Harman Kardon PM640, what is this burnt thing?
- Thread starter Sir.Byrd
- Start date
terra1
Addicted Member
Nope. My ego isn't going to take any of this that seriously. I hope I have a sense of humor about this. Hey ... It's not my machine that needs work.
I don't know why you are considering ordering resistors online. You can get them at Fry's for 95 cents for a 4 pack and a pack of 5 at Radio Shack for $1 or $2 not more than that. I got the carbon resistors.
My issue was not with you. It's always good to get additional input for consideration. I just desperately wanted kenwood61 to focus on the resistors and get that done first.
1. I knew these were special fuses.
2. The fuses in my PM640 look exactly the same as the ones in Kenwood61's PM640 which he got from Sir.Byrd.
3. What are the chances of gremlins replacing the fuses with the same "Frankenshtein" fuses I got in my PM640? What kind of demented sense of humor could the person have to do that?
4. And now there's a debate whether they are slo-blo?
5. According to Sir.Byrd the PM640 was in working condition.
So that's why I wanted kenwood to focus on the resistors that ecluser recommended replacing. And with those same fuses in --- the temp dropped dramatically on my PM640.
Sir.Byrd
Lunatic Member
I was surprised that I had to turn my soldering station to max temp before the solder would melt. And I did NOT practice on anything. I figured I've successful operated a torch on my roof with torchdown material, and I've soldered speaker wire, and transplanted an original tonearm on my AR XA turntable desoldering and soldering hairthin wires . . . so why not just jump in with both feet!!
So now I'm trying to figure out how to use my DMM. The instructions aren't so good, so I'll see what I can find online. So I have NOT yet adjusted the bias.
I did run the amp for about 30 minutes and the heat sinks did get hot, but not too hot for me to touch, and I had to get my hand down in between the sinks to get the most warm part.
One last thing. My DMM says something about a K type thermoelectric couple to measure temperature. I guess that is something else I would need to buy . . .
Thanks for the help guys!! I hope to report back as soon as I get the bias adjusted and take a listen.
If you bring the amp to me I'll show you how to do the bias adjustment with your DMM. Also I have a temp probe for my DMM which could be used then.
terra1
Addicted Member
Congratulations. :thmbsp:I was surprised that I had to turn my soldering station to max temp before the solder would melt. And I did NOT practice on anything. I figured I've successful operated a torch on my roof with torchdown material, and I've soldered speaker wire, and transplanted an original tonearm on my AR XA turntable desoldering and soldering hairthin wires . . . so why not just jump in with both feet!!
So now I'm trying to figure out how to use my DMM. The instructions aren't so good, so I'll see what I can find online. So I have NOT yet adjusted the bias.
I did run the amp for about 30 minutes and the heat sinks did get hot, but not too hot for me to touch, and I had to get my hand down in between the sinks to get the most warm part.
One last thing. My DMM says something about a K type thermoelectric couple to measure temperature. I guess that is something else I would need to buy . . .
Thanks for the help guys!! I hope to report back as soon as I get the bias adjusted and take a listen.
The major concern is the heatsinks around the "burnt" transistors. Those were the ones that got hot enough to char the thermal paste and were too hot to touch for more than a second.
I have a picture of the K type temp probe in post #58. It actually consists of two parts: the K type probe with the yellow plug which plugs into the white adapter which in turns plugs into the + - meter jacks for your probes. The tiny end tip is used to sense the temperature. I think Sears may have these sold separately, not sure so you need to call or just check their website.
But for now even without a temperature probe, if you can hold on to the heat sinks with the burnt transistors without jerking away in pain, it looks like you did ok.
Adjusting the Idle Current will help set the amp output to spec. Follow the service manual instructions on how to set up for adjusting the Idle Current.
Sir.Byrd
Lunatic Member
QUESTION: It appears that the solder on the board is different than what I'm using. I'm using a rosin core 60/40 by MG Chemical, but when I went back to add more solder it "burned" the solder and the new solder just beaded up into a ball . . . didn't do that last night, using the same solder at the same temp level.
So I left well enough alone. But moving forward . . . it would be nice to know if the 60/40 is what is on circuit board connections, or if it's silver. I have silver solder, and wouldn't mind learning how to use it if that means getting the clean look of the circuit boards on this H/K.
My Process: Since there was a good mound of solder on the wires, I was able to use it (recycle). It was very clean looking after melting, so I was able to add to it, but I was not effective in using the desolder bulb, and I had a technique developed which allowed me to get the old resistor out using my suture clamp on the wire (top side) and going back and forth melting each point until I got out. Then using the reverse to pull through. Once through, I bent the wires criss-cross to keep in place, then once solid, quickly melt/move each wire straight out. Cut wire and done. Looks clean and solid hold, top-side nice and clean with no solder blead through.
I was surprised that the new resistors were much smaller than the old ones. Is that just new development in technology? The larger NTE resistors seemed to go up in wattage and Ohms.
This is good stuff to learn
Did you not replace them with a different type of resistor? I thought you might have purchased the lower noise resistors which are probably more standard now than in 1981 when this was made.
Sir.Byrd
Lunatic Member
Let it stabilize for 30 minutes before you adjust the bias.
Then you may want to do it again in a few days to make sure you got it right.
terra1
Addicted Member
Are you sure it's a metal resistor? I believe mine was a regular carbon resistor from Radio Shack. If it's metal it will probably say so on the package.
Yes the resistor I used was smaller than the original. You will find this true in many replacement parts mentioned in various threads here. The important thing is the ohms and watts.
I used the 60/40 solder from radio shack. If solder looks burnt, you may have heated it too much. Proper technique will yield a shiny cone around the stem of the resistor like a Hershey kiss like the other soldered stems around the board.
The bulb sucker is a bit to big for a lot of intricate work like this, but if they go hog wild on solder you really do need it.
SOUND: the purpose of the resistors is NOT to improve the sound. It is to provide resistance and reduce the heat.
Adjusting the Idle Current should bring the output back to spec. If the amp was already sounding good, you may notice marginal improvement in sound. What I think I usually notice after adjusting Bias/Idle Current or DC balance if applicable, is that the sound will sound richer and fuller. Better imaging, especially if the amp was out of spec.
The Idle Current adjustment on the HK, if I recall, is one of the easiest and more responsive of the amps I have adjusted. The readings as with all adjustments will usually swing like a pendulum. The HK is one of the few that actually seems to hold well. At least for a few minutes. You can wind up nudging it for hours as you see it slowly rise and fall and cycle. When you get tired of that, quit and accept that you are allowed a margin of error.
I usually do the initial after at least a half hour as recommended, but I may take longer depending when I get back to it. Will check it later after a couple hours. I also check the readings at the speaker terminals. Take a look at echowar's thread. At the speaker terminals you want it to be as close to 0 mV as possible. Although Idle Current adjustment is to 33mV at the internal test points, just remember these are different readings at the speaker terminals than at the test points when adjusting. I think mine were around 14mV or less at the speaker terminals, even though the Idle Current adjustment was adjusted to 33mV at the test points. Under 15 at the speaker terminals as echowars says, is damn good.
After the Idle Current adjustment, you have my permission to consider replacing fuses and transistors and whatever else you can think of. My work here is done.
terra1
Addicted Member
Funny, I would have thought the Concept would sound better since that has more wattage. But good to know and make me respect the HK even more.
But Yes. The meter will also go crazy when you remove one or both probes and you can see the numbers fly around.
That's also why you want to make sure you have good contact with the test points. If you are not secure [the contacts - not your state of mind], you can get some false readings [maybe I am talking about your state of mind
]. That's why I got the adapter clips to hook on to the test points.As long as you had power on, volume down, set to Aux, speaker switch in front selected, tone defeated, then you should be ok and should see some readings fluctuate. Remember with readings at the speaker terminals, you do want to see it close to 0. See echos thread. 0-15mV is very good. You might even wind up seeing negative readings but that's ok. On my PM665 I think it read 000.3 left and -1.7 Right which was fine by me. Close enough!
If you did not have the speaker terminal selected, I think it would drop like a rock to 0.00. That's why you need to have the speakers selected.
As you gain more experience, you will find that different amps will have different methods. Some will have you touch the Positive to the test point and the Negative to the chassis as a Ground or Earth.
Congratulations! You should be very proud of yourself.
You got yourself another AK Audio Cubbie Badge. :thmbsp:
Sir.Byrd
Lunatic Member
Wow, I didn't get an email reminder on this. I just saw, but where do I pick up my AK Audio Cubbie Badge????? :thmbsp:
Thanks Terra1 . . . I wouldn't have even tried this if not for you and others on this thread encouraging me, and especially for Sir.Byrd giving me the opportunity to have this cool amp!
My readings were very close to 0.00, so even with fluctuation, were in what Echowars considered the best range to be in.
As far as my simple and not comprehensive test with the ADS speakers, I hadn't hooked them up to the Concept since fixing. The A150s sound really good with the Concept which I think is probably one of the better receivers of it's vintage, styling, power class and price/value. I know there are better, but for the 60w and under, I'm very content with it and while I know different receivers will have different sound characteristics, it's not like I find myself thinking I should replace it to find something "better" . . . but what I found interesting is the the ADS and H/K setup sound best on the jazz station. It's a combination (I think) of the type of music, source quality, strong reception, along with the circuitry of the H/K and the 2-way ADS speakers, that sound really good to my ears. I think it's the way they image, in the environment they are in. I should hook up the Kenwood KR-4070 again now that the ADS are fixed, to see the difference.
The Concept sounds significantly better than the H/K, in part because of the beefy guts and power, in comparison. But it has better detail, less 3D imaging, but really clean to my ears. What was interesting is that after listening to the ADS and H/K, I just assumed the ADS would sound even better with the Concept. But when going back and forth between the 3-way A150's and 2-way ADS, it got to a point where neither speaker was sounding "great". It's interesting how your ears can "demand" something different than what you're hearing . . . if that makes any sense. In short, if I could only keep the Concept or H/K, I would keep the Concept without a second thought. It's that good. I think the 3D imaging of the H/K overcomes the lack of power. I have to keep it in normal to just getting too loud for the sound quality to be at it's best. But even at too loud, it's surprisingly good for what it is.
In conclusion, despite some comments earlier in this thread that sounded like there was a general agreement that Harman/Kardon should have designed it's circuitry different in terms of heat dissipation, I would have to disagree—now with the 220 Ohm resistor upgrade.
I'm really curious to see what ecluser has been up to and look forward to his comments at some not-to-far-in-the-future posting???
So where is the 640 headed now?
terra1
Addicted Member
When ABing give your ears some time to readjust (reacclimate). When going from a brighter speaker to a warmer speaker, the the warmer speaker may sound a little muddy and boomy at first. Then going from the warmer to brighter the brighter can sound thin and shrill. And then listener fatigue can set in without a break.
Also with vintage components I like to let everything warm up before comparing. Consider even amp bias adjustments recommend about 20 minutes for it to stabilize. Also some vintage speakers can sound a little grainy at first. Not sure if it's the speakers or receiver/amp, but it seems to clear up after 15 to 30 minutes for me.
I like the HK because as you notice it is very smooth and clean compared to some "warm" receivers that seem to add some more ambience or bass to the sound. I particularly like the detail in the mids and highs. It's just a very pleasant listening experience.
Sir.Byrd
Lunatic Member
Now try a hk 930.....................
Yeah I wish I knew Matt when I was giving away a HK 430 to a friend... ended up getting it back and selling it.
ecluser
Super Member
The situation in the PM655 is very different than it is in the PM640 because the driver stage in the PM655 is a complementary feedback pair (Q433 and Q437 in the PM655 forms a high power NPN driver). If we start to talk about the PM655 here, I think it will create some confusion.