Peavey XXX

[Valvehead]

Working on a 100w XXX head. The amp wont switch to the clean channel. It does go from Crunch to Lead . Its not the switch .
The Clean Led doesnt light ( has -17v at it) . I dont hear a relay click when going to Clean mode.

I have -17vdc at CR3 .
I dont have a fsw for it - its some weird 5 pin Din thing .

Where should I start measuring?

Peavey-XXX-Schematic.pdf

[Valvehead]

Would Q8 or Q10 cause the relay / Led not to work ? They are in the area called Clean bypass

[tedmich]

As Enzo used to say, its usually the over stressed JFETs used in the channel switch /mute circuit that fail (Q2 and Q12 = jfet J174)

OR it could be a bad relay and resistor like here:
https://forums.peavey.com/viewtopic.php?t=49554

[Valvehead]

Thanks !!! R86 is new . i think i have some J174 here

[Valvehead]

Would a J175 be an ok sub for a 174 ??

[Jon Snell]

A J174 has a Drain - Source ON resistance of 85 Ohms, the J175 is 125 Ohms.
Probably won't make any difference but Mouser stock J174 (if you don't want to lose points at the show for fitting the wrong component).

[tedmich]

Peavey doesnt seem to think so (see below and attached) but they look similar, maybe test?

[Jon Snell]

J174 - 176 are no longer manufactured. There are many equivalents; jfet_j174_j175_interfet-2888180.pdf

Take a look at the specifications. They are from the same die, just have slightly different specifications. All are basically interchangeable with Peaveys' requirements.

[Valvehead]

Thanks... ill try swapping the j174

[Valvehead]

Replaced Q2 ..Q12 . No change

After a long search its a dead end on that relay . Google ..ebay.....cant sign in to Peavy forum ..etc...

Anyone know where to get one?
peavey bom = K2 = 70460097 , 12v DPDT . Part number on relay is FRT2H-S

Cant find one anywhere

[Delta362]

You have the wrong part number. It's 71322378. On the BOM, the part number comes first, then the component identifier. The spacing on their BOMs makes it look like the part number is after the identifier, but it's not. It's a 12VDC non-latching DPDT relay,



It's either going to be an Omron G6S or G5V. I don't recall what spacing you need on it. Check the datasheets on the two options below and please let us know.

Possibly this one: https://www.mouser.com/ProductDetail...uv0QsFzA%3D%3D
or this one: https://www.mouser.com/ProductDetail...fCr9o1Dw%3D%3D

Edit: Just found the datasheet for the FRT2H relay. Looks like 5mm spacing so that will make your relay Omron G5V-2-H1-DC12.

[Valvehead]

Thanks !!!!!

[Valvehead]

No luck. New relay . Cr21 shows voltage change when operating the ch switch .

[Delta362]

Can you hear the K1 (not K2) relay activating when going to clean?

Looking deeper into your issue, I don't think K2 is related to your issue. Clean mode needs K1 to activate. R65 (270 ohm that connects to K1 coil) has to connect to ground when the S1 is in clean mode. Confirm that R65 switches from roughly +17 to 0V when you go into clean mode (or check it without power to measure resistance at that node). What do you have across CR14 in all modes?

What do you have on R72 when in clean, crunch, and dirty? Could be Q8 on the effects loop board is the issue.

[Valvehead]

K1 does not click going to clean
R65 does NOT go to ground in any mode


R65
lead 14v
crunch 15v
clean 15v

CR14 volts
lead 14v
crunch 15v
clean 15v

R72
lead 3.6v
crunch 14.5v
clean 14.5v

Oddity found = when checking R38 to ground , the Clean led lights up - no relay click