Alright, as you, good people, suggested, I have checked diodes in the power supply, all are ok. So then I replaced the fuse, connected the primary leads to the transformer, then turned it on, green power led lighted up (YAY!). Then i took a multimeter, and tested voltages on the secondary, which returned 27,5 - 0 - 27,5 (again, YAY!) So that means, we know for sure, the power supply is OK.
Now for the next part, i have connected all the parts of the amp, and tried it once more. Again, no fuses going boom. Just green light everywhere, where it needs to be (YAY!). So time to play some music I thought. I connect speakers and a CD player, put some music, and i hear so long waited sound (YAY!). But it is not a story about luck just yet. Then i try to turn balance to left and to right, and here is some problems. The right channel is playing perfectly, but the left is not. If i turn slightly more volume, then i hear a sound of music from the left channel too, but it's very much distorted, a lot more silent than right.
So it seems, i still have some interesting things to enjoy
Ok now, i try to touch the big aluminum heat sink, and one side of it is quite warm, but the other is rather cool. What should I do next?
Now for the next part, i have connected all the parts of the amp, and tried it once more. Again, no fuses going boom. Just green light everywhere, where it needs to be (YAY!). So time to play some music I thought. I connect speakers and a CD player, put some music, and i hear so long waited sound (YAY!). But it is not a story about luck just yet. Then i try to turn balance to left and to right, and here is some problems. The right channel is playing perfectly, but the left is not. If i turn slightly more volume, then i hear a sound of music from the left channel too, but it's very much distorted, a lot more silent than right.
So it seems, i still have some interesting things to enjoy
Ok now, i try to touch the big aluminum heat sink, and one side of it is quite warm, but the other is rather cool. What should I do next?
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Ok, so now this is what i have done. Took out all the transistors (I have marked where they were and put them into separate boxes, one box for left channel, one for the right channel. These are the transistors i have:
C3423 (two of them, smallest ones)
C3182n (two of them)
A1265n (two of them)
So i have found data sheets for them, find out where is Collector, Emitter and Base. Then started to measure and compare them following this procedure: How to Know Bad Transistors | eHow.com
And, by measuring resistance, all of them shows good results and all the pairs seem identical. But i cannot measure the gain, as I have no testing gear for it.
Also there is one "looking-like-transistor" thing in the middle with four legs which are marked as + ~ ~ - not one hundred percent sure how to test that, but if test by the diode method, then it seems allright too.
C3423 (two of them, smallest ones)
C3182n (two of them)
A1265n (two of them)
So i have found data sheets for them, find out where is Collector, Emitter and Base. Then started to measure and compare them following this procedure: How to Know Bad Transistors | eHow.com
And, by measuring resistance, all of them shows good results and all the pairs seem identical. But i cannot measure the gain, as I have no testing gear for it.
Also there is one "looking-like-transistor" thing in the middle with four legs which are marked as + ~ ~ - not one hundred percent sure how to test that, but if test by the diode method, then it seems allright too.
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Yes, I think, I can confirm, that all transistors are good. What I did, was soldering them back, but this time, i have switched them (ones that were taken from the left channel, i have soldered into right channel, and ones from right, soldered to left). Now lets listen, same problem, right channel is working well, left is working badly. Also tired to swich speakers, and connected couple sources (cd-player, laptop) to all of the inputs, results are the same.
Only one interesting thing to mention is when i leave cd-player playing and connected to cd input and switch to aux (where is nothing connected) i still hear my cd playing, softly but clearly enough to hear). I don't know if this is significant or not important at all, just thought this should be mentioned
Well, the plan for tomorrow is test left channel components, i think to begin with capacitors, also found some little diodes, and possibly resistors (but there is so many of them :O ).P.S.
Is it weird to like this amp even more, although it's not even playing right, but i get this nice feeling as i know and understand it better
As far as I know, fuses are put to protect your house from fire, not to protect your electronic equipment. At least that is written in many service manuals
One question thou, it seems, that i could fairly easily obtain toroidal transformer something similar to this one: Antek - AN-2230
Would this work?
Transformers fail from heat. You didn't get it hot so it likely hasn't failed but you did make some big errors. You had parts left over (those missing insulators weren't always missing) when you turned it on. You might have blown rectifier diodes. You might have blown the power transistors and could have blown the drivers.
Here's how I would approach it and that is in phases.
1: Take pictures of the unit before you do any more changes.
2: Disconnect the secondary winding(s) from the main power rectifier. Replace the fuse and power it up. Does the fuse blow? Is there AC voltage on the disconnected winding(s)?
3: If the transformer is OK (I give it 99% odds as OK) check the main rectifier for shorts. Replace any bad diodes or bridge rectifiers. Reconnect the secondaries. but remove all the power transistors and then power it up. Is there DC on the main filter caps?
4: DC OK? Test the power transistors with diode check mode on the meter. ALSO check for emitter / collector shorts even if you read normal diode values base / emitter and base / collector.
5: Many power amplifiers will function normally into NO LOAD with the power transistors removed. Verify drivers only operation with a scope.
6: Install good transistors and power it up again and set the bias.
If you did NOT know to power the unit off between steps then don't even try this and 'Refer all servicing to qualified personnel'.
BTW there are many places where skinny wire is fine.
G²
Yes, missing those insulators was a silly thing to do, but i honestly worked very carefully, yet noticed those insulators on the ground only when it was too late. But what can I say, too late is too late, now Ii have what I have, and one should try to make most of what he got. So now i have learned very well to check those insulations ten times before power up . Also, i am really happy to have an opportunity do do this stuff, I have learned a lot already, especially on how components work, and how to test them, this knowledge is far more valuable to me, than any amplifier, and I know that if I can make this amp work by my own effort and good advices of more experienced people, then I'll be twice as happy
Now, the current progress is:
* Diodes, and capacitor in power supply circuit are OK
* Replaced fuse, tried transformer only, it works OK (as many of you said in a first place)
* Even more carefully reassembled main board, connected everything, again no fuses going boom
* Tried to play some music, found that left channel is working badly, but right channel is working well.
* Took out all the transistors from under the big heat sink, marked them, so i know from which channel are they. Tested and compared them, all OK. Soldered back, but switched places (ones from left goes to right, ones from right goes to left), assemble again. No boom. Listen music. Again, right channel works fine, left is working badly.
1: I agree, that is not very wise to proceed without photo camera, but I did used paper and pen, to draw the components, connections, colors of wires etc. Also made notes.
2: Did everything precisely, found out transformer is OK
3: Did that, but "DC on the main filter caps?" is a good question, i assume it's good, but check in the evening, to verify.
4: Checked for shorts on transistors, all were fine, but will check on dc.
5: I do not have a scope at home, but it is possible to use the one at work, but only if really really necessary
6: So far, I think transistors are good, but a good tip.
I DO know very well, that i have to power the unit off before i have to place a finger inside. I am a computer technician, and my job is to test laptop components, that involves a lot of checking for such things.
Yes, I did not go frenzy on all the wires i could find. I have only replaced wires for the output channels, because original ones were too long than they needed to be. And way to thin and hard to be used for audio signal. I call this a little mod (experimentation maybe).
Thank you very much for these tips.
I have one silly question though, many of you are mentioning drivers, so I want to verify, that I understand correctly what they are. So are these two little C3423 transistors, found under the big heat sink, the drivers?
Many thanks for support, I found use in every answer
Great forum.
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When I mentioned using a scope to see the amp output without a load, you can 'sort of' do it by ear but you'll need a pair of headphones. Turn off the speakers and plug in the head phones and listen to it. The drivers will have enough capacity to drive the phones to modest levels. If the distortion is much better with headphones, check the small value (usually 0.1 to 0.47 ohm) resistors in series with the output transistors. If one of them is open (high ohms reading) it will 'disconnect' one of the power transistors and have BAD distortion under load. If the resistors are OK it could be an open E-B junction on one of the power transistors but if you checked them before re-installing that shouldn't happen. The driver transistors are the 'current boosters' between the voltage amplifier and the output transistors. One of those could have failed. Fortunately you have a good channel to compare with.
G²
Drivers are the last transistors before the output transistors, usually the emiters of drivers are connected to the bases of the output transistors. You should have one of PNP type and the other one of NPN type. They should be same in size and very simillar in electrical characteristics, just with different polarity.
If you changed all transistors from good chanell (right) to bad one (left) and you still have the problem with left chanell, i think all transistors are ok. As many people said, look for a damaged resistors in the left chanell (the bad one). Meassure all resistors conected with output transistors and drivers. If that wouldnt help, you should check the preamplifier also, more because you said that you can listen the CD input even when the AUX is chosen.
Make some photos also and post.
If you changed all transistors from good chanell (right) to bad one (left) and you still have the problem with left chanell, i think all transistors are ok. As many people said, look for a damaged resistors in the left chanell (the bad one). Meassure all resistors conected with output transistors and drivers. If that wouldnt help, you should check the preamplifier also, more because you said that you can listen the CD input even when the AUX is chosen.
Make some photos also and post.
Good day,
Today i have tried to measure DC on filter caps, and they show 83V, which is a bit weird, because originally there was capacitors with parameters 12000uF 50V :/ another interesting thing is, how they show those 83V.
Lets take left channel filter capacitor, to measure the voltage, i take ground from amp case, and take + from the capacitor, it shows 83V. Now take capacitor for the right channel, and test same way, it shows 0V. But if i take ground from the capacitor it self, then both caps shows 83V. Maybe it is one of the wonders of electronics world, but it seems odd to me.
Here are couple of pictures:
What do you think, is 83V bit too high? Should i suspect that thing with four legs, which produce 83V? or it is normal and i am looking for trouble where there is none?
Today i have tried to measure DC on filter caps, and they show 83V, which is a bit weird, because originally there was capacitors with parameters 12000uF 50V :/ another interesting thing is, how they show those 83V.
Lets take left channel filter capacitor, to measure the voltage, i take ground from amp case, and take + from the capacitor, it shows 83V. Now take capacitor for the right channel, and test same way, it shows 0V. But if i take ground from the capacitor it self, then both caps shows 83V. Maybe it is one of the wonders of electronics world, but it seems odd to me.
Here are couple of pictures:
An externally hosted image should be here but it was not working when we last tested it.
An externally hosted image should be here but it was not working when we last tested it.
What do you think, is 83V bit too high? Should i suspect that thing with four legs, which produce 83V? or it is normal and i am looking for trouble where there is none?
Ok, that "four leg thing" actually does have a name, D5SB20 General Purpose Rectifiers(200V 6A). Found data sheet for it, and it shows that inside there are 4 diodes:
So i again take it out, set multimeter to diode, and start to measure it. All seems ok, no short circuit, no passing backwards. So 83V must be there because something else is "asking for that much" (my wild guess).
http://category.alldatasheet.com/index.jsp?semiconductor=6A
An externally hosted image should be here but it was not working when we last tested it.
So i again take it out, set multimeter to diode, and start to measure it. All seems ok, no short circuit, no passing backwards. So 83V must be there because something else is "asking for that much" (my wild guess).
http://category.alldatasheet.com/index.jsp?semiconductor=6A
Another status update
So, I have disconnected the transformer, took out the main board, discharged all capacitors with spare high wattage resistor. Then started to poke around with multimeter probes, checking for a bad resistors. And i have found a bad resistor, it is marked as R407 on the PCB:
To verify, i have found R408 in the right channel chain, which is identical, but shows a 3.8 Ohm resistance:
I'll continue to check on the rest of resistors, just had to thank you again for pointing me into the right direction
So, I have disconnected the transformer, took out the main board, discharged all capacitors with spare high wattage resistor. Then started to poke around with multimeter probes, checking for a bad resistors. And i have found a bad resistor, it is marked as R407 on the PCB:
An externally hosted image should be here but it was not working when we last tested it.
To verify, i have found R408 in the right channel chain, which is identical, but shows a 3.8 Ohm resistance:
An externally hosted image should be here but it was not working when we last tested it.
I'll continue to check on the rest of resistors, just had to thank you again for pointing me into the right direction
Just change the bad resistor.
Make sure you check the square white resistors near the output transistors.
The filter capacitors are not for right or left channels. They are for positive and negative DC supply for both channels. Check the voltage at the two terminals of each capacitor. Should be around 35 volts or so.
Your photos are too large. You should post smaller photos.
Make sure you check the square white resistors near the output transistors.
The filter capacitors are not for right or left channels. They are for positive and negative DC supply for both channels. Check the voltage at the two terminals of each capacitor. Should be around 35 volts or so.
Your photos are too large. You should post smaller photos.
At first I did not understand what are you talking about, i see them small, and they become big if you click on them. But had to use another computer without Firefox in there, and omg, on chrome, those pictures are huge :O But, i can't edit my posts now, cannot find any edit buttons for them...
Well, as for the matters with this Harman/kardon I have changed the bad resistor, and now all I hear is silent, any of the channels work anymore, however, the resistor is slightly different, but color markings and size is the same :/ However color of the casing is lightly brown, and as you can see in these pictures, old one is green.
R407 is a 3.3R fuse resistor. It has infinite resistance because it is blown. You should definitely not replace it with an ordinary resistor from your local parts store!
There are several fuse resistors in the HK 620. R407 is used in the 38 V rail prior to the VA-stage. It is blown because of a shortcircuit to ground, either caused by a bad component or your repair attempts.
I advise you to bring your HK 620 to a competent and knowledgeable HiFi repair service.
There are several fuse resistors in the HK 620. R407 is used in the 38 V rail prior to the VA-stage. It is blown because of a shortcircuit to ground, either caused by a bad component or your repair attempts.
I advise you to bring your HK 620 to a competent and knowledgeable HiFi repair service.
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