Parts and help repairing GK heads?

[impactwrench]

The Backline 600, 400RB series, and 700RB seem very similar inside. I have a couple of amp heads which Im told have blown power amps. Is this the transformer or a different part? Any idea what these cost or where to get parts? Is it as simple as plug and play? Thanks!

[danomite64]

Blown power amp could mean any part of the power amp circuit has gone bad. If those were my amps, I'd take the one I thought was most useful to a repair shop, and maybe later on fix the other one. And no, I haven't forgot about the Backline. That one I'd sell for parts on ebay.

[impactwrench]

Let me clarify a bit. I gig with a Backline and a 400RB-III head. I bought a used/broken 400RB-IV and 700RB from an electronics shop. They said the power amps are broken on both. Looking in the 400RB-IV it seems that the different PCB's, transformer, and fan are plug and play. Where could I order parts for either amp, or could I use backline or 400RB-III parts to make the other two work again? I have little electronic experience other than physics classes but know my way around a multimeter. Im not much of a solderer either.

[WingKL]

Perhaps it's best you pass the parts amps to someone who can actually do something with them. If you are going to troubleshoot and repair the amps, you will need electronics knowledge, be willing to learn to solder and desolder and have a good set of tools which include a oscilloscope, some sort of signal generator, a good soldering station and ideally a vacuum pump desoldering tool like the Hakko 808, pliers, wire cutters and strippers, lead free solder etc. Also, removing parts from a working amp is a very bad idea. You could turn 2 non-working amps into four non-working amps. Most of the electronics parts like transistors, capacitors and resistors can be bought from electronics supply stores online like digikey. Parts like the transformer may be custom made for GK and are probably available only from GK.

[bassyRyan]

You are buying a headache.

[impactwrench]

Originally Posted by bassyRyan

You are buying a headache.

Not really. Next time a GK combo shows up on CL I already have the lids to take the heads out now. The knobs, lids, plastic nuts, rack ears, handles, and rubber feet are worth more than I paid for both amps. I can keep a small fleet of these amps going with the parts alone.

Its really not hard to fix these things, if you can order a whole circuit board from somewhere. They are put together in modules--basically the EQ, power amp/fan/heatsink, and the transformer. I'm not going to get into desoldering resistors and caps, because yes, it's over my head and I have no desire. If I would have to solder one board to the next maybe I could, but its all plug and play with wiring harnesses.

So I still propose the question, is there a place/way to buy the different PCB boards? Or are they only available to service centers?

[BassmanPaul]

There is nothing plug and play about repairing amplifiers. The models that you have are repairable at the component level. Usually the problems lie with the output stage but you have to know what the faulty parts are.

[WingKL]

You can probably get the power amp board from GK but I'm pretty sure it's not going to be cheap. It would be kind of like buying a whole new engine when maybe all you need are spark plugs.

[MIJ-VI]

Originally Posted by impactwrench

Let me clarify a bit. I gig with a Backline and a 400RB-III head. I bought a used/broken 400RB-IV and 700RB from an electronics shop. They said the power amps are broken on both. Looking in the 400RB-IV it seems that the different PCB's, transformer, and fan are plug and play. Where could I order parts for either amp, or could I use backline or 400RB-III parts to make the other two work again? I have little electronic experience other than physics classes but know my way around a multimeter. Im not much of a solderer either.

Serious injury or death by electrocution awaits those novices who attempt amp repairs without first educating themselves on the subject. (Filter capacitors can store a substantial charge for many hours after an amp has been unplugged from an AC outlet.)

Have you contacted Gallien-Krueger for the relevant schematics and advice on how to proceed?

[KramerBassFan]

If you have to ask, then, you shouldn't.

Sorry, but thats just the way it is.