Harman Kardon PM640, what is this burnt thing?

Sir.Byrd

Sir.Byrd

Lunatic Member
I got this Harman Kardon PM640 amplifier from a previous customer who bought 4 of my Fisher speakers for a party. He said he powered them with this amp and he overheated it by playing it for too long at a high volume. He gave this to me saying it didn't work anymore, but it works fine, that is, until I cleaned it today and noticed these...

What are these, do I need to replace them, where do you get them, and how much do they cost? There are two that are burnt out, the first two pictures are of the same one, and the last picture is the other one (macro didn't work on that one.)
IMG_0593.jpg
IMG_0595.jpg
IMG_0598.jpg
 
The Q prefix on the circuit board means they they are transistors. If you can take the heat sinks off (I am guessing that is what the metal bits are) and read the numbers on the transistors, you should be able to find replacements. I just recently got a PM650 and it is a really nice sounding amp. I will just have to remember not to run it so loud I burn up the transistors. :thmbsp:
 
They are transistors. Too small to be outputs. Most likely, voltage regulation, drivers, or pre-drivers. I'm thinking regulation from their location and quantity. Could also be bias. Snap a wider pic so we can see the whole board and get an idea of what they are for. There could be more blown then just those.
 
x_25 said:
The Q prefix on the circuit board means they they are transistors. If you can take the heat sinks off (I am guessing that is what the metal bits are) and read the numbers on the transistors, you should be able to find replacements. I just recently got a PM650 and it is a really nice sounding amp. I will just have to remember not to run it so loud I burn up the transistors. :thmbsp:
Click to expand...

The numbers on the transistors would be burnt off? Do you mean the ones written on the board? Where would I get replacements?
 
Unless that circuit is mirrored on the other channel, you will need a service manual to get the part numbers. There are (were) numbers printed on the transistor cases behind the heatsinks.
 
jhal said:
Unless that circuit is mirrored on the other channel, you will need a service manual to get the part numbers. There are (were) numbers printed on the transistor cases behind the heatsinks.
Click to expand...

Okay, now, where do I get a service manual?
 
It looks like some other non-heatsinked transistors could be bad as well (such as the one towards the top of the last pic between the silver cap and the resistor with the white, possibly ceramic spacers). Can you take a pic from the front of the unit showing the board they are on? I know it's a pain in the rear, but it would help.

As far as getting a service manual, there are many online places to obtain them. Some are good some are pitiful. Trying to remember the name(s) of some "good ones". Someone who buys them regularly may chime in.
 
Those look to be the Output drivers.
You can find the service manual at:
"http://manuals.harman.com/hk/Service Manual/pm640 sm.pdf"

Q417,Q418 2SC945 (K)or(P)

Q423,Q424 2SC667 A(C)

Q425,Q426 2SB647 A(C)

Hope that helps.
 
gpavia said:
Those look to be the Output drivers.
You can find the service manual at:
"http://manuals.harman.com/hk/Service Manual/pm640 sm.pdf"

Q417,Q418 2SC945 (K)or(P)

Q423,Q424 2SC667 A(C)

Q425,Q426 2SB647 A(C)

Hope that helps.
Click to expand...

Indeed, now what?
Where do I get these now?
 
Take a look at 'PARTS EXPRESS' on the cover page in this forum. Sinse I believe you are too young to own a credit card, find out how much the parts are, and give the money to your mom or dad so they can order them off of their credit or bank cards. It looks like your previous customer doesn't know how to properly drive an amplifier. Those parts should never burn up like that unless the device is being severly abused, meaning very distorted or unclean sound at very high levels for long periods of time. Severe distortion will even fry speakers even if the speakers are rated higher than the amplifier can put out. For the heck of it, I once blew a 120 watt speaker with just a 5 watt amplifier. Check out some of the idiots on YouTube that are blowing speakers for the fun of it. On the YouTube website, type in 'BLOWING SPEAKERS' and see what comes up. Some of those are just hilarious!
 
Actually, he could have burnt them with the other pair of speakers he had, then he gave those to me.
But yeah.
 
This thread is very interresting. It is a good indication that the drivers transistors are too small in this family of HK amplifiers and receivers. They fail before the output transistors.

The original part for Q423 and Q424 is 2SD667A (C), and not 2SC... as said before

What the picture doesn't show, there is two drivers (one is not visible on the picture, he is behind Q417 or Q418), and the Vbe multiplier transistor, for each channel.
 
ecluser said:
This thread is very interresting. It is a good indication that the drivers transistors are too small in this family of HK amplifiers and receivers. They fail before the output transistors.
Click to expand...

Well apparently the previous owner said it overheated from playing at high volumes too long, so it seems some abuse contributed.

All I know is my PM640 has survived from the previous owner and sounds great. No barbecue parties. ;)
 
Now that you have the schematic, we can establish that these transistors are part of the output drivers to the speakers. I would check all the transistors within the output to the speakers (TE1, main speakers). You noticed Q417 & Q425 were fried. Jhal noticed Q??? (a close-up pic would help to ID this one) was also fried. I noticed some discoloration on the circuit board around Q413 (the black transistor, bottom left of Q417 & Q425). Start with Q427 & Q429 (at the right of the schematic) and work your way to the left, checking all the transistor voltages. I'm starting to see a pattern in your overheated transistors. Good luck!
 
x_25 said:
The Q prefix on the circuit board means they they are transistors. If you can take the heat sinks off (I am guessing that is what the metal bits are) and read the numbers on the transistors, you should be able to find replacements. I just recently got a PM650 and it is a really nice sounding amp. I will just have to remember not to run it so loud I burn up the transistors. :thmbsp:
Click to expand...
Take the metal heatsink off and they will probably crumble to powdered charcoal..
 
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