I need help! A real amp challenge….

[tsk_02]

I have a Crate GX-212+ combo amplifier that I bought in 1996.  In about 2000, lightning struck my house and did something to the amp.  A guitar cable was connected to the amp's input, with the other end not connected to anything and lying on the hardwood/concrete floor in the basement.  I figure the current must've entered through the guitar cable, since I saw burn marks on the disconnected end's tip and that the area of hardwood flooring underneath it was basically damaged (Dad was pissed!)

Prior to the lightning strike, the amp was flawless and awesome.  But since then, here's how the amp is thru now:
– When powered on and guitar connected, the amp is ALWAYS stuck in the distortion channel.  The distortion is not that heavy, probably where the distortion level was when lightning struck. 
- Pushing the channel switch/button does nothing. 
- Not sure if the clean channel works or not, since it won't switch out of the distortion channel. 
- The increase of actual volume level is limited at '2' even though I can still turn the knob up to the '10'-mark.
- All other controls (e.g., EQ, reverb, shape) still seem to work fine.
- I removed and inspected the circuit board and found NO burn marks, exploded capacitors, or anything that would be considered obviously broken or damaged.

For a long time, I did nothing about this, but after remembering how much I really enjoyed the amp, I would like to fix it somehow before I take it to a repair shop (the diagnostic fee itself may not be worth the repair).

Based on this description, is it obvious to anyone where the issue lies or what I can do to fix the (1) channel switch and (2) volume limiting issues?

Any help or ideas are appreciated.  Thanks in advance!

-Tony

[benzer]

- I removed and inspected the circuit board and found NO burn marks, exploded capacitors, or anything that would be considered obviously broken or damaged.

if the lightning hit the input cable it should burn up anythin it sees,,
thats pretty weird , anyways maybe some IC's or caps are burnt in the input stage and its not obvious,should check on that.

second, are you sure the speaker is still fine (magnet) after the lightning struck???

reason for not having high volume could be :
1/pots damaged
2/transistor or op amps damaged
3/make sure if the supply still works fine

i would suggest you change the circuit input stage ,,just buy same caps pots ,,so cheap.

[teemuk]

1: Dead transistor(s) in switching logic circuit or dead switching JFETs.

2: Likely dead opamp(s).


However, this problem with the volume control could be anything. You did verify that the power amp is not blown by batching to it directly using the insert jack?

Also, can you provide a schematic? Without a circuit diagram it is next to impossible for anyone to help you.

I have schematic for GX-65/120/212 from '98 but it provides no help since the circuit of the particular channel is different in older and newer models. I can merely guess here: Likely the volume control potentiometer controls the gain of an opamp stage and the opamp in question has failed.

[tsk_02]

First, Thanks so much for the replies, helpful advise and questions.  I had a friend who knows how to use the Oscilloscope look at my OpAmps and he believes those are fine.  But perhaps I could look at replacing the switch and volume pot.   Also, I do not have the schematic, which is something I've been looking for forever.  If you have it, that would be awesome (at least I could compare the written schematic with what I can observe of my actual board)!  Otherwise, it will be very tough to trace through the board.

Again, very much thanks guys

[teemuk]

If you PM me your email address I can post you the schematic. But like I mentioned before, the one I have is not the correct one. If you are lucky it might be helpful with the switching logic circuit, though - and if nothing else then at least it will give you a general idea of the circuit. I'm pretty sure they haven't changed the concept very much.

Likely at least power supply and power amp sections of both models are very similar.

"For any questions concerning owners manuals or schematics please contact the LOUD Technologies Inc. Service Center at 1-800-898-3211." is what is written in the support section of Crate website. ...In case you really urgently need a correct schematic.

I don't know if it's such a good idea to start guessing, which parts might be faulty: If your friend has an osilloscope he can trace the signal path and see which gain stages are not working properly. That will often point out the culprit rather quickly as well. Unfortunately, those lightning strikes usually create a FUBAR: The damage is often very random and even if you get the thing fixed there still may be a vast amount of stressed components that will fail sooner or later.

Anyway, let's hope for the best.