Fault Tracing a Carver M-500t

[Enzo]

OK. I think you probably provided all that information over the life of the threads, I just didn't recall. Obviously I didn't recall the geneology of Carvers companies correctly. At this point in my life I am lucky to recall breakfast.

I could not remember the name - Tritronics Inc, I now know - of a company I used to buy consumer parts from. SO I googled {brand name} parts distributor. RCA part distributor, Emerson parts dirstributor, etc. Many brands return the same suppliers, but often each brand turned up a new guy. I'd then open the distrib web site and query your part number. That is how I found those potential sources. You might try that for as many brands as you can think of. I don't know who else in stereo land used that IC, but it wasn't custom for Carver. If we find someone else who used it, it might direct us towards a source. I never got as far as Panasonic, Kenwood, and a lot of the large ones.

[Steve Conner]

*cough* hot glue... duct tape... cable ties... extra bits of wire soldered on to relay... replace meter driver chip with op-amp wired as peak detector...

[Enzo]

Yeah, we talked about glueing somethign else in there, but I think he still holds hope for a drop-in.

[bob p]

thanks for checking in Steve. BTW, did you see that video I posted of the guy in Oklahoma with the backyard lightning generator? i thought of you when i saw it.

back to the amp, Enzo I've given up on the drop-in. its unobtainable. i think i mentioned that i already have an Omron general purpose power relay to replace the oddball original. it was only after i purchased it that i found out that its position sensitive. it only cost US$10 for the part, so its not worth returning it. i may just mount it on the side of the chassis to find out just how position sensitive it really is!

regarding the opamp, I have no clue how to do the peak detector thing, or how to rewire the circuit to accommodate it.

[Planerguy]

Carver M500t, blows HOUSE fuses, on or off!

Maybe someone here has experienced this? As soon as it's plugged into the wall, power switch OFF, it blows the 110volt fuses in the house. My background is tube, and regular everyday solid state, but this magnetic field stuff is completely unfamilar territory for me. At the AC line, it shows about 1 ohm from prong to prong, but nothing obvious like a shorted AC lead.
Any ideas?

[Enzo]

Field,schmield, the powr switch is off and it blows fuses. What would you do if a tube amp acted that way? Do the same thing here.

Obviously it wouldn't be a bad tube with the power switch off. In fact with the power switch off, it wouldn;t even be a bad power transformer... because the power is off. Likewise it won't be a transistor here, and magnetic resonance coil sounds impressive, but it still is just a transformer for our purpose. And woth the powr off....

What does that leave us? SHorted power cord. Shorted cap across the mains inside. Mains wiring that came loose inside and is touching. A screw or nut or some other hardware came loose and is shorting something. A circuit board shifted so the underside touches something.

Of course, there could be some problem in the circuit that wants to blow fuses, and the power switch itself is broke and stuck ON.

[Planerguy]

carver 500t

No - nothing like a bad power cord or a bad switch. There is a shorted component which I believe to be a Triac? It's a Mitsubishi BCR16GM.
I am looking for data on it, but so far in the brief time I had available today, no luck. Again, maybe someone else in this forum has experience with these?

I'm sure this is just the beginning, but I'll plug away at it. Just not in the wall yet, eh?

[Enzo]

Oops, you are right, the power switch is not directly in the mains line. I was too busy trying to boost your confidence to forget it is unfamiliar, that I neglected to read the schematic first.

Mainwhile, yes, I have serviced numerous Carver amps of this series. DO you have a variac so we can bring it up slowly? Will the amp run at about 50VAC on the mains? If so, the problem is most likely contained in the power supply.

Still, I would set my meter to diode test and go down the power supply board and check every one, and the bridges, including the large off-board one.

The power imput is really moer simple than it looks, they may call it a magnetic resonance something, but it is still a power transformer. It is just designed to be controled by that triac. The power switch enables the triac through the phase control circuits.

Think of it as a dimmer control running the power supply. It sits at half way up and turns itself up and down in response to power demands.

1 ohm across the mains cord is still suspicious. Check C502,503,504 (near the corner of the power board near the triode connections) for shorts.

Pull the wires off the triac and see if it is indeed shorted. A failure in the phase control circuit could leave it turned on hard.

The triac is called out as the BCR16GM-10L but I also see it listed as SM16JZ41. I don't think there is anything special about it. it is a TO3 style triac is it not? The square thing on a TO3 plate? One tab smaller that the other two? I stock Q4025 and Q4040 types for light dimmers and as power switches in large Peavey and other amps. I would sub one of those in here if I needed to. Mine are in the TO3 "fastpack." They come in other package styles yo udon't want.

In any case, I believe it to be a plain old 16A 400v triac.