Gibson GSS-50 - Solid State - Trem Issues & Other Problems

[Pick-n-Strum]

I've got a Gibson GSS-50 (solid state) on my bench that I could use some help with.  I picked it up for a great price locally.  The speakers and reverb were disconnected and cab was pretty rough.  I added a grounded cord and cleaned up the cab but am having trouble tracking down a few issues. 

Thanks to EL34 World, I have a schematic attached here.  It does say preliminary schematic but as far as I can tell, my amp is the same as the schematic except C20 (reverb circuit) appears to be 1000uF on my amp instead of 500 as shown in the schematic.

After cleaning the board, jumpering a couple traces that lifted, replacing the electrolytics, and replacing the jacks, I got to testing it out.  The reverb and tremolo don't work and there is a fairly loud oscillating (???) noise. I will post a picture of my scope to hopefully help show what I mean...On the scope, the sine wave is not a perfect line - it's almost like there are 5 lines right next to each other (at least that's the best way I can explain).  Please see attached photo.

One thing to note, if I remove the tremolo circuit from the rest of the circuit (by lifting R34), I get a nice clear sine wave at the output.  I'm not well-versed in tremolo circuits at all but judging by this, I assume my problem is somewhere in that area.  I've replaced the capacitors (C24, C25, C27) in the tremolo circuit but have the same issue.  The other thing to note when I lift R34 and engage the tremolo footswitch, I still have a clean sine wave that tremolates for about 10 seconds before slowly dying out.  Not sure if that is notable or not (but again, that's when I have R34 lifted).  The tremolo behaves the same way when R34 is properly connected except it still has that dirty sine wave.

Voltages at Q1, Q2, Q3, and Q4 seem very close to schematic.  When getting into the tremolo circuit, they were a bit higher.  Apologies that I don't have exact voltages posted here - I'll let you know ASAP.  During some of my tests I accidentally burned out R63 so I'm waiting for a replacement. 

Any thoughts on what I should check after replacing that R63?  I was wondering if it might have anything to do with the incandescent bulb coming off the frequency pot.  I assume that's incandescent but have never seen that circuit symbol.  I don't know if I even get a replacement on that if it is my issue - I have no value for that bulb.  I haven't tested it out of circuit yet so take this with a grain of salt, but I'm reading about 585 ohms as it sits in the circuit.  I don't know the proper way to test that.  If anyone thinks I should test that, could you give me a quick procedure on how to?

I should add, I'm currently only working on the trem/reverb channels.  The non-trem/verb channels don't work but I need to replace jacks at the very least on that end.  That work is for another day.

Any help, insight, or advice is greatly appreciated.  See attached schematic and photos.

Happy Holidays!

Tommy


Scope photo 1:  R34 connected as normal - wide / dirty sine wave at output

Scope photo 2: R34 lifted - clean sine wave (though not as large)

[Pick-n-Strum]

Good News:  I got my tremolo up and running.

Bad News:  I was the cause of the trouble  .  I mistakenly jumped a trace that had lifted to another trace that I thought it attached to - Not sure if I had an early board of this model or if they didn't make a ton of them but there were several points on the board where it looked like traces attached to other traces but I think they were clipped out at the factory (hope that makes sense) - there were also some other strange things on the board that I thought may have been done at the factory.  Anyways, it took me a while to track this down.  That R63 that I thought had shorted out was actually jumpered when I connected that lifted trace - it was supposed to be dropping voltage but wasn't so I thought I had shorted and fried it while testing things. 

Thank you all for taking the time to read the thread! 

Now on to troubleshooting the reverb.  I may be posting back to this if I can't get that straightened out.

Thanks again!

[tubenit]

I always appreciate when someone shares the solution to their amp problems. Plus it helps others who may encounter a similar situation.  Thanks!


Jeff