Crate VTX200s Assistance

[keithb7]

Tonight I picked up a free 2004 year Crate VTX200s amplifier. Owner told me he's an electrician and the power transformer was fried.
Not sure how honest he is, just a stranger in my town. It was free, looked good too, so I took it. Got home unscrewed the rear panel. Three output
wires out of the transformer (2 red, 1 green) are disconnected from the board. I found a schematic on line. Hooked up the wires to the correct
points on board. Fired it up. Buzzing sounds for a few seconds. Blue flash and then nothing. Opened up, fuse blown.

Are these guys still in business? Can I order a new transformer from them? Thanks, Keith

[52 Bill]

Hooked up the wires to the correct points on board. Fired it up. Buzzing sounds for a few seconds. Blue flash and then nothing. Opened up, fuse blown.

The correct test would be to fire it up with the transformer unhooked from the board, then if the fuse blows, it is the transformer. With the transformer connected to the board it could also be a shorted component in the amp causing the fuse to blow.

[Enzo]

Agree^^^

The guy says the transformer is bad, so the first thing to do is test that, not reconnect it.

If you do need a transformer, Crate is certainly still around, they are a part of Loud technologies (Mackie, etc) The part number will be right on the thing.

[keithb7]

Thanks for your guidance. Yes I should test transformer next. I thought I'd plug it in, see what happens. Transformer is labeled that it has an internal thermal fuse. Was thinking maybe there was a chance it just got hot, shut down, and previous owner just parked it. This is not the case it seems. I suppose I need some type of controlled power supply to put power to the transformer to test it? I was watching a few online videos. A person was using a variac. I don't have one. If I plug the transformer in to the wall AC power, I assume the fuse will blow again immediately due to a internal short, allowing high amps through. Is there another way to easily test it without a power supply?

I contacted the new Crate owners, they no longer service this amp. I am on my own to locate a transformer, if indeed this is the problem. Here is a schematic I located. I am not sure how to read it.
Am I on track thinking I need 120V in, 250V out? Or is is 200V out? See here. Thanks for your help.

[g1]

The transformer gets 120V input from the wall.
Disconnect J9,J10, and J11. Plug it in to the wall and see if the fuse still blows. If it does not, the transformer should be ok and you can start looking elsewhere.
If the fuse still blows with J9,10,&11 disconnected, then the transformer is bad.

[52 Bill]

If I plug the transformer in to the wall AC power, I assume the fuse will blow again immediately due to a internal short, allowing high amps through. Is there another way to easily test it without a power supply?

Assuming that the transformer is bad is not the correct approach here. You need to test it to see if it is bad and then figure out what you need to do.

If you don't have access to advanced test equipment like a Variac, you can build a light bulb limiter that will save your fuses at least. The fastest test would be to disconnect all of the transformer secondaries from the circuit, replace the fuse and then turn on the amp. If the fuse blows, then you can assume that the transformer or wiring has a problem.

As for replacements, I don't know where you got the 200 volt figure. The power supply is rated for plus and minus 40 volts dc. The new transformer needs a secondary of about 60 volts ac, center tapped.

[Enzo]

Loud may no longer "service" the amp, but the thing to ask them for is simply the part number. If you ask about the AMP, they look it up on a sheet that says they don't support it. if you ask for a part number - don't mention what it is for other than it is a transformer - they look it up in inventory.

And if you let US know what the part number is, we MIGHT just have one. But do the tests first.

Many power transformners have internal thermal fuses. They open the primary when they blow. So if your thermal fuse was blown, the transformer would sit there like a brick and do nothing. simple test is measure for continuity through the primary, it is open or it is not.

They guys told you, make a "light bulb limiter" - very simple - and use it. Disconnect all secondary wires from the circuit and leave only the primary wired. If the bulb glows bright, your transformer is probably bad. if it stays dim, it is likely good.

[DrGonz78]

Am I on track thinking I need 120V in, 250V out? Or is is 200V out? See here. Thanks for your help.

You are reading 250v at C25 which is a capacitor rated at 250 volts. That is on the primary side of the transformer(left side) and on the secondary(right side) there are D12-D15 rectifier diodes that have a voltage rating of 200v. Don't get the overall voltage rating of a component confused with the "Working" voltage that amp produces for it's power supply.

[keithb7]

Thanks for your responses. I am fairly comfortable getting by, servicing tube amps. I am used to high voltages seen in tube amp circuits. I am pretty much useless around solid state amps. I have not studied them and do not understand yet how they amplify.

"As for replacements, I don't know where you got the 200 volt figure. The power supply is rated for plus and minus 40 volts dc. The new transformer needs a secondary of about 60 volts ac, center tapped."

On the schematic seen above, there is a 250V number near bottom left of transformer, and 4 200V markings to the right near what I think are diodes? Not knowing how this circuit works, I thought I was on to something looking at those voltages.

I will consider building a Light Bulb limiter as instructed above for future use.

I did remove the wires from the transformer to the circuit. Inserted a 3 amp fuse. Plugged in and turned it on. The fuse did not blow. I then powered off the amp, I plugged the wires from the PT to the circuit, and turned the amp back on.
Fuse blows immediately. I think this one is over my head. I don't see any signs of problems in the board when inspecting. Maybe I could remove the board and flip it over? Have a look at the back, maybe I'll find a burned spot?

[J M Fahey]

Sorry but it does not work that way.

You'll have to plug the amp into a bulb limiter for safety, turn it on without a load and start measuring voltages to begin with.

One thing is (or was) certain, the internal thermal fuse had NOT tripped because otherwise the transformer would have just sat there, doing nothing, not even buzzing.

Of course, it might have died later in the middle of the blue flash explosion.
Good thing is that you can repeat the test ... with the bulb inline of course and secondary disconnected.
If the bulb blinks, there's still hope; if it shines bright ....

As of SS vs Tube circuits comparisons: 80% of things work exactly the same.

You could have recognized the bridged rectifier, used by many including Marshall JCM900 (just an example) plus if supply voltage was clearly given as +40V and -40V , they come from 40*0.707=28VAC secondaries ... same as in capacitor input tube supplies (all modern ones, modern meaning after 1940).

As of diode PIV rating, popular 1N4007 stands 1000V ... yet are used in, say, 300 to 450VDC supplies.

[nickb]

Here is the complete schematic

[Jazz P Bass]

Not too sure if this was addressed.

The wiring of the power transformer secondaries to the PCB is as follows:
The two Red leads : one each goes to J10 & J11.
The Green lead goes to J9.

[g1]

Well, you have made at least some progress, you have proven that the power transformer is not the problem.
The fault will be somewhere else in the amp, and will likely not be visible like some burnt spot.
There are some resistance checks that can be done without having to power up the amp.