Boss DD-20 internal short circuit?

[Roberto]

I've a Boss DD-20 (attached the service manual) that does not start up.
When connected to a switching power supply, the power led blinks rapidly and nothing else lights up.
Correct voltage and correct polarity.

I've tried a second switching power supply with a lower current, and the blink is slower.
While blinking, the voltage at the inlet of the power supply ramps up and down, same applies for the other supplies.
This makes me think that there's some sort of short circuit inside the pedal.

Is it a common issue on those units?
Can someone guide me on what to check?

Thank you!
Regards

Roberto

[Helmholtz]

same applies for the other supplies.

Does this include batteries?

[Roberto]

I've not tried batteries, because I've not enought AA.

[Helmholtz]

I've not tried batteries, because I've not enought AA.

Please try fresh batteries first. Some SMPS have higher (dynamic) source impedance which may cause instability.

[Roberto]

With batteries it works. Well, I've not tried with audio, but it lights up, memory calls work, on/off works, etc...

[Roberto]

Please try fresh batteries first. Some SMPS have higher (dynamic) source impedance which may cause instability.

So the issue could be in the two power supplies I've used, rather than in the pedal itself?

[Helmholtz]

So the issue could be in the two power supplies I've used, rather than in the pedal itself?

Yes, could be a compatibility problem. Do you have a chance to try a linear 9V/200mA supply?

With batteries it works.

That's good.


I recommend to check the 100µ/16V e-caps C95/C83.

[Roberto]

Thanks Helmholtz, I will give it a try with a linear amplifier.
I have a linear power supply, probably 12V, but it has a big heat sink where I can install a 7809 instead of the 7812.
I will update you, thank you very much!

Roberto

[Roberto]

Well, I tried with a current limited power supply, and I've found that the 3.3V power supply gives out 4.0V.
The CPU is indeed hot, but the unit has switched on for a few minutes, then off with only the power led lightly on.

https://elektrotanya.com/boss_dd-20-...wnload.html#dl
I've bought some IC12s ( https://eu.mouser.com/datasheet/2/36..._e-1202901.pdf ) shown as regulators at bottom right of page 28, to see if it can solve the issue.
IC8 becomes warm when switched on.

I've found a similar issue here: https://www.diystompboxes.com/smffor...topic=109285.0
Is it common with those units? What can be done if even with 3.3V the unit won't start-up?

Thanks
Roberto