"Z" Transformfer problems

[stubbsO]

I picked up a old Z over the weekend. I took it apart and cleaned out all the cobwebs, dust, dead bugs, etc., replaced the cord and rollers and put it back together, kept my fingers crossed and plugged it in.  No problems! Turned up all the throttles and took a volt meter to it to see how much juice it throws out, 25 volts like the other 2 that I have, good! Now for the test of checking the C.B., I took a wire and shorted it out at the lugs, man did that thing spark big time. Bigger than I've ever seen before! The C.B. popped pretty quick, then there was a good puff of smoke comming from the C.B. area. I tried this twice with the same results. I haven't taken it apart yet to look at the C.B. to see if I really cooked it or if it's something else. Do you guys think that the C.B. is toast or might it be something else? I plan on replacing the C.B. anyway just to CMA, but want to get some second opinions on what it might be. Thanks

[lionelsoni]

I think the circuit breaker is toast, or it might be something else...;-)  Actually, the only way to know whether the circuit breaker is working properly is to test it under a known load.  Unfortunately, a straightforward test involves a large and expensive resistor.

So here's another test that might work.  I have not tried it; so you do it at your own risk.  With the transformer not plugged in, connect a parallel combination of 120-volt incandescent lamps whose power ratings add up to 100 watts in series with the line cord.  Turn output A (for example) all the way up and connect a minimum-14-AWG wire between A and U.  Clamp an AC ammeter onto that wire.  Plug the thing in.  I expect that you might see roughly 10 amperes on the meter but less than 15.  If less, turn the A control down until the ammeter reading goes up to about 10 amperes.  Wait a while.  If the circuit breaker trips, it is too sensitive.  Otherwise, carefully turn the A control down until the current passes 15 amperes.  Keep going until it reaches about 20 amperes.  Do not go any farther.  If the circuit breaker does not trip within a minute or two after you pass 15 amperes, it is not sensitive enough.  Unplug the whole thing.

If the circuit breaker passes this test, you should leave it in place, since you will have just proved that it is in working order and properly calibrated, which is more than you know for sure about any replacement that you might buy.