1. 0.67V
4. 1.3V
2. 0.06V
5. 0.7V
3.
6.
I have a bit of difficulties to measure the last points because the OL-2 board is not connected and the amp turns itself off. I have put the diodes to the cable which goes to the OL-2 board. I had this similar behavior before. Do you know why it happens?
4. 1.3V
2. 0.06V
5. 0.7V
3.
6.
I have a bit of difficulties to measure the last points because the OL-2 board is not connected and the amp turns itself off. I have put the diodes to the cable which goes to the OL-2 board. I had this similar behavior before. Do you know why it happens?
It seems that all predrivers are ok and so are the 8 end stage transistors.
So
That’s very strange.
When you remove the 4 diodes, the voltages drop over the 100R resistors are becoming almost 85 Volt, true ?
But what is at that moment the voltage between the two WHs
Hans
So
you have disconnected the OL2 board, but the amp switches off ?
That’s very strange.
When you remove the 4 diodes, the voltages drop over the 100R resistors are becoming almost 85 Volt, true ?
But what is at that moment the voltage between the two WHs
Hans
But this is even more strange; I took the diodes off and powered the amp and there is only 1.3V over the resistors! 2V was between the WHs. Even with the OL-2 board connected. I was also able to do the biasing by turning the pot and voltage over the 100R resistors starts to increase.
Somehow without notice I have repaired the amp. I remember that in some point I scraped beween the TO-220 transistors soldering pads to make sure that there is no shorts. Maybe that was the reason, who knows.
But this leaves the sitation a bit open because no clear explanation...
Somehow without notice I have repaired the amp. I remember that in some point I scraped beween the TO-220 transistors soldering pads to make sure that there is no shorts. Maybe that was the reason, who knows.
But this leaves the sitation a bit open because no clear explanation...
It may be that a short called solder whisker was causing the trouble, a growing piece of solder going from one trace to another because of a large voltage difference.
So we solved a problem that hopefully doesn’t come back, altough it can also be a bad solder joint or a crack in a trace.
These are both very temp dependent so it’s a good idea to let the amp warm up over a longer period.
Hans
I just purchased this amp second hand. Obviously someone was in there before. I suspect something happened on this board that was repaired. I don't know why the LED was replaced, but I will remove that abomination and replace it with a correctly mounted LED. The resistor I need the value for has a crack so I will replace it. After cutting one end I measured 30 ohms but am not confident it is correct.
