Peavey XR600E (Dead)

[R.G.]

To test a transformer:
1) Remove the transformer leads from the circuit, noting where they are soldered in so you can get it back in the correct way. This removes issues of bad AC wiring and open fuses.
2) With your ohmmeter, test each winding for continuity (resistance) from end to end and to each tap. Each winding for most tube amps will be between nearly zero ohms (heater windings) and several hundred ohms (high voltage). Solid state amps' transformers will tend to be 0 to something less than 100 ohms. This checks to see if the winding is open (i.e. broken wire inside)
3) Again with the ohmmeter, test each winding to NOT make contact to any other winding that's supposed to be isolated.
4) Test for either (a) AC voltages out on every winding when one winding is fed an AC voltage or (b) neon-flash on the shorted-turns tester.

A good first test is to unplug the cord from the wall, hook an ohmmeter between the line and neutral (i.e., not safety ground) prongs, and turn the power switch on. This should return a resistance of near-zero to perhaps 100 ohms or so with the power switch on. If it's near-infinite, something is open. If it's open, check the fuse. If the fuse is good, check the transformer primary. If the transformer primary is resistive, not open, you have an AC wiring problem, possibly a burned contact on the power switch.

DON'T MESS ABOUT WITH THIS UNLESS YOU ALREADY KNOW HOW TO DO IT WITHOUT ELECTROCUTING YOURSELF.

[Jazz P Bass]

Big thanks for the schematic JP Bass, much needed for the library....Jazz P Bass....the heaviest damn guitar I ever wore....ugggg
Much appreciated bud,
W00d

Actually it is an 80's jazz bass special, Pbass body a pbass neck pup and a jazz neck and bridge pup.
3 way pickup switch and separate volume controls.
MIJapan. The body is very light. A tad too light. The head stock tends to drop down.

[TomCarlos]

Hw00D - BEFORE you do anything else, follow the instructions in the previous posts. Just as R.G. states, "DON'T MESS ABOUT WITH THIS UNLESS YOU ALREADY KNOW HOW TO DO IT WITHOUT ELECTROCUTING YOURSELF!!"

I have an extra Peavey 705-18715 that I keep for a rainy day. In addition to the resistance tests discussed previously, I wanted to verify the voltages on the Molex connectors.

I connected the AC line in (the black and blue) to a Molex connector that has two female leads. The other end of the females go to an AC power cord that has a 1 amp resistor in series with the hot lead (black). I take the AC power cord green lead and connect that to the transformer case- so the case is grounded. The power cord then goes to a current limiter (with a bulb) that has a shut-off switch. Once I know my connections are solid, I apply power.

The Red leads should produce around 70 volts AC on the outer ends of the Molex Connector. The Orange leads should produce around 40 volts AC on the outer pins.

If you do this test, you can disconnect all three Molex connectors so that the transformer is out of the circuit. BE EXTREMELY CAREFUL when inserting test leads or alligator clips into the Molex connectors to make these measurements.

[Enzo]

Agree, unplug the primary, the black and blue wires, and measure resistance right at the connector.

If you do wind up needing a transformer, PLEASE ask Peavey first before going to outside suppliers. PV prices tend to be reasonable.

[DrGonz78]

Juan had it right about those Mercury Transformers being displayed at Tiffany's shop windows. Couldn't resist!

[Hw00d]

jesus christ, the transformers toast, why in the hell some of you guys dont believe this is beyond me. Have been repairing peoples junk since the 70's. Open Primary equals burnt winding, hence toast. Now need to find one

[nashvillebill]

Well, you never said you measured the resistance right at the primaries, only at the AC plug blades. We cannot surmise the transformer is bad with other components still in series with the primaries.

And it may very well be that the transformer is bad, but it must be checked at the primaries. Don't surmise, test!

[R.G.]

jesus christ, the transformers toast, why in the hell some of you guys dont believe this is beyond me. Have been repairing peoples junk since the 70's. Open Primary equals burnt winding, hence toast. Now need to find one

And you have to understand that we don't know that you have any repair expertise at all.

This forum is absolutely full of Junior Members with only a few posts asking similar questions. And that very often, a new member's first post to the forum says something like "My amp is dead. It's the transformer, isn't it? I've never done any repairs before, but I think it's easy. Can I flip the AC power switch with a screwdriver?"

It's not that we don't believe you - we don't know you yet. I hope we get to, because that much experience would be a useful addition to the forum. So take the replies for what they were: a cautious reply to someone who MIGHT be a newbie needing a lot of cautions. We hate to see people get themselves in trouble, so we err on the side of caution.

We really want people to stay alive. If you're experienced, GREAT. The simplistic answers were born out of our collective experience with new posters.

[g1]

It's not completely clear whether you have tested at the primary leads yet. If you just checked at the plug, it can still be a problem with switch, fuse, wiring, etc.
If you disconnected primary leads at the transformer and measure open circuit, then yes, the primary is open.

That was a pretty straightforward question. It would have been a lot simpler to just answer it instead of flipping out.

[Enzo]

Agree with RG. We cannot assume any particular experience or skill level based on less than 10 posts.

By the way, when I measure an open primary, my experience has been that many if not most of them are due to an open thermal fuse inside the tranny rather than a burnt winding. Burnt windings more often will be blowing fuses.

And transformers are THE single most overdiagnosed parts in an amp. Novices routinely assume their transformer is bad for no reason at all. In anther current thread, someone said, "My high voltage fuse is blowing, must be my transformer, right?"

[nsubulysses]

When you first start you think transformer. After being wrong 100 times you start forgetting about them. Transformer is probalby the most robust part in the amp, as they say.

[Alex R]

Customer brought this in, wants it for 4th O JUly gig, I don't have the schematic for this mixer. I've surmised it's the power transformer in it. I have a 120 AC into it, there are two-3-wire outputs, one to main board audio amp, other to front mixer board, I have nothing out of either one of these, So am I to assume the transformers ka-put??? If so, is there a place, online to find an OEM transformer for this??, I don't know the outputs on this one, or I may have something lying around. Thanks in advance for any help.

I think that word 'surmised' might have given us the impression of inexperience. I mean, as well as blaming the transformer. I dunno what it is about transformers that makes them targets for the blame all the time, maybe they have a guilty look or their eyes are too close together.

Open windings are much rarer than shorted turns, in fact I don't recall ever seeing an open primary that wasn't just an open thermal fuse.

[nsubulysses]

I thought the thermal fuse was inaccessible. is that right or maybe it varies?

[nashvillebill]

I thought the thermal fuse was inaccessible. is that right or maybe it varies?

I had a vacuum cleaner motor with an open thermal fuse, it was very accessible right on top of the windings. In the interest of...ahem...experimentation, I easily bypassed the open thermal fuse and the vacuum cleaner is still running (experimentally, of course) years later.

But I had a friend bring me an 8 track recorder a couple of years ago with an open thermal fuse in the transformer and it was buried deep in the windings so it could not be easily saved (even "experimentally").

[R.G.]

I thought the thermal fuse was inaccessible. is that right or maybe it varies?

It varies. I've seen reports of them being right under the outer paper/nomex wrapper. I know that some transformers bury them under the outer winding layers where they're inaccessible.

The next question/comment is going to be "Can I replace the thermal fuse?"/ "I've replaced thermal fuses...".

IMHO, this is a bad idea unless you can positively guarantee that the so-fixed transformer will never leave your hands, for liability reasons. For a customer, replace the transformer.