Help! My beloved solid state amplifier is having issues

[jay4321]

Hi, I own an old Yamaha 212-G100 solid state amp which I love dearly. I purchased it used and for a solid state I think it's amazing, very much in the vein of a Roland Jazz. It's from the early 80s or so.

When playing the soudn cuts out or suddenly goes weak. It's old and past it's prime, but I was hoping someone could tell me what kind of problem this sounds like, and if they are generally worthwhile to repair. I can replace this for about $150 as there is a used one at the local GC. Any knowledgable input greatly appreciated.

 

[jay4321]

Also, side question: If I buy an amp head can I run it through the speakers on this thing (if I go that route)?

Obviously I don't know much about the inner working of amps.

 

[Super Turbo Deluxe Custom]

Yes.  Just impedance match the ohm values of the head and speakers and be sure that both are similarly rated in watts.

 

[mayfly]

going weak on you on a solid (i.e. PCB) amp is likely a solder joint that became weak over time or a pot gone bad.

Does it have an effects loop or other channels?  Try those out to see if you can isolate the problem.  Try cleaning the pots - that might help identify a bad one (if that's what the probelm is). 

Once that's done, get ready to take it out.  It's gonna be brutal to get the PCB to where you can see the underside solder connections - but you did say you love this amp.

Post some pics when you are ready and we'll help out.

 

[Patrick from Davis]

I have to say, I have significantly less knowledge with solid state amps.  I would have to agree with Mayfly's assessment of the situation.  I would go to Radioshack and pick up a can of electronics cleaner.  This stuff is great and can fix a lot of problems.  For 10-20 bucks it might fix it, I wouldn't get my hopes up, but a bad input jack connection can ruin a day.  It sounds like something heats up and a connection in the signal path is lost.  That could mean that you have to know what part it is, or that you need to re flow the solder joints.  Mayfly's suggestion about effects loops and power amp ins and out is another great one.  It will help you narrow where the problem is.  If you plug into the effects loop return (this tends to be right before the power amp, and it works fine, then it should be in the preamp section.  You see how you can narrow things down.  Have you looked for a schematic?  Is there one at the back of the manual?  This would also help to narrow down the search for "areas" of trouble.  Good luck.
Patrick

 

[jay4321]

I took it to a new shop in the area, as part of a package deal with a setup for one of my guitars. I took a cursory look and didn't want to take it on.

Since you guys went through the trouble of giving some help I'm not going to use (thank you by the way), might as well tell you about the great find this amp has been. It's an early '80s Yamaha G100-212 III. 100w. The amp is just superb clean, very "punchy" and works well with pedals. The reverb and distortion are terrible (I don't even have a reverb tank in it anymore), and it's incredibly heavy to lug around. The models in this line can be had very cheap and aren't terribly hard to come by. Anyone looking for something in the vein of a Roland JC should take a look at one of the G50s or G100s in this line. This is a stock pic of the thing (the II version has different grill cloth but you get the idea).

It's a beast.