5150 combo controls unresponsive

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stefanwest
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5150 combo controls unresponsive

Post by stefanwest » Wed Jul 05, 2017 10:41 pm

So I finally joined the 5150 craze. For $200.
Powers on, and. Ok.
What works: pregain, channel switch, sound.
What doesn't work: everything else.

All knobs besides the pre gain are unresponsive.
The amp is as if it's turned to post gain 10 even are barely 1.

I'm getting some 2005 Sed winged c 6l6gc matched with late distortion and retubing with new preamp tubes.

But I have a feeling new tubes aren't going to fix this .

I've retubed a framus cobra of mine with great results but it was already working fine.

I hear Enzo is the one to ask but I can't contact him and maybe he will chime in , but until then, how bad does this sound to everyone ? How much will I need to spend here?
Is this a transformer issue, caps, board ribbon, ect?
I'm just a player not a tech at all.

I'm Stefan , this is my first post so you can roast me on that, but in hopes of finding a solution.

stefanwest
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Re: 5150 combo controls unresponsive

Post by stefanwest » Thu Jul 20, 2017 11:11 pm

bump

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Enzo
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Re: 5150 combo controls unresponsive

Post by Enzo » Thu Jul 20, 2017 11:44 pm

I cannot imagine how a tube in this circuit could disable controls. But I can imagine that a loss of ground connection to the controls would do so.

stefanwest
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Re: 5150 combo controls unresponsive

Post by stefanwest » Fri Jul 21, 2017 11:16 am

Where on the board would I find a possible disconnection ?

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Enzo
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Re: 5150 combo controls unresponsive

Post by Enzo » Fri Jul 21, 2017 2:02 pm

Loss of contact between input jack and chassis. Cracked copper trace on the board near the front, broken solder on a wire link. Open 47 ohm "ground to ground" resistor.

sweatyk
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Re: 5150 combo controls unresponsive

Post by sweatyk » Sat Dec 15, 2018 6:10 pm

I see that this post was left unresolved. Enzo you have seen my post on Electronics Music Forum on this issue. After reading this thread is sounds exactly how I was trying to describe what mine is doing. I get nothing thru the return on the effects loop. I have checked the 47 ohm double grounded resistor. R118 and or R119 if I'm correct.....both good. I have scoured up and down the board looking for hairline breaks. I have touched up any sketchy looking solder joints. Swapped out the tubes. I have the board out of the chassis at the moment so it is a good time to pull parts out of the circuit to get a reading on them. Any advice?

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Enzo
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Re: 5150 combo controls unresponsive

Post by Enzo » Sat Dec 15, 2018 6:43 pm

I almost never pull parts off a board to check them, unless I have a very good reason to think that part is bad.

And the way to look for cracked circuit traces etc is with an ohm meter. If I measure from the lower leg of a volume or tone control to ground, I expect a low resistance, if it is not there, then I have an open somewhere.

The 5150 combo is laid out like a Classic 30, which mean ther are little wire jumpers itching to break off between boards.

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