Harman/Kardon HK6500. Loudness not working when button is pressed

[KrisBlueNZ]

R557 and R558 will be fine. C532 and C530 won't be damaged but you can replace them if you want, to keep everything looking the same.

Yes, Q520 is a PNP and Q519 is an NPN. These are the two that are bolted to the heatsink, right? They are called "TO-220" packages. There will be some kind of insulating shim between each transistor and the heatsink, and there will be plastic collars around the screws that hold them to the heatsink as well. You have to keep these and refit them. If the insulating shims are made from a thin fragile glass-like sheet called mica, they may be damaged, so you might want to remove the old transistors first and check, and/or just get some spares anyway. Ask for mica insulating washers for TO-220 packages.

All of the transistors I listed are suitable. They are listed roughly in order of increasing cost. The last two on each list are actually "Darlington" transistors, which are a bit different from normal transistors, but they're equally suitable. I just mention this because the person at the store may query it.

If the shop has them, you could also pick up some replacements for Q907 and Q908 in case they are damaged too:

Q907 PNP --> MPSA56, BC640, BC327
Q908 NPN --> MPSA06, BC639, BC337.

 

[Rickedafied]

Q519 and Q520 had the screw and collars, but they only had therrmal paste and they were stuck on the heatsink pretty hard.

Is there any way to test Q908 and Q907 out of circuit?

Oh and remember how I told you about Q427, 423, 425, 421, 422, 426, 424, and 428 were getting real hot and have the board looking dark under and around them? I use to run this amp for years not knowing they were hot. Do you think they're ok, or should I replace those too? I'm not sure if those are expensive.

 

[Rickedafied]

Does the schematics say what the wattage and ohms are for R954?

 

[Rickedafied]

R557 and R558 will be fine. C532 and C530 won't be damaged but you can replace them if you want, to keep everything looking the same.

Yes, Q520 is a PNP and Q519 is an NPN. These are the two that are bolted to the heatsink, right? They are called "TO-220" packages. There will be some kind of insulating shim between each transistor and the heatsink, and there will be plastic collars around the screws that hold them to the heatsink as well. You have to keep these and refit them. If the insulating shims are made from a thin fragile glass-like sheet called mica, they may be damaged, so you might want to remove the old transistors first and check, and/or just get some spares anyway. Ask for mica insulating washers for TO-220 packages.

All of the transistors I listed are suitable. They are listed roughly in order of increasing cost. The last two on each list are actually "Darlington" transistors, which are a bit different from normal transistors, but they're equally suitable. I just mention this because the person at the store may query it.

If the shop has them, you could also pick up some replacements for Q907 and Q908 in case they are damaged too:

Q907 PNP --> MPSA56, BC640, BC327
Q908 NPN --> MPSA06, BC639, BC337.

I wasn't able to get all parts you recommended, the guy at the parts place today wasn't that helpful. Can you tell me if all the parts I got will be suitable?

For Q907 I got NTE159
For Q908 I got NTE287

For Q519 I got NTE377
For Q520 I got NTE55

For D503 & D505 I got 1N969B Zener Diodes.
For C529, C531, C530 and C532, I got 330uF 35V Electrolytic Capacitors.

For R555 and R556 I got 10 ohm 1watt resistors. Pack of 4.
For R954 I got 820 ohm 1/2 watt resistor. Pack of 6.

 

[KrisBlueNZ]

Q519 and Q520 had the screw and collars, but they only had therrmal paste and they were stuck on the heatsink pretty hard.

If they're both on the same heatsink, and they both have metal tabs, at least one of them must have an insulating washer. Have a close look. You may want to remove the heatsink compound (white goop) using toilet paper and/or a cotton swab, and replace it with new compound when you've replaced the transistors.

Is there any way to test Q908 and Q907 out of circuit?

Yes, but it's not reliable, and why bother? They're cheap; just replace 'em.

Oh and remember how I told you about Q427, 423, 425, 421, 422, 426, 424, and 428 were getting real hot and have the board looking dark under and around them? I use to run this amp for years not knowing they were hot. Do you think they're ok, or should I replace those too? I'm not sure if those are expensive.

They're about USD 0.50 each to replace.

Q421,422,425,426 (originally 2SA1124) can be replaced with Fairchild KSA1013Y (http://www.digikey.com/product-detail/en/KSA1013YBU/KSA1013YBUFS-ND/1048937).

Q423,424,427,428 (originally 2SC2632) can be replaced with Fairchild KSC2383Y (http://www.digikey.com/product-detail/en/KSC2383YTA/KSC2383YTACT-ND/4213849).

These replacements have the same pinout as the originals.

You should also check that area carefully for possible damage to the PCB - tracks lifted, charring around edges of holes. Also any other components in that area that look like they have overheated, or where the board is more badly discoloured.

It's probably a good idea to replace any electrolytic capacitors in that area, since they will have been dried out by the excess temperature.

Does the schematics say what the wattage and ohms are for R954?

Yes, R954 and R957 are both 820Ω 0.5W fusible. The closest I can find at Digi-Key is http://www.digikey.com/product-detail/en/RL20S821GRE6/1135-1383-2-MIL/3193978. That's not fusible but it does have a "flame-retardant coating".

I wasn't able to get all parts you recommended, the guy at the parts place today wasn't that helpful. Can you tell me if all the parts I got will be suitable?

For Q907 I got NTE159. For Q908 I got NTE287.
For Q519 I got NTE377. For Q520 I got NTE55

Those aren't what I recommended, and NTE's transistors tend to have low gain specifications, but they'll probably work.

For D503 & D505 I got 1N969B Zener Diodes.

You mean D503 and D504? That's fine.

For C529, C531, C530 and C532, I got 330uF 35V Electrolytic Capacitors.

Good.

For R555 and R556 I got 10 ohm 1watt resistors. Pack of 4.
For R954 I got 820 ohm 1/2 watt resistor. Pack of 6.

Those resistors are supposed to be fusible. They are designed to fail cleanly when they overheat, rather than catch fire and make a mess of the insides of your product. If you can't get fusible ones, I recommend good quality ones with "flame-retardant coating".

Did you go to Radio Shack? Their component range is pretty poor. You should look into signing up with Digi-Key (http://digikey.com) or Mouser (http://mouser.com).

 

[Rickedafied]

I didn't go back to RadioShack because I expected the electronics store to have everything.
The resistors that I told you I bought in post #64 all say "flameproof" on the packages.
The NTE55 and NTE377 both came with new washers and tabs, plus I bought thermal compound.

Those 8 other components that are getting hot.... Are they overheating because of the other components blowing out? Im gonna replace them for sure, but should I wait to turn on the amp with the other new components installed? Plus I'm curious if they will still be hot

 

[KrisBlueNZ]

The resistors that I told you I bought in post #64 all say "flameproof" on the packages

Good.

The NTE55 and NTE377 both came with new washers and tabs, plus I bought thermal compound.

Good.

Those 8 other components that are getting hot.... Are they overheating because of the other components blowing out? Im gonna replace them for sure, but should I wait to turn on the amp with the other new components installed? Plus I'm curious if they will still be hot

I think there's probably a separate problem that is causing those transistors to overheat. It's unusual that both channels would have the same problem, so I suspect it's something common to both channels. It may be related to the low power supply voltage.

I doubt those eight transistors are faulty, and it's probably safe to power up the amp before you've replaced them. When you do power up the amp, whether those eight transistors have been replaced or not, check them to see whether they're getting hot.

 

[Rickedafied]

I think there's probably a separate problem that is causing those transistors to overheat. It's unusual that both channels would have the same problem, so I suspect it's something common to both channels. It may be related to the low power supply voltage.

I doubt those eight transistors are faulty, and it's probably safe to power up the amp before you've replaced them. When you do power up the amp, whether those eight transistors have been replaced or not, check them to see whether they're getting hot.

Finished installing all parts. As soon as I turned it on, R556 and R555 started smoking so I turned it off right away.

 

[KrisBlueNZ]

OK. Did you insulate Q519 and Q520 from the heatsink? If not, that will be why R555 and R556 are going up in smoke.

If you did, there may be a short on the output of those regulators. Can you find CN401 and CN402. They should be near Q519 and Q520. CN401 connects to the tone control PCB and CN402 connects to the "BASCON" board. The fault could be on either of those boards, but is more likely on the tone control board.

So unplug the plugs from CN401 and CN402, power up with your eye on R555 and R556 and see what happens.

If they both start smoking again, there's a fault in the regulator. Check that Q519 and Q520 are properly insulated from the heatsink and connected the right way round.

If they don't start smoking, refit the plug into CN402 and try again.

If they still don't start smoking, refit CN401 and try again. Assuming they do start smoking now, there's a fault on the tone control board.

Let me know how you go.

 

[Rickedafied]

The got mixed. They don't say cn401 or cn402. I see jp468 and the other marking for the other connector is covered by the connector so I can't read it. I know one set went to the top board with loudness button on it but I think I got them mixed some how

 

[Rickedafied]

Ok I had the wires for the board with the loudness button backwards. The resistors ore not smoking or getting hot anymore, but those other ones I told you about, they're still getting hot.

 

[Rickedafied]

This isnt a recent photo, but just to show you, i had these wires that go into here, backwards! Thats why it was smoking. I hope I didn't blow more things out. I tried the headphones to see if if I get sound still, and I do, but it sounds low like it lost power. The loudness button is working now, but instead of it sounding louder, it sounds less powerful, like if the bass is being canceled or like its working the opposite way than its supposed to. I tried connecting speakers and it sounds the same way through the speakers.

 

[Rickedafied]

I turned on the amp with no jacks or speakers connected and I went feeling around the main board and the other boards to see what's getting hot right away and I noticed another set of transistors on a heatsink just like the other ones I replaced on the main board. They're getting really hot. I have the yellow arrow pointed at them. I don't see any CN401 or CN402 but I see CN403 on the main board and those wires are coming from the board where the arrows pointed at also.

It seemed I was so close to fixing it... but now I can't tell if those other transistors are getting hot because of the new parts, or because of my mistake.

 

[KrisBlueNZ]

These other transistors that are overheating could be the reason why the power supply rail voltages are low. They're on PCB 6, the equalizer board, in the phono input section. You can just disconnect the wires from CN403 on the main board. You won't even need the phono circuitry unless you have a turntable - those old contraptions for playing vinyl records!

After you've done that, can you measure the voltages at the following points, relative to the 0V rail:

• CN403 pin 1 (labelled "+B")
• CN403 pin 2 (labelled "-B")
• Q519 emitter (rightmost pin) - should be about +22V
• Q520 emitter (rightmost pin) - should be about -22V
• Q908 emitter - should be about +12V
• Q907 emitter - should be about -12V

 

[Rickedafied]

Ok.

Pin 1 reads 47.6V
Pin 2 reads -47.5V

Q519 Emitter reads -01.4V
Q520 Emitter reads -21.5V

Q908 Emitter reads -2.10V
Q907 Emitter reads -13.01V

 

[KrisBlueNZ]

OK. Keep CN403 disconnected. The phono board must have a fault that makes it draw a lot of current, because with it disconnected, your ±50V rails have increased from about ±40V to ±47V. This is good!

So you've fixed the problem that was causing R555 and R556 to go up in smoke? Was it caused by the transistors being shorted together on the heatsink?

So Q519 emitter has no voltage. Check that there is about +47V on both ends of R555. If one end has nothing, R555 is open circuit and needs to be replaced again.

If there is about +47V on both ends of R555, check that D503 is round the right way, and see whether Q519 is getting hot, and measure the voltages on all pins of Q519 and post them.

 

[Rickedafied]

OK. Keep CN403 disconnected. The phono board must have a fault that makes it draw a lot of current, because with it disconnected, your ±50V rails have increased from about ±40V to ±47V. This is good!

So you've fixed the problem that was causing R555 and R556 to go up in smoke? Was it caused by the transistors being shorted together on the heatsink?

So Q519 emitter has no voltage. Check that there is about +47V on both ends of R555. If one end has nothing, R555 is open circuit and needs to be replaced again.

If there is about +47V on both ends of R555, check that D503 is round the right way, and see whether Q519 is getting hot, and measure the voltages on all pins of Q519 and post them.

R555 Reads -01.4 on one end and -47.1 on the other end.
R556 Reads -46.5 on one end and -46.9 on the other end.

Q519 Reads
B -00.7
C -01.4
E -01.4
The heat sink for them feels like its getting hot, but I can't tell if its just Q159 or Q520 because I can't fit my finger between it and the capacitors

 

[Rickedafied]

The cause of R555 and R556 must have been cause the wires on that connector I showed you was backwards. I had connected it the right way and turned it back on and it didn't smoke.
I used the washers and thermal compound when installing Q519 and Q520.

 

[KrisBlueNZ]

R555 Reads -01.4 on one end and -47.1 on the other end.

OK. As I said...

Check that there is about +47V on both ends of R555. If one end has nothing, R555 is open circuit and needs to be replaced again.

... you need to replace R555 again.

The cause of R555 and R556 must have been cause the wires on that connector I showed you was backwards. I had connected it the right way and turned it back on and it didn't smoke. I used the washers and thermal compound when installing Q519 and Q520.

OK. Good.

 

[Rickedafied]

Ok I replaced it. Its reading +47V on both ends now