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mike49504 15th February 2012 12:52 AM

MTX Thunder 81001
 
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 15th February 2012 10:40 AM

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

mike49504 15th February 2012 12:01 PM

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 15th February 2012 12:19 PM

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 15th February 2012 04:28 PM

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 16th February 2012 01:50 AM

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 16th February 2012 01:51 AM

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

mike49504 16th February 2012 01:52 AM

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 16th February 2012 02:24 AM

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 16th February 2012 03:07 AM

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


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