MTX Thunder 81001 component value/schematics

[Perry Babin]

Install a good cap there and re-check.

 

[Maxikill97]

Same readings

 

[Perry Babin]

Are the ± rail voltages clean DC?

 

[Maxikill97]

I measure a clean 81v rail voltage

 

[Perry Babin]

What DC voltage do you see (with the scope) on the 3 legs of FET191

 

[Maxikill97]

Pin1: strange waves +-39V DC
Pin2: clean -82v rail voltage
Pin3: sawtooth wave looking +-29v DC

 

[Perry Babin]

What do you see on the base of Q110?

Negative 82v?

 

[Maxikill97]

Correct

 

[Perry Babin]

What do you see on the base of Q110?

That's the positive regulator. It makes no sense that the voltage is negative.

 

[Maxikill97]

You are right. The source I used for a 1D transistor pinout seems to be not right.

MMBTA42 (1D) base is +-31v with a wave on it. Collector has steady -82v rail voltage

 

[Perry Babin]

There should be only positive voltages on that group of parts. Check the probes where they plug into your meter. The reference (black probe) should be the main ground terminal.

Measure directly across D104 (red probe on striped end). If it measures outside of 15v ±10%, it needs to be replaced.

 

[Maxikill97]

D104 measures 15.15V, so within tolerance.
Re-measured Q110, the collector really is -82v. Referenced to main GND

 

[Perry Babin]

Are R145 and R146 within tolerance?

 

[Maxikill97]

Yes, R145 and R146 are within tolerance.

Also, do you know what value R213 has to be? I can't read the marking on it.

 

[Perry Babin]

100 ohms.

What's the DC voltage on R146?

 

[Maxikill97]

With R213, can you re-check? It reads excactly 1000ohm

Voltage over R146 is as good as 0v.
0.005v
Both pads of R146 has minus rail voltage, -82v

 

[Perry Babin]

Do you have a negative rectifier in place of a positive rectifier? The circuit below is what I have for that regulator.

See attached. for the resistor.

 

[Maxikill97]

This circuit seems to be correct. I beep every component in the right place.
The rectifiers installed next to it are negative rail.

The rectifiers on the other side of the heatsink/ board have positive rail.
Attached is a photo from that side.

 

[Perry Babin]

What's the resistance between C118's negative terminal and the primary and speaker grounds?

 

[Maxikill97]

A high resistance.
About 15Mohm