Happy new owner of a HK430 with - with a weak phono input (please help).

[Testacorsa]

Hi all, I'm new here, so hello and happy new year from Denmark

I hope you can help me with a weak phono input problem, but first let me tell you about my new receiver.

A couple of days before christmas I got lucky, and picked up an early present from my local recycling centre, a Harman Kardon 430 Twin powered.
There is a room there dedicated to reusable things that are too nice to be recycled, so you can either donate or take stuff, free of charge.
I had never seen a HK 430 before, but I instantly recognized the sheer beauty of it which made me lightly panic, afraid that someone might grab it before I had sprinted the 10 feet over to get it, haha. Feeling very good about my new treasure, I got into it right away, so took the top, bottom and front plate off, and gave everything a good clean. It did clean up very nicely, and has remarkably few marks for a nearly 50 year old receiver. Only three bulbs had burned out, so I ordered those up, right away.



I hooked it up to my old “Nordlyd” speakers (Danish made cabinets with drivers like KEF Cadenza) and my CD player, and to my surprise everything seemed to work, besides an occasional scratchy volume pot. I put on my favorite track on (La Femme d'argent by AIR) and sat down between the speakers and listened. Just like many before me, I have since found out, I was very impressed! The sound was very pleasant and neutral, but what impressed me the most was the stereo separation, which was almost like listening with headphones, but felt better and freer, if that makes any sense?
I connected my 1990 Sony 550ES amp again to compare the two, and my ears couldn't really make sense of it, as the Sony suddenly sounded really narrow and almost out of phase!
I'm still straching my head on that one, as I have used the Sony ES for many years, and will repeat the comparison, once I fix the 430.

I was gifted a denon DE-70 EQ some time ago, so I connected that up next, through Tape out/Tape monitor, which worked well, and gave me the option to twaek the sound just a smidge, and gave me two extra inputs as well. I think they look great together, and it even matches my TV, which coincidentally also has a “sound by Harmon/Kardon” badge put on it.
All this on top of the lovely sound made me very happy, so I guess I have a new hobby now.

Here it is on top of my trusty ole Sony ES stack, which will soon be put up for sale.


Well, the trees don't grow into the heavens, as we say in Denmark, so connecting my record player, reveiled a problem with the right input.
I am going to trry and fix this myself, but I haven't got any specialized equipment or knowledge, just a very basic abilities with multimeter - and google...
Maybe I'm being naive, but I would enjoy a go at it, and hopefully with the help of you good people, find the culprit, or at least try to narrow it down.

The Problem:
Right channel phono input is very weak and sounds distorted.

What I know:
- switching the left and right input does't move the problem to the left channel.
- The turntable works as it should in my Sony amp.
- The sound goes to both speakers when the mono button is pushed.
- The tape monitor on/off to my EQ doesn't make a difference.

Pictures of the the insides, the distorted phono input, and the phono board:



What the research told me:

Harman Kardon 430 Twin: Left Channel out in Aux, Phono. Works in Tape Monitor

Grabbed a well-loved HK 430 Twin recently. It sounds perfect when I hook up a device to tape monitor function, but when I try phono or aux I get silence from the left channel. Same results with headphones. The Mono button, when pushed, silences the sound entirely. I de-ox'ed everything...

audiokarma.org

The 430 is effectively identical circuit to the 330c.

All the inputs go through the same circuit, the tone preamp, except for the phono input. That goes through the phono stage first.

View attachment 1581777
View attachment 1581778

Noisey channel HK430

Hi all, I am looking for a little advice on a problem I am having with a recent HK430 purchase. The unit was in good condition and when I opened it up the insides also looked in good condition with the correct fuses etc. All bulbs were also all working. After cleaning the pots with some DeOxit...

audiokarma.org

Another thing is to check the tape monitor push switch for cleanliness. On my 430, I sometimes need to give that a wiggle/tap/poke to get both channels to come in, particularly when I'm in phono mode.

Harman Kardon 430 Twin: Left Channel out in Aux, Phono. Works in Tape Monitor

Grabbed a well-loved HK 430 Twin recently. It sounds perfect when I hook up a device to tape monitor function, but when I try phono or aux I get silence from the left channel. Same results with headphones. The Mono button, when pushed, silences the sound entirely. I de-ox'ed everything...

audiokarma.org

Tried incessantly pushing the tape mon button while some music was playing on aux (mono button pushed as well). When the button is about halfway depressed, just before it clicks, I get full sound for a split second from the left channel. I'm assuming this means tomorrow I should apply de-oxit and more de-oxit on those two switches? Is it possible the last round of De-oxit made it worse by loosing some other oxidation up?

This sounds easier than a lot of things so I'll give it another go.

Hoping this is what's affecting the tuner output as well. Almost inaudible even at highest volume and no sound out of left channel for tuner either (I was wrong above, earlier). Thanks everyone for the input so far!

Harman/Kardon 430, left side audio issue

I started having an issue with my Harman/Kardon 430 this morning; I noticed the signal was not as good on the left side only in PHONO mode. I switched it to FM and it's fine. Where would I start checking/de-oxing? I tested two different turntables through the phono input just to make sure...

audiokarma.org

(All of this with a grain of salt as I'm new and might be corrected by someone who knows what they're talking about, but I'll have a go...)

The phono preamp board is the separate board mounted vertically, with a metal cover, on the back of the right side. It's basically symmetrical - two input points at the back, two outputs at the front. It could be worth checking the voltage coming out on each channel, at the front, is roughly the same.

Just a thought - there's four 2SC1344 transistors on this board. I'm probably pointing the finger too quickly as one just went bad elsewhere on my HK 430, but someone else might know - would one of the two on the left side be a good place to start? Everything else on there is caps and resistors.

And a lot of other general hints, like the legs on transistors go black, which they are on my phono board.

Where to start?
I suspect the problem is in the phono board, which is just a guess, but sice the aux and tuner input works flawlessly, and every input goes to the same circuit that seems like a reasonable quess.
I have de-ox'ed anything yet, as i didn't have any (ordered it with the bulbs) and there is barely a scrach from anything. Testing a short in the transistors should be faily easy to do as well.

Where would you start? Any input appreciated!

 

[dlucy]

If you want to diagnose and maybe find the problem, you can use the voltage chart on page 8 of the service manual, check the voltages on each leg of the two (four) transistors on the equalizer board (phono board). If your voltage s are not within 10-20% of the listed voltages, then you have a measurable problem and can diagnose why the voltages are wrong ( getting help from us here in this thread).

If you want to skip the diagnosing part and go straight to (hopefully) the working stage, then you can "shotgun" replace the know-to-go-bad parts and potentially solve the problem (without too much work and without learning stuff).

Check the voltages:



Shotgun-replace the known-to-go-bad parts:

Q701-Q703 2sc1344 with KSC1845F

There are three (six) electrolytic caps (tall gray cylinders) that are likely dead or dying. You should replace them with similar electrolytic caps (with higher voltages if you can't find the exact voltages due to no longer in production). Nichicon KL series is preferred here, but any will do OK.

C701,C702 10uF 16V electrolytic
C717,C718 100uF 25V electrolytic
C705,C706 47uF 6.3V electrolytic

There is one (two) tantalums that should be replaced with polyester or poly propylene film cap (again, higher voltage is OK if you can't find the exact one needed).

C711,C712 0.47uF 35V tantalum with 0.47uF 35V film

 

[Testacorsa]

Wow, thanks a lot Doug!

That gives me something to go for. My new bulbs and deoxit is in the mail, so I will take it apart again as soon as it arrives,
and service the switches and pots forst, to take those out of the equation - as much as possible anyway.

Just one question (for a start, haha):
Once the doex is done I will get to measuring the voltages on the Equalizer board, but I'm unsure if those voltages are the same for a european model with a 220V
power supply. I have only found the american service manual so far, but will keep looking.

It's probably a very good idea to replace the caps, and transistors as you say, and thanks for the part details, and instructions as well!
I read something about transistors needing to be matched, and a few other things, but I will cross that bridge when I get there.

Looking forward to tinkering with this!

 

[dlucy]

Wow, thanks a lot Doug!

That gives me something to go for. My new bulbs and deoxit is in the mail, so I will take it apart again as soon as it arrives,
and service the switches and pots forst, to take those out of the equation - as much as possible anyway.

Just one question (for a start, haha):
Once the doex is done I will get to measuring the voltages on the Equalizer board, but I'm unsure if those voltages are the same for a european model with a 220V
power supply. I have only found the american service manual so far, but will keep looking.

It's probably a very good idea to replace the caps, and transistor as you say, and thanks for the part details, and instructions as well!
I read something about transistors needing to be matched, and a few other things, but I will cross that bridge when I get there.

Looking forward to tinkering with this!

In all the stereo gear I’ve ever seen, the voltages from the power transformer secondaries to everything else in the schematic are identical no matter which country. The power transformer primaries are where the differences are. For instance:

USA power transformer 110VAC primary and 24VAC secondary
vs
European power transformer 240VAC primary and 24VAC secondary.

There are sometimes differences in the FM emphasis circuit of the FM board, but that’s it.

 

[dlucy]

That Denon EQ is gorgeous... and goes perfectly with your HK 430. When I first looked at your photos, I thought there was some awesome HK EQ that I'd never seen before.

 

[dlucy]

You may want to read through this thread, look for other AK members who've worked on HK 430, and mention them here... to attract their attention and chip in with answers to your questions. https://audiokarma.org/forums/index...-kardon-gear-what-have-you-worked-on.1068393/

 

[dr*audio]

2SC1344 transistors are suspect. Replace them with KSC1845. While you are in there replace all the electrolytic caps on the board. Dlucy, 2SC1344 is on your list of noisy transistors, I'm surprised you didn't catch that.

 

[dlucy]

2SC1344 transistors are suspect. Replace them with KSC1845. While you are in there replace all the electrolytic caps on the board. Dlucy, 2SC1344 is on your list of noisy transistors, I'm surprised you didn't catch that.

I didn’t think past “phono stage in a vintage HK”. That’s an easy “replace all the transistors with KSC1845/KSA992” call.

Thanks for keeping thinking.

 

[Testacorsa]

In all the stereo gear I’ve ever seen, the voltages from the power transformer secondaries to everything else in the schematic are identical no matter which country. The power transformer primaries are where the differences are. For instance:

USA power transformer 110VAC primary and 24VAC secondary
vs
European power transformer 240VAC primary and 24VAC secondary.

There are sometimes differences in the FM emphasis circuit of the FM board, but that’s it.

Good to know, thanks. Excited to see what voltages I get.

That Denon EQ is gorgeous... and goes perfectly with your HK 430. When I first looked at your photos, I thought there was some awesome HK EQ that I'd never seen before.

So pretty! A lucky coincidence, that they match so well. Looking for a cd player and record player to join the party next

You may want to read through this thread, look for other AK members who've worked on HK 430, and mention them here... to attract their attention and chip in with answers to your questions. https://audiokarma.org/forums/index...-kardon-gear-what-have-you-worked-on.1068393/

Uuh, interesting thread, I will defitely look through that.

2SC1344 transistors are suspect. Replace them with KSC1845. While you are in there replace all the electrolytic caps on the board. Dlucy, 2SC1344 is on your list of noisy transistors, I'm surprised you didn't catch that.

Doug mentioned those in his first post, or am I missing something?

 

[Testacorsa]

Well, turns out the right phono input starts working after the receiver has been warming up for about 20 - 30 minutes
I have been able to repeat it four times now, one before deox and three after.
I deoxidized the pots and buttons very thoroughly yesterday, but it hasn't made a difference to the problem.

Does that give a clue to what it could be?

 

[gslikker]

Remembering some deterioration of some parameter (HFE?) when taking all the graphs from KSC1845 using my DCA75 transistor tester looking on the computer, I decided to NOT use KSC1845 in low VCE situations.
In this preamp, this would be Q701 and Q702, which have definately less than 2 Volts between C and E. Maybe use BC549C, BC550C,2N5210 ?

Well, turns out the right phono input starts working after the receiver has been warming up for about 20 - 30 minutes
I have been able to repeat it four times now, one before deox and three after.
I deoxidized the pots and buttons very thoroughly yesterday, but it hasn't made a difference to the problem.

Does that give a clue to what it could be?

Probably one of the transistors, but if that is the case, the problem probably can be found using the chart @dlucy provided. Maybe it is also possible to find the offending piece using a little piece of whatever from the freezer ;-). But as people stated, it is better get rid of all four old transistors.

 

[Bruno Primas]

All with red dots should go. The whole receiver would benefit from a rebuilding as well.

 

[Testacorsa]

Remembering some deterioration of some parameter (HFE?) when taking all the graphs from KSC1845 using my DCA75 transistor tester looking on the computer, I decided to NOT use KSC1845 in low VCE situations.
In this preamp, this would be Q701 and Q702, which have definately less than 2 Volts between C and E. Maybe use BC549C, BC550C,2N5210 ?


Probably one of the transistors, but if that is the case, the problem probably can be found using the chart @dlucy provided. Maybe it is also possible to find the offending piece using a little piece of whatever from the freezer ;-). But as people stated, it is better get rid of all four old transistors.

Thanks for the input. I have read about HFE i relation to transistors that need to be HFE matched, but what it means is a bit "over my pay grade" (yet)
When I'm further along in my new hobby, I'll come back to this. I have found 2SC1344 trasistor locally, so would that be the safest bet, or are they too old hat?

And you are ofcourse right about just doing what @dlucy suggested, and hopefully I find the time to do that soon.

 

[Testacorsa]

All with red dots should go. The whole receiver would benefit from a rebuilding as well.

View attachment 3391888

Thanks for that, I have already started looking for parts for the EQ board, and If that goes well, I think I will rebuild the rest. It seems pretty straight forward - famous last words, haha.