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Old 15th February 2012, 01:52 AM   #1
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Default 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?
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Old 15th February 2012, 11:40 AM   #2
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If the collector of Q101 goes to pin 4 of the 494, post the voltage on all three legs.
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Old 15th February 2012, 01:01 PM   #3
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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
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Old 15th February 2012, 01:19 PM   #4
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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.
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Old 15th February 2012, 05:28 PM   #5
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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..
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Old 16th February 2012, 02:50 AM   #6
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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
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Old 16th February 2012, 02:51 AM   #7
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Did you have the pin configuration wrong previously or has something else changed?
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Old 16th February 2012, 02:52 AM   #8
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I looked up one datasheet and it was marked wrong..

I looked up a different datasheet and got the pin config right this time..
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Old 16th February 2012, 03:24 AM   #9
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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
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Old 16th February 2012, 04:07 AM   #10
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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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