Need help with Peavey PA

[gsr]

I just picked up a Peavey series 260 Standard PA mixer-amp. It does not power on at all. I have built a couple of tube guitar amps, but don't have much of a clue as to solid state stuff. So far, I have repaired the plug, tightened up loose jacks and fuse holder, and replaced the fuse. I have cleaned the circuit board and inspected for burnt components or traces. Everything looks rock solid to me. Before I take it to a tech, is there any simple things I could check? Has anyone else had similar problems? Thanks

[kvimbo]

Peavey usualy used a second fuse inside, in series with the normal mains fuse. They cleverly defend their amps from "nails" in the socket of main fuse.
Check if there is such a "secondary" mains fuse, and if it is blown.
Well, there are many other things to check for, if you have a multimeter.
Are there 220 - 240 volts directly at the leads of the primary winding of the power transformer?
If no, check all wires and connections at the primary part. If yes, then check the voltages at the secondary windings (AC), then the DC at the electrolytics after the rectifier.
After this, the problem should be revealed itself.
Good Luck!

[gsr]

I looked around for a second fuse, will check again. I do have a dmm so I will check your recommendations. Thanks

[gsr]

Peavey usualy used a second fuse inside, in series with the normal mains fuse. They cleverly defend their amps from "nails" in the socket of main fuse.
Check if there is such a "secondary" mains fuse, and if it is blown.
Well, there are many other things to check for, if you have a multimeter.
Are there 220 - 240 volts directly at the leads of the primary winding of the power transformer?
If no, check all wires and connections at the primary part. If yes, then check the voltages at the secondary windings (AC), then the DC at the electrolytics after the rectifier.
After this, the problem should be revealed itself.
Good Luck!

There is no second fuse. There is a "thermal breaker" before the first fuse. I am getting 118 volts at the the primary side (I live in California). Secondary windings I'm only getting 1.4mV ac on each wire referenced to ground. If I test across the two wires it reads 2.8 mV ac. After the rectifier, one side reads .4mV dc and the other reads 39.1mV dc. Both referenced to ground. Am I testing the voltages correctly? The Peavey schematic says I should have +39V on one and -39V on the other at the big filter caps after the diode rectifier.

[Enzo]

You have 118VAC across the primary. Not that it matters, but is that a blue and a black wire in a molex?

Power off, unplug the amp. Unplug the primary wires, and measure resistance through the primary winding. Is it open? If so, you need a new transformer. If that happens, we might be able to help if PV no longer stocks it.

You have no voltages on the secondaries, so there will of course be no DC resulting.

[gsr]

Enzo,
First, thanks for helping. I am beginning to understand tube amps a little, but I am feeling inadequate here. Anyway, the primary wires on the pt are shiny black. The secondaries are red, with a yellow/red centertap run to the negative side of one of the big power caps. The secondaries run to plugs on the board; one to each end of the diode rectifier. I Unsoldered the black primaries from the switch and across the wires my meter reads "shorted." By the way, the indicator light doesn't light. Its wires were connected to the same two poles of the switch as the black primaries. Could be burned out I suppose, but how do you check it? It is a sealed unit and must run on 120VAC, unlike Fender style.

[kvimbo]

Sorry, I missed that the mains in USA is 117V! (Here we have "about" 230...)

[gsr]

Sorry, I missed that the mains in USA is 117V! (Here we have "about" 230...)

No need to apologize, I appreciate the help!

[Enzo]

OK< your primary sounds OK. A good primary will have a low resistance. Put the wires back. I'd be thinking at this point you have a fault in the primary side wiring.

ANy amp, when the power switch is on, offers a complete circuit to the power coming from the wall. Basically, the mains power runs up one side of th AC cord, through the power switch, through the fuse holder, through the primary, and back down the other side of the AC cord. So if you unplug the power cord from the wall, and hold the plug in your hand, flip the amp power switch to the ON position, you should be able to measure resistance between the two main prongs of the power cord, and see the resistance of the primary winding there. if you measure between those two prongs and get an open reading, then the wiring in the amp is open.

If that is the case, it could be a bad power cord or plug, the switch could be broken inside. The fuse could be bad but look OK, or the fuse holder could be broken inside.

AHA! there is also probably a thermal breaker in the power wiring. Is there a twisted pair of wires from the power cord wire to the fuse holder that run over to a little thing bolted onto the rear panel or even to one of the power transistors? The thing is round like a stack of 5 or 6 pennies in size. with two connector tabs sticking out the top for the wires? Unplug the amp and measure resistance across this device. It should show shorted. If it shows open, it is bad and needs replacement.

[gsr]

Enzo,
You are spot on. I replaced the plug end, but never checked the cord completely. It had been bent so many times just outside the strain relief, the neutral wire had broken. I kept thinking it is something so simple, why can't I see it! I was testing the primaries to ground and so I was getting readings. I kept thinking the switch was bad. Lesson learned. I finally checked continuity from the plug prongs to the power cord entry points and found the open neutral. I humbly ask forgiveness for wasting everyone's time but hope this may save someone time later on. And at least I acquired a great old PA head for a song. Glen

[Enzo]

And I hope you see why readings to ground ar not useful when working with the primary mains wiring, other than to look for leakage. The circuit is from hot to neutral, not hot to ground.