Peavey Classic 400 won't power up

[Andy]

I just drove all the way to Detroit in a raging blizzard to pick up this amazing amp and cab. I got it home, and I was going to play with it, but when I plugged it in, connected the speaker cable, and turned it on, the indicator lights came on for about a second, I heard a bit of crackling/fizzing from inside the amp, and everything went dark. I checked the line fuse, and it is intact, so I pulled the chassis out and checked the other 8 fuses. all of them are intact, and nothing appears to be burned or damaged in any way. Not even the cooling fan (powered by the 120V line) comes on when I flip the switch, so I'm guessing it has to be somewhere in the line side of the power transformer.

So I guess my question is....

Has anyone here worked on one of these, and perhaps seen this problem before?

[Andy]

Okay, so I did some poking around on the board that handles the line voltage, and found that the leads to the power transformer get 1.5mV with the power switch off, and about 8.25V with the switch on. I've verified that there is line voltage in the places where it needs to be on the board, and that the switch has continuity when put in the 'on' position. I'm starting to suspect that the triac on page 7 of this schematic is no longer functioning and needs to be replaced.

[Enzo]

Worked on an amp that went dead? Sure, many times. I am quite sure it is nothing specific to that make and model.

Did you test the fuses out of their holders with an ohm meter? I think the mains fuse is ceramic, so you cannot tell by looking. There is a small square board with a fuse on it, is that one OK?

Was it still cold from outdoors when you powered it up?

Due to the high currents of this amp, the power switch does not carry the mains current. There is a large power triac that handles that, and the power switch turns the triac off and on. The 1A slow fuse on the little AC board serves the triac. Open triac fuse and the mains will not come on.

Of course it is always possible a wire came off, the switch failed, or even that the power cord is bad.

[Andy]

Worked on an amp that went dead? Sure, many times. I am quite sure it is nothing specific to that make and model.

I guess I was wondering if there were any known common problems that occur with this make and model.

Did you test the fuses out of their holders with an ohm meter? I think the mains fuse is ceramic, so you cannot tell by looking. There is a small square board with a fuse on it, is that one OK?

I pulled each fuse out of its holder and tested with an ohm meter. All tested ok.

Was it still cold from outdoors when you powered it up?

I wouldn't exactly say it was cold. It had just ridden the previous 6 hours in the back of a warm car. the only cold it saw was the 20 feet from the car to the house, and I wouldn't expect that components inside the chassis would be affected in the amount of time that it was exposed. Perhaps I'm wrong about this. The amp did sit in the car over several nights. is it possible that the E-caps froze, and need to thaw out?

Due to the high currents of this amp, the power switch does not carry the mains current. There is a large power triac that handles that, and the power switch turns the triac off and on. The 1A slow fuse on the little AC board serves the triac. Open triac fuse and the mains will not come on.

as I said, the fuses are all fine, and the switch has continuity in the 'on' position

Of course it is always possible a wire came off, the switch failed, or even that the power cord is bad.

I suppose any of those is possible, but I looked it over pretty thoroughly, and everything appears in order. I'll check the power cord after work tonight, but I highly doubt that the cord is the problem.

[Enzo]

I was writing while your second post went up, so there is overlap. If the switch works, verify the 22 ohm resistor in the switch circuit didn;t open. Not much to the triac circuit after all.

All the triac does is act like a switch. it has three terminals - two main terminals and the gate. The gate post is smaller than the two main terminal posts. The wires would be heavier on the main posts compared to the gate, I'd bet.

Connect the two main terminals of the triac together with a clip wire, then plug the amp into the wall outlet. Does it come on now? if it does, then either the traic is dead or it is not being turned on by the switch.

[Andy]

Connect the two main terminals of the triac together with a clip wire, then plug the amp into the wall outlet. Does it come on now? if it does, then either the traic is dead or it is not being turned on by the switch.

I considered this, but I'm hesitant because I don't know what caused the problem in the first place, and I don't want to do further damage to the amp if the triac fried due to some other problem. I don't have a 15-amp variac to test with either, so I'll have to give it some careful thought.

[Enzo]

Let us say the triac works. When you flip on the power switch, it immediately connects those two terminals together inside itself. Either way power is applied to the power transformer. We cannot service an amp without applying power to it at some point.

Do you have a smaller variac? The amp only draws 15 amps from the wall when it blows its mains fuse. It draws less when fully cranked. And when ther is no signal coming through it it draws considerably less. SHort the triac, bring it up on a smaller variac with a current meter in series for monitoring.

Or look up "light bulb limiter" and stick that in oplace of the mains fuse or otherwise in series with the mains cord. Search for that term here.

[Andy]

If the switch works, verify the 22 ohm resistor in the switch circuit didn;t open.

I checked the resistor, and it shows open, so I think this is it. I'll hit up radio shack tomorrow and see if I can't get a pack of resistors. I'm still a bit concerned about what might have caused that resistor to open in the first place, but since it's a 1/4 watt unit, as opposed to the 1000W triac, any old transient on the AC line might pop it, I guess. I've heard stories of these amps being a bit sensitive to the quality of the power you feed them.

I have pretty lousy power in my basement where my band practices. I have about 12VAC between neutral and ground, so that's certainly not good. I'm currently bidding on a 1500VA isolation transformer on ebay, and I plan to use it with this amp every time I turn it on going forward.

[Enzo]

More likely vibration cracked it.

[Andy]

A new resistor fixed it. I wasn't able to get 1/4 watt resistors on short notice, but radio shack had 1/2 watt resistors in stock, which will work just fine. the amp sounds great, and it's f**king loud.

[Enzo]

Loud indeed. I had one once, and it blew all the hair off the top of my head. It never grew back.

[Andy]

I hope the same doesn't happen to me... I'm a lucky hair survivor with a genetic predisposition to losing it. My mom's brother was mostly bald by the time he was 17. I'm now almost 31, and I haven't lost a single strand. I have a show on Saturday, so I'm eager to try this thing out in a live situation. it was completely overpowering at band rehearsal tonight - even with the volume below 3, so it should be just about right for a gig. a few months back, I bought a brand new peavey tour 700 head, and it wasn't nearly this loud, even fully cranked. I also couldn't get the tone I wanted out of it, so it went back to the store (gotta love guitar center's 30-day return policy) and magically turned into a really nice condenser mic and some other miscellaneous items. I think this amp will be a keeper. I'm already looking around for more of them. if I go on tour this summer, I'll need a backup head for sure.

[Enzo]

I am twice your age, so comb it while you got it.



And did we mention the thing weighs 20 pounds more than an SVT?

[Andy]

And did we mention the thing weighs 20 pounds more than an SVT?

...and sounds as good or better for half the price?

I picked up this amp and cab from a guy in Westland, MI who was basically liquidating inventory to get his collection down to a more manageable size. I got both units for $800, and the cab (a peavey 810TX) once belonged to Ted Nugent's band. Driving in a blizzard across Michigan is not exactly my idea of a good time, and I'm sure you'll agree, but it was totally worth it. This amp could bring down whole buildings in the wrong hands. The power is just awesome.

[determined2play]

Don't ya just love happy endings. BTW I am in the same boat as Enzo, folically speaking. I am 37 and have been slick for 10 years. Thanks Granda Bill.