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Old 3rd May 2012, 11:39 AM   #1
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Join Date: May 2012
Default Next Q24 not powering up

Hello!

I have a Next Q24 car amplifier that does not power up. Next Q24

There are no burned/exploded components inside. I have changed KIA494AP to TL494IN because I had one extra piece of them and they seem to match. I replaced some capacitors also in case I was lucky.
I measured TL494 pin voltages and here are results:

TL494
Pin 1: 0,00
Pin 2: 4,96
Pin 3: 4,77
Pin 4: 1,70
Pin 5: 1,80
Pin 6: 3,65
Pin 7: 0,00
Pin 8: 12,63
Pin 9: 0,00
Pin 10: 0,00
Pin 11: 12,63
Pin 12: 12,63
Pin 13: 4,97
Pin 14: 4,97
Pin 15: 0,06
Pin 16: 2,46

What should I do next?
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Old 3rd May 2012, 06:17 PM   #2
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Join Date: Nov 2003
Location: Louisiana
It's being shut down because pin 15 is lower than pin 16. Pin 16 may be the reference (1/2 of the voltage on pin 14). If that's the case, follow pin 15 back to see what's driving it low.
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Old 4th May 2012, 10:58 AM   #3
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Thank you for reply. What could propably drive it low? Transistor?
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Old 4th May 2012, 12:36 PM   #4
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I replaced two old 2sc3198Y transistors to 2sc3198O because local shops did not have anything else. http://www.semtech.net.cn/script/pro...1234218412.pdf As you can see, gain is lower with these new ones. Now pin 15 voltage rises slowly to 2,00 volts but other pin voltages are same as I posted earlier. What transistor(s) could match properly to sc3198y?
And thanks again for helping me.
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Old 4th May 2012, 05:11 PM   #5
diyAudio Member
 
Join Date: Nov 2003
Location: Louisiana
Is there a transistor driving pin 15?

Is there a capacitor connected to pin 15?

If you short pin 15 to pin 14, the amp may power up. This will disable the protection circuit so you'd have to be careful (transistors clamped, 10 amp fuse in the B+ line...) but if all channels produce clean audio, you know to troubleshoot the protection circuit. If it doesn't, you know which channel to troubleshoot.
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Old 6th May 2012, 04:20 PM   #6
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Yes, it is connected straight to NPN transistor with heat sensor driving it and also to PNP transistor that is drived by another PNP transistor. There is one capacitor connected to pins 13 and 14 and they are connected to pin 15 through a 56,2 ohm resistor.
I shorted 14 and 15 and the extra fuse burned. Repeated the test and extra fuse burned again.
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Old 6th May 2012, 06:04 PM   #7
Mote is offline Mote  Estonia
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Location: Estonia
Have you checked the power supply FETs and output transistors? There are very useful links in Perrys signature.
__________________
Tools: Perrys tutorial, C1-76 o-scope, Weller WHS40, Mastech MAS830L multimeter, Mastech MY6243 LC meter, 16A supply
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Old 7th May 2012, 03:23 AM   #8
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Location: Louisiana
That probably means that it has shorted output transistors and the protection circuit is preventing the amp from powering up.
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Old 6th September 2012, 06:38 AM   #9
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Output transistors were shorted as you thought. Unfortunately they are too expensive to be bought for this amp.
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