maybe try exchange the two big power supply caps with each other to see if the output voltage will shift to -V when startup
What a weird malfunction.
Looks like the 12V is unable to shift TR1 and open TR8.
Can be low current TR3, so check R6 also.
Or R9 to high? Or faulty c5?
And it last far too long, I suspect ELKOs, it tend to make such problems.
Looks like the 12V is unable to shift TR1 and open TR8.
Can be low current TR3, so check R6 also.
Or R9 to high? Or faulty c5?
And it last far too long, I suspect ELKOs, it tend to make such problems.
OK, I measured across the components.:
V1 - 0.69v
V2 - 0.7v and increasing
V3 - 0.7v and dropping
V4 - 0.12v and rising
V5 - 0.2v and dropping
R6 measured 17.97K out of circuit original value 18K
I also swapped the main smoothing caps and it seemed to go to minus but then quickly dropped to around 150MV and dropping
do you have good spare smoothing caps to replace both of them, like take it form another amp
V1-V5 voltages seems normal
V1-V5 voltages seems normal
Last edited:
That increasing and dropping is unlogical.
Can you check all grounds for possible potential between them?
Solder joints?
Can you check all grounds for possible potential between them?
Solder joints?
Last edited:
I connected the probe to ground of audio input and it jumped a bit but then went to 0.91V and rising slowly
Same thing. Had the leads in the wrong way round. Connecting the black probe to speaker out gave me -0.9V and slowly rising
It spikes very quickly and my meter cant keep up. But it looks like on startup when all capacitors are discharged it goes as high as 20v and then drops with 1 sec to 1v and slowly decreasing from 1v... I haven't left it on for more than 1 minute to see how far it drops.
It is quite normal transient in turn on state. That´s why we use protection circuits with turn on delay.