alpine 3553 amp, 5 amps at idle & runs hot

[an2ny888]

my alpine 3553 amp got flooded a while ago, all the 2sd1669 ( 6pcs ) blew so i replaced them, now the amp works but runs extremely hot and draws 5 amps, even without speakers attached. any suggestions on what to do? a tech guy here said i should adjust the bias, any one care to explain how this is done?

 

[Perry Babin]

With all transistors clamped tightly to the heatsink, does the heatsink heat up under the power supply transistors (the ones you replaced) or under the output transistors?

If it gets hot under the outputs, the bias may need to be adjusted, especially if someone has moved them from their original setting.

It's also possible that some component has been damaged by the moisture and that's causing the overheating.

 

[Plammox]

If it turns out not to be the bias:
Were the old transistors isolated from the heatsink, or was the heatsink isolated from the chassis previously?

 

[an2ny888]

its heating up under the power transistors i replaced, it only takes a couple of minutes to get really hot. turns out there are no provisions to adjust the bias, i dont see any trim pots. the transistors are clamped to the heat sink, any suggestions what to check out next?

 

[Perry Babin]

I don't have any information on that amp. Can you post a photo of the inside of the amp (specifically the area near the transistors you replaced).

 

[an2ny888]

here some pics

 

[Perry Babin]

There are 1 and 10 ohm resistors just in front of the power supply transistors you replaced. You need to check each of them to confirm that they're within tolerance.

If those are OK, check the C3852 transistors. You will need to desolder them to check them.

 

[an2ny888]

i checked the resistors and they read all 1.5 and 4.5, i attribute the 4.5 ohm reading to the fact that its connected to the transistor. i replaced the c3852 transistors, turns out they weren't bad. Now the power supply goes up to 10 amps when i turn the amp on! what did i do wrong?

 

[Perry Babin]

Remove the resistor and re-check it.

 

[an2ny888]

rechecked the resistors, they're .5 ohms over spec, is that a big deal? or is that within acceptable spec?

 

[Perry Babin]

The resistors should be within 5% of the marked value. Did you subtract the resistance of the meter leads from the resistance you measured across them?

Are there two C945 and two A733 driver transistors? They would be connected like Q812-Q815 in the attached diagram. If so, remove them and check them. In addition to confirming that no transistor is shorted, you need to confirm that each transistor has two good PN junctions (base to emitter and base to collector -- should read ~0.6v on diode check).

 

[IrishboyM4]

did you ever get this working? i can get you numbers from my working 3553 if you want. i have it ripped apart right now...