Ampeg BA210 Shut-off Issue

[Ba55playa]

Greetings all,

This is my first thread. Good to know this community exists.

So, I purchased an older Ampeg BA210 from an acquaintance. Initially, it worked okay, aside from an occasional electronic popping sound it made. I took it to a local amp guy here in Reno who gave the amp a once-over, changed a couple output transistors and attributed the popping sounds to "dirty" electrical power in my home, since the amp made no noises in his shop. I've used it sparingly at home, where it continues to make the popping sound, but now after about ten minutes of playing-time, the amp abruptly shuts-off. Red LED goes out; no sound output. It will not turn back on until five minutes, or so, later. Then, this shut-off happens more frequently.

On the surface, this seems to be a power supply issue but I was hoping I could get a point in the right direction. I do have some basic electrical knowledge but have never worked on amps. Any suggestions on where to start?

Many thanks in advance.

Andy

[Enzo]

The lights go out and it sits dead. When this happens, is the chassis real warm in back? it may be cycling into thermal protection.

Also, when it happens, ball up your fist and whack the top hard. Does it react to that? That exposes loose connections in side.

[The Dude]

Welcome to the place!

Schematic here:

http://music-electronics-forum.com/a...-schematic.pdf

[The Dude]

The power LED is supplied by the +16V supply, which is tapped from the +50V supply. So, the problem is likely there or before. When it dies, check both of those supplies and you may be able to narrow down the problem.

Edit: A good bet might be solder on those 330 ohm resistors for the +&-16V supplies (R66 & 68). They can run hot and crack loose sometimes.

[Ba55playa]

Alright. I got it to fail just now and gave it a good whack on top of the cabinet. It came back on immediately, but did cut out again repeatedly as I played for a couple more minutes. Looks like I will have to open her up and check for anything loose (I had done that already but it appears I missed the culprit.) Anyone think I could have more than one issue here? One issue causing the popping sound and another causing the shut-off?

[Enzo]

A tip from a veteran. Think about one problem at a time. get it running first, then worry about popping. You might find the popping is really just the same cutting out thing but just not going as far. In other words, you just might fix the popping by fixing the turn off thing.

Give it a good look over inside yes, but loose connection also includes things like loose solder joints. It isn't usually a wire coming off.

We can also poke at the board and parts on it with something insulated, like a wooden chopstick. Sometimes flexing parts exposes their connection failure.

[Ba55playa]

Hellos all,

I got the amp apart and pulled the "power" board from the chassis. No sign of anything out of the ordinary. All caps, resistors, junctions & diodes are intact and the board itself is sound. As a precaution, I hit all the soldier points with an iron. With respects to resistors R66 & R68, I looked for an hour for those dang things and I can't find them. I don't mean to be thick, but where the hell are they?!?

[Enzo]

Look at the schematic. They are 330 ohm 10 watt resistors.

Now look at your photo. See the six 10 watt resistors? The white rectangles? Four of them are 0.33 ohm, and two are 330 ohm. The two 330 ohm ones are your resistors in question.

So where are they? Right in front of your nose, as my mom would say.

[cjenrick]

better to replace all the pwr transistors at once, and the drivers, they are cheap anyway, why not?

may as well set the bias while you are in there, see the note on the schemo

maybe take a look at the power sw, bypass it if you are good with hi voltage, fuse holder can get crusty over time also, just pop the fuse out and take a look,

[Enzo]

Wondering why he should replace all the transistors? The amp is intermittent and mechanically sensitive. It works until it cuts out. That doesn;t sound like a bad transistor to me. He has exposed a loose connection and is looking to correct it.

[J M Fahey]

There´s a few connectors in the path, first from mains plug (which by the way is a connector itself) to transformr primary, fuse holder and power switch are also specilized connectors, and after that from transformr secondary to the power amp boars tself.
Any of them can be iffy/weak.
You may gently chopstick all of them, one by one, gently wiggle wires, until one thumps or clicks.

Or you may wait until power cuts off, and carefully measure whether mains voltage reaches transformr primary, or secondaries reach proper points on the PCB

Or some connector pin may have some cracked solder on the underside, although I guess you took car of that by now.

In a nutshell, what Enzo said above, only using more words

[MarkusBass]

better to replace all the pwr transistors at once, and the drivers, they are cheap anyway, why not?

This is extremely bad advice (as it was already mentioned). It would be wiser to send some money to e.g. Africa . It's clear that this is a mechanical problem. I was fixing this model of the amp (most probably with similar problems) and , as far as I remember (I do not make notes in such cases), it was something very basic like e.g. one of the 10W resistors not correctly soldered. If you already check this, I would take a look at connectors between the power supply and the power amp. Is anyone of them loose?

Mark

[52 Bill]

I will ask, when did the local guy change the two output transistors and give this a once over?

It doesn't look like any of the outputs have ever been changed.

[cjenrick]

sorry for the confusion, i meant when replacing output transistors in a old amp, it is standard practice to replace all of them since the good ones might be ready to fail, this adds "mean time between failures", and also saves taking the lid off, removing the circuit board, on a rework job.

what i usually do is pull the old transistors and check them for Ic/Ib, (gain), if they are all pretty well matched and show no leakage, i put them back, usually what i find is that the new transistors i install will have a different gain than the old ones which some people leave in, so in order to have a well balanced output stage, we try to match gain. when you order new transistors they usually come from the same lot, so i get the new transistors in, check them for gain just in case, and if they are matched pretty well, then we solder them in them along with the drivers. this results in many years of trouble free service and thus, my business increases do to word of mouth advertising. living in a small town means that bad news travels quick.

yes, this sounds like a mechanical issue, so get out the chop sticks, turn the amp on and do a drum solo on the pc board, and all the other components and wiring.

does this thing have regulators? that would be my next guess, maybe a 7815 going into overload protection mode,

maybe i should check the schematic, doh,

[MarkusBass]

sorry for the confusion, i meant when replacing output transistors in a old amp, it is standard practice to replace all of them

So you meant: when replacing at least one output transistor in an old amp, replace them all. The problem is that in this case no one is replacing output transistors. And if you look at the photo of the power amp board, you'll find that it looks almost like new.
So maybe your advice is good but not in this case . Details are important.

does this thing have regulators? that would be my next guess, maybe a 7815 going into overload protection mode,
maybe i should check the schematic, doh,

Yes, you should. It's because the amp has no 7815. It uses 330R/10W resistors and Zener diodes and this was clearly indicated by Enzo just few posts below (if you haven't checked the schematic).

To OP:
Since you said that:

Red LED goes out; no sound output.

It's clear that when it happens, +15V power supply rail is off. Most probably also the HV supply (for the power amp) is off.
You already got very good guidelines from Juan:

There´s a few connectors in the path, first from mains plug (which by the way is a connector itself) to transformer primary, fuse holder and power switch are also specialized connectors, and after that from transformer secondary to the power amp boars itself.

I can only add: additionally check soldering of the bridge rectifier. And don't forget to check the power cord too.

Mark