Harman/Kardon 730 Twin Receiver - CL find, right channel problems

M---

New Member
Hi all,

I picked up a Harman Kardon 730 Twin Powered receiver for $30 at a garage sale this weekend. She's a little rough around the edges (a few scratches on the case, a chip out of the top corner of the glass, couple little dings on the faceplate, and the Tape Monitor 2 switch is missing its aluminum cap.

When I hooked her up yesterday, I was initially disappointed-- with my iPod on Aux 1, the left channel was OK, but the right channel was dead. With the volume cranked all the way up, I could hear some faint sounds, like headphones with the volume maxed out. Then I flicked it over to FM, and I got nice clear sounds from both channels. So I plugged my iPod into the Aux 2 input, and I have great stereo sound! Both channels are working beautifully!

But the pots were all scratchy, so today I picked up a can of MG Nu-Trol control cleaner, sprayed it into the pots, and into the selector switch, and worked them all. While I was at it, I noticed that one of my fuse-style bulbs is missing... Maybe this is my opportunity to go LED for the backlights?

The pots are all working beautifully now-- no scratchiness! :thmbsp:

...But I'm disappointed: I've lost the right channel for all inputs. Aux 1, Aux 2, AM, FM are all missing the right channel. All I get is that faint sound like headphones that are turned up loud. :tears:

Can any of you suggest any hints as to where I should start my search for a problem?

I think I can rule out the volume control, since the faintness turns up and down. Same thing for the balance control, since the right (however faint) does fade in and out smoothly. I can't tell if the bass/treble controls are working on the right channel, because the sound is so minimal.

Sigh, I guess my project for tomorrow will be to flip her upside-down and trace the input selector switch.

Once I get it fixed, then I'll be on to the next task: finding a new cap for the Tape Monitor 2 switch. And grinding out the little crunch in the top edge of the acrylic face. And buffing the front face of the glass so that she shines. Maybe I'll go LED for the bulbs, rather than replacing the fuse-style lamp (those things are expensive! And I haven't even found the right voltage of bulb yet! ...But unfortunately the amp is feeding the light panel with AC).

...And I've got to figure out what to do with my previous receiver, a Sanyo 2050 in absolutely pristine condition. Wife says to sell it, so that's probably what I'll do, but it's a shame because it's in perfect shape, just one faint scratch on the aluminum top edge.
 

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One clarification: now that I'm thinking about it, I think yesterday I was having problems with the left channel, today the right channel isn't working. *sigh*
 
Speaker switches are OK.

I'm suspecting the input selector switch... I plugged my iPod into the Tape Monitor 1 input, and switched on the tape monitor-- both speakers suddenly had sound! :banana:

Tonight I'll pull it apart to see what's going on with the input selector switch.
 
Deoxit is your best friend, especially with that receiver. I have four of them they all had some sort of problem related to dirty switches. Pay particular attention to the Tape Monitor buttons.
 
I recently came across a HK 430, loved it, so I picked up a 730 off of ebay. With both I was having the similar problems. I had to really, really, really clean the pots and switches. I mean I had to clean them like I never have had to clean the pots on any others. Faceplate removal was a must and made the difference in the end. This is not difficult to do on these units.
 
I recently came across a HK 430, loved it, so I picked up a 730 off of ebay. With both I was having the similar problems. I had to really, really, really clean the pots and switches. I mean I had to clean them like I never have had to clean the pots on any others. Faceplate removal was a must and made the difference in the end. This is not difficult to do on these units.

Same with my hk75. Regular cleaning did not fix the problem.
Next step "super clean".

It seems that this is an ever present condition in older SS hk recievers. :thumbsdn:


Steve
 
Love my 430c, it has been very problem-free over about a decade and a half of ownership. I also have a 330b and 590i from a bit later. All have been great receivers. A few years ago, I think my 430 had to go in for some work re a channel dropping out, but it was an inexpensive repair. If I needed more power, I'd go for a 730, but don't really need it at the moment given my room/speaker complement.
 
Thanks to all for your help-- instead of tracing problems with the input selector, I gave it a thorough cleaning.

Just finished cleaning the input selector switch-- I was able to get good access to it by opening up the bottom of the case. Sprayed it with cleaner, worked it many times, then at first nothing worked, then one channel came in on some inputs, then both channels started to work as I kept rotating the switch.

Yes, it works! :D

I'm actually using MG "Super Contact Cleaner with Poly Phenyl Ether". I think I called it by a different product's name in my first post. I was having trouble justifying the cost of DeoxIT ($25) compared to this product ($12), especially considering that DeoxIT was almost as much as I spent on this receiver!

I found an eBay seller with the fuse lamp I needed for cheap, so that's on the way. I'll try an LED conversion for another amp, sometime in the future...

While looking over the wiring diagrams, I saw that there's a "stereo" lamp... Funny, mine doesn't seem to light. I guess that's another bulb that I'll have to source...

Still on the to-do list:
-Grind out the poorly-repaired chip in the corner of the glass
-Polish up the front glass
-Source & install aluminum cap on broken switch
-Install fuse bulb (when it arrives)
-Source & install stereo bulb.
 
Thanks to all for your help-- instead of tracing problems with the input selector, I gave it a thorough cleaning.

Just finished cleaning the input selector switch-- I was able to get good access to it by opening up the bottom of the case. Sprayed it with cleaner, worked it many times, then at first nothing worked, then one channel came in on some inputs, then both channels started to work as I kept rotating the switch.

Yes, it works! :D

I'm actually using MG "Super Contact Cleaner with Poly Phenyl Ether". I think I called it by a different product's name in my first post. I was having trouble justifying the cost of DeoxIT ($25) compared to this product ($12), especially considering that DeoxIT was almost as much as I spent on this receiver!

I found an eBay seller with the fuse lamp I needed for cheap, so that's on the way. I'll try an LED conversion for another amp, sometime in the future...

While looking over the wiring diagrams, I saw that there's a "stereo" lamp... Funny, mine doesn't seem to light. I guess that's another bulb that I'll have to source...

Still on the to-do list:
-Grind out the poorly-repaired chip in the corner of the glass
-Polish up the front glass
-Source & install aluminum cap on broken switch
-Install fuse bulb (when it arrives)
-Source & install stereo bulb.

Yeah, I still need to fix my stereo lamp in the 430. I haven't even begin to look at what it is going to take to fix it.
 
Oddly enough, after I wrote that post last night, I walked back into the bedroom, and the stereo light was shining happily!

Sigh, more loose/bad connections, I guess.
 
Yet another reason this site and the helpful people here are great. After a couple of weeks with no problems since picking it up an cleaning it with Deoxit, I had the exact problem described. I went through everything I knew to check - fuses, trying to get in behind push buttons, spraying pots again and again from front after removing faceplate, and none of it seemed to help. I was about ready to put it up for sale. And then I saw this thread and removed the bottom cover. Lo and behold, the contact points for the selector switch knob way underneath (and toward the back of the receiver) needed to get hit with Deoxit. And now it works perfectly. Thanks for following through with comments on what worked! The HK 730 is now about to take up residence under our TV as the home theater/living room audio unit!
 
Also, you can clean up the preamp jumpers on the back of the receiver.

I completely re-capped my 730, and the sound is incredibly good, for a 35 year old receiver. Just know that there's NO output protection circuitry, so any fault in the output transistors will result in blown speakers.
 
I forgot to mention I had cleaned the jumpers too. So I felt out of options, until I saw this thread, and it was THE answer. I had no idea you could spray Deoxit into the selector switch pot from the front and it wouldn't really get anywhere.
 
. I was having trouble justifying the cost of DeoxIT ($25) compared to this product ($12), especially considering that DeoxIT was almost as much as I spent on this receiver!
You'll think that way until you need to redo the same job in short while.
 
Just a quick follow-up photo for anyone down the road who runs into this issue - contact points at the far end from the knob (near top of first photo, to the right on second photo).
 

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So, as it happens, a couple of years ago I came across another HK 730. This one was in near-pristine physical condition, and best of all it was free (CL free section, somebody had a CRT TV (who wants those?) + stereo (HK 730!) + furniture, the deal being take it all).

Turns out the seller found somebody to take the furniture, but nobody wanted the TV + stereo. Except me! Took the TV to a place that donates furniture and electronics to new immigrants, and kept the pristine HK 730 for myself.

The major problem with it was that all but one of the backlights were burnt out. Everything else worked. So I sold the stereo that I originally posted about, ordered some bulb fuses, and put it back together! Didn't bother cleaning anything internal, since it was all working.

All was well until a few weeks ago, when the left channel dropped out 97%. Just a little bit could be heard. Finally got around to checking it today-- the left channel was gone for all the inputs. Argh. Potentiometers seemed to operate smoothly, so figured that wasn't the problem.

Googled the problem, and came up with my 4-year-old thread here on Audiokarma! Crazy how the internet works.

Anyway, turns out the balance pot was bad. So much for assuming the potentiometers were fine! Shot some contact cleaner in there, and it cleaned right up. Amp works great again! :music:

For my own future reference, or for anybody else who comes across this post, here was my troubleshooting:

1) test with headphones, to isolate whether it was a pre-amp or power amp problem. Headphones had the same problem, so assume the issue's the preamp.
2) plug a known-good sound source (eg CD player or ipod) into one of the tape monitor inputs, these bypass the finicky input selector switch. Same problem existed, so I decided to play around some more with the pots.

For anybody who wants to clean out the potentiometers on these receivers, please note the following:
1) DON'T spray cleaners through the front face. It won't get into the pots. I pulled off the front face (it's easy to do, that's how you get at the bulb for the "on" switch, or at the tuner needle). But if you spray contact cleaner there, it won't get into the pots. Not at all.
2) To clean the pots, just take the top cover off. The volume pot is open to the elements and easy to get at. The other pots are enclosed... Try to get your cleaner in through the gaps in the potentiometers' casings.
3) While you're at it, take the bottom cover off so that you can clean up your cleaning fluid that doesn't make it into the pots.
4) While you're at it, since you've got the bottom cover off, spray some cleaning fluid into the finicky input selector switch. The contacts are near the back of the unit, only accessible from the bottom.

Cheers!
 
Just figured I would add my little experience to this thread as well. I too have a 730 that I love and cherish. It is my main receiver and worked flawlessly until moving.. I even had it in the front seat of my car to make sure nothing happened to it(Hey, she is in great shape and I didn't want anything to happen to that pretty face).

Well, we're in the new house now. I hook everything back up and all of the sudden the right channel isn't working well. Some sound, but mostly static if anything. Both speakers, 1&2 the right channel is out. Stereo, Mono, all inputs, etc. Completely bummed, I worried something had happened during the move that would require servicing. After playing around I noticed I got the right channel to come back for a moment or 2, then it would go again. So I figured I would tear her apart...

Anyway, long story short I ended up cleaning the push button switches with deoxit and that resolved the issue for me. I had scratchy volume knobs and cleaned the pots previously. But never really got into the push button switches aside from trying to spray the front and working it like that.. It was very easy to access the switches once you remove the bottom plate of the 730. Then you can really get in and clean those switches. You can see them switch and where to clean when you push the buttons. The bottom row is very easy with it right there for you, top row a bit trickier but I still got the deoxit straw in there and cleaned them out without having to really take apart the 730. Not sure exactly which button it was that messed things up.. But that was the only thing I did and it resolved a pretty much dead right channel for me.

Crazy how something so seemingly simple can cause severe issues.
 
I own (and have enjoyed for a long time) an A-402 integrated amp and an h/k505 integrated amp.

My advice for other owners: purchace some stock in DeOxit (or whatever entity owns them) and then order a 55-gallon drum of the stuff.

You'll need it!
 
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