Power tranny ht voltage?

[chuckb]

hey guys, i have a 18 watt marshall clone here that belongs to a friend of mine. I'm getting a voltage reading -189v on the HT wires on the power tranny. The spec sheet for this 20 watt transformer says the it should be 325v @270ma. jsut wondering what could be causing the negative voltage?I'm not getting any reading off the B+ at all. The amp lights up so there is power going through the heater wires and the voltage across the 6.3 winding is correct.

Chuck.

[Enzo]

OK, think about it, -187v on the transformer? That is a DC reading, and transformers make AC. Once you put it in a circuit, it will be rectified and DC voltages will result. You want to know what the transformer is doing? Disconnect its secondary and measure AC voltage between the wires. Not to ground. If the transformer does not make voltage, or lacks continuity through the winding, then there is your problem. If the transformer works, then install its wires, and trace the loss of voltage through the power supply. Diodes can be open, or solder joints broken, circuit board traces can be broken.

[Chuck H]

I was thinking something similar. It's probably a rectifier failure. Just guessing but the -V might be due to the DC reading actually being one half of the AC voltage.