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

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

    Hey guys, I bought a Peavey CS800x power amp. Brought it home, opened it up to look inside, and all looked OK, so I powered it on, with the top cover off, and the fan was starting & stopping, and I smelled something getting hot, so I quickly, pulled the power. Nothing looks burnt on the power supply. I'm trying to check the big 15,000uf-90vdc caps, but my fluke meter only goes to 9999uf. Arghhhhhh...

    Is Q35 a voltage regulator?

    I hate to see this thing go to waste, Any advise as to where to look first. Much appreciated.

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    Supporting Member Jazz P Bass's Avatar
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    What is a Q35?

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    Senior Member Enzo's Avatar
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    Forget the big caps, they are not very likely what is getting hot.

    Q35 is a triac that controls the fan speed. You COULD think of Q35 as a voltage regulator, sorta. The fan has a big 400 ohm 20w in series with it to make the fan run slow. Q35 shorts across that resistor to make the fan go to full speed. SO your fan SHOULD run slow all the time until the thermal sensors turn on Q35 and make the fan go fast. If the cfan cycles between off anf fast running, then that big resistor is probably open or disconnected.
    Education is what you're left with after you have forgotten what you have learned.

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    Thanks Enzo for your reply! I tested that 400 ohm/15 watt resistor, out of circuit, and it tested 418 ohms. So, I guess I'll check other componants in the power supply board. I welcome any other advise. Thank You Again for your time and help!
    Coop
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    Senior Member Enzo's Avatar
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    Well, find out what is getting hot. Don;t just start randomly measuring parts hoping to find one out of spec. SOme parts are normal to get hot, like zener dropping resistors.
    Education is what you're left with after you have forgotten what you have learned.

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    So, should I just turn it on and see what smokes? At least I may find out what part is bad, huh ? I know that sounds stupid, but I dont know how to find whats wrong if I cant keep it powered up? Thanks
    Last edited by CoopDaKill; 02-27-2013 at 03:00 PM.

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    Supporting Member Jazz P Bass's Avatar
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    Your best & safest bet is to build yourself a 'Lamp Limiter'.
    One leg of the mains runs through the lamp filament, thus helping to limit the amount of current the amp draws.
    In this way you can try to find what is getting excessively hot.
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    I'm a complete dumby. I have a lamp limiter, that I built years ago. I'll dig it out and put to use. I'll let you guys know what I find out. Thanks

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    I've had amps here that won't even power up properly with a 60 watt lamp, but usually a 100 watt lamp will work in those situations.

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    Supporting Member Jazz P Bass's Avatar
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    Components that get hot usually show some kind of a sign that something is amiss.
    Granted, the voltages will be lower when using a lamp limiter, but you can still check your main voltage rails.
    That includes the opamp power supplies.

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    Quote Originally Posted by bkahuna View Post
    I've had amps here that won't even power up properly with a 60 watt lamp, but usually a 100 watt lamp will work in those situations.
    I put a 100 watt bulb in my light limiter, and no power on the CS800x, but the bulb glows bright on the light limiter. Is this a possible bad transformer? Should I try the variac on about 50 - 60 volts?

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    Well my variac needs a fuse, so I just said, "To Heck with it", and plugged it in the wall. I know, not the best thing to do, but I didn't have a ton of cash invested in this CS800x. So, I powered it on / off, long enogh to build up a little heat and smoke. (On channel A ) R104,105 & R108,109, were so hot that i burned my finger tips. All 4 resistors are 33 ohm/10 watt. It's the four 33 ohm / 10watt resistors that are closest to the front of the amp. What would make these resitors get so hot, so quick? Thank You.
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    Supporting Member Jazz P Bass's Avatar
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    The bright lamp was the clue.
    The lamp should go bright at power on (capacitors charging) & then go dim (output section is stable)
    Look at the schematic, specifically the parts that are getting hot.
    Ask yourself why.
    In a normally proper operating output section as this, the base voltages on the output transistors should be low.
    Under 500mv's.
    I have a feeling that you will not find this.
    I would start checking the transistors for a shorted condition.
    They are in parallel so if one shows bad, keep pulling them until you find all of the bad ones.(and 'good' ones).
    If any are found bad also check the driver transistors & of coarse any resistors around failed devices.

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    Senior Member Enzo's Avatar
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    Look at your schematic, and see those four resistors connect directly to Q102,103,104,105.

    So either all four of those transistors are failed or they are all being turned on hard by Q100,101 or something on the driver board.
    Education is what you're left with after you have forgotten what you have learned.

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    Thanks Enzo. I follow where your going with this. I've found the four 83180 output transistors at mouser, but I'm having a hard time finding 6018 (Q100), and 81180 (Q101). I found them both at Vibroworld, but I'd like to locate an equivalent at mouser. Any advise on this? Thanks

    Vibroworld cart link: https://www.vibroworld.com/cgi-bin/s...mmand=calcship
    6018 cross ref part#: PV#70406018 SJE 6018
    81180 cross ref. part#: PV#70481180 SJ-81180 Transistor

    Peavey parts cross reference list link:
    http://www.ampix.org/albums/userpics..._Cross_Ref.pdf

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    Senior Member Enzo's Avatar
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    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.
    Education is what you're left with after you have forgotten what you have learned.

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    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.

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    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.

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    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 ?
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    Last edited by CoopDaKill; 03-02-2013 at 03:45 AM. Reason: Spelling

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    Senior Member Enzo's Avatar
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    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.
    Education is what you're left with after you have forgotten what you have learned.

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    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.

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    Quote Originally Posted by CoopDaKill View Post
    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.

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    Senior Member Enzo's Avatar
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    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.
    Education is what you're left with after you have forgotten what you have learned.

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    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.
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    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.

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    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....

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    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...

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    Quote Originally Posted by gtrmann View Post
    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.
    Last edited by CoopDaKill; 03-03-2013 at 08:08 PM.

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    cs800xoutputboardpicture.png
    CR105 is between the last 2 transistors on the left of each row in the above picture

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    Supporting Member Jazz P Bass's Avatar
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    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.

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    I was thinking, this was it (see pic). Big diode on bottom left. I circled it too. But it's marked 1N54??. Is this it?

    EDIT: Sorry Jazz P Bass, I was posting about the same time as you. Thanks for describing CR105, now it's an easy find. I'm thinking the one blown 73180, will get back up and running. I'll call Peavey Monday.
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    Last edited by CoopDaKill; 03-03-2013 at 09:53 PM.

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    I didn't realize the amp didn't work. Fix the amp first and look at the bias after. The output transistors Peavey uses are relabeled MJ15024 and MJ15025. You can get those at Mouser and Digikey last time I checked... Real cool experiment with a diode, clip one on a ohm meter in the diode check mode and put a iron on the lead ... Watch the reading change with the temperature rise ....the meter is reading the voltage drop across the diode in the diode check mode..

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    Thought I'd check some other components, while waiting on parts to arrive. Performimg diode test w/ DMM, on 1TB2 & 2TB2, test shorted. Are they both bad, or is this something that I've yet to learn about heat sensors? As always, Thanks!
    Coop
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    Old Timer km6xz's Avatar
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    Thermal switches are normally closed type or normally open type. These are normally closed. There is one for the fan speed that is Normally open that is mounted on the heat sink between the two channels and one on power transistor of each channel a power amp board that are normally close. So these is normal to measure shorted. They will open when it too hot.

    I am never a fan of randomly replacing parts, the cost aside, it introduces more points of failure such as bad solder joints, or mounting problems. Replace only those which you can prove are defective or not meeting spec.

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    The schematic is marked showing what kind of Thermal Breakers they are.

    1TB2 is marked N.C. which stands for Normally Closed. It is a temperature controlled switch that is closed until it is heated to the trip point where it opens the contact. So if you get a continuity reading of zero ohms that is normal at room temperature.

    The fan is also controlled by one of these, TB1 which is a normally open switch that closes when it reaches the trip point.

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