OK thanks, with resoldering the board (caps) I smell some electrolyt. So exchanged 4 x 470uF/16v Nichicon PF caps to Panasonic FC, from the defect channel the two were leaking. Testing...
An externally hosted image should be here but it was not working when we last tested it.
After testing I found out:
At >30V output voltage amp right channel got in protection.
At about 30V output it switches over to the highest rail voltage +/-75V.
The +/-50V and +/-25V gives no problems (load or without load) anymore.
railvoltages measured:
+21,8 / -19,5
+49V / -46V
+ 71V / -68V (after a few seconds it shutdown)
Adjustment can be done to +75V / -75V etc., but gives no solution.
There are two adjustment pots, one for the railvoltage and another near the opamps and amp driverboard see picture in the posting above this one.
Question...what does this potmeter do, bias or signal to railvoltage or..???
At >30V output voltage amp right channel got in protection.
At about 30V output it switches over to the highest rail voltage +/-75V.
The +/-50V and +/-25V gives no problems (load or without load) anymore.
railvoltages measured:
+21,8 / -19,5
+49V / -46V
+ 71V / -68V (after a few seconds it shutdown)
Adjustment can be done to +75V / -75V etc., but gives no solution.
There are two adjustment pots, one for the railvoltage and another near the opamps and amp driverboard see picture in the posting above this one.
Question...what does this potmeter do, bias or signal to railvoltage or..???
Last edited:
If they're trimmer pots, it's likely that they're for bias.
I've seen amps do something similar to what you described when a replacement transistor with a lower voltage rating was used. As the voltage exceeded the transistor's breakdown voltage, the amp would malfunction. It could be that you have a component that is breaking down due to the high voltage.
What happens if you drive the other channel (only) to cause the amp to switch to the high rails, does the defective channel still drive DC to the speakers?
I've seen amps do something similar to what you described when a replacement transistor with a lower voltage rating was used. As the voltage exceeded the transistor's breakdown voltage, the amp would malfunction. It could be that you have a component that is breaking down due to the high voltage.
What happens if you drive the other channel (only) to cause the amp to switch to the high rails, does the defective channel still drive DC to the speakers?
I think they are for bias also, but want to know for sure...
The railvoltage switching is following the input of the audiosignal for each separate channel.
When I drive only the R-channel inputsignal up, only the R-channel has the rail voltage go up to 25V-50V-75V.
There is no DC on both outputs, about 50mV noise.
To be continued....
The railvoltage switching is following the input of the audiosignal for each separate channel.
When I drive only the R-channel inputsignal up, only the R-channel has the rail voltage go up to 25V-50V-75V.
There is no DC on both outputs, about 50mV noise.
To be continued....
A picture from measurement:
blue signal: pin 1 of the TL594 erroramp input (pin 2 is the same but inversed)
red signal: speaker output without load
Normal voltage is 2,3V, then a few pulses 0V and 0V, and the TL594 shutdown. The speaker output signal still is normal and fades away when the railcaps are uncharged.
blue signal: pin 1 of the TL594 erroramp input (pin 2 is the same but inversed)
red signal: speaker output without load
Normal voltage is 2,3V, then a few pulses 0V and 0V, and the TL594 shutdown. The speaker output signal still is normal and fades away when the railcaps are uncharged.
An externally hosted image should be here but it was not working when we last tested it.
I think you're going to have to disable all protection circuits to see if the amp functions normally on the the defective channel. If it does, you'll have to determine which protection circuit is malfunctioning. If you see that there is a problem with the audio section of that channel, you'll troubleshoot that problem. Disabling the protection circuit is risky but you need to know what circuit is causing the problem.
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