Another MARSHALL Valvestate 2000 AVT150 Blowing fuses......

[blearyeyes]

OK I built a light bulb limiter and I feel like Thomas Edison. I fired it up and the bulb was bright. I disconnected the 32 v secondary and the bulb was dark, the fans came on the switch light was on. I had the power IC circuit boards plugged in. Hmm. Bulb Limiter is good tool. Back to testing the bridge rectifier on the high side.

[blearyeyes]

With meter in diode test mode I got readings from all pairs of pins except the two center pins which gave me 0v with the probes either way.

[Enzo]

Disconnect the wires from the power transformer to check your bridge, otherwise the two AC pins will seem shorted. You are seeing the low resistance of the transformer winding.

[blearyeyes]

Disconnect the wires from the power transformer to check your bridge, otherwise the two AC pins will seem shorted. You are seeing the low resistance of the transformer winding.

The power transformer was disconnected.

[blearyeyes]

I tested it again. It goes up to .9v and drops to 0. Then stays at 0. So I'm flummoxed.

[olddawg]

I tested it again. It goes up to .9v and drops to 0. Then stays at 0. So I'm flummoxed.

Nothing says you have to use the diode test scale. Use your ohm meter to see if any diode junction in the bridge is shorted. Do it out of circuit. Just make. Sure you put it or a replacement back with the same orientation. On thing I do with every repair now is take a picture of what I am working on before I start.

[52 Bill]

I tested it again. It goes up to .9v and drops to 0. Then stays at 0. So I'm flummoxed.

Please be sure that by "0" you mean zero, just as if both meter leads were touched directly together, and not O as in open or ut of range, infinity.

[blearyeyes]

Nothing says you have to use the diode test scale. Use your ohm meter to see if any diode junction in the bridge is shorted. Do it out of circuit. Just make. Sure you put it or a replacement back with the same orientation. On thing I do with every repair now is take a picture of what I am working on before I start.

I was thinking of doin that. Just pulling the thing to eliminate the rest. I'll snap a shot of the area before I do it. Great advice.

[blearyeyes]

Please be sure that by "0" you mean zero, just as if both meter leads were touched directly together, and not O as in open or ut of range, infinity.

I was using the diode test setting which I have never used and really don't know about. When the leads are not touching anything it reads 0L. When touching together is reads 0.000v when touching the two center pins it reads 0L. When I use the continuity checker I do not get any audible short sounds.

I'll pull the freakin thing and use the ohm meter to see if it is shorted anywhere.

Should I check pins 1-2, 2-3, 3-4 and 4-1?

This would be so much easier if I knew what I was doing. It must take quite a long while to get good at this. If you guys ever need to know anything about Forensic audio video examination and image analysis let me know. Har har.

[Enzo]

OL means open then, so the two center pins show open between them, as they should.

WHile the bridge is in circuit, it is still connected to the filter caps and the rest. Your meter tried to charge those. That was what you saqw before it went OL.

As for shorts, you have four legs. Just check each combination:
1-2, 1-3,1-4,2-3,2-4,3-4

[blearyeyes]

I also unplugged all connectors to the front board and the short remained.

[blearyeyes]

The rectifier bridge is not shorted.

How do I test the various rails are not shorted to ground or + to- ?

Or where should I test them is the better question.

[blearyeyes]

The rectifier bridge is not shorted.

How do I test the various rails are not shorted to ground or + to- ?

Or where should I test them is the better question.

Talking to myself as usual. I tested the secondary inputs to the board and none showed a short to ground or from + to -

[blearyeyes]

I checked the voltage regulators for shorts and didn't find any. Input pin to ground, input pin to output pin. Ground to output pin.

[g1]

Just to be clear, which secondary are you calling 32V?
Here is a lind to the schematic for anyone following along: MARSHALL AVT150 AVT275 Service Manual free download, schematics, eeprom, repair info for electronics
I gather that you mean when W106 and W107 are disconnected, the bulb stays dim, but when they are connected the bulb lights bright?
Please try to be more specific in your descriptions, we can only see the schematic, so when you say "disconnected the front board" you need to say which board and which connector number.