MTX Thunder 81001

[mike49504]

Amp will not power up ..



TL494

Pin 1:0
Pin 2:4.75
Pin 3:0.06
Pin 4:4.53
Pin 5:1.48
Pin 6:3.16
Pin 7:0
Pin 8:13.89
Pin 9:0.02
Pin 10:0
Pin 11:13.89
Pin 12:13.89
Pin 13:4.90
Pin 14:4.90
Pin 15:4.90
Pin 16:0

Atleast it appears to not be powering up no power light now voltage on the gate legs ..

Any ideas?

 

[Perry Babin]

If the collector of Q101 goes to pin 4 of the 494, post the voltage on all three legs.

 

[mike49504]

Its marked 2G so im assuming its a MMBTA56 if so the base connects to
pin 4 of the 494


Base:0.91
Emitter:4.82
Collector:4.90

 

[Perry Babin]

The base shouldn't connect to pin 4 as far as I know.

It appears to be shorted collector to emitter and open base to emitter.

 

[mike49504]

Replaced Q101 and tested voltages I get the same voltages on the new one..

There is an led lit on the board that says for service only..

Also Led 400 is lit .. Its right next to the op-amps in the output section..


Amp powers up but idle's around 8 amps of current draw not sure if thats normal for this amp..

 

[mike49504]

Ok Q101 has its collector connected to pin 4 of the 494.. I put a brand new one in the amp and this is what i get for voltages..


Collecter:0.34

Base:4.85

Emitter:4.90

 

[Perry Babin]

Did you have the pin configuration wrong previously or has something else changed?

 

[mike49504]

I looked up one datasheet and it was marked wrong..

I looked up a different datasheet and got the pin config right this time..

 

[mike49504]

Ok theres a problem in the output section of this amp..

I pulled the rectifiers (all 4) for both supplys amp powers up and idles fine now..

So i guess i will check some stuff there to see what i come up with

 

[mike49504]

Im not with it tonight there is only one supply in this amp.. I will do a lil more checking to see if i can find whats making it go into protection

 

[mike49504]

Ok i dont know why i didnt catch this before..


All outputs test fine But i have full rail voltage on the output terminals

123.6 volts...


Any ideas?

 

[mike49504]

I found some shorted transistors resistors and a diode..

Anyone have a high res pic of the area Around the rectifiers ??

I need the side containing D105,Q109,Q11 ect..

This is right behind the rca inputs

 

[Perry Babin]

See attached.

That is the -15v regulator.

 

[mike49504]

R127 is a 5.11K resistor its measuring 5.42K is that close enough to the tolerance or should i change it ?

 

[mike49504]

Ok i replaced the following components:

D105
R119
R123
R127
Q109
Q111
Q108
R122

All of theese were defective..

Should i check anything else before powering it up?

Also Do you have an idea on why all of theese were defective ? Seems like alot of parts were bad in this one area

 

[mike49504]

Ok I powerd it up and the for service only lite it still on..


I have 8.95 volts of DC across the output terminals Any ideas?

 

[Perry Babin]

The service LED indicate that the caps are charged. Post the DC voltage on both of the op-amps near the opto-couplers.

 

[mike49504]

NE5532D

Pin 1:2.02
Pin 2:8.48
Pin 3:8.40
Pin 4:6.94
Pin 5:1.73
Pin 6:8.55
Pin 7:9.10
Pin 8:15.67



NE5532D

Pin 1:15.56
Pin 2:13.99
Pin 3:14.35
Pin 4:6.95
Pin 5:14.50
Pin 6:14.04
Pin 7:15.42
Pin 8:15.72

 

[Perry Babin]

No negative supply.

 

[mike49504]

On the non stripped side of D105 i have -15 volts

On the other side i have 0 volts

Directly across D105 i have - 15 volts

So do i need to follow the traces abck to see where im losing the -15 volts ?