Boss DD 2/3 only dry signal is outputted

[tegaki]

Hi, I have Boss DD-3 MIJ which is basically DD-2.

The problem is when pedal engaged only dry signal is heard without delay.

I checked this topic and have the following findings:

IC7 pin 31: have signal in but it is very distorted

R73 R2R: have output signal

IC2b NE570 pin 14-15: have signal but very quiet

IC2b NE570 pin 10: have signal but very quiet

Pin 13 (after E.Level): even level maxed out signal is still quiet


After investigating for a bit I thought maybe caps are problem and have found:

C34: on - side sound is extremely loud but on + side very quiet


Does it mean the problem is in capacitor? Can capacitor reduce volume of signal?

[antonis]

Hi & Welcome..

Can capacitor reduce volume of signal?

Only when it exhibits veeeeeeeeeeryyyyyyyyyyyy high ESR...
(drying of the electrolyte solution or bad electrical connection..)

[tegaki]

Ok here is the update:

I replaced C34 with 10uf/25V (it was leaked) but the pedal started outputting high frequency garbage.

I traced the problem to the input of the IC2a NE570 (5th pin) and checked caps nearby.

The problem was the signal gets scrambled after C18 electrolytic cap. I replaced it but the problem still persist.

I suspect C19 is broken (do mylar caps actually go bad?) but right now don't have cap with exact value. I assume I need to replace every electrolytic cap.

[ElectricDruid]

Welcome Tegaki!

I assume I need to replace every electrolytic cap.

Why? Assuming is a very bad practice. Much better to actually find out, and replace only things that are bad. If you take a random approach, you'll get random results...

It sounds like so far, you've been going through it systematically, replacing anything that seems to bad as you go. Keep doing that, and you'll get there. It's the right approach. Someimtes it can be quite dispiriting and long-winded, but it's really the only way.

[Slowpoke101]

Replace C18 (10uF/16V) and C31 (10uF16V. You may also find that C30 (47uF/6.3V) is unwell too but check it first.
Don't change caps at random or go shotgunning as this can cause more damage that you intend. Work through the problem logically.
It is quite normal for the DD2/3 to cook its electros when you consider just how hot this little bricks normally run. Also these caps are well past their manufacturer's estimated lifespan - even unused and in storage these caps probably would have dried out due to the seals failing.

[tegaki]

Thank you for responses,

I assumed because I saw video on youtube that some japanese guy repaired DD-3 with same symptoms (no effects applied, only dry signal) and he claimed that it is due to old/leaked electrolytic capacitors and to be sure he replaced all of them.

Replace C18 (10uF/16V) and C31 (10uF16V. You may also find that C30 (47uF/6.3V) is unwell too but check it first.

I already replaced C18 but it didn't solved the problem. What I find strange is that after C18 both C19 and R28 output very loud high frequency noise could it cause NE570 to break?

I will definitely check C30 and C31 but it is hard to decide when NE570 outputs garbage.

Btw is it okay to replace elec. caps with not same but close voltage rating (like 10uf/25V)? Would it change sound?

[antonis]

Btw is it okay to replace elec. caps with not same but close voltage rating (like 10uf/25V)?

More than OK..

Would it change sound?

Definitely not..

[tegaki]

Last update:

I had free time this weekend and finally was be able to fix the pedal!

Following advice from @Slowpoke101 I started from changing C31 capacitor and yes it was leaked! I just changed it and checked the output and delay sounds get back!!

All modes are working and what's interesting if I crank feedback all the way up and shorten delay time the massive self-oscillation occurs. Guess need to fiddle with trimpots but I like the way it is now.

Thank you all for the support!!!

[ElectricDruid]

Excellent work! Isn't it nice when you get a successful fix?!?