A bit of a novice here and getting more and more into DIY, I was thinking of replacing the two large filter caps in my 21 year old subwoofer plate amp. In order to do this I need to remove the board but and as you can see the PCB and transistors are screwed to the heatsink and behind the transistors is thermal paste between them and the heatsink.
How does one go about removing the board without damaging the transistors? Once off does the thermal paste then need to be removed and I would need to apply new paste?
Any help would be appreciated. Thanks!
How does one go about removing the board without damaging the transistors? Once off does the thermal paste then need to be removed and I would need to apply new paste?
Any help would be appreciated. Thanks!
Don't do this if there is no problem. It's a big mess, and there is too much that can go wrong.
You could practice on some junk boards. It's a single sided board, and all the transistors (and sink)
would have to be cleaned off with alcohol, and remounted with fresh insulators and thermal grease.
Capacitors appear to be made in Feb 2002. You'll probably see the caps bulging before any problems happen.
But if and when you do this, buy quality capacitors like Nichicon, not "Jun Fu".
You could practice on some junk boards. It's a single sided board, and all the transistors (and sink)
would have to be cleaned off with alcohol, and remounted with fresh insulators and thermal grease.
Capacitors appear to be made in Feb 2002. You'll probably see the caps bulging before any problems happen.
But if and when you do this, buy quality capacitors like Nichicon, not "Jun Fu".
Last edited:
Thanks, rayma. There are no issues and wondered if I might be advised not to do anything. These Jun Fu caps are cheap and am shocked they are still kicking. In the event a cap fails in the future and I want to replace it how the heck does one remove the pcb away from the paste assuming it will be adhered? Heat gun?
The grease won't be a problem when removing the pcb from the sink.
I would never do this if there is no problem, but I'm lazy.
Remove connector.
Remove all screws from semis on sink.
Remove assembly from sink. Grease is probably dried out.
Watch for shoulder washers falling off devices (if used).
Replace capacitors on pcb. They may be glued onto the pcb.
Clean sink with alcohol.
Clean semis with alcohol.
Buy new isolators (never reuse them) and new thermal grease (never reuse it).
Apply grease to semis, very thin layer.
Add isolators to semis.
Apply grease to isolators, very thin layer.
Reinstall shoulder washers on semis (if used).
Drop assembly onto sink.
Install semi screws, torque properly.
Plug in connector.
Test semis for proper isolation from sink.
Throw away all your clothes covered with heat sink grease, which will not come off.
I would never do this if there is no problem, but I'm lazy.
Remove connector.
Remove all screws from semis on sink.
Remove assembly from sink. Grease is probably dried out.
Watch for shoulder washers falling off devices (if used).
Replace capacitors on pcb. They may be glued onto the pcb.
Clean sink with alcohol.
Clean semis with alcohol.
Buy new isolators (never reuse them) and new thermal grease (never reuse it).
Apply grease to semis, very thin layer.
Add isolators to semis.
Apply grease to isolators, very thin layer.
Reinstall shoulder washers on semis (if used).
Drop assembly onto sink.
Install semi screws, torque properly.
Plug in connector.
Test semis for proper isolation from sink.
Throw away all your clothes covered with heat sink grease, which will not come off.
Last edited:
Thanks, rayma! I appreciate all of that. I wasn't sure how easy that board and semis would pull away from the sink but it sounds like it won't be a huge deal. Yes, I had CDE and Nichicons picked out for the replacement and was leaning CDE. This is all very helpful and good to know for the future, thank you!
a lot of people jump on Chinese brands such as Jun Fu, but used properly (ventilation) and with reasonable headroom (voltage) they can easily last 20-30 years. I generally see the actual PCB design is the bigger reason for parts going bad because of too much heat and insufficient ventilation around them.
Agree with rayma - if it works, just enjoy it. If you really want to dip your feet into DIY, buy a cheap broken something from eBay and get help on here to fix it, then your no worse off if you can't fix it, or make it a lot worse.
Agree with rayma - if it works, just enjoy it. If you really want to dip your feet into DIY, buy a cheap broken something from eBay and get help on here to fix it, then your no worse off if you can't fix it, or make it a lot worse.
Good idea, go to the resale shop and find something broken for $2 that you can try to fix.
If you can't fix it, no biggie.
If you can't fix it, no biggie.
Don't replace them, but add new caps in parallel via wires on the pcb underside. It would not be the most elegant repair, but this way you don't really have to worry about the original caps as they go dry....
Well, the problem is if you look at the pic, to get to the bottom of the board I have to remove the transistors away from the sink. See what I mean?
It does look like the right-most resistor has seen better days. But it could just be the picture. It looks like the enamel is peeling off of it and the board is charred. If that is indeed the case, it could be worthwhile replacing the resistor, assuming its value can be determined.
It does look like the capacitors are glued in place, so they could be challenging to replace.
As pointed out above the thermal grease has probably dried out. That'll make the transistors stick to the heat sink. Somehow you'll have to bump the transistor package enough that the grease lets go. Then follow the steps @rayma provided above. Don't ream on the screws when you put everything back together. Usually you only need about 0.5 Nm of torque on the screws which is only slightly beyond finger tight. Maybe finger tight plus 1/4 turn or something. I use a torque screwdriver...
Tom
It does look like the capacitors are glued in place, so they could be challenging to replace.
As pointed out above the thermal grease has probably dried out. That'll make the transistors stick to the heat sink. Somehow you'll have to bump the transistor package enough that the grease lets go. Then follow the steps @rayma provided above. Don't ream on the screws when you put everything back together. Usually you only need about 0.5 Nm of torque on the screws which is only slightly beyond finger tight. Maybe finger tight plus 1/4 turn or something. I use a torque screwdriver...
Tom