1980's Roland BN-100, Need schematic

[spsimmons]

I get a similar reading with the jumper wire lifted, about -260mV.

[Enzo]

OK, so the supply itself is bad, check the diode voltage and the transistor. Oh, and check that 330 ohm resistor feeding into the Q103 collector, R4, is it open?

[spsimmons]

Enzo, if by "across", you mean anode to cathode with the circuit energized, I get about -260mV in one direction and 0V in the other.

[spsimmons]

R3 and R4 check out as good.

[The Dude]

If you look, +VCC goes through R3 to D2 and C2. If D2 was replaced and R3 is good, C2 may be bad.

[Enzo]

Sorry, I missed your earlier post that D2 was bad.

Zener diode puts 16v on the base of the pass transistor, the +50 comes through the 330 ohm to the transistor collector. The diode sets the voltage which results in about 15v on the emitter, the output of the supply.

Scroll down to figure 3.
Transistor-Zener Diode Regulator Circuits

[spsimmons]

Unfortunately, I don't have the proper replacement for D2. Would it be worth swapping D1 and D2 as a test? Would that risk further damage to the circuit?

[The Dude]

I would just wait. You'll have to get one anyway. FYI it's a 16V - 1/2W zener diode. The part number doesn't matter a whole lot as long as it fits these specs.

[spsimmons]

Thanks guys. I've been putting together a list for a couple of other amps I've been working on. I think I have enough now to justify the shipping. I'll report back on this (and another thread) when I get it put back together.

[Enzo]

Do you have a 15v zener? A 1N4744? If so, stick it in there for now. It is only one volt off and will allow the work to continue. Put a proper one in later.

[spsimmons]

I got a 16V zener from a local repair shop. After installing it the amp works again.

I now get +13.9V on the 8 pin of the ICs and it remains constant. I get -14.5V on pin 4.

Should I consider this to be within tolerance, or should I try to get the + voltage up closer to 15V?

[Enzo]

Close enough, it is just a guitar amp.

[spsimmons]

That's funny, thanks. Thanks everyone! I'll bolt it back together.

[Sniknej]

The Dude wrote.....in 2010........Unless I missed it,...... have you tried plugging a sound source into the main input jack to verify if the power amp works? My BN-100 has the same no sound problem but I did this and found sound. Can I run the amp like this to use it Dude?

[g1]

You can use it like that as a power amp. Depending what you are doing, you will probably still need some kind of preamp or pedal for tone shaping, etc.