hk lucas 600 poweramp sub

[piem]

howdy,

i'm trying to fix the amplifier of the subwoofer of an hk lucas 600. i found a related thread here on this forum.

the fuse were blown, and i found that 2 of the output transistors were shorted. so i replaced all four on the board, 2x MJ4032 + 2x MJ4035, with MJ21195G and MJ21196G. now the fuses are not being blown anymore when powering on the device, but the sub produces a hum and 2 of the output transistors are overheating, so i quickly turned off power. the 2 output transistors that are overheating is the pair that i changed even though they were not shorted.

did i pick the wrong replacement parts? any clue how to debug the issue?

thanks, piem

 

[davenn]

did i pick the wrong replacement parts?

maybe ? did you compare the different parts by comparing datasheets for compatibility ?

 

[Bluejets]

The originals first up are high gain darlington....your replacements are not.

The originals although obsolete, are still availible apparently in the US and the UK on Ebay at least.

 

[piem]

thanks for your answer @davenn, and @Bluejets.

i did, but i guess i have done it wrong. here are the links to both datasheets and the specs i looked at:
old darlington pair (MJ4032 / MJ4035)
- Vcbo/Vceo 100V
- Vebo 5V
- Ic 16A
- Ib 0.5A
new transistor pair (MJ21195G / MJ21196G the ones i picked)
- Vcbo/Vceo 400/250V
- Vebo 5V
- Ic 16A
- Ib 5A

@Bluejets, what new parts would you recommend as a replacement?

 

[piem]

also, would it be useful to add a thermal insulator such as this one ?

 

[Bluejets]

what new parts would you recommend as a replacement?

Original, as I said above.

 

[Delta Prime]

Do you have a schematic this is all I could find.
Do you know what year your unit is? the number of the PCB itself and what revision it is?
Can you take a photo of your board both sides component side,solder side, please thank you.
Happy belated welcome to Maker Pro!