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GK 800RB Need's Repair?

#2
Get a short instrument cord and use it to jump from "out" to "in" in the effects loop. Sometimes these sockets fail and it effectively cuts off the preamp from poweramp. If it doesn't do it again that's the problem. I had that problem on a GK400RB as did several others.
 
#3
You know this might be something as simple as the plug or lead your using to plug into the amp.Check all the simple things first.It also might be something alot more serious. However for best results I would post in the amps forum. Ask a mod to move it.
 
#4
I checked all plug's and they are clean and look good. Basically it shut's off, then if I wait a few minutes it comes back on. This is intermiten and I can't figure it out. Anyone know where I can get scematics, I heard that there might be a thermol cut off sensore inside when it gets too hot.
 
#5
Try what I said first. Sometimes these jacks become intermittent. It might be it. It's not a matter of them being clean or not. There's a 3rd connector in these jacks that sometimes fails.
 
#6
Fito Moreno said:
I checked all plug's and they are clean and look good. Basically it shut's off, then if I wait a few minutes it comes back on. This is intermiten and I can't figure it out. Anyone know where I can get scematics, I heard that there might be a thermol cut off sensore inside when it gets too hot.
Click to expand...

Hey man I have a .pdf of the schematic. If you PM me your email address I'll send it to you.
 
#7
Fito Moreno said:
Anyone know where I can get scematics, I heard that there might be a thermol cut off sensore inside when it gets too hot.
Click to expand...
That's not something you'd want to do, unless you know that the sensor is malfunctioning, which is something you probably won't be able to determine. If it's shutting off due to thermal conditions, it's better to have it shut off and return 5 minutes later than to let it stay on for 5 minutes more and possibly burn out forever.

Does the sound cut out and the light stays on, or does the light go off as well? If it's the former of the two, definitely try running a cord between the effects send and return as suggested. Otherwise, any experienced amp tech should know an 800RB inside out and be able to get you fixed up.
 
#11
B-string said:
Open the case and spray a quick shot of DeoxIT or RidOx on the effects return jack with a cable plugged in. Un-plug and plug back in several times. Problem solved.
Click to expand...

Thanks. I tried that. Still wierdness that keeping the effects loop closed fixes. Sometimes a tap, or flipping the power switch can make the sound come and go. But if effects cable is in its solid. Must be some other circuitry in the picture? The inside of my unit is incredibly clean as well.
 
#13
jcpassport1 said:
...7 years later....
resurrecting my 800RB.... was having intermitent drop outs...sure enough the cable in the effects loop solved the problem.
Thank you!
Is there a real fix worth doing??
Click to expand...

Yup. Hard-wire around (bypass) the effects loop jacks. I was having these problems with my GK 800RB, replaced those jacks countless times, Finally decided to just bypass the dang things. No problems since. Of course, now the effects loop is disabled and no longer functions. But i've never used effects. :smug:
 
#14
i know in the 400RB that the effects loop connects to the main PCB through a white molex connector.. the coating on the pins and the sockets on the plug are two metals that cause a galvanic reaction.. if the 800RB has a similar molex connector, pull it and use a stiff bristled toothbrush wet with DeOxit 5% and scrub the pins and the molex connector.. then spray the connection and plug it back together..

if it's wired directly to the PCB, either reflow the solder.. or desolder it and resolder with a better grade of solder.. at the same time, you might want to check the actual wire to see if it is corroding inside the jacket.. if so, replace the wires in the entire effects loop..
 
#15
jcpassport1 said:
Thanks. I tried that. Still wierdness that keeping the effects loop closed fixes. Sometimes a tap, or flipping the power switch can make the sound come and go. But if effects cable is in its solid. Must be some other circuitry in the picture? The inside of my unit is incredibly clean as well.
Click to expand...

The corrosion that happens is called "fretting", it happens to low voltage/low current connections. You could either try re-tension
of the effects return jack (this will also provide a new contact point), replace the jack or wire around it.
 
#16
throbgod13 said:
i know in the 400RB that the effects loop connects to the main PCB through a white molex connector.. the coating on the pins and the sockets on the plug are two metals that cause a galvanic reaction.. if the 800RB has a similar molex connector, pull it and use a stiff bristled toothbrush wet with DeOxit 5% and scrub the pins and the molex connector.. then spray the connection and plug it back together..

if it's wired directly to the PCB, either reflow the solder.. or desolder it and resolder with a better grade of solder.. at the same time, you might want to check the actual wire to see if it is corroding inside the jacket.. if so, replace the wires in the entire effects loop..
Click to expand...


OK.
I traced most of the effects jack wires going back to 1 fat white molex connector on the preamp board. pulled it off, it looked clean..but I wiped down the spikes on the board, and sprayed the plug. Put it back together, now I could faintly hear the bass w/o the effects cables in.
So opened it up again... got a brush did all the molex jacks I could easily reach. Now sound is back..after an initial static. Will keep checking it for the next couple of days.
Thank you all!
Time to become a supporting member for sure.
 

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