpsm4svbo2d.jpg

I believe the resistors are still hot.
 

R!f@@

Joined Apr 2, 2009
9,750
OK..I got a few minutes here.

Look at the picture.
When I say GND I am always meaning Reference GND point shown in picture..remember that.
Now if you have IC's out of the PCB, fine, no need to solder them but you need to put the whole thing together, i.e plug in all the cables and mount the sink as powering up will heat the power amp if it is not mounted on the sink.
Now power up. Music or not does not matter.
Just measure the DC voltage at point V1 and V2 marked with reference to GND and post them.

Note...it should be stable.
 

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Thread Starter

notnulled

Joined Jan 9, 2016
19
The video that I made (measuring the resistors), the IC's were soldered already.
Ok here are the results:
V1 is showing 32V
V2 is showing - 32V (reversed polarity)
 

Thread Starter

notnulled

Joined Jan 9, 2016
19
Ok here are the results:
V3= 5.0
V4= -2.3
V5= 2.1
V6= -1.1
V7= -2.3
V8= 2.1
V9= 0.1
V10= 2.1
V11= 0
V12= -0.1
V13= -2.3

Thank you for your time
 

R!f@@

Joined Apr 2, 2009
9,750
Only V3 is OK.

So next test..
See the PIC

You need to disconnect all the cables except Power cable from this (only) board. I believe you can unplug them.
Only power cable connected, power up and do the test in post #37.
Measure all of em from 1 to 13.
Remember. Only ±32V cable needs to be connected. If the others need to be disconnected.
 

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Thread Starter

notnulled

Joined Jan 9, 2016
19
Ok I did that:
And results are almost the same:
V1= 31.8
V2= -32
V3= 5.0
V4= -2.4
V5= 2.2
V6= -1.1
V7= -2.4
V8= 2.2
V9= 0
V10= 2.2
V11= 0
V12= -0.1
V13= -2.4
 
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