HARMAN KARDON 330A - Dead Right Channel

[JB8]

Crew-

I have another 330A, dead right channel, here's were I'm at.

• Initial testing revealed TR904 was bad so I replaced all four output transistors with 15034's
• TR608 & TR606 tested bad as well, replaced them with 1220 and 2690 (also replaced on left channel, I did this will all components I replaced so both channels would be matching)
• Since the issue persisted I finally pulled the jumpers to test main vs pre-amp - the pre-amp out signal was L/R, Main In with other signal injected only produced left channel content (jumpers are back in)
• I then started replacing caps since the remaining transistors tested fine - still no right channel
• When testing voltages everything but the second half (back half) of the right channel is testing well
• If I probe the front leg/contact point of VR601 I get .68v DC, front leg of left channel VR501 is 16.2v
• VR602 front leg is .60v, VR502 is at 20.8v
• B+ test points are good for both channels
• Resistors all seems to test fine for both sides - I haven't pulled legs to test them but in-chassis comparing right to left they're all similar readings
• I also just swapped out the 828's at TR607/TR507

I keep eyeballing the VR's but the resistance on all four are fairly similar when checking with power off.

Candidly, there have been many times where I've prematurely reached out for help only to have someone say, "well, is it plugged in?" To which I reply, "crap, I knew I was missing something." In other words, something obvious that I wasn't smart enough to recognize. In this case, however, I feel like I've done some decent probing before reaching out so I won't be too embarrassed when the glaring issue is pointed out, ha! Instead of just continuing with this shotgunning I'd really appreciate some advice on next steps, thanks in advance!

 

[Warren-Oates]

Have you tested the 1/4 resistors voltages while under dimbulb? There still could be a bad one. Also if you find one that has strange voltage it may be a clue as to what else to test. Measure from chassis to one leg at a time, compare to good channel.

 

[JB8]

Thanks, @Warren-Oates , I appreciate you jumping in! I've been testing resistors while on DBT, comparing right to left, and I've drawn a line where the right channel goes dead. I don't fully understand how the flow moves through the main amp so that's likely my blind spot. If everything on the lower half of this board is comparable side to side are there any specific junctures from lower to upper (front to back) that I should focus on?

 

[Warren-Oates]

That image is pretty small on my screen. You have no DC power above that line on the right channel? I do see some resistors connected to the power trace above that line, on their left side there is no voltage? Just want to make sure I understand.

 

[blhagstrom]

Went overboard on a Pioneer tuner lately hunting a problem. Eventually discovered a dirty switch!!!!

The push button switches on that series of Harman Kardon are known to be tricky and about impossible to deoxit. FWIW, are you rigged with an o-scope to chase the audio signal and see if a dirty switch is messing with you?

 

[blhagstrom]

Then there was the time I rebuilt a 330B.
Thought it was good to go.
Sold it, shipped it.
Dead channel.
Got it back.

One bad solder joint.
I’ve done a million solder joints.
It looked good but wasn’t.

Dammit

 

[JB8]

Hey @blhagstrom , I think you've helped me in the past, thanks for jumping in again! I've had the same thing happen, one little fiddly thing after the item has been shipped, frustrating but still satisfying once the new problem is identified and tackled, man...

Yes, O-scope in-hand, it only has one good channel but I figure that's all we'll need. I'll dig it out, and send a pic of how it's currently set up - still lots to learn about o-scope action. After that, let the probing begin!

 

[JB8]

This is how I left it after using it last, let me know what tweaks I should make and next steps, excited to track down the culprit!

 

[JB8]

Whelp, I did it again... It's just, so, embarrassing! You think you're hitting all the troubleshooting steps, this looks good, that's fine, leave that alone, etc. And then you start probing.

I initially started probing with the O scope and saw the signal moving through both channels pre's equally, cool. Then started a more in-depth probe of the main amp looking for where the DC pooped out. Now don't get me wrong, this was a great lesson to learn, but, when you spend a couple hours and dollars replacing parts then find that the speaker fuse you eyeballed is actually faulty, well, no bueno.

I know other people like me will read this, so please let this be a lesson for you as well. Eyeballing a fuse is not enough to determine if it's working, ha!

At any rate, replaced the fuse, sounds sweet, yada yada yada. Man, I'm such a dope!

Thanks again for the support, I'll be back!

 

[Mumbles]

Ha! I think we've all been caught with our pants down by this one. Now you just gotta figure out why the fuse blew in the first place. Hopefully nothing too serious.

You will enjoy the 330A. I have a couple of them here, including the one I bought new in Dec '71 shortly after they were first released. It's been sitting on the 'to do' rack for several years now with both channels out. Some day.....

 

[blhagstrom]

Yup, use a meter to check fuses.

40+ years of heating and cooling cycles can open them just like a light bulb.