Peavey CS800x problem - Smell it getting hot when powered on - HELP!

[Enzo]

From the peavey guide:
6018 is an MJE340
70481180 is an MJ15020 (of MJ13330)

Or pick up the phone and call the PV parts department and get the real parts.

[CoopDaKill]

Some of you may think this is kind of elemntary, but I just want to make sure that all caps are discharged, for my safety. I'm not new to amp repair,but do not claim to be a pro either... I've built a discharge probe, and it has always worked well. So today after discharging caps, I also tested the big power caps with my multi-meter, before tearing into this amp. But I just experianced something different, I checked the big 15,000uf caps with my meter, one read 12.0 v and the other 0v. I didn't think too much about the 12v, so I procedded to disaassemble the CS800x. I took off one screw that holds the bottom board to the wind tunnel, and when I touched my ratchet to the next wind tunnel screw, I got a little arc. My left hand was on the chassis, so I did'nt feel anything. It was probally the 12v stored in that big cap. Please give your thoughts on this. Feel free to use a few choice words if you like. I deserve it. LOL... Safety is number one.
Thanks

Also, Thanks to Enzo for your parts help. Found them all except 81180.

[52 Bill]

A couple of things from me here. Do you have the correct fuses in this thing? I would have thought that the fuses would have blown with the shorted outputs.

Secondly, I assume that you do not have a speaker or load resistor connected to the amp, which you should not have until the repairs are done. Because of that fact there is nothing to quickly draw down the power supply caps as well as any other caps in the circuit. Use your discharge probe and then use you meter just like you did, but wait til the voltages are all gone before working in there. Even if you don't hurt yourself, an arc can do damage to the circuitry.

[CoopDaKill]

Found some problems with CR103 (SCA187 Triac)

Thanks 52 Bill.
Yes, it has the correct, 1A 250v (313) fuses. And No Load (speaker, resistor), connected. So, after pulling and checking Q102,103,104,105, (83180 transistors), All tested good with the multimeter diode check. So, I looked at the SAC187 Triac (CR103 on schem.) on channel A, and noticed a burnt board trace on pin 3, cracked solder joint on pin 1. See pic. Probally why it shorted. So, I pulled it, and it 's shorted, per m-meter diode test. This is my first run in with a Triac. I read an older post, where Enzo had mentioned it. So, after some research, I think I've found a replacement. BTA16-700B. I've read that it has been used as a succesful replacement for the SAC187 Triac, by some Peavey authorized service shops.

I'll call Peavey, Monday, and see if they have it in stock. But if not, I've found it at the mouser.
BTA16-700BRG STMicroelectronics | Mouser

And Thank You, Enzo, for making me ask myself, "Why"?

EDIT: Should I still check Q100, & Q101 ?

[Enzo]

I'd be surprised if the triac died from cracked solder. It almost always dies because the amp channel kills it. DOn';t replace it until the rest of the amp works. It would only get in the way. The trace to thye center pin looks like it burnt open, which tells us the part was conducting enough current to do that. That generally means DC on the output.

[CoopDaKill]

Interesting, Enzo! No matter which way I touch my meter leads to the pins / pins to case, it shows a dead short. Should I not see a small voltage reading from pin to pin? Like I said, I new to dealing with a Triac. What do suggest I do / check next? Thanks Again.

[52 Bill]

Interesting, Enzo! No matter which way I touch my meter leads to the pins / pins to case, it shows a dead short. Should I not see a small voltage reading from pin to pin? Like I said, I new to dealing with a Triac. What do suggest I do / check next? Thanks Again.

I think you've misunderstood Enzo's post. It's not that he doesn't think that the triac is shorted, it's that he doesn't think that it was caused by a cracked solder joint.

The triac is toast and was probably caused by a power amp problem that put dc voltage on the speaker line. But that's what it's supposed to do. If it senses dc on the output, it is supposed to conduct and cause the power amp to shut down and save your speakers from a dc voltage.

It does not need to be there for the amp to work, so you can continue testing without it in the circuit.

[Enzo]

Exactly. I believe you that it is a shorted part, and if it is shorted you will not measure any voltage drops. it is a sacrificial part. When the channel goes south and makes DC, this part shorts across the output to prevent your speakers from catching fire - seriously. It almost always gives its life in the process.

Triac, schmiac, whatever it is, it shouldn;t be shorted, y'know?


By not replacing it, I meant yes remove the bad part, but do not install a new one until we are done with the repair.

[CoopDaKill]

And I thought I had done something right, for a change. LOL.... Thanks for the info on the Triac. Another good learning experience for me.

Well, I checked Q101 (81180), and Q100 (6018) on channel A, out of circuit, and they both check good. Check pics for me pleas? . I had to educate myself on transistor testing with a DMM. Most of my experience has been with tube stuff. Not sure where to go from here. Any and all advise is welcome. I'm not gonna let this CS800x, beat me.

Thank You all for your help, and patience. I hope to someday, be at the level of you guys. It's amazing, the vast knowledge you guys possess. I have total respect for you.

[52 Bill]

Your photos show the correct procedure for testing a power transistor and it shows that the transistor you are testing is okay.

You need to test all of the power transistors in the same way and then do the same for the driver transistors.

[gtrmann]

If the fan was staring and stopping because the amp was running hot, the amp might be over biased. That is very common in that model. Did you build the load lamp yet ??...... Bias is checked my reading the voltage across the emitter resistors on the output devices. I believe these are .33 ohm 10 watt..... They should be around 12 millivolts or less..... I usually tweak it out to be around 2 mils... Far below the spec, but the amp runs real cool then....

[gtrmann]

Thanks for the schematic someone posted earlier in this thread. The dual diode CR105 goes out of spec and the bias gets hot. I have hand picked this diode to get the bias under control. I have also put a resistor across CR101 to lower the bias voltage, dont remember the value..... Think it may have been 47 ohms...

[CoopDaKill]

Thanks for the schematic someone posted earlier in this thread. The dual diode CR105 goes out of spec and the bias gets hot. I have hand picked this diode to get the bias under control. I have also put a resistor across CR101 to lower the bias voltage, dont remember the value..... Think it may have been 47 ohms...

I've looked for an hour, and cant seem to locate CR105. I see it on the schematic, but cant find it on the boards. Does it look like a standard diode? From my research, it's Peavey part# 70413886. Field replace# MZ2361. Please tell me if I'm wrong. Thanks

EDIT: I've found a blown transistor. (Q1083) one of the 73180 pnp transistors. Still checking other channels' transistors.

[telecaster]

CR105 is between the last 2 transistors on the left of each row in the above picture

[Jazz P Bass]

CR105 has to sense the heatsink temperature.
So that is where you will find it.
It will not appear as a diode.
It is a package with two wires.
I would not worry about any of that, beyond simply checking that there is a double diode drop (it is two diodes in series).
Get the amp working before you fool around with the bias.