Harman Kardon 430 powers up but no sound

[keyonce]

Wow this is really great advice. I do have the desoldering tool (simply vacuuming one) as well as the desoldering wick. I’ve only used these on parts that I was replacing anyway but I honestly didn’t know I could do damage to components by lingering too long. Being that we hope to keep this part I may wait until the heat sink arrives (I might not have much free time between now and then anyway). It will probably be a couple of days or possibly the weekend before I will update this thread.

I just want to thank everyone so far for the guidance. I’ve probably been asking some silly questions but you’ve all been really helpful!

 

[EastPoint]

You shouldn’t need a heat sink when installing transistors—I’ve never needed one. The KSC1845FTA is fine. They say 300-600 hfe but they’re all around 370-400 generally. The Ksc1845U is basically impossible to find now and isn’t a relevant sub because of that.

 

[captouch]

You shouldn’t need a heat sink when installing transistors—I’ve never needed one. The KSC1845FTA is fine. They say 300-600 hfe but they’re all around 370-400 generally. The Ksc1845U is basically impossible to find now and isn’t a relevant sub because of that.

It really depends on your soldering technique and experience. While I’ve never (that I know of) ruined a component due heat, I’m sure I’ve prematurely heat aged something here or there in the early days. Sometimes you don’t have a great angle or work longer than you should when you’re tired and mistakes happen. I’ve lifted a few solder pads in my time and while a heat sink wouldn’t have helped that, I’m sure the component that was getting all that heat when I was working slowly enough to cause a solder pad to lift didn’t appreciate it.

Once you have reasonably good technique and can work pretty fast, I agree there’s no practical need, but it’s a good fallback to have if you’re unsure or are working with a rare/NLA component that you can’t afford to risk.

 

[keyonce]

I tried to resolder the transistor and it did seem to help a little bit the problem still exists. There is slightly less white noise and popping but it’s still there and poking the transistor can still trigger the channel to cut out. What should be my next step? I was looking to order something and I think it would take a little while to arrive and the cost is pretty low. Should I order enough to replace just the one or go ahead and do the 4?

As for the heat sink it was a little tricky to get onto each leg while working but I could definitely feel it had picked up heat when moving between legs.

 

[captouch]

I tried to resolder the transistor and it did seem to help a little bit the problem still exists. There is slightly less white noise and popping but it’s still there and poking the transistor can still trigger the channel to cut out. What should be my next step? I was looking to order something and I think it would take a little while to arrive and the cost is pretty low. Should I order enough to replace just the one or go ahead and do the 4?

As for the heat sink it was a little tricky to get onto each leg while working but I could definitely feel it had picked up heat when moving between legs.

So you’re confident that it’s soldered in there really well now? I ask because if it is, then I’m a little surprised that poking it can cause it to cut out. And you took care of the loose cap as well?

Usually the bulk of the cost is shipping, so might as well order 4 as I don’t think it’s going to up your cost much.

 

[keyonce]

So you’re confident that it’s soldered in there really well now? I ask because if it is, then I’m a little surprised that poking it can cause it to cut out. And you took care of the loose cap as well?

Usually the bulk of the cost is shipping, so might as well order 4 as I don’t think it’s going to up your cost much.

I went ahead and ordered the MPSA18 that you suggested, it will be here hopefully by next weekend. Is there something I can check with my multimeter to help confirm this is the problem component? I now have the j-hook leads that would be helpful. I wouldn’t guarantee that my soldering is in there really well.

 

[captouch]

I went ahead and ordered the MPSA18 that you suggested, it will be here hopefully by next weekend. Is there something I can check with my multimeter to help confirm this is the problem component? I now have the j-hook leads that would be helpful. I wouldn’t guarantee that my soldering is in there really well.

I think it was another member that recommended that part.

As far as what you could do with your multimeter, the only think I can think of would be to put your multimeter into ohm mode and clip onto one lead of the transistor with one J-hook and clip onto another component that should be shorted to it with the other.

You’ll have to look at where the trace lines go to see which components are electrically shorted to that lead.

If you clip on that lead, you should see 0 ohms for the meter reading. The if you wiggle the transistor, it shouldn’t move from the zero reading at all. If it does, that connection may be flaky. Repeat for all 3 transistor leads (of course you’ll have to move the other lead to the appropriate component that should be electrically shorted to that lead.

That’s the only think I can think of doing with a meter. But, really, if you have that loose a solder connection, I would think if you looked on the back/solder side and wiggled the transistor from the other/top side, I would think you’d see one of the 3 legs move just a bit in reaction to your wiggling. Which could be done without getting your meter involved.

 

[keyonce]

Update: I got the transistors replaced. I ended up also replacing Q405 and 406 along with the Q401,402,403,404. Everything is buttoned up and the white noise is gone! Thanks everyone for the help on this, it’s been fun and so rewarding to resolve this problem.

I have one follow up question for now. While I had things open I started to poke some of the capacitors around the transistors I replaced. I noticed that touching C401,402 and C407,408 with my finger produced some feedback. Touching with a wooden stick did not. Is this anything to worry about? The C401,402 were a little wiggly as well but I’m not sure if this is more due to how they are installed on some plastic legs (there’s probably a much better term).

 

[cademan]

Those capacitors are probably in the signal path and by touching the tops (outer cans), they act just like touching bare inputs with the volume control turned up a little so not really any problem there.

 

[keyonce]

Those capacitors are probably in the signal path and by touching the tops (outer cans), they act just like touching bare inputs with the volume control turned up a little so not really any problem there.

Great! So I think I’m done with this receiver for now. Thanks everyone for your help. Now I just need to find some replacement speakers. Not sure but I’m wondering if the speaker that blew was the cause of the fuse problems.

 

[cademan]

If the 430 passed DC to the speaker, the voice coil could probably be fried but have you checked the speaker itself to see if it was bad?

 

[keyonce]

If the 430 passed DC to the speaker, the voice coil could probably be fried but have you checked the speaker itself to see if it was bad?

I posted a separate thread on this but the woofer in one speaker is bad. I isolated it and tested it with the multimeter and got 0.03 ohms. I don’t know which problem occurred first but I think I have the receiver working well now (at least through the headphones).

https://audiokarma.org/forums/index...-33a-woofer-replacement.955551/#post-14687580