Power transformer for stereo - shorted - why?

One day MaxVT got dressed and committed to text

I'm thinkin you might be in "over your head" on this one ??

-- Regards ..... Rheilly Phoull

You can disconnect the capacitor to see if it is shorted. If it is, it might have damaged / ruined the power transformer. The primary can be checked with an ohmmeter, and should read a near-short. If it's an open-circuit, the tran is bad. If these tips don't help, you may indeed be in over your head. The AC input / rectifier stage of a linear power supply is a simple circuit, but with no training or test equipment, your chances of fixing anything more than a bad fuse would be slim.

Mark Z.

You may be misreading which wires are parts of which windings. It's not too unusual for two independent windings to be connected to each other in funky ways to choose 120VAC vs 240VAC inputs, for example.

Big leap time: plug it in, see if you get AC out of the transformer and DC volts across the filter caps.

Tim.

Multiple windings on a transformer are many times jumpered (or shorted) to produce desired voltages. Is the "capacitor" really a MOV? .... or if it really is a capacitor or not, you can unsolder one of the leads from the circuit and measure it to see if it is indeed shorted...... brilliant idea..... huh?

If the resistors are very low ohm (did you "READ" the value on the resistor?) they can appear on some meters to be just about a short.... or if they are inductors or PICO fuses they can read almost a short. Again, unsolder one of the leads so you won't be confused with the low resistance of the transformer winding that it is connected to.

I am th;inking here that you may want to call in one of your tech friends with a little more electronics knowledge and repair experience to assist you with this troubleshooting.

Thanks for all input, everyone! Now, the saga continues...

I've checked the transformer: one winding produces +19.2v, -19.2v and (I assume) ground, the other produces 10v and ground.

Continuing to main board, there is a diode bridge and from there 3 regulators: 5v standby, and +15v / -15v controlled with a relay.

A relatively big resistor immediately before the input to 5v regulator is cracked and the solder has evaporated from its connection. Also, there is a leaked cap in the -15v circuit.

I can replace the resistor and the cap, however how can I check that the regulators (7805C, 7815C, 7915C) are OK and the load is not excessive, so as not to create any additional leaks and explosions?

BTW, I do have electronics knowledge (B.Sc in EE), however zero repair experience... One has to start somewhere :)

Thanks,

MaxVT

Check with a multimeter that they're not shorted, otherwise they have internal overload protection so you can apply power and measure the output voltages.