MTX Thunder 3401

[S Merlington]

I get -70.4 volts measured directly acroos the speaker terminals..

I removed the NE5532 and the voltage drop to -50.3 volts..

All outputs test fine..

On the pads for the NE5532 i get the folloing voltages

Pad 1:-0.58
Pad 2:-8.32
Pad 3:0.00
Pad 4:-49.6
Pad 5:0.00
Pad 6:0.00
Pad 7:0.00
Pad 8:48.8


Does it appear that the regualtors have failed??

 

[Perry Babin]

Yes. Expect other failures as well (op-amps, open 10 ohm resistors...).

 

[S Merlington]

Replaced the regulators LM317, LM337,

Also replaced the TL072 that sits behind the RCA Jacks. The NE5532, R138,R139..

Replaced all the 10 ohm resistors on the preamp board..

I didnt plug the preamp board in yet i powerd the amp up and Got + -15 volts on the op-amps but after a min the regulators failed again..

Any ideas what to check?

 

[Perry Babin]

Were the regulators clamped to the heatsink?

 

[S Merlington]

Yes i had the regulators clammped tightly to the heatsink

 

[Perry Babin]

When they failed, did they again drive rail voltage to the op-amps?

If not, how did you determine that they failed?

Did the 10 ohm resistors open again?

 

[S Merlington]

When they failed I noticed i get 50 volts on the speaker terminals..

I have + - 50 volts on pins 4 and 8 of the NE5532..

10 ohm resistors are still measuring good..

 

[S Merlington]

Amp works with preamp board removed and jumpers in place..

I replaced all the TL074's and 10 ohm resistors on the preamp board..

Also replaced the TL072 on the preamp board

When i plug the preamp board into the main board amp has no output..

Any ideas on what to check?

 

[Perry Babin]

Do you have both positive and negative supply voltage on every op-amp on the preamp board?

 

[S Merlington]

No

 

[S Merlington]

I overlooked 2 10 ohm resistors..

Amp is up and running Thanks Perry,