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

[KrisBlueNZ]

No, measure ACROSS the two pins of TM403. Black probe to one pin, red probe to the other.

 

[Rickedafied]

Just reads 1 .

 

[Rickedafied]

When I change the voltage setting from 20 to 200 on the meter, I get -39.7v on one of the pins of D1

 

[Rickedafied]

Instead of the meter set on 20 DC, I set the meter on 200 DC, I got these readings.

C4 Reads 39.7v on one of the pins
C5 Reads -39.7v on one of the pins

R556 Reads -39.8v on one side and -01.2v on the other side

Q520 Reads
B -01.6v
C -00.9v
E -00.9v

Q519. Reads
B 04.7v
C 03.8v
E 03.7v

 

[KrisBlueNZ]

OK good. You had your meter set to the 20V range so it couldn't display voltages greater than 20V. Those voltages you're getting on C4 and C5 are low - they should be about ±50V - but let's worry about that later.

Q519 and Q520 should have significant voltage on them. Q520 gets its voltage through R556, which has voltage on one side but nothing on the other. If it's not getting very hot, it has failed. Q519 gets its voltage through R555, which has probably failed as well.

These are 10Ω resistors and from your photos in posts #18 and #19 they look like they're rated for about 1W dissipation. Radio Shack have a pack of ten 10Ω 2W resistors for USD 1.86: http://www.radioshack.com/product/i...&filterName=Type&filterValue=2-watt+resistors which would be a good choice unless you know of a proper electronic component shop in your area.

When you've replaced R555 and R556, connect your multimeter across one of them before you power up the amp, and watch them both for signs of overheating. If the multimeter reads more than about 3V then there is something wrong downstream of those resistors and the resistors will overheat, so turn the amp off and we can do some more testing.

 

[Rickedafied]

the radioshack close by only has 10 ohm 1/2 watt 5% tolerance resistors. Can i use those?

 

[KrisBlueNZ]

The power rating is not high enough, but you can make a 2W 10Ω resistor from four 10Ω 0.5W resistors, or from four 39Ω 0.5W resistors, like this:

 

[Rickedafied]

I don't think 4 resistors are gonna fit in there all together. I only have 5 of those 10 ohm resistors I just bought anyway. I guess I'm gonna have to take a drive out to the parts store and get the right parts.

 

[KrisBlueNZ]

Stack them. That's why I suggeted the 39 ohm ones. Start with the top one, bend both leads at 90 degrees to make a C shape, then solder the other three across, between those leads. Keep the resistors close to each other so there's plenty of lead length left, and mount the whole thing raised up, so if the resistors get warm, it won't char the board.

 

[Rickedafied]

Ok. I might be able to go to the parts store later, but I was curious if you can tell if the resistors on the right are the same watts as the ones I pulled out on the left in the photo

 

[KrisBlueNZ]

Yes. They're about the same size so I assume they're about the same wattage.

 

[Rickedafied]

Can I try those then?

 

[KrisBlueNZ]

Yes, but connect your multimeter across one of them and make sure the voltage doesn't exceed about 2V. If it does, turn the thing off, because the resistor is going to overheat. And keep an eye on the other resistor (the one the multimeter isn't connected to) to make sure it doesn't overheat.

If possible, mount the new resistors raised above the board.

 

[Rickedafied]

Ok theyre reading -39v and and the other 39v

 

[KrisBlueNZ]

OK, now we need to work forwards from there.

1. Check the voltages on the emitters of Q519 and Q520. This is the rightmost pin when you're looking at the marking side of the transistor with the leads pointing downwards into the PCB. Be careful not to short the pin to the heatsink or to the middle pin. Q519 emitter should have about +23V and Q520 should have about -23V.

2. If those voltages are OK, go back to Q907 and Q908, and find R954 and R957 nearby and measure them. R954 should have about -23V and -15V on its ends, and R957 should have about +23V and +15V on its ends.

3. If those voltages are OK, measure the positive and negative supply rails on the loudness board as I described in post #5.

 

[Rickedafied]

Q519 Emitter is +39.3v and Q520 Emitter is -22.1v

 

[KrisBlueNZ]

Q519 emitter should not be 39V. Check the voltage on D503 at the anode - the end opposite the end with the band around it. It should be 0V. If it's not 0V there is a problem between that point and CN401 - possibly CN401 is not properly mated with JL501 on the other board. I'll continue, assuming that the voltage on D503 anode is 0V.

Q519 is most probably faulty, and D503, C529 and C531 are probably damaged. Personally I would replace Q520 and D504 as well because they are the same age and may have been stressed if there was a separate fault that caused Q519 to fail. Here are suitable replacements.

Q519 NPN TO-220: BD239, KSD526, TIP112, TIP122
Q520 PNP TO-220: BD240, KSB1017, TIP117, TIP127
D503, D504 22V 0.5W zener: 1N5251B, 1N4748A
C529, C531 330 µF 25V electrolytic: Any general purpose 330 µF 25V or 35V electrolytic such as http://www.digikey.com/product-detail/en/ECA-1EM331/P5154-ND/245013

These are all available from Digi-Key. I don't know how many of those semiconductors are available at Radio Shack. Probably none of them will be in stock locally. See if you can find a good local electronic component retailer, or at least a mail order supplier nearby that doesn't charge too much for postage/courier.

 

[Rickedafied]

D503 is showing 0V

 

[KrisBlueNZ]

OK, so the rest of post #57 applies. You need to replace, at a minimum, Q519, D503, C529 and C531, but I recommend also replacing Q520 and D504.

 

[Rickedafied]

Thanks for all the information! Ok. Im going to a parts store tomorrow to get them all. Is there any other components I should check before installing all the new parts?

I see R557 and R558 are right between those resistors and diodes you told me to replace, should those be replaced also and capacitors C532 and C530?

Oh and Q520 and Q519 are called PNP and NPN Transistors right?