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

[CoopDaKill]

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.

[Jazz P Bass]

What is a Q35?

[Enzo]

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.

[CoopDaKill]

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

[Enzo]

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.

[CoopDaKill]

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

[Jazz P Bass]

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.

[CoopDaKill]

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

[bkahuna]

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.

[Jazz P Bass]

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.

[CoopDaKill]

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?

[CoopDaKill]

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.

[Jazz P Bass]

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.

[Enzo]

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.

[CoopDaKill]

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