crossfire cfa-602, car audio amp problem

[tuneman]

hi

i actuall posted this in the wrong section, so ill have another go

i have a crossfire cfa602 amp that is making a weird high piched noise about 10 sec after its turned off! it slowly drops in pitch for about 4 or so seconds then dissapears, almost like a cap or something discarging.
thats with the rca's dissconected, mostly in the right channel and a little in the left.

the amp still works fine its just annoying

i know this amp is getting on a bit(10-12years old!) but its 1 of 6 i am using at the moment, this one powers a set of usd HLCD's
if i recall correctly the amp at one stage of its life accidently had its 2 channels wired together, it shorted and blew the 30a fuse in one channel.

was that the likely cause?

anyone with any idears on what it is, i dont have a huge knowege of how they work but i can usually fix most things.

thanks

[tuneman]

ok, hears some pics,

i have been told to check the output protection circut, any idear when that may be located?

[Perry Babin]

Do any of the following transistors connect to a trace that goes back to the power supply end of the amp? The trace could be on the top or the bottom of the board.

Q130
Q131
Q132
Q230

[tuneman]

ok,

yes they do, Q230, Q131, and Q130 all have a trace from there centre pin that jumps the power supply caps and goes to a resistor R313 in the small group of components on the power side of the board

Q132 does its own thng, no trace from that one

[Perry Babin]

Monitor the DC voltage on each end of R313. Place the meter probe on the resistor and power up the amp (apply remote voltage). The voltage should change significantly after a few seconds. Switch the amp off. The voltage should go immediately back to the voltage that's on the resistor initially (just after remote voltage is applied).

Place the black meter probe on the amplifier's ground terminal. Place the red meter probe on the point where you need to measure the voltage.

Post what you find.

[tuneman]

ok heres what i got

measurements on either side of R313 were the same

with power connected but remote lead off, measured nothing
connected remote and took a second for the amp to turn on and power light to glow
but as soon as it went on the voltage went from nothing straight up to 40v

disconected the remote lead and it drops to 23v or so then continues to drop to 2-3v in about 4min and i assume is going to drop to nothing like it did initially

what does that mean?

[tuneman]

actually i also grabbed another 602 and measued that, its the same.

i did notice they changed a few components between the 98 and 99 models, a few different sized caps and some extra circutry in the 99 model

[Perry Babin]

What is the number on the face of Q304?

Do you read ~0 ohms between any leg of Q304 and the ground terminal of the amp?

[tuneman]

q304 is -

K849
A1268

if im looking at the face, the 3 pins from left to right measured to ground -

4.1 meg, 30.3k, and 3.7 meg

[Perry Babin]

Remove Q101 and Q201. It may pop when turning on or off. Does that prevent it from making the noise when turning off? Does it make the noise worse?

Reclamp ALL heatsink mounted components BEFORE applying power.