disgnosing a shorted transformer?

marko

Member
2004-05-08 11:40 am
donnyuk
i have a rockford 250.2 (silver/gold), just replaced all the power supply transistors as they had obviously blown :eek:, also swapped a couple or outputs out that were bad now the outputs all seam ok but the power supply still has a short somewhere..

i think (hope not) that the transformer is shorted but not sure how to test it?

Mark.
 

marko

Member
2004-05-08 11:40 am
donnyuk
It appears that you have some defective driver transistors and possibly some defective gate resistors.

Did you confirm that all gate resistors were within tolerance?

What is the DC voltage on pins 9 and 10 of the TL494?

What is the DC voltage on the bases and emitters of all of the power supply driver transistors (Q1, Q2, Q4 and Q5?)?

2 of the driver transistors look shot (very hard to tell but the have a small bump in the middle!)

2 of the gate resistors are shot, one is reading 88 ohms and the other is blown apart, there again these sm's are so small i miss them :eek:

i don't want to put +/- 12v on as the amp starts to draw 30amp rather quickly..
 

marko

Member
2004-05-08 11:40 am
donnyuk
sorry for the bad picture! you can see the p2's are blown and are reading low ohms, the p1's seam fine (the replacments for p1's were the small ones anyway)

DSCN4171.jpg
 

marko

Member
2004-05-08 11:40 am
donnyuk
well, had a bit of luck :) replaced the p2's and also swapped the 3 22ohm resistors but just with regular ones (rats nest:rolleyes:) until the sm ones come and it works! only thing i've noticed is it's pulling 4.5 amp on idle, maybe a little higher than i would of thought for this amp, maybe the bias could be tweeked?