[sdiy] Tr-808 issue

Oakley Sound oakleysound at btinternet.com
Fri Sep 14 10:29:41 CEST 2018

I'm probably completely wrong, but the mains power wiring that feeds the 
power switch and then goes back to the PSU runs very close to some 
sensitive parts of the main PCB. The mains transformer itself can also 
couple into the main board once the lid is back on. Both of these could 
cause issues if there is switching noise on the mains power line. You 
can replicate this problem on clean mains by deliberately pressing a 
mains power switch really slowly and letting it arc.

It's really worth getting a scope in there though. DVMs are useful but 
they'll not show ripple, noise or oscillations.

If you think the PSU is delivering too much current so it's dropping out 
- check the voltages across R2 and R5. If either is over 0.6V then it is 
indeed going into current limit which is a bad thing. If they are under 
0.5V then all is probably well.



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