YAMAHA G100 410: Intermittent problem

[ngw]

I am new to TGP and am hoping I can get some help with my Yamaha G100 410. I am OK at getting around valve amps, but get a bit lost with Solid State stuff.
The G100 intermittently starts making crunchy sounds followed by loud pops/bangs like a small calibre gunshot and goes dead, then comes back to life a few seconds later and then repeats the process. Sometimes it works for a long time before this happens. It does this with all controls at zero which indicates to me that the problem is in the power stage as signal has no effect on the frequency or level of the noises.
Any one have any suggestions where I can look and what to test?
Thanks for any assistance.

[ngw]

can anyone recommend a website for info on solid state amps which may help with finding this fault.

[kornowsd]

The problem may, or may not, be in the power stage of the amplifier. This sounds, to me, more like a power supply issue than anything else. You probably should start poking around there, first. If you have an oscilloscope, I'd monitor the DC supply voltages through the amp. If you can get a schematic for the thing, send it to my email address (kornowsd@zeecon.com) and I can help walk you through it.

T-shooting solid-state is pretty much like t-shooting tube stuff - the differences: lack of "big iron", and smaller components and much lower DC voltages. The rest of the stuff is about the same - including tone-stacks, bias stuff, etc.

Hope that gets you pointed in the right direction.

Dar

[donnyjaguar]

This will be a fun one to fix - especially without the schematic.

Wild guess is an electrolytic capacitor that is conducting DC voltage when the mood hits it. That said, I'd check for cold solder joints and loose ground returns first as you won't need a schema for this. :)

DJ

[beefour]

See if it's mechancially sensitive. (bang on it a little with a rubber mallet or a semi firm closed fist)

It's most likely you've got broken solder inside somewhere. If it's going dead as in 'the power light goes out' then it's definitely power supply. That should be easy to find with a close visual inspection.

If the fist test works on the outside, get the chassis out and take a REAL good long look at all of the solder joints and connections. If you don't see the problem, power the thing up with a speaker connected, and tap lightly in different areas of the amp. Use something hard and non-conductive. I have a piece of plastic rod that came out of something I can't identify any more.

At any rate, you should be able to find the area with this method. If you are still not absolutely sure exactly which connection it is: Unplug it from the wall and carefully resolder the connections in that immediate vicinity, and plug it back in and re-test until the symptom is really gone.

Regards,
Bill

[1kidc]

I've got two yamaha combos - a g100 and a g50. They both work great. VERY dependable amps that I've used on and off since about 1980. I was recently thinking about gutting these combos and using them as extension cabs in another rig. If you'd be interested in buying either of these trannys send me an email!

All the Best,

d2

ddemusic@comcast.net

[Boogs]

I had my decades-old G100-115 serviced at one point for "startling noises". Made loud crashing sounds intermittently, though it's been so long I can't exactly remember. It had bounced around in so many cab trunks that the trannie had come loose or something. $70 worth of repairs later and it was good, with no problems since.