Crate GT1200H Volume Loss after 20-30 min's

[SunfireSSR]

I have a Crate GT1200H that loses volume (10-15%) after playing for 20-30 min's. It doesn't matter which channel either. I notice it more on the clean channel only because of no distortion. I pulled the chassis out and with everything plugged in, I noticed I found that (2) of the 5 Watt resistors (R95 and R96) both are to hot to touch. All of the other 5 watt resistors are cool or warm. Could this be the problem ? Thanks for your help in advance...

[The Dude]

Welcome to the place!

I would check solder connections throughout the board. Give it a good inspection, particularly any high heat areas.

[g1]

Try it with a patch cord connecting FX send to FX return (or pre out to pwr amp in).
R95 & R96 normally run very hot, but check their solder connections, like The Dude said.

[SunfireSSR]

I just got the PCB out. All of the solder joints look good. No hot spots on the board either. Looked at it under a magnifying glass. I run all my effects (pedal board through the front jack. Do I need to get a "Y" cable or just build a "jumper" for your test on pre-in / Pre-Out ? Also, the cereamic on R95 and R96 aren't burned or dis-colored, but the little insulators around the legs are burned. The other 5 watt res.'s don't have that.

[The Dude]

Nope, run the amp as you normally do. What g1 is getting at is that the effects return jack is a switching jack and sometimes the switch part of the jack can become intermittent. If you run a standard cable from send to return, you eliminate the switch from the circuit. This will tell you if the problem is at the switching jack or not.

[g1]

That's just heat discolouration, so you don't need to worry about it.
Just put a normal cord in the FX loop, connecting out to in. Then try with your guitar connected to the input with a second cord. Don't use any pedals or effects for testing.

[SunfireSSR]

Ok. Will re-assemble the chassis tonight. Just ruined the only male-stereo jack I had trying to jumper the tip to the ring. But, if you look at page (2) of the schematic on the left hand-side, J21 may give me an option to put a jumper across Pins 1 and 2 if I'm correct. What do you think ?

[SunfireSSR]

Ok.

[g1]

Sorry, I thought this was a standard loop, but I guess it's an insert type? The jacks aren't shown in the schematic I have, but your mention of a y-cord makes me think you were talking about an insert cable.
So yes, you should be able to just jumper 1&2 of J21.

[SunfireSSR]

Ok... Jumped Insert Jack. No difference. But !!! Before I did that, I did play the amp for about 30 min's without any noticable volume loss. I had also put a heat sink on top of R95 and R96. So, the only thing I can guess is that after re-installing the PCB in the chassis, maybe I got a connection tighter than before even though they were a pain to pull off. Have not put the chassis back in the cabinet yet. Going to install a 80mm Low speed fan just because I believe it needs it. Won't hurt unless it creates signal noise. The amp is quiet right now. Thank You g1 and The Dude for your help... Great responses from both of you. Next question is about using the efffects insert. Will try to post in the proper area. Thanks Again...

[g1]

You say "no difference" but it is no longer cutting out?
Even plugging a jack in and out of the insert can sometimes clean it, so did you touch the jack at all before the 30min test when it was fine?

[SunfireSSR]

Did plug a stereo plug in with the tip and ring jumpered (no -Y- needed.)

Will be playing it this weekend. Will know if it holds up in the heat...

Thanks to you Guys for helping me out again...

This is the forum to get real help...