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BasmntMadman

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Location: Off-White Gardens

Posted: Oct 12, 2009 - 11:49am

Beaker wrote:

I'm not picking on deoxIT at all - just reverting to basic troubleshooting technique. Namely, find the source of the problem and then determine the best repair solution.

If its the tape monitor switch, cycling that viscously a few times should bring back some of the signal, if even staticy/distorted. If no action there, it could the the input selector switch(s). Not all switches are suitable for use with deoxIt and similar - as they may be sealed against contamination. In that case, the only solution is replacement, or if you are ever so brave - removal for total disassembly, clean and reassembly. Of course this all assumes its oxidation that is the cause of the woe - which is indeed often the case. Could just as easily be a cold solder joint on one of the switches, interrupting the signal for that channel - also a very common issue in amps where the pads for the low level signal switches are soldered directly to the board.

Could also be a minor failure in the preamp circuit. The fact that the unit still has power and apparently hasn't popped any fuses may indicate a problem somewhere in the preamp area, and not anywhere near the outputs.

As I said, I'm not familiar with deoxIT as its been a while since I've done any work requiring such a product. I'd be leery of any high-priced solution that removes oxidation. Its not like this is a new issue at all - back when I was servicing systems, one of the best products I found was these small green aerosol cans from Sony called ... wait for it ... "Sony Lube".

Can't recall where we got it at the time, but I liked it much better than other lubes we used - it had a low residual and was silicon based, IIRC. As you likely know, there is never one spray, lube or protectant that does it all in every circumstance. My shop bench is a testament to that, as is any decent electronic bench - with at least five different spray cans awaiting the next victim/patient.

And yeah, audiokarma is a good place for info. As always, read, digest and read some more before applying any miracle fixes that anyone is touting. That said, there's still plenty of good info on vintage audio repair to be found on Usenet / Google Groups.

What?? Do it methodically and efficiently? Have you no sense of adventure?

Heh...that's the problem with any of these diagnose by internet things. So much can go wrong, and all we know about this problem is that a channel doesn't play music. I seem to recall someone castigating HK for cold soldered connections, anyway.

It really takes an experienced tech asking a lot of questions to guide a seeker to a solution. Occasionally, I've seen it done.

Of course, if the HK has separate pre and power amp jacks, the pre vs power amp question could be readily resolved: could he play his powered speakers with the preamp outputs?

.

BasmntMadman

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Location: Off-White Gardens

Posted: Oct 12, 2009 - 11:22am

Beaker wrote:

How many years did you spend as a tech doing electronics servicing for consumer electronics? "Large-ish" "output capacitors"?? Say what??

Sounds to these ears like you are applying the tiny bit of knowledge you may have acquired in fixing a computer motherboard with "bad caps".

OK, the HK is almost certainly direct coupled anyway; only the older stuff is capacitively coupled, unless it's McIntosh with their (expensive!) autoformers. As the ads in the seventies said: "no output capacitors to stand in between you and the music!!" Yeah, and no capacitor to stand in the way of your voice coils and lots of DC voltage if power amp circuits to control DC output go bad or age bad.

So anyone buying an old amp is advised to measure DC voltage on the output terminals with volume down and no input signal - anything over 100mV ( 0.1V) is definitely dangerous; below 50 mV much preferred, and below 15 mV is really good. Zero volts means something's wrong or it's capacitively coupled

Actually output capacitors are fairly large, at around 1200 microfarads, from what I've seen. We could get into a furious flamefest over whether that's really large or not.

My little bit of knowledge comes from the school of hard knocks thumps

mzpro5

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Location: Budda'spet, Hungry
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Posted: Oct 12, 2009 - 11:02am
mjmurphy61 wrote: Thanks mzpro, this one "looks" good, and the price is right... You really can't beat it at $123. Might pick one up for my garage.

BasmntMadman

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Location: Off-White Gardens

Posted: Oct 12, 2009 - 10:57am

Beaker wrote:

Before applying any fixes, fluids, let alone a soldering iron, it is necessary to diagnose the specific area of failure. Oxidized tape monitor switches are indeed a common failure - proving they are the cause is straightforward. Methods for fixing the tape monitor switch are not always reliable, and are dependent upon construction of the switch - unless the part is replaced with a new switch from the oem.

As for "chinese fakes", I suppose you mean subs from NTE and the like - for the 2Nxxxx devices...

Oh, usually deoxIT can't hurt, if applied judiciously to controls. If it did, there'd be a whole generation of vintage equipment owners with destroyed gear, and they'd be wailing on the boards. And sometimes merely working the switch re-establishes contact.

There are exceptions to beware of - the click-on switch in, for example, a Sherwood S-7100A, has a plastic arm that can be fractured by deoxIT resulting in no click-on function. Of course, I read about that after deoxIT-ing mine - but with no ill effects.

Any other such specific caveats? If it prevents destroyed controls, it'd be a service to all the vintage equipment owners.

As for the Chinese fakes, it's a constantly recurring bitch on audiokarma from some very experienced people. Though NTE is routinely dissed, I think a lot of it refers to what's found on eBay auctions. Sometimes I get the impression that finding anything of any quality is almost impossible.

NTE seems to be a controversial thing - some people think their stuff is OK, especially for small signal transistors, others think it's like month-old hamburger. I just hope I'm not confronted with the need to replace output transistors anytime in the near future.

(former member)

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Posted: Oct 12, 2009 - 10:54am

Maybe off topic, but I picked up a Harmon Kardon 7.1 (or 5.1 and a stereo second zone) with Infinity speakers (7.1 of them) at Costco that I've been EXTREMELY happy with. The electronics are sophisticated and malleable (e.g., I have it set to input my TV cable in component, the TV sound inputs in optical, and the whole mess outputs as HDMI to the big screen; also, it senses the output of the movie playing in the external Blu-Ray and changes the speaker output to the appropriate one - mono, stereo, DTS, etc).

Has three HDMI inputs as well as component and others, so you can bring in a lot of stuff (like Wii, Apple TV/Mac Mini, separate Blu-Ray machine) and it sounds really nice.

Expensive at $800 as a package - but cheaper than finding components separately, and much simpler. I had started by wondering if I wanted an NAD, but abandoned all hope.

mjmurphy61

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Location: Saint Louis, MO
Gender: Male

Posted: Oct 12, 2009 - 10:39am
mzpro5 wrote: If you are looking for a decent 2 channel receiver try this Sony 2 channel Receiver - $160 Amazon has it for $123 Thanks mzpro, this one "looks" good, and the price is right...

BasmntMadman

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Location: Off-White Gardens

Posted: Oct 12, 2009 - 10:30am

cc_rider wrote:

Man, I use that line all the time!

But seriously, it's not as bad as it sounds. And it's already busted, right? Can't break it any worse by messing with it. Heck, if I was close enough I'd take a look at it myself.

I have several 70's-vintage Sansui receivers that are still going strong. The one my Dad bought in 1970 is still solid after many years of abuse, and it'll kick the doors off a lot of new gear. The old transistor gear is pretty rugged, and fixable. The new chip-based amps are far more difficult, if not impossible, to repair.

I'd say "mess with it, but with a schematic in a service manual" You don't have to be an electrical engineer to be aided by a schematic. Also, replacing electrolytic capacitors can't hurt, but for chrissake get the polarity right!

There's also my surefire troubleshooting strategy: whine on audiokarma.org and hope one of the very knowledgeable and helpful people there can assist you. They may even have a free schematic. Why not? You might get into something new and interesting.

My instincts tell me it's either something as simple as a switch, or a transistor. Or an IC, which could be "unobtanium"; at least, judging from my experience with a Sony STR-7055 tuner section. Even replacement output transistors can be pretty dicey propositions to find; small signal transistors seem less problematic, even if you might have to resort to NTE . Fortunately, HK was a classy brand at the time, and those brands tended to pride themselves on using discrete components.

There is a small legion of dedicated Sansui fans. Apparently, Sansui started life specializing in power supplies, and they had a reputation for paying attention to this vital part of an amp.

mjmurphy61

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Location: Saint Louis, MO
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Posted: Oct 12, 2009 - 10:21am
triskele wrote: you can fix it.... Fix what the spelling or the amp - "everything is broken"

triskele

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Location: The Dragons' Roost

Posted: Oct 12, 2009 - 10:15am
mjmurphy61 wrote: . Oops. Your right should be one "c" and two "m" 's.... Dang, I really was an English major. you can fix it....

mjmurphy61

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Location: Saint Louis, MO
Gender: Male

Posted: Oct 12, 2009 - 10:15am
Thanks tor all your advice. It's been really helpful! I think I'm gonna try to get under the hood, because after all it "IS already busted" while I wait til next month to come up the extra dough for a new system. I can listen in mono right now with both speakers, but just knowing I'm listening in mono drives me NUTS!

mjmurphy61

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Location: Saint Louis, MO
Gender: Male

Posted: Oct 12, 2009 - 10:14am
meower wrote: I'm a really bad speller, but that Recommended word looks all wrong. . Oops. Your right should be one "c" and two "m" 's.... Dang, I really was an English major.

meower

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Location: i believe, i believe, it's silly, but I believe
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Posted: Oct 12, 2009 - 10:03am
I'm a really bad speller, but that Recommended word looks all wrong.

cc_rider

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Location: Bastrop
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Posted: Oct 12, 2009 - 9:47am
dmax wrote: See, I use THAT line all the time! Amen brother!

mzpro5

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Posted: Oct 12, 2009 - 9:42am
If you are looking for a decent 2 channel receiver try this Sony 2 channel Receiver - $160 Amazon has it for $123

(former member)

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Posted: Oct 12, 2009 - 9:35am
cc_rider wrote: And it's already busted, right? Can't break it any worse by messing with it. See, I use THAT line all the time!

cc_rider

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Posted: Oct 12, 2009 - 9:33am

dmax wrote:

Reminds me of the old Steve Martin routine about how to make a million dollars and never pay taxes!

"First, make a million dollars...."

(former member)

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Posted: Oct 12, 2009 - 9:27am
cc_rider wrote: Which will require removing the circuit board, de-soldering the old cap(s), and installing new ones. Reminds me of the old Steve Martin routine about how to make a million dollars and never pay taxes! "First, make a million dollars...."

cc_rider

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Location: Bastrop
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Posted: Oct 12, 2009 - 9:24am

mjmurphy61 wrote:

Yay, my trusy Harmon Kardon HK380i tuner/receiver/amplifier circa 1979 just lost it's right channel. I was using it in my living room streaming to an Apple Airport Express, so RP is currently playing though one speaker. Got a good 30 years out of that sucker!

Now I get to go audio shopping. Oh yeah. Wait a minute, I'm broke! Well not totally, can anybody reccomend an inexpensive powered speaker system. I've been kind of looking around lately and so much is surround sound stuff that I'm just not into. I just want something in the 1 to 2 hundred dollar range that will do the job. I'm using a pair of Edirol powered speakers in my bedroom that sound great, but I'm not sure I wan't two pair of those, besides those are more studio monitors (near field) than I would like for the living room.

Anybody using anything that they love?

Don't throw that amp away!

It is entirely possible your amp is fixable. Since it's just the one channel, my guess is one of the capacitors on the output side has gone out. It's not as difficult as it sounds. Since you've admitted you're broke (get in line, fella), it's worth doing a little investigating.

Unplug it first, but you knew that. The top cover should come off with a few screws: two on each side, one or two on the back. Lift the top off carefully. Blow the dust off: compressed air is great if you have it, but be careful you don't blast it too hard. A very soft brush, like a feather duster, is okay.

Near the speaker connections, there will be some large-ish cylinders, those are the output capacitors. Often colored BLUE but they can be any color. If you follow the wires carefully you might be able to see which is the right and which is the left channel circuit. The most likely scenario is one of the big caps is bulged out, either at the top or sides. It might be blackened, but if you haven't smelled smoke, probably not. Also check the smaller capacitors for the same symptoms. Any capacitor that is bulged out has gone bad and needs to be replaced. Which will require removing the circuit board, de-soldering the old cap(s), and installing new ones. Which is not nearly as crazy as it sounds, and might cost less than $20, especially if you already have some soldering gear.

Since it's already busted, a little reconnaissance is not gonna cost you anything, and you might be able to: 1) save your precious baby from the scrap yard or parts bin, and 2) save the money and hassle of buying a new unit.

keep us posted...

c.

BasmntMadman

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Location: Off-White Gardens

Posted: Oct 12, 2009 - 8:44am

mjmurphy61 wrote:

So, it looks like you have non-powered speakers in the living room, the line level outputs of the Airport Express go to the line level inputs of the HK, which drives the speakers. If you got powered speakers, you wouldn't need an amp.

What are the speakers you're using in the living room? It may be a shame to replace them because of an amp problem.

Before totally giving up on the amp, sometimes an application of contact cleaner like deoxIT on switches and controls can restore a bad channel. And the tape monitor switch is important, even tape deck isn't in the system. If that control doesn't work right, it can stop the music. Sometimes just flipping/rotating the switch re-establishes contact.

If it's a blown output transistor, there are all kinds of Chinese fakes out there as bogus replacements.

As for powered speakers, if you hang around Radio Paradise, it's AudioEngine A-2's or A-5's. All the writeups and opinions I've seen on them have been very good, though I've never heard them in person.

islander

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Location: West coast somewhere
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Posted: Oct 12, 2009 - 8:28am

mjmurphy61 wrote:

I would recommend an hour w/ a screwdriver set and a multimeter. I'd start with the speaker connections, and then move to the inputs. just check continuity between the posts and the landings inside the receiver. You might find something that $0.05 worth of solder will fix.

Then go hit the used audio places like Milo suggests.

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