Mesa Maverick Blowing Fuse

[AtomicMassUnit]

This is a little puzzling. With the power tubes and rectifier tube pulled, with the rectifier switch set to tube, the fuse doesn't blow. With it set to solid state rectifier, no tubes in, it does. The rectifier diodes all test good, and with the switch set to tube, I measure approx the right voltage on either side of the rectifier diodes (running it through my current limiter lamp).

With the rectifier tube plugged in, and the switch set to tube, it is not drawing too much current, but I am not getting DC voltage on pin 8 either.

EDIT* I tried a different rectifier, and it is drawing too much current now in both settings, so the first rectifier tube wasn't working, and there is also a problem in the power supply. One of the 30uf filters is reading 105 ohms to ground, but when I lift it, the cap isn't shorted, the trace connected to the + side still reads 105 ohms to ground.

[AtomicMassUnit]

The OT center tap is shorted to ground.

[g1]

With it disconnected from the circuit?

[soundguruman]

There's a couple things you need to know about boogie amps:
1. Resistors laying directly on top of circuit tracks. Sometimes the resistors burn through to the circuit tracks. The insulation breaks down.
Lift the resistors off the tracks, so that there is a space between the board and the resistor. Look for a burn spot under the resistors.
Happens more often when the amp is used in humid conditions, like near the ocean, or where it rains a lot, in high humidity climates.

2. Burning through fiberglass, arcing between closely spaced circuit tracks. Look very carefully with a magnifier. Look for a small burn spot between two closely spaced circuit tracks.
Once the arcing occurs, it burns the fiberglass, it turns the fiberglass into carbon. When the carbon forms, the carbon IS a resistor.
Any carbon spot that forms must be cut or drilled out. This can cause the fuse to blow or it can cause erratic operation, popping, noises, distortion.
The most common place in a mesa amp for the burning to occur is between the grid and the plate tracks, or between the plate and the heater tracks.

As you can see, the circuit tracks are very closely spaced, in fact too close. It arcs and burns.
Burning between the resistors and the circuit tracks, or between circuit tracks, is well known in mesa amplifiers.

[AtomicMassUnit]

There's a couple things you need to know about boogie amps:
1. Resistors laying directly on top of circuit tracks. Sometimes the resistors burn through to the circuit tracks. The insulation breaks down.
Lift the resistors off the tracks, so that there is a space between the board and the resistor. Look for a burn spot under the resistors.
Happens more often when the amp is used in humid conditions, like near the ocean, or where it rains a lot, in high humidity climates.

2. Burning through fiberglass, arcing between closely spaced circuit tracks. Look very carefully with a magnifier. Look for a small burn spot between two closely spaced circuit tracks.
Once the arcing occurs, it burns the fiberglass, it turns the fiberglass into carbon. When the carbon forms, the carbon IS a resistor.
Any carbon spot that forms must be cut or drilled out. This can cause the fuse to blow or it can cause erratic operation, popping, noises, distortion.
The most common place in a mesa amp for the burning to occur is between the grid and the plate tracks, or between the plate and the heater tracks.

As you can see, the circuit tracks are very closely spaced, in fact too close. It arcs and burns.
Burning between the resistors and the circuit tracks, or between circuit tracks, is well known in mesa amplifiers.

I will definitely keep an eye out for that. I unsoldered the OT center tap, and it reads dead short to ground. With it removed, the stby switch, caps etc are no longer reading shorted to ground.

What was throwing me off was that dead rectifier tube, never saw one that didn't blow the fuse when bad, so I thought it was working.

[soundguruman]

That's not to say that conventional, normal failures occur also. Like a shorted OT.
I thought I would mention the arcing burning failures also, just for future reference.