Peavey 5150 combo won't switch channels

[booj]

peavey_5150_combo.pdf

All the filaments light on the preamp and power tubes. The +/- 23 volt supply is at R110-R111 and R116-R117. I replaced the Q1 and Q4 clamping FET's (at the output of the lead and rythm post controls and the input to the reverb drive) and the CR9 triac connected to the lead and rythm switching circuit. Q8 and Q12 in the switching circuit read normal with a digital meter. The switch itself is good as far as I can tell.
The amp works normally in the low gain mode but won't switch to high gain either with the panel switch or with a make-shift stereo plug / jumper clip combo.
I've checked all the 5150 posts on this forum and can't find a similar issue already posted.
C57 was leaky and I replaced that.
Suggestions welcome. Thanks in advance!

[Enzo]

You replaced all that stuff for channel switching?

Look at the schematic. Channel switching is a matter of turning on and off several relays. They run off the +23v. That may be there at the source, but we would check that +23 is getting to the relays themselves. So completing a circuit to ground from the other end of a relay coil should turn it on.. In this amp, the low end of the relays K1, K2 find their way to ground through the LED CR5, the panel switch and the FS jack. That jack is on the panel at the end of a ribbon cable, so any ground at the end of the circuit comes through that ribbon.

If the K1,2 are stuck off, they will have +23 on both ends. And through Q8 that means the clean relay K3 will be stuck on. So. An open or unsoldered CR5 LED would kill the relays, and a bad panel switch. Switch is good far as you can tell? Either it has continuity when closed or it does not, check that with an ohm meter. One simple test is to plug a cord into the FS jack, but only half way, just to the first click. Now at the free end of the cord, measure for DC voltage on the tip. If you see +23v - more or less - on the tip, the circuit through the relays is present. The panel switch should turn that voltage on and off.

Oh I guess one odd possibility would be diode CR6 across the two relay coils could be shorted, but I think we'd have a REAL bright LED or blown fuses.

[J. Scarborough]

PEAVEY 5150 Combo Switching problem

Peavey 5150 Combo switching:

Hello, all - I'm new here.
I hope this thread is still being followed - it's very similar to the above convo. Pls let me know if I should make an entirely post?

I have a Peavey 5150 Combo. The power supply that feeds the switching relays seems fine - 23V.
When I use the panel switch to engage the Lead ch, I hear the relays kick in, and the lead indicator lights, but both Rhythm PRE and POST volumes stay active.
I have plugged a 1/4" plug in the FS jack, just far enough in to contact the ring, and it reads very little if the CHANNEL switch is off, and again around 19V if the CHANNEL switch is ON, or depressed.
Can anyone point me in the right direction here?
Thank you,
Jeff

[tedmich]

check this thread
http://music-electronics-forum.com/t26407/

I think pontiacpete saw a similar oddness with the volume pots, he's an active member here so you could PM him about the PITA of fixing the 5150 combo as that thread just ends unresolved.

[J. Scarborough]

Thank you, tedmich, I'll take a look.

[Jazz P Bass]

If the relays are clicking, then check across the contacts to see if they are switching state.

[J. Scarborough]

If the relays are clicking, then check across the contacts to see if they are switching state.

That's what is baffling me. I do hear relays clicking, but K1a is not redirecting to the Lead Pre-pot, nor is K1B redirecting to the Lead Post-pot.
Ahhh, well you made me think: K1A and K1B is the same relay! Duh!
I'll source the relay and replace.

Thanks all, for your help
- J

[dorrisant]

What would cause this amp to keep blowing the LED for ch2?

I have replace K1 & K2 relays, Q8 (replacement parts directly from Peavey). I replaced the LED (also from Peavey). When I turned the amp on, with the switch set for ch 1 there is no issue. All voltages look right at the places they should be available. When I switched to ch2, the red LED flashed but it turns back off. If I cycle the switch a few more times the LED flashes dimmer and dimmer then will not come on and then the ch1 green LED stays lit regardless of ch switch position.

My only guesses are 1) there is not enough current limiting to keep from burning up the LED as if it needs a series resistor or 2) something else is pulling enough current to burn the LED out.

I had tried just replacing the LED with parts from a different supplier... Two in a row popped immediately on the first time ch 2 was switched on... Obvious puff of smoke. The ones I bought seem to make it through 3-4 cycles of the ch switch before they burn up, no visible smoke but still give off that burnt smell. That is the reason that I ordered the parts directly from Peavey but they don't seem to be right. What could I be doing wrong? Could it possibly that I installed them backwards? I wouldn't think so, but this thing has me stumped otherwise.

This amp is built so that it is nearly impossible to monitor all of the control voltages as the amp is running and channels being switched.

I am going to pull the board and replace CR6 just to eliminate that possibility... Gotta change the LED anyway.

Tony

[g1]

Any luck with the CR6 replacement?
What are the resistances of those relay coils?