GK800RB blowing fuses

[Garrett335]

Helloo and happy Saturday,
My buddy brought me his GK800rb amp to look at, it's blowing fuses when powered on.
I wanted to see what the proper test procedure is for SS amps, I have a current bulb limiter to plug it into, but what are the steps you take on these kinds of amps, without plugging in to get voltage readings etc?
(Obv visual inspection for shorts, loose parts, broken cracked solder joints) I'm seeing some powder residue around several of the large caps on the power board (Not like fully exploded, but could be a culprit)
Just wondering how you test without injecting power to the circuit that is shorting. Pull the power board and test the transistors. I know it's a big question but any bullet points would be awesome lol. Thanks guys!

[shooter]

schematics are real handy with SS amps


My "typical" is to disconnect the PS from the load.  That may be 2 wires or 10. 
I bring it up with meters on the big volts wires, typically the Rail supply
if the fuse hold n the volts are stable;
ohm the "load" wire to ground, many thousands ohms is good, a couple ohms is bad


If you use a variac, verify it!  put a good working amp of similar watts on it and measure the AC from the variac n make sure it jives with what you expect

[Garrett335]

Thank you for replying Shooter!
I apologize in advance, what is the load on this power supply?
I've attached the PS schem for this amp?

(Maybe its the G wire off of the 5 lead area at bottom right)

[shooter]

A though F are the PS feeds for the Amp parts (The load)
so hopefully A-f are on a molex connectors so you can just disconnect.


once you're happy that only the PS is "in circuit" ANDDDD the Disconnected wires are taped off or don't pose a short/shock hazard I'd just install a new fuse, plug into the wall n see if she blows.  fuses are expendable troubleshooting tools   

[Garrett335]

@shooter
You sir are awesome!!!
A/B are a molex clip
C-G are hardwired : /
Aaand the whole board it attached to an L metal as a heat sink and ground.
Got a little work to do here haha...

[shooter]

take LOTS of pics so when you put the wires back!!!!!!


It looks like the wires have enough "extra" that you could just cut them about 1/2" off the PS board.  That gives you enough to attach meters to and know which wire goes where when you re-solder them.

[PRR]

I used to repair trany amps on salary.

I don't think this GK800 is one to start on. That is a big powerful machine. When it burps, a lot of expensive parts die quickly.

[Garrett335]

Thanks guys!
Shooter, I tested the power supply solo and it did not blow a fuse, or engage my current limiter. The voltages looked correct according to the schem, on the PS board.
I reattached and that current limiter bulb went crazy. Soooo, there is prob something going on with the output section with those transistors.
I'm going to return to my friend and suggest a qualified tech look at this. But I do need to start learning about these Transistor things lol, so many people ask me to fix SS stuff for them.
Thanks for all of your help.

[shooter]

I've passed on most SS amps, especially anything with CCP circuit boards build since the '90s
most of the old amps from the 70's n B4 are "worn-out"  It takes so many man-hours, parts, aggravation.  I simply tell the customer to shine it up and display it as an art piece from the way back days 
the "easier" stuff I can usually strip the board n rebuild pretty easy, small, single board lo-watt'rs