amplifier power supply question

[ampjunkielikeme]

i have a amp setting her that somebody else has repaired before . (a kicker kx1200.1) they replaced all the power supply transistors with IRF3205's . now all 8 of these parts are french fried....so my question is.....lol
how can i find out what the amp originally had ? other than seeing another one...lol... can you go off of what voltage/ amp values of the rectifiers?
would it be a good idea to just replace them with the irf3205's again?

[Perry Babin]

The 3205s are a good choice if the gate resistors are less than 100 ohms (47 ohms were used in later models). What are the numbers on the gate resistors (R22, 23, 24...)?

Before you replace the FETs, you need to check the gate driver transistors (Q05, Q11?) near the TL494.

Does the amp have any shorted output transistors?

[djQUAN]

I have used 3205's on a ZX1000.1 and it still works nicely so it should be a good replacement.

[ampjunkielikeme]

perry, the gate resistors are marked 101. they are the surface mount kind....they read 22ohms...

there are no shorted outputs, i found a q11, but it is a tiny tiny 3 leg part. one leg on to p 2 on the bottom....lol
how do i test it?

i also have a jbl1200.1 that had mismatch parts in the power supply that is blown...it had the irf3205, and a few of the original irf3710's . i went ahead and got the original parts to go back in , but the gate resistors are 47ohm....
would it be ok to use the irf3710 parts with the 47ohm resistors?

[Perry Babin]

If the defective power supply FETs are in the circuit, they are causing the gate resistors to read low. You can't use the 3205s with the 100 ohm gate resistors.


Q05 is very near Q11. They are both KTA1504Ss. Look up the datasheet for that transistor or the MMBTA56 (the transistor I recommend you use instead of the 1504).

The original parts were the 3205s. The 3710s won't be as reliable in the power supply as the 3205s. Use the 3205s.

[kim707]

Originally posted by Perry Babin
The original parts were the 3205s. The 3710s won't be as reliable in the power supply as the 3205s. Use the 3205s.

Yeah use the 3205s

[ampjunkielikeme]

ok, im going to use the 3205's..lol...

can you give me a part number from mouser for some 47ohm surface mount resistors?

[Perry Babin]

If they're 1206 size:
660-RK73B2BTTDD470J

[ampjunkielikeme]

im not sure what size they are...here is a pic of the original ones.

[Perry Babin]

If they're just slightly longer than the center-center distance between the legs of the transistor, they are 1206s.