SWR Workingman 300

[Techknowman]

I repaired a SWR Workingman 300 about 2 months ago.
It had blown (shorthed) all of the + and - 2SC3264 outputs. Q9,10,11,12

Got it back in again yesterday and this time only one rail is shorted and 1 driver caught fire and some burned resisters as well.

Anyway all I had was a schematic no board layout with reference designators so I went about creating one. In doing so I found differences in my PCB and the schematic.
Long story short, my PCB is a revA the schematic is a revD.
Should I make the changes to my board to reflect the revD? I'm not sure these changes had anything to do with the re-failure of this unit but I though I would ask. This is an expensive unit to repair. The 2SC3264's are about $9 each here in the U.S. I got mine from china at about $4 each and I don't think they are fakes.

[Techknowman]

This is the PCB with Reference designators.
Some components are removed so I could clean up the board and prepair for replacement parts, Again

[J M Fahey]

The 2SC3264's are about $9 each here in the U.S. I got mine from china at about $4 each and I don't think they are fakes.

Well, they *might* not be, after all.

Should I make the changes to my board to reflect the revD?

I wouldn't. You never know whether the changes you see are accompanied by others you miss.
And the original one *did* work for quite some time.
I'd only mod it if SWR sent some bulletin about it because of known errors on the old one which *must* be corrected.
Maybe you should burn it in, as many serious factories do, before sending it to the customer.
That head, a power resistor with a fan cooling it and the surrounding area and an MP3 looping, say, some ACDC at close to clipping levels for a couple hours will seriously test it.
After 1 hour even the power transformer and chassis will be quite hot, let alone the heat sink.
Good luck.
PS: tell your friend to be a little more careful with that head; he's probably pushing it to the limit.

[Techknowman]

Unfortunately its a customer of a customer. I repair things for a local guitar / amp shop.
The unit was originally a customers who brought it in. blown up. While I was repairing it the owner and the guitar shop did some trading. So it became the shops unit.
He then sold it to a new owner. So who knows what its life is/was like. I don't even know how long he had it. It may be warranty it might not. still needs repair.
When i repaired it last i did put it on a 4ohm 1KW dummy load and pushed it to near clip for 20 minutes or so, mostly to check that the bias circuit wouldn't thermally run away and would work correctly.
From what I recall the thing didn't get that hot.
I know there is a lot of problems with counterfeit transistors but from what I read most of those are TO3 types that are getting rare. The 2SC3264 is such a unique case style and type, it would be harder to counterfeit.
Most plastic case units like this show sand blast "damage" when someone tries to change the numbers. these are smooth and look etched properly with Sanken logo and all.

[Techknowman]

Looking back at my repair log i see that the main outputs were all that I changed.
I didn't change the T0220 drivers. Doh! they "tested" good.
Thats probably what bit me in the ars on this one!

[Jazz P Bass]

Yeah.
I had to walk on the difficult path also.
Blown outputs.
New drivers.
Period.