Peavey CS-800 no power

[nosaj]

No I have not Will give that a shot tomorrow.
Thanks,
nosaj

[nosaj]

yep shorted triac. order some of these from mouser
BTA16-800SWRG

thanks
nosaj

[nosaj]

I would like to speed up my game and since I have pretty much winged it with lots of help from guys.
What I would like to know is using image for example.
When powered up it blows a fuse.
How can i quickly tell which size has the short? (other than pulling every TO3 and testing individually. There 5 on each in addition to a driver.
nosaj

[g1]

How can i quickly tell which size has the short? (other than pulling every TO3 and testing individually. There 5 on each in addition to a driver.

Did you mean 'which side has the short'? And by side you are referring to the top set or bottom set of T03's on the board?
The short will usually be from C to E. It will show up across either all the top set, or all the bottom set. Unless there is a short on both top and bottom sets.
You should also be able to tell from whether the short was on the positive or negative rail of the power supply (each corresponds to either top or bottom sets).

Once you know which set, you still have to pull them to find out which one(s) are shorted.

[nosaj]

Ok i got that. i was just hoping there was an experienced tech trick i was missing.
nosaj

[g1]

i was just hoping there was an experienced tech trick i was missing.

I may be mistaken, but I think Enzo used to say there would be a tiny bit less resistance at the bad part. Like .001 ohm or maybe .01
This would be due to extra resistance of the traces I guess.
If it's easier to disconnect emitter resistors than remove the T03's, I guess you could isolate them that way?

[nosaj]

Unfortunatly no you have to pull all the the TO3's and the heatsink to get at the resistors.
nosaj

[nosaj]

Ok one is wrapped up finished it with replacement triacs on the outputs its good to go now.

The third one i have the PT is bad. Looking at the schematic it really just looks like a 1:1 isolation transformer. I'm gonna ask out loud here to see if someone has an amp for a doorstop with a good PT.

nosaj

[The Dude]

I don't doubt you nosaj, but I've worked on hundreds (if not thousands) of these and have never replaced a transformer. I was doing Peavey warranty work when these were manufactured. Was it over-fused? Out of curiosity, is it open, shorted, etc. What kind of fault do you have?

[nosaj]

i should be doubted .

I have 3 of these an now I've gotten to the Dog.
Here the situation on it.
Somewhere in the past the molex connector disappeared the brings the 81 volts to the power board someone had soldered the wires to the board and it looks like there was arcing between 2 terminals and the coil on the output.
No power up. So I've pulled the PT an going to power it directly bypassing everything else.
Looking at the schematic it looks like I will tie
BL/YL and BK/YL together and BL and BK together to power it up
Then see what I have on the other side.

It wouldn't be the first time i jumped the gun on thinking i needed something. So does that look correct on the terminal wiring?
thanks,
nosaj

[The Dude]

Yes, you have the colors correct for a transformer test.

[The Dude]

Just FYI: Although I never replaced a transformer in one of these, I did replace plenty of bad power switches.

Also, reading back through the thread, you were wondering if there's a way to tell which side has the short. If you mean which amp channel, a quick way to tell which channel is shorted, you can just put your DVM in the output banana jacks of each channel on diode check. and see what readings you get. A working channel usually charges to OL on the meter (or at least something close). The shorted channel will read lower resistance and sometimes dead shorted if the triac shorts. When I fixed a lot of these amps, that was always my first test. Most of the time, you can know which amp channel is shorted before you even open up the amp.

As far as finding the shorted output transistor(s), unfortunately there's not really a shortcut. It's best to just unscrew them all and test each separately. A powered screwdriver makes pretty quick work of it.

[nosaj]

Well The transformer with an input of 119v shows 118.4 on the output no load. What would be an acceptable load for this PT?
The switch works on one side and middle but no on the other side. The fan switch is the same. Also the thermal switches which are are the power amp heatsinks measure about .3 ohms.

thanks,
nosaj

[Helmholtz]

Well The transformer with an input of 119v shows 118.4 on the output no load. What would be an acceptable load for this PT?

I'd say the PT is good.
If you like to test with a load, use an incandescent bulb of 100W or higher.

[nosaj]

duh.... facepalm.

nosaj