i have a rockford 250.2 (silver/gold), just replaced all the power supply transistors as they had obviously blown 😱, 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.
i think (hope not) that the transformer is shorted but not sure how to test it?
Mark.
on closer inspection the transformer looks like it got more than a little hot, looks like the amp is a right off unless i can wind a new one but this is new teritory for me!
Connect only remote and ground to the amp (no B+). What is the DC voltage on the gate legs of each of the power supply FETs?
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?)?
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 😱
i don't want to put +/- 12v on as the amp starts to draw 30amp rather quickly..
Replace the parts that you know are defective and recheck the gate voltage with no B+ applied. All should be approximately the same (which is typically ~5v).
Q1,2,4 and 5 appear to have p1a 59 on them, hard to tell as they are so small, is this correct? can't seam to find much info on them..
resistors should be easy to find although in 500's!!
resistors should be easy to find although in 500's!!
just recieved the transistors but the MMBT3904 is about half the size as stock, is this ok? i got them as a matching set so strange one would be smaller than the other 😕
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)
MMBT3904 and MMBT3906
but on them they say AMx and 2Ax, the 2Ax are the correct size but the other ones are half the size 😕
The AM part may be an MMBT3904W. It should work for testing but I don't know if they will be reliable. Their power dissipation rating is a bit less.
that makes sense, luckily i don't think i need to replace those ones as they check out ok..
will report back when i have swapped the p2's and 22ohm resistors..
Mark.
well, had a bit of luck 🙂 replaced the p2's and also swapped the 3 22ohm resistors but just with regular ones (rats nest🙄) 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?
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