kicker 1200.1

timwebb · 2011-06-01 5:19 am

i got had a blown power supply. i replaced the drive transistors with MMBTA56.
also the 494 ic gets to warm and the drive transistors over heat.

Perry Babin · 2011-06-01 10:53 am

Does the amp produce rail voltage before the driver transistors overheat?

If not, do you get a square wave output on pins 9 and 10 of the 494?

timwebb · 2011-06-01 12:35 pm

this is the signal from the 494 pin 9-10. volts div-.5 time div- 2us

timwebb · 2011-06-01 12:38 pm

this is the signal on q11.and there are no transistors in the power supply.

Perry Babin · 2011-06-01 3:10 pm

Which pin of Q11?

Does the same pin on Q5 look the same?

What's the DC voltage on pins 11 and 12?

timwebb · 2011-06-02 3:35 am

Q11 on the emitter
pin 11 10.74
pin12-11.45

the amp goes in protect with Q5 in the circuit so i pulled it.

Perry Babin · 2011-06-02 11:20 am

If that was the emitter and the base has the same signal as pins 9 and 10 on the 494, the a56 is defective.

timwebb · 2011-06-05 2:42 am

i pulled the drive transistor and the signal still the same.

Perry Babin · 2011-06-05 3:56 am

Replace the driver transistor with a new MMBTA56.

timwebb · 2011-06-05 7:00 pm

ok i did now im getting 1v on the gate resistor.for q11
q5 is getting 5v at the gate resistor. i cant find what is pulling Q11 down.

Perry Babin · 2011-06-05 7:51 pm

Post base and emitter photos for both drivers.

timwebb · 2011-06-05 9:00 pm

Q11. the first is the base second is the emitter.volts/div1.time/div 2us

timwebb · 2011-06-05 9:13 pm

Q5.first one is the base second is the emitter.volts/div .5 time/div 2us

Perry Babin · 2011-06-05 9:18 pm

Q5 appears to be defective. The diode that is connected between the base and emitter of Q11 appears to be defective.

timwebb · 2011-06-05 9:21 pm

what would be a replacement diode? these have no part number on them.

Perry Babin · 2011-06-05 9:27 pm

This should be a good sub.
LS4148-GS18 Vishay Semiconductors Diodes (General Purpose, Power, Switching)

If you have a leaded 1N41438 or a 1N914 (Radio Shack), you can install it to allow further testing.

timwebb · 2011-06-05 10:01 pm

i have 1N4740A

Perry Babin · 2011-06-05 10:06 pm

That's a Zener diode. You need a switching/rectifier diode.

timwebb · 2011-06-06 12:25 am

ok ill sit this to the side till the parts come.

timwebb · 2011-06-07 3:01 am

ok i changed the diode same thing. so i pulled both transistors and still got the same wave as before.