Crate Gremlins

[DrGonz78]

I did some searching and found one place that this is readily available... MCM. However, I am not so sure their shipping charges are very competitive last time I checked. Anyhow here is the link.

On-Semiconductor Bipolar Transistor NPN 140v | MJ15001G | On-Semiconductor

Look on find chips and it shows quantity 8 available...

MJ15001G Stock and Price by Distributor | FindChips.com

[twisted6buick]

I did some searching and found one place that this is readily available...

Ordered. Thx a bunch.

[twisted6buick]

What does C15 do? If it went haywire would it toast R11 & R21?
Because I replaced the transistors and the two trashed resistors, only to fry R11 and R21 again. Trying to deduce what is in the circuit before R11 and R21 leads me to think something is off with C15. (220uF +50v Cap?)
Oddly enough it is directly next to the trans I thought I tapped on to cause the problem. It's the blue cylinder at the top portion of the photo I posted earlier in the thread.
??

[Jazz P Bass]

C15 is a reservoir capacitor for the negative voltage rail.
IF it was shorted (unlikely) it would probably try to take out R21.
But it would not damage R22.
If Q4 was shorted, maybe the excess current through R22 would make it go open.

This is a fairly complicated SS output section.
I do not think that one part is bad, but several.

[teemuk]

it would be wise to have a light bulb limiter ready to go.

Obviously talking to deaf ears. This should have been the first thing to do.

I have a hunch plenty of more parts will burn before this thing is fixed. It's not always the best option to embark on projects that are way over one's head.

This is a fairly complicated SS output section.

No it's not. That is a very simple SS power amp.

Still, 19 posts already and so far only random part swaps and no real clue of what caused the issue.

What does C15 do?

Filter for the negative supply of input and driver stages.

IF it was shorted (unlikely) it would probably try to take out R21.
But it would not damage R22.

But the voltage amp trying to source/sink too much current would kill both. As is, I would systematically start checking for failed parts because probably the fault has already escalated to stage where it keeps killing part after part.

BTW, possible short of C15 is verified faster than typing "unlikely".

Q4 seems OK though. It didn't glow or smoke.

That doesn't indicate anything! You actually need to TEST its condition. Components can be totally faulty while visually looking allright.

THEN

Learn to limit current! Learn this before you even touch the amp again.

Period.

Then start with the basics:
- quick visual inspection to spot the most obvious issues: e.g. failed parts including solder joints. These you can fix instantly just to get them out of the way. Just don't assume it fixes the issue with the amp. It likely just fixes the results of that issue. Power it on and those components will keep dying unless you locate and fix the real fault.

- verify condition of the components, at least upstream from power amp's input stage. No, visual inspection usually isn't enough for this. You need to dig out your test gear.

- DC tests to verify power amp's rail voltages, output voltage and practically all other voltages of dubious nature. Isn't it nice that SLM provided data about test points to do this? That data isn't there because its something to ignore. Probably while you perform this step you find issues that do not comply with the normal operation of the amp, as indicated by the test points. Since you will likely encounter incosistencies this step will give nice clues of where the problem lies and narrow down the area of troubleshooting. BUT, you can't do this reliably without first limiting the current the amp can draw. Fail to do this and the failure will just keep spreading more and more while rendering all your previous work on the amp practically useless. Each time a part goes up in smoke there probably is a handful of other parts that failed but didn't give a visual indication about it,

- verify that the bias circuit works. On that note, I would actually just short the entire bias circuit until you get the amp fixed. After the problems have been found and fixed remove the short and bias the amp properly. You need to do this anyway because I assume you are replacing power transistors.

These simple steps will get you further in half an hour than replacing burned parts (only to kill them again) or trying to GUESS what the issue in this amp is.

[soundguruman]

I have a Crate Gx-2200H (Excalibur) 220 watt SS head. What happens is the distortion channel (A, Gains 1&2) switches to clean channel (B) on it's own. When it does, signal is lost somehow. No output, no buzzing, no static, & no bueno. The amber Clean Channel LED will be lit though. As you may have guessed, a quick shot to the head would make it right. After awhile even that doesn't work.
I have read quite a few threads here on the forum trying to get an idea what it may be.
" A large proportion of problems with electronics generally are due to dirt in the wrong place."
So I hosed the innards down with electronics cleaner, paying special attention to the channel select button..TINY switch..somekind of little blue square detent (?) switch.
" the channel switching circuit runs THROUGH the FS jack, and those contacts complete the circuit when the jack is empty. SO if they get dirty, or their solder cracks as you found, as far as the amp is concerned it is the same as plugging in a foot switch an clicking the switch to open."
And..
" many Crate amps also have a footswitch jack that can have the same problem, only then it results in random channel switching...."
But my amp will do it's goofy switching even with the footswitch plugged in.
So I've come to think I may have to just start touching every doggone solder-joint on the board to try to eliminate any cold solders.
I was thinking if there was a way to narrow it down, I would try. I can run a multimeter, read a schematic, and tin/solder electronics. I've never worked on an amp though.
The best I could find on the web is an Owner's Manual, but it does give a good idead of the control layout and switches.
I really like this amp and do not want to replace it. I've had it since 1996. Plus, I listened to too many Terry Date produced records as a kid, so it has the perfect metal tone for my ears when dialed in.