peavey max (firebass) 700 problem

[boog]

I was brough a peavey max 700 to try to fix, it turns on, fans at full speed, no relay click, no led, no blown fuses, 20v ac at the fuses, 72.5 vdc out of the rectifier, I've tested most of the diodes on the power amp board, all have checked good, 16v rail is present, I'm not getting anything on the relay +
that's where I'm at with it, just wondering if anyone has any experience with these, or might have any ideas where to look next, unfortunately I don't have a scope, all I have to work with is a dmm and a capacitance meter.
the scematic for the firebass 700 appears to be the same as the max 700 as far as the power amp board goes, as far as I can tell.

[boog]

it was 1 of the 2 thermistors open, I soldered in a 1k resistor and it fired up and everything worked, played on it for about 10 minutes, now to order the part.

[Enzo]

A convenient place to measure power supplies is the cases of the big power transistors. Half of them should be about 75v and the other half about -75v. Measured to ground they ought to be close to even. If you have one at say 50v and teh other -100v or some other serious offset, that is the issue.


And lower left area of schematic is the source of relay coil current - RELAYV+. If that circuit is bad - or just doing its job - that might explain it all too.

[boog]

I forgot to mention I had the -75 and 75 on the cases of the power transistors, I had also lifted 5w resistors to isolate each transistor checking for shorts.
The part numbers aren't a lot of help, I found the problem to be an open thermistor "2kj102j 1k tempsistor"

[Enzo]

Part numbers are all you need to get the parts, CALL parts at Peavey. #70240215

[boog]

I'll have to give them a call tomorrow, I know it's a 1k ptc, other than that and pysical size I don't know if it would be safe to guess and order one elsewhere

[Enzo]

I just entered the part number into google - 2kj102j

DO that. I see Mouser sells them, and you can see data sheets and etc.

But when PV has the exact thing - I assume they are still in stock - wwhy not go there. PV has a small minimum, like $5 I think, and if I only need a 50 cent part, I just add on a 12AX7 or something to my order.

[boog]

Thanks for the info on peavey, I've never dealt with their parts department, I did google and saw that mouser had thermistors but not that specific part number, I'm sure I could guess and get something that would work fine, I'll call peavey later during business hours and see where I get with them, thanks again.

[Enzo]

I don't know the brand of the original part, but these should be equivalent:

https://www.mouser.com/Passive-Compo...=1KOHM&FS=True

[boog]

if I don't hear back from peavey by the end of business monday I'll go with one of those, I called the 800 number sevetal times and it just rang, on the direct number I left a message.

[boog]

I didn't get a call back from peavey so I ordered 2 from mouser, figured it would be best to replace both so they are the same part.

[boog]

new thermisors from mouser installed and all is well, jammed on it for about an hour tonight with no problems, but probably not loud enough to really heat it up.
This is what I used, it had the glass type in it but I opted for this one bacause it had a tighter tolerance, and seeing as the old one was broken, I figured these might be more durable.
https://www.mouser.com/ProductDetail...joV50RPXCSU%3D