gk800rb

[oo3]

so a shorted speaker cable crawled into my cable case - i then used it with the gk 800rb and of course blew the fuse - so far i have only found 1 shorted output - Q20 - plan on replacing it and Q24 - what else would you check? - hmmm i see they use the same outputs in the 100wt section for biamp i dont use --no no,i wont do that - on side note - about 1/3 of amp set on end in katrina water for about 1 day - cleaned it up and working fine until now - oo3

[Enzo]

If an output transistor blows, then always check the resistors associated with it. No schematic handy, but I assume there are some ballast resistors - the 0.22 ohm or whatever types. And then we always want to check the driver transistors.

Work with NO speaker load until you know the amp is not blowing fuses and not putting DC on the output.

This is exactly the case where you want to bring the amp up on a variac while watching the mains current.

[oo3]

thank you for input - i am out of practice in this area - checking some more still only finding the one transistor shorted - will have to order some parts - oo3

[grooveman1961]

I work on these alot...

I would recomend r48, 49, 50, they make test ok, but you may want to look on the potted side for cracks or discoloration,maybe consider just replacing them since you have to unsolder one side anyway.... also D10, R47,51

Also, a 60 watt light bulb in series with the transformer primary will keep you from reinjuring your newly installed components if you've missed something. ( unless you have the aforementioned variac and amp meter)

[Phostenix]

Also, a 60 watt light bulb in series with the transformer primary will keep you from reinjuring your newly installed components if you've missed something.

Hmm. Seems like I've heard about that somewhere....

[grooveman1961]

Hmm. Seems like I've heard about that somewhere....

Yeah, back in the day when i was so broke I couldn't pay attention, I started working on a blown rb800 that I bought as a box of parts. I can't remember where I saw it either, but I made a rig with a ceramic bulb base. It saved me alot of parts.

It may seem hokie, but it works.

[Enzo]

Hi groove, welcome to the forum. I think Phos is funning with you a little. "Light Bulb Limiter" is a favorite around here.

[grooveman1961]

Hi groove, welcome to the forum. I think Phos is funning with you a little. "Light Bulb Limiter" is a favorite around here.

I'll take your word for it.

[Phostenix]

Yeah, back in the day when i was so broke I couldn't pay attention, I started working on a blown rb800 that I bought as a box of parts. I can't remember where I saw it either, but I made a rig with a ceramic bulb base. It saved me alot of parts.

It may seem hokie, but it works.

I was thinking more of this:
http://music-electronics-forum.com/t16164/#post131917

As always, Enzo is right.

[David King]

Hi Folks,
Sorry I rarely venture out of the pickup winders area onto the varsity field but was hoping to get a quick reaction to the photo of an 800rb that also tried to drive a .01 ohm load for an unspecified period of time. Unfortunately the fuse is in perfect condition. Is this amp figuratively toast? If it's potentially repairable where would I look for a schematic?
Thanks

[MarkusBass]

It looks bad. I would remove burned components and clean the PC board. If the board is carbonized, I wouldn't repair it but rather try to replace it. And the schematic was posted here on this forum many times. Have you tried searching it?

Mark

[Jazz P Bass]

Literally toast.
With the heat that was generated & all of that carbon, no way will that come back & be reliable.
By the way, what is a '.01 ohm load' ?

[MarkusBass]

Shorted speaker wire?

[g1]

C'mon guys, it always looks worse than it really is . I wouldn't want to condemn the board before seeing it cleaned up.
We aren't dealing with high voltage like a tube amp here (even in such cases, there is always liquid arc-proofing Super Corona Dope | MG Chemicals).
Any bad burns can be dremeled out and the traces jumpered back together.
Give it a scrub like MarcusBass suggested and post new pics.
Depending on your experience, the trick to this repair will be figuring out which components go where, unless there is a component layout drawing for the board revision# available.

[MarkusBass]

Here is a slightly similar situation - SWR SM400 power amp. I fixed it without any problem. I had to dremel about 1 square centimeter and rebuilt missing 3 or 4 tracks. In your case there maybe slightly more tracks to be fixed but as I said previously: remove the components and clean the board first. Post a photo here and we will see what can be done. The layout with components is available without any problems.




Mark