Next Q24 not powering up

[ransaahi]

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?
http://amp-performance.de/296-Next-Q24.html

 

[Perry Babin]

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.

 

[ransaahi]

Thank you for reply. What could propably drive it low? Transistor?

 

[ransaahi]

I replaced two old 2sc3198Y transistors to 2sc3198O because local shops did not have anything else. http://www.semtech.net.cn/script/product/manage/pic/3191234218412.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. 🙂

 

[Perry Babin]

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.

 

[ransaahi]

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.

 

[Mote]

Have you checked the power supply FETs and output transistors? There are very useful links in Perrys signature.

 

[Perry Babin]

That probably means that it has shorted output transistors and the protection circuit is preventing the amp from powering up.

 

[ransaahi]

Output transistors were shorted as you thought. Unfortunately they are too expensive to be bought for this amp.