Ampeg BA210

[AustinC]

I am attempting to repair an Ampeg BA210 that is not powering on.

The current problem lies in the +16V/-16V rails as they are reading approximately +1.5V/-1.5V respectively. R68 and R66 are still reading close to +50v/-50V on the terminals connected to C19 and C38, which is causing a large drop across these resistors and are therefore giving off a LARGE amount of heat. I believe the problem to be in the zener diodes D11 and D12, but I would like an expert's opinion before replacing anything. How should I begin to diagnose the issue in the +16V/-16V rails?

[soundguruman]

Yank out the diodes and start testing. Replace w/ 5 watt size if you can.

I am attempting to repair an Ampeg BA210 that is not powering on.

The current problem lies in the +16V/-16V rails as they are reading approximately +1.5V/-1.5V respectively. R68 and R66 are still reading close to +50v/-50V on the terminals connected to C19 and C38, which is causing a large drop across these resistors and are therefore giving off a LARGE amount of heat. I believe the problem to be in the zener diodes D11 and D12, but I would like an expert's opinion before replacing anything. How should I begin to diagnose the issue in the +16V/-16V rails?

[52 Bill]

Welcome. While anything is possible, I don't see both Zener diodes failing at the same time very often. Test them with your meter to find out.

The two 0.047 caps would be suspect. As would any of the ICs. Try taking resistance readings along the 16 volts busses to ground to try and find a short.

[Enzo]

Seems REALLY unlikely BOTH zeners would fail to exactly the same low voltage together. However, if you look at what those 15v supplies power, I see a bunch of ICs, and if one of them shorts internally, it can shunt the two supplies together, and does exactly that. Feel of each op amp IC on the board, any getting hot? Don;t burn yourself.

[lowell]

Can you please repost these schematics AustinC? These links aren't working. I have one in that has a lot of hiss. Thanks in advance.

[mozwell]

i had a note somewhere on this that the power amp was a "marginal" design & prone to oscillation, i don't know if this is true.

I would add an output Zobel network on the power amp output, 8 ohm 5W and 100n 100V in series, between the amplifier output & 0V, this should be connected before the output inductor.

[AustinC]

I tried uploading the schematics again, and I couldn't get the links to work. I searched on Google and found that I got the schematics from you originally, Lowell.
Here's the thread they were originally posted in: http://music-electronics-forum.com/t20631/

[Enzo]

Mozwell, there already is a zobel, R28 and C17. Look inboard a little left of the output inductor on the schematic.


But it is certainly a good idea to check it, if that resistor is burnt open, then the stability is no longer assured.

[MarkusBass]

I have one in that has a lot of hiss.

Lowell,

It depends on what you mean by "lot of hiss". This amp has the STYLE switch, which consists of several (complex) filters. Depending on the switch position you can get more or less hiss. It is definitely much more than in other bass amps. Does the hiss depend on the switch position in your case? Does it depend on the GAIN settings? If you disconnect C11 in the power amp, do you still have hiss?

Mark

[mozwell]

Enzo, missed that totally....

Austin, are any of the ic's getting hot ?

[lowell]

Ha that's funny. Well I am at a different computer and don't have my files but I guess I need to get those transferred or uploaded somewhere that I can access regardless of what computer I'm using.

[lowell]

I have come to the conclusion that there is nothing wrong with this amp. I have another one here and it is not as hissy but just realized the tweeter isn't working so that explains why THIS one seems hissy.