Harman Kardon 330b - Left channel is there but much weaker than right

[redpackman]

OK. I'm working on a nice HK 330b. The left channel is very weak. The only way I can get the channels to "balance" is to turn the right channel down about 85% with the balance knob. The sound is not distorted, just very, very weak. That's not good.

Here's what I've done so far: cleaned all the controls and switches with Deoxit and worked them back and forth vigorously. No scratchy sound, but the left channel is weak. I've checked the fuses for the two channels. Both are intact. I took out the jumpers and wired it so the pre-amp of the 330b was going into my Kenwood 8300. The channels are nicely balanced then, perfectly so, which leads me to believe that the problem is not the pre-amp but the left channel output amp. I've visually inspected the left side of the amp and can see no blown transistors or capacitors...at least to my eyes (which are far from experienced). I took readings from the left channel output transistors with the unit operating (very carefully) and compared them with the readings from the right channel's outputs. They seem quite similar. In-circuit, I've checked the resistors readings to see if any are open or way off and compared them with the resistors in the right channel. They seem similar once again, but I'm not sure I've got every last one. I tried reflowing a number of the solder joints in the left amplifier channel section. Not sure I got all of them, but no change.

I'm stumped. Any ideas? Are there any components in that section that are known to go bad and exhibit symptoms like this.

 

[dlucy]

Great work so far!

If you believe the problem is in the main amp board and it doesn't sound like an output transistor is blown (then you'd have no output on one channel), then I would recommend the following:

1. Deoxit the main in jacks and use a small brush like a mascara brush to get deoxit at the insides of those two jacks, and if that doesn't fix it then...
2. Recap the main board (relatively few caps) especially the large output caps, and if that doesn't fix it then...
3. Replace the known-noisy 2SC458 small transistors on the main amp board, and if that doesn't fix it then...
4. Replace the output transistor's resistors and trimpots

If you want to do any of the component replacements above, you'll need to identify which variant of the 330B you have in order to get the parts list correct.

Which variant do you have? http://www.audiokarma.org/forums/in...on-330-variations.396817/page-2#post-10334200

BOM threads:

• http://www.audiokarma.org/forums/in...nt-3-recap-and-restore-bom-parts-list.781479/
• 
  
• http://www.audiokarma.org/forums/in...store-and-upgrade-bom-part-list-kinda.739572/

Don't hesitate to ask questions. I've got all 3-4 variants here and open in case you need some reference of some kind.

Have you gotten the service manual from hifiengine yet? Again, you'll need to know which variant you have (mainly the difference is B-1 series versus B-2 series and that is often labeled on the rear panel in the lower right corner).

 

[redpackman]

I must have the Taiwan series of the 330B because the boards are silkscreened....very helpful, in fact. Thanks for all the input. Ken

 

[redpackman]

I think I might have found the issue. In the left channel of the amp section one of the caps (C404 I believe) had a lead that was simply burned off (220uf 63v). I'm replacing that one, plus the 2SC458's (which still test good, but I know they'll eventually get noisy or fail) and some of the other caps in the amp section. We'll see. Thanks for the help thus far, dlucy!! (BTW I have a B-1 labelled 330b made in Taiwan with the silk screened circuit board...a great help to me, frankly).

 

[JamesML]

Great work so far!

If you believe the problem is in the main amp board and it doesn't sound like an output transistor is blown (then you'd have no output on one channel), then I would recommend the following:

1. Deoxit the main in jacks and use a small brush like a mascara brush to get deoxit at the insides of those two jacks, and if that doesn't fix it then...
2. Recap the main board (relatively few caps) especially the large output caps, and if that doesn't fix it then...
3. Replace the known-noisy 2SC458 small transistors on the main amp board, and if that doesn't fix it then...
4. Replace the output transistor's resistors and trimpots

If you want to do any of the component replacements above, you'll need to identify which variant of the 330B you have in order to get the parts list correct.

Which variant do you have? http://www.audiokarma.org/forums/in...on-330-variations.396817/page-2#post-10334200

BOM threads:

• http://www.audiokarma.org/forums/in...nt-3-recap-and-restore-bom-parts-list.781479/
• 
  
• http://www.audiokarma.org/forums/in...store-and-upgrade-bom-part-list-kinda.739572/

Don't hesitate to ask questions. I've got all 3-4 variants here and open in case you need some reference of some kind.

Have you gotten the service manual from hifiengine yet? Again, you'll need to know which variant you have (mainly the difference is B-1 series versus B-2 series and that is often labeled on the rear panel in the lower right corner).

I note with interest you suggest if an output transistor is blown then you would get no ouput signal at all.
I have a Harman Kardon Five Thirty which was working fine up until recently. Then the right channel kept
dropping out (but with weak output) until it eventually just failed permanently. However there is still a
weak signal. If I turn the volume control to half past four it sounds OK.
I was assuming either one of the output transistors was blown or the secondary winding on the offending output transformer
was compromised. Unfortunately I have no test equipment apart from a multimeter which makes it difficult for me to diagnose
the problem. The AC signals from the driver section (primary winding seem about equal).
Also both channels on the Driver board are getting 25v DC as per specifications.
I'm reluctant to remove any of the transistors. Because, I just know, with my soldering skills, I'll fry the transistor when
I put it back.
Don't know if anybody has any suggestions.

 

[dlucy]

I have a Harman Kardon Five Thirty which was working fine up until recently. Then the right channel kept
dropping out (but with weak output) until it eventually just failed permanently. However there is still a
weak signal.

The best first step is to create a new thread here on AK specific to your Five Thirty and explain your situation and the symptoms.

 

[JamesML]

The best first step is to create a new thread here on AK specific to your Five Thirty and explain your situation and the symptoms.

Noted and thanks dlucy. I'm feeling unwell at the moment. Confined to my bed. But, as soon as I feel better I'll fire up a thread.
P.S. 'Transistor tester and Curve Tracer guide' is excellent. Come to think of it I already have a cheapo transistor tester somewhere. I'll dig it out when I'm vertical.

 

[JamesML]

Harman Kardon Five Thirty follow up.

Some good news. Shook the dust off this receiver and put on my workbench to have another attempt to restore the bad channel.
Just using my multimeter at first, I noticed that the primary inputs on the Driver Board on duff channel had approx 1/10th of the
signal as for that of the working channel.
Duh! I'm sure I checked this before (a couple of years ago now) with different results.
Anyways, I have removed the Driver Board (not too difficult) and re-capped the electrolytics (1 was duff). Bingo! Sound back now and
both channels equal.
Then bad news. Very noisy operation. Loud HUMMM. But, I recapped all the big power caps which has fixed the problem.
One cap I haven't done yet. It's a double cap (2 x 500mfd 50v). Guess I can replace it with 2 individual caps.
All working good now. No Hum, good sound. But, and it's a big wobbly But. Despite the FM stereo beacon being activated (by transistor Q403) I'm getting mono.
I'm sure it was all working fine when I originally tested the receiver.
Guess I'll have to do some voltage checks on the MPX board.
I like this receiver and would very much like to get it up and running in tip-top condition. I'll keep trying.

 

[JamesML]

Pix : Power Supply Recap (most of).
Diodes on MPX board all check OK. (Splitter I guess).
Another guess. I'm thinking maybe I've got a voltage problem somewhere. From past experience some components expect a certain voltage
to decide upon whether you can have stereo or not. But, I'm quite likely wrong here. Hoping that the MPX transistors are OK.
Will do some more checking tomorrow if it's not too hot.
The UK is on fire at the moment according to the news.

 

[JamesML]

Harman Kardon Five Thirty REVISITED (Extended remix).
I guess I should have started a separate thread for this. But,...

Got this beautiful receiver out onto my bench today for another look (No stereo separation at last test).
I proceeded to check out the three transistors on the MPX board. One tested OK. For 2 the readings were a little spurious.
Whilst contemplating de-soldering the base on each transistor I left the radio FM up and running. Sounding good.
And, my ears pricked up! Glorious STEREO!
What the?
I can only guess that I must have moved a connection which started the Five Thirty to sing to both ears!
AM I PLEASED? YOU BETCHA!

In this sort of situation, from my experience, you can bet that the stereo will drop out again, maybe, maybe.
If it does I'll remove the MPX board and re-solder all connections where appropriate.

I love this amplifier and plan on keeping it in good order.

STARTS SINGING.

 

[laidbacklark]

Harman Kardon Five Thirty follow up.

Some good news. Shook the dust off this receiver and put on my workbench to have another attempt to restore the bad channel.
Just using my multimeter at first, I noticed that the primary inputs on the Driver Board on duff channel had approx 1/10th of the
signal as for that of the working channel.
Duh! I'm sure I checked this before (a couple of years ago now) with different results.
Anyways, I have removed the Driver Board (not too difficult) and re-capped the electrolytics (1 was duff). Bingo! Sound back now and
both channels equal.
Then bad news. Very noisy operation. Loud HUMMM. But, I recapped all the big power caps which has fixed the problem.
One cap I haven't done yet. It's a double cap (2 x 500mfd 50v). Guess I can replace it with 2 individual caps.
All working good now. No Hum, good sound. But, and it's a big wobbly But. Despite the FM stereo beacon being activated (by transistor Q403) I'm getting mono.
I'm sure it was all working fine when I originally tested the receiver.
Guess I'll have to do some voltage checks on the MPX board.
I like this receiver and would very much like to get it up and running in tip-top condition. I'll keep trying.

Resurrecting after 3 years. I have the same issue with mine. When I turn the balance knob all the way to one side, there’s a very weak signal output to the speaker. A slight turn of the balance knob and all the signal goes to the other speaker. Intermittently I hear crackling on the weak channel. The inside of the amp was very dirty, the pots were literally stuffed with gunk. Cleaned it the best I could with DeOxit. But yeah just one channel’s working. Any suggestions or should I go the same way as the fix in the quoted post ? Thanks

Edit: Never mind, mine is a 330b and the fix above references a 530. Sorry about that, will look elsewhere. But would still like suggestions for the single channel issue. Thanks

 

[kwayde]

Resurrecting after 3 years. I have the same issue with mine. When I turn the balance knob all the way to one side, there’s a very weak signal output to the speaker. A slight turn of the balance knob and all the signal goes to the other speaker. Intermittently I hear crackling on the weak channel. The inside of the amp was very dirty, the pots were literally stuffed with gunk. Cleaned it the best I could with DeOxit. But yeah just one channel’s working. Any suggestions or should I go the same way as the fix in the quoted post ? Thanks

Edit: Never mind, mine is a 330b and the fix above references a 530. Sorry about that, will look elsewhere. But would still like suggestions for the single channel issue. Thanks

See post #2.

 

[laidbacklark]

See post #2.

Thanks. Could be a stupid Q, when we say ‘main in jacks’, are we referring to the RCA inputs ? Tested all 3 (Phono, Tape In and Aux) with the same result

 

[kwayde]

Thanks. Could be a stupid Q, when we say ‘main in jacks’, are we referring to the RCA inputs ? Tested all 3 (Phono, Tape In and Aux) with the same result

Main-in jacks are where the pre-out/main-in jumpers are.

 

[laidbacklark]

Main-in jacks are where the pre-out/main-in jumpers are.

View attachment 3580881

Thank you, will do that and also try the pre-out to power amp route to isolate the issue one more step. Need one more help - the treble and bass knobs are held in place with a tiny screw in the knob. I haven’t removed them because of that unique ‘second’ pot knob attached to it which varies the left and right side of the tone controls. Two questions:
1. What’s the finctionality of that outside knob (on the bass and treble) that separately turns to either side ?
2. Is there special care to be exercised when I remove the entire control knobs for cleaning ? Don’t want to damage/misalign anything mechanical inside due to the ‘two-on-one’ knobs arrangement

 

[Mumbles]

What’s the finctionality of that outside knob

The function of the split bass and treble knobs is to allow individual adjustment of each channel. You can hold onto one knob while adjusting the other. Not all HK's came with this feature so I'd consider it a bonus.

To remove them, just loosen or remove the set screw and pull off the outer knob, which holds the inner knob in place.

 

[kwayde]

Thank you, will do that and also try the pre-out to power amp route to isolate the issue one more step. Need one more help - the treble and bass knobs are held in place with a tiny screw in the knob. I haven’t removed them because of that unique ‘second’ pot knob attached to it which varies the left and right side of the tone controls. Two questions:
1. What’s the finctionality of that outside knob (on the bass and treble) that separately turns to either side ?
2. Is there special care to be exercised when I remove the entire control knobs for cleaning ? Don’t want to damage/misalign anything mechanical inside due to the ‘two-on-one’ knobs arrangement

One part is to control bass/treble in the left channel, the other is for the right channel. If one desires they can use them separately but most turn both together for convenience.

No special care is needed. When removed you'll see that the shaft is actually two shafts, an inner brass shaft with teeth and an outer. When replacing them just align the inner one with the extreme left or right marks on the face plate, being sure the shaft is rotated all the way in that direction, then put the outer one in place and tighten down.

 

[laidbacklark]

The function of the split bass and treble knobs is to allow individual adjustment of each channel. You can hold onto one knob while adjusting the other. Not all HK's came with this feature so I'd consider it a bonus.

To remove them, just loosen or remove the set screw and pull off the outer knob, which holds the inner knob in place.

View attachment 3580929

Much obliged for this info. The unit has been in storage for many years. There were loads of dirt in the other pots. Even though not scratchy while in operation, I want to remove these tone control knobs and clean them out as I expect to see dirt in them. Also the pots are better reachable by removing the base plate. Can’t wait to get this beauty singing on both channels. The one channel on which it performs sounds awesomely warm and vintage

 

[laidbacklark]

One part is to control bass/treble in the left channel, the other is for the right channel. If one desires they can use them separately but most turn both together for convenience.

No special care is needed. When removed you'll see that the shaft is actually two shafts, an inner brass shaft with teeth and an outer. When replacing then just align the inner one with the extreme left or right marks on the face plate, being sure the shaft is rotated all the way in that direction, then put the outer one in place and tighten down.

View attachment 3580936
View attachment 3580937

This help is much appreciated. Now I feel confident of removing the knobs