50 Caliber + w/ Odd Problem!

[Fret Blisters]

I have a 1990 .50 Caliber + that I have owned for close to 6 years. It has recently developed a problem...

After playing through it approximately 10-20 minutes (low volume), the sound suddenly changes to a very low volume and sounds "grounded out" with a buzz in the background. I have found four things that corrects the problem for a few seconds...

1. quickly rolling the gain to 10 and back sometimes corrects for a few seconds. ( I suspect the vibration of the sound corrects something)
2. toggling the ground rocker switch to another position corrects for a few seconds.
3. switching to standby and back sometimes corrects for a few seconds.
4. lightly giving a touch to the cooling fins of the 6L6s with the metal tip of a screwdriver corrects the problem for a few seconds.

I have replaced power and pre-amp tubes and this has not corrected the problem. If I let it sit for a while (cool down I guess) I play through it another 10 minutes or so.

I have tried with my very limited knowledge of how amps work to figure out how these quick fixes relate to one-another and all I can figure is maybe a short of something. I have visually inspected all wires, circuit board, etc and see no problems. Any help or suggestions from the board would be greatly appreciated.

Shane

 

[Fret Blisters]

I can run my POD xtLive through the effects loop and the problem does not show up. I am thinking the problem is isolated to the preamp section.

Shane

 

[BPski]

It sounds like a loose connection on the PC board. To fix problems like this with different types of amps (including Mesa) you really have to isolate the bad connection on the board. I use a Sharpie to tap around and get in the area. Of course the amp is on and hooked to it's speaker. This can be dangerous as we all know. After I can get it to a certain area I shut down the amp and unplug it. Then visually look at the solder joints. You can sometimes find it right away. If not then I just touch-up all the solder joints in the area. This takes a little time and patience. Use a soldering iron with a very small tip and not too much heat. That's my best guess. Post more symptoms if you come across any.

I hope this helps.

 

[LHanson]

Might try retensioning the tube sockets. I guess the cooling down part sounds suspicious, I'm trying to remember if the 6L6 version has the power tube sockets mounted directly to the PC board. I don't think it does, but I've never taken mine out of the chassis to find out. Anyway, maybe the tube sockets are gradually heating up something on the PC board or something.

 

[Fret Blisters]

The 6L6's are mounted separately from the circuit board. I did try re-tensioning when the problem first developed and unfortunately that did not solve it for me. Thanks for the responses so far...

Shane

 

[RussB]

I suspect the effects RETURN lack.

Plug a jumper (short guitar cable) in the send and return jacks, and see if the volume drop off goes away.

FWIW, I have had to replace the jacks on both my 22+ and 50 CAL+. They get a bit oxidized, and loose the signal. Claening them didn't seem to cure the problem, but replacing them sure did...they're a bit of a hassle to work with, BTW.

HTH,
Russ

 

[aaronl]

shane and i live next to each other and work together.
this is indeed odd, i was there today and his amp just like cuts out, like sorta as if you were playing it then boom you drop one of the volumes all the way down or something....

i dont know maybe we should record it doing this and u guys could hear it, but it is odd...

 

[Fret Blisters]

Russ, a few weeks ago when I called Mesa Boogie they recommended I clean the effects loop send and return jacks. I cleaned them and it did not cure the problem. I played for around 20 minutes this morning and when the problem started, I plugged the jumper cable into the send and return jack of the effects loop as you recommended and WALA, problem solved! Guess I will undertake replacing the jacks. Now, for archive history sake and for my curiosity,

1. Why does it take approximately 10 minutes for this problem to occure.
2. What exactly is happening when this problem occures.
3. Why does jumping the effects loop correct the problem.

Thanks for everyone's help and suggestions.

Shane