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Harman Kardon Twin Power 730, low right channel output

R

redstarjedi

AK Subscriber
Subscriber
I just snagged a HK 730, for 30 bucks!

A few questions.

Right channel is a bit lower than the left. I didn't fully de-oxit the speaker selector switches and the balance knob is still scratchy. If more de-oxit doesn't solve it. What could it be?

I got a re-cap kit from eBay, that includes quite a few transistors, on all the boards. If that doesn't solve the balance issue, where should I look next? (Re-capping it means I can actually get to all the switches and de-oxit them)

I connected my yamaha CX-800 preamp and bypassed the internal native preamp of the HK 730. The problem went away.

It is clear that the problem is NOT the amplifier section. I assume it is the native pre-amp section.

So, if it is not dirty switches what could it be?
 
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redstarjedi said:
I just snagged a HK 730, for 30 bucks!

A few questions.

Right channel is a bit lower than the left. I didn't fully de-oxit the speaker selector switches and the balance knob is still scratchy. If more de-oxit doesn't solve it. What could it be?

I got a re-cap kit from eBay, that includes quite a few transistors, on all the boards. If that doesn't solve the balance issue, where should I look next? (Re-capping it means I can actually get to all the switches and de-oxit them)

I connected my yamaha CX-800 preamp and bypassed the internal native preamp of the HK 730. The problem went away.

It is clear that the problem is NOT the amplifier section. I assume it is the native pre-amp section.

So, if it is not dirty switches what could it be?
Click to expand...
Use FaderLube F5 for pots, and DeOxit D5 for switches.
These have a few of the "true blue" colored electrolytic caps in them. They are well known to leak and corrode and can be causing the issue. Since it is "working" there doesn't seem to be any major issues. Start with the preamp/Tone board so you can get at the switches and pots, and change the electrolytic caps. Also change any "known to go noisy" transistors if you have them. If not, put it back together anyways and test it out before moving on to anything else.
 
bum cap not a bad guess, but I'd start with the controls. If that does nothing, do the caps just in the line stage first to see if that sorts it before introducing a ton of variables.

isolating the preamp from the power amp is a good way of doing that, and its usually where I start as well.
 
An electrolytic cap would be my first suspect. As already stated, the blue-plastic-wrapped electrolytics on the tone board are always (in my experience) bad.

Recommendations:

Deoxit the pots and switches.
Remove the RCA back plane, deoxit the stiff connector wires and their sockets.
Replace all the electrolytics on the tone board, the power amp board, and the phono board.

Good luck!
 
redstarjedi said:
It's those blue tear drop shaped ones right ? I don't think the kit I ordered included them. But I'm sure they only cost a few cents.
Click to expand...

Think he's referring to to the wrapped electrolytic cans. Tear drops sound like tantalum caps w/o a plastic wrap. Some peeps replace those on sight.
 
dlucy said:
An electrolytic cap would be my first suspect. As already stated, the blue-plastic-wrapped electrolytics on the tone board are always (in my experience) bad.

Recommendations:

Deoxit the pots and switches.
Remove the RCA back plane, deoxit the stiff connector wires and their sockets.
Replace all the electrolytics on the tone board, the power amp board, and the phono board.

Good luck!
Click to expand...

If you do these different boards. Stop and test after each one. That way you'll know where the problem was, and if you do something wrong, you'll know right away and not have to try to figure out which board it's on.
 
On the tone control / preamp board, I have found these dark-blue-plastic-wrapped electrolytic cans (not the teardrop-shaped tantalum caps on the tuner board) fail very, very often:

IMG_0710.JPEG

AK IMG_1359.jpg


While you have that board pulled out, you could replace all the electrolytic caps...
IMG_0722.JPEG

Or literally everything except the pots:

IMG_0728.JPEG
 
dlucy said:
On the tone control / preamp board, I have found these dark-blue-plastic-wrapped electrolytic cans (not the teardrop-shaped tantalum caps on the tuner board) fail very, very often:

View attachment 2543619

View attachment 2543622


While you have that board pulled out, you could replace all the electrolytic caps...
View attachment 2543620

Or literally everything except the pots:

View attachment 2543621
Click to expand...
the kit i bought has wima film caps as replacements. I think they guy read your other thread and assembled the kit from your suggestions.
 
dlucy said:
On the tone control / preamp board, I have found these dark-blue-plastic-wrapped electrolytic cans (not the teardrop-shaped tantalum caps on the tuner board) fail very, very often:

View attachment 2543619

View attachment 2543622


While you have that board pulled out, you could replace all the electrolytic caps...
View attachment 2543620

Or literally everything except the pots:

View attachment 2543621
Click to expand...
also, do you use a wire wrap tool (which i don't have) or just solder the wires back to the posts? My father is saying there is no harm just soldering them back.
 
once you un-wrap those wires, the only way to really re-terminate them properly is to strip and re-wrap. The sharp corners of those posts dig into the wire and creates weak spots. Pretty much guaranteed the wire is going to snap at one of them if you try and bend it back.
 
redstarjedi said:
also, do you use a wire wrap tool (which i don't have) or just solder the wires back to the posts? My father is saying there is no harm just soldering them back.
Click to expand...
The wirewrap was for solderless assembly at the factory. You can just solder them back on and they'll be just fine.
 
I believe those dark blue caps were also Matsushita (Panasonic). They're about as bad as the lavender sleeved caps from the same era. Glad they got their act together, as the FM, FC, FR, etc caps are quite good. If you see caps that look like these, remove on sight.

eIMGP4832.JPG
 
As I said before. I plan on doing a recap, meaning the preamp board and a few transistors there too.

However I just noticed something interesting. The problem isn't there when on FM, or AUX 2.

The problem is on AUX 1. Other than the above, what should I look for on input board ?
 
The problem being lower level on the R than L channel? Check the wires leading to the Tape monitors. I found a solder bridge that was knocking out a channel, but that's not quite the same as just lower volume on one source.
 
Get the service bulletins for the 730 on hifiengine. I had dropouts on some of my sources because I needed to re-flow solder at the inputs and at the pins from the selector board to the phono board.
 
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