Electronics Repair (sci.electronics.repair) Discussion of repairing electronic equipment. Topics include requests for assistance, where to obtain servicing information and parts, techniques for diagnosis and repair, and annecdotes about success, failures and problems.

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Old October 5th 18, 04:54 PM posted to sci.electronics.repair
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Default Harman Kardon 930 lost channel. Hoe to trouble shoot ?

Well just lost a channel at my Harman Kardon 930 Vintage geek as I am I
want to keep my great Reciver and repair it..

What I done sofaar

Check Fuses ( They are OK)
Moving the speakers between the channels left-Right And A and B speaker
outlets.

With this info I understand that the left Channel is ALMOST dead turning
the balance to Left channel I can hear a faint OK sound. (Like the tiny
transistors trying their best before the end power transistors do their job.

My conclution.

1 Not enough power to the end transistors on the left channel.
2 Broken End Trasistors (two 2SC897 according to the scematics)
3 End of preamp broken on left channel.


Most likely End transistors..

Is my thinking OK or did I miss something ?

I am a beginner in HiFi electronics but have basic skills in electricity
as an electrician for 25 years and do know how to solder..


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Old October 5th 18, 05:11 PM posted to sci.electronics.repair
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Default Harman Kardon 930 lost channel. Hoe to trouble shoot ?

On Friday, October 5, 2018 at 11:54:11 AM UTC-4, Steff wrote:
Well just lost a channel at my Harman Kardon 930 Vintage geek as I am I
want to keep my great Reciver and repair it..

What I done sofaar

Check Fuses ( They are OK)
Moving the speakers between the channels left-Right And A and B speaker
outlets.

With this info I understand that the left Channel is ALMOST dead turning
the balance to Left channel I can hear a faint OK sound. (Like the tiny
transistors trying their best before the end power transistors do their job.

My conclution.

1 Not enough power to the end transistors on the left channel.
2 Broken End Trasistors (two 2SC897 according to the scematics)
3 End of preamp broken on left channel.


Most likely End transistors..

Is my thinking OK or did I miss something ?

I am a beginner in HiFi electronics but have basic skills in electricity
as an electrician for 25 years and do know how to solder..



Normally, blown outputs (is this what you mean by "end"?) will open fuses or low value resistors.

You really need a meter to go farther. If you get one or have one, you can compare voltages and resistance from the good side to the bad. If the receiver has a pre-amp out and in (or tape monitor) arrangement, you can reverse those to see if the problem trades sides. If it uses metal U shaped jumpers, remove them and use RCA patch cords to cross swap.

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Old October 5th 18, 06:04 PM posted to sci.electronics.repair
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Default Harman Kardon 930 lost channel. Hoe to trouble shoot ?

On Fri, 5 Oct 2018 17:54:06 +0200, Steff wrote:

Well just lost a channel at my Harman Kardon 930 Vintage geek as I am I
want to keep my great Reciver and repair it..

What I done sofaar

Check Fuses ( They are OK)
Moving the speakers between the channels left-Right And A and B speaker
outlets.

With this info I understand that the left Channel is ALMOST dead turning
the balance to Left channel I can hear a faint OK sound. (Like the tiny
transistors trying their best before the end power transistors do their job.

My conclution.

1 Not enough power to the end transistors on the left channel.
2 Broken End Trasistors (two 2SC897 according to the scematics)
3 End of preamp broken on left channel.


Most likely End transistors..

Is my thinking OK or did I miss something ?

I am a beginner in HiFi electronics but have basic skills in electricity
as an electrician for 25 years and do know how to solder..

Try pushing the tape monitor and other push button switches on the
front panel a few times to see if the channel comes back. If it does,
spray the switch with DeOxit 5 or equivalent.
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Old October 5th 18, 06:40 PM posted to sci.electronics.repair
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Posts: 171
Default Harman Kardon 930 lost channel. Hoe to trouble shoot ?

In article ,
Steff wrote:
Well just lost a channel at my Harman Kardon 930 Vintage geek as I am I
want to keep my great Reciver and repair it..

What I done sofaar

Check Fuses ( They are OK)
Moving the speakers between the channels left-Right And A and B speaker
outlets.

With this info I understand that the left Channel is ALMOST dead turning
the balance to Left channel I can hear a faint OK sound. (Like the tiny
transistors trying their best before the end power transistors do their job.

My conclution.

1 Not enough power to the end transistors on the left channel.
2 Broken End Trasistors (two 2SC897 according to the scematics)
3 End of preamp broken on left channel.


Most likely End transistors..

Is my thinking OK or did I miss something ?


Those are possibilities. Here's what I would suggest for further
troubleshooting. [Turn the power off before changing any cable
settings, of course.]

First: the manual and schematic show that the preamp and amp are
linked together via a set of jumpers on the back panel, going from
"pre amp out" to "main amp in". First thing to do is remove and
re-insert the jumpers, to see if you simply have a bad connection in
the connectors there. If removing and re-inserting fixes the problem,
then clean the connectors and jumpers with contact cleaner, reinsert,
and you should be OK.

Second thing to do is disconnect those jumpers, and replace them with
a standard red/black RCA-connector interconnect cable. This time,
swap the two channels - connect the left channel "pre out" to the
right channel "amp in", and vise versa.

If the problem remains in the left channel, then the fault lies in the
amplifier section.

If the problem moves over to the right channel, then the fault lies in
the preamp section.

If it's in the amp section: it might be the fuses (I'm not sure if
these are among the ones you checked). It could be bad speaker on/off
switches, but it seems unlikely that you've had the same failure in
the A and B channel switches (but it is possible... the speaker-B
switch might have failed long ago and you might not have noticed it
until now).

If the switches and fuses are all OK, and you're confident that the
amp is getting a valid input signal, then you'd need to trace the
signal through the amp section with a 'scope and DMM - see if your
B1/B2 power supply voltages are OK, and see how far the signal gets
through the left-channel amp before it vanishes.

If it's a failure in the preamp section (if the dead channel "moves"
when you switch the cabling between preamp and amp) then I think the
big two suspects would be:

- Bad, or dirty selector switches. In particular the "tape monitor"
switches for Tape 1 and Tape 2 are both right in the signal
path... if one of these has an open contact you'd lose a channel.
It looks as if the "tone control defeat" switch is also a suspect,
for the same reason.

- An electrolytic interstage coupling capacitor which has failed in
an "open" state.

Here, also, signal tracing is your friend. Feed a known-good line
level signal into the "tape 2 in" jacks, turn on "tape monitor 2", and
see if you get a good signal... this is the last input "in the path".
If that one works OK, try "tape 1 in" and the "tape monitor 1" switch
setting. If that works OK, use "aux". With this approach you're
working "backwards" from the preamp/amp interconnect, looking back
along the circuitry a step at a time to see how far back you can go
before the signal disappears.

I've seen enough older receivers/preamps with dirty-switch problems
that this is my lead suspect in cases like this. There's a reasonable
chance that cleaning all the switches will fix your problem. Put a
small squirt of DeOxIt D-5 into each switch, operate the switches a
dozen times or so to break up any old grease and dirt and oxide and
tobacco-smoke tar and etc., use another small squirt to flush out and
lubricate the contacts. Put a small squirt into each RCA jack, then
plug and unplug a cable a few times to break up the oxides and
crud. Let dry for a few minutes, then test again.

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Old October 5th 18, 07:30 PM posted to sci.electronics.repair
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Default Harman Kardon 930 lost channel. Hoe to trouble shoot ?

You can narrow this down to the AMP section by removing the shorting plugs (pre-amp out to AMP in metal plugs) and replacing them with an RCA cable.

Let assume that the left channel is not working. Using a standard RCA to RCA cable, connect the left pre-amp out to the right AMP-in. If the right channel has sound as expected, then the pre-amp section is OK and the problem is with the amp section.

With the power off using a meter, A/B the left and right channels. Measurements of the corresponding components should measure about the same.
If you have access without the possibility of shorting components, use a DC meter and measure some voltage points. Again, the two channels should measure the same.

With the symptom of slight sound in the output, I would suspect that a voltage is missing. You may have an open resistor that feeds the output section.


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Old October 7th 18, 02:24 AM posted to sci.electronics.repair
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Default Harman Kardon 930 lost channel. Hoe to trouble shoot ?

On Friday, October 5, 2018 at 8:54:11 AM UTC-7, Steff wrote:
Well just lost a channel at my Harman Kardon 930 Vintage geek as I am I
want to keep my great Reciver and repair it..

What I done sofaar

Check Fuses ( They are OK)
Moving the speakers between the channels left-Right And A and B speaker
outlets.

With this info I understand that the left Channel is ALMOST dead turning
the balance to Left channel I can hear a faint OK sound. (Like the tiny
transistors trying their best before the end power transistors do their job.

My conclution.

1 Not enough power to the end transistors on the left channel.
2 Broken End Trasistors (two 2SC897 according to the scematics)
3 End of preamp broken on left channel.


Most likely End transistors..

Is my thinking OK or did I miss something ?

I am a beginner in HiFi electronics but have basic skills in electricity
as an electrician for 25 years and do know how to solder..


You got some very good advice already. Just want to point out that failed output (end) transistors nearly ALWAYS short out and blow fuses. I've replaced thousands over the years.

I also want to point out that soldering as an electrician is probably different from soldering in a receiver. I recommend getting an old piece of electronics to try replacing a component and see if you can do it reliably. Better to find out on a piece of junk. Older circuit boards have a higher failure rate due to excessive heat. I had an old Sony board where the pads lifted too easily with a 700° tip but were OK with a 600° tip (Metcal).

I like old HK gear and would prefer to hear you have it working again.


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Old October 7th 18, 09:06 PM posted to sci.electronics.repair
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First recorded activity by DIYBanter: Feb 2018
Posts: 5
Default Harman Kardon 930 lost channel. Hoe to trouble shoot ?

Den 2018-10-07 kl. 03:24, skrev :
On Friday, October 5, 2018 at 8:54:11 AM UTC-7, Steff wrote:
Well just lost a channel at my Harman Kardon 930 Vintage geek as I am I
want to keep my great Reciver and repair it..

What I done sofaar

Check Fuses ( They are OK)
Moving the speakers between the channels left-Right And A and B speaker
outlets.

With this info I understand that the left Channel is ALMOST dead turning
the balance to Left channel I can hear a faint OK sound. (Like the tiny
transistors trying their best before the end power transistors do their job.

My conclution.

1 Not enough power to the end transistors on the left channel.
2 Broken End Trasistors (two 2SC897 according to the scematics)
3 End of preamp broken on left channel.


Most likely End transistors..

Is my thinking OK or did I miss something ?

I am a beginner in HiFi electronics but have basic skills in electricity
as an electrician for 25 years and do know how to solder..


You got some very good advice already. Just want to point out that failed output (end) transistors nearly ALWAYS short out and blow fuses. I've replaced thousands over the years.

I also want to point out that soldering as an electrician is probably different from soldering in a receiver. I recommend getting an old piece of electronics to try replacing a component and see if you can do it reliably. Better to find out on a piece of junk. Older circuit boards have a higher failure rate due to excessive heat. I had an old Sony board where the pads lifted too easily with a 700° tip but were OK with a 600° tip (Metcal).

I like old HK gear and would prefer to hear you have it working again.



I love HK products and specially the older septon ones. So giving life
to my old 930 have high priority for me as well. Mu dad buy it new and
had some JNL speakers with it.. I got is when I left home in 1979 as a
19 year old and it have been with me ever since, so ofcourse I will try
to keep it alive. Best Amp I ever had. I did have a Sansui that was OK
but still this one is the best.

I also have an oscilloscope and multimeter så I will try to separate the
pre amp from the poweramp and se if the prombel is located in the power
amp for sure. I already order some effekt transistors to prepare to
change them since i Still belive it is in the "end transistors"
I found 3 off them in Italy for a decent price (25 USD for 3)

So thanks so far for all advise I keep updating until it works hopefully
with all you guys help.

Sorry for my English My native language is Swedish so bare with me please.


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Old October 8th 18, 12:58 AM posted to sci.electronics.repair
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First recorded activity by DIYBanter: Jun 2017
Posts: 359
Default Harman Kardon 930 lost channel. Hoe to trouble shoot ?

On Sunday, October 7, 2018 at 4:06:45 PM UTC-4, Steff wrote:
Den 2018-10-07 kl. 03:24, skrev :
On Friday, October 5, 2018 at 8:54:11 AM UTC-7, Steff wrote:
Well just lost a channel at my Harman Kardon 930 Vintage geek as I am I
want to keep my great Reciver and repair it..

What I done sofaar

Check Fuses ( They are OK)
Moving the speakers between the channels left-Right And A and B speaker
outlets.

With this info I understand that the left Channel is ALMOST dead turning
the balance to Left channel I can hear a faint OK sound. (Like the tiny
transistors trying their best before the end power transistors do their job.

My conclution.

1 Not enough power to the end transistors on the left channel.
2 Broken End Trasistors (two 2SC897 according to the scematics)
3 End of preamp broken on left channel.


Most likely End transistors..

Is my thinking OK or did I miss something ?

I am a beginner in HiFi electronics but have basic skills in electricity
as an electrician for 25 years and do know how to solder..


You got some very good advice already. Just want to point out that failed output (end) transistors nearly ALWAYS short out and blow fuses. I've replaced thousands over the years.

I also want to point out that soldering as an electrician is probably different from soldering in a receiver. I recommend getting an old piece of electronics to try replacing a component and see if you can do it reliably. Better to find out on a piece of junk. Older circuit boards have a higher failure rate due to excessive heat. I had an old Sony board where the pads lifted too easily with a 700° tip but were OK with a 600° tip (Metcal).

I like old HK gear and would prefer to hear you have it working again.



I love HK products and specially the older septon ones. So giving life
to my old 930 have high priority for me as well. Mu dad buy it new and
had some JNL speakers with it.. I got is when I left home in 1979 as a
19 year old and it have been with me ever since, so ofcourse I will try
to keep it alive. Best Amp I ever had. I did have a Sansui that was OK
but still this one is the best.

I also have an oscilloscope and multimeter så I will try to separate the
pre amp from the poweramp and se if the prombel is located in the power
amp for sure. I already order some effekt transistors to prepare to
change them since i Still belive it is in the "end transistors"
I found 3 off them in Italy for a decent price (25 USD for 3)

So thanks so far for all advise I keep updating until it works hopefully
with all you guys help.

Sorry for my English My native language is Swedish so bare with me please..




Sad to say, you're English is better than many native speakers...

I've changed many hundreds of outputs over the years, and have never seen one "open". High current/wattage devices *generally* fail catastrophically, not open benignly, although there certainly are exceptions to every rule. So with a basic DMM, check for low ohm shorts. Out of circuit they should read a few hundred K ohms minimum if anything at all. On the diode scale, you should get two combinations that read about 0.600 if the outputs are silicon.

I can't speak for your particular HK, but most amplifiers (not all) use a common speaker protection relay so a shorted transistor on one side will prevent the speaker relay from engaging, rendering both sides mute. Your HK being an older vintage piece may be configured differently.



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Old October 8th 18, 02:44 AM posted to sci.electronics.repair
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Default Harman Kardon 930 lost channel. Hoe to trouble shoot ?

OK. Read.

First of all that is a good piece. Not the most advanced but so what.

The amp is a standard quasi comp design, not hard at all.

Now, first of all for the outputs 2N3773s would be great. that is a JEDEC (US) number though and you might not be able to get them there. the originals are TO-3, try to stick with that and not use the plastic equivalent, I don't like how they mate to the original holes. the original design calls for less than a certain thermal resistance there and upsetting that is not good. If you got a friend in the US those 2N3773s are not expensive and fit alot more than just that amp.

So take the outputs out. Short the base and emitter terminals of each as well as TR 624 and 604 (?) the bias transistors emitter to collector, if unsure of the basing just short it all the way around. Not with the outputs though, the basing is clear enough, the pins are E and B, those are what you short. (not to the other transistor...)

Now use a DBT for the fuse whether it is blown or not. When powering up the lamp should light then dim gradually until it is about out. The voltage at the speaker outputs should be zero or close. If not, one of the drivers may be shorted, if you care to that can be checked with no power using the DVM on the -|- scale of course.

With a scope you should even be able to see an audio waveform at the output, put on some rock music, the waveform should be pretty much symmetrical up and down. DO NOT connect a load like a speaker or dummy or you will blow the drivers if they aren't already.

Once you got that all straightened out and have it with not outputs in then put in the new ones. Leave the short across that bias transistor and connect speakers. There will be much distortion at low levels getting almost clean as you approach maximum power.

Once it passes that test, remove power and discharge the filters. Remove the short from one of the bias transistors, power on, if that light does not dim as it did before there is a fault in the bias, do not run it like that load or not.

All this assumes the resistors that join at the speaker outputs have been checked and are not open. Usually there is no smoke or burn so they need to be tested electrically. forget the exact value, to measure it accurately you need the right equipment, either a meter on which you can null the lead resistance or a Kelvin connection. If it is not open, 95 % of the time it is good.

Those are the live tests mainly, there is not reason not to check the transistors and low value resistors before even starting the powered tests. Main thing you want id no open transistors and no shorted transistors.

These methods have made me a bunch of money because I do not waste silicon. And BTW, did you say something about 3 of them ? They need to be replaced in pairs. If one shorts, the feedback in the circuit tries to pull the voltage back to zero and that can exceed the design maximums of the other output in the channel.

If the original AC fuse is not blown use that meter and look for open resistors all over those output circuits, if anything shorts something has to give. If what gives it in the bias circuit you could lose your new outputs in less than a second, that is why the first run is done with zero bias.

As far as making sure the problem is in the output stage, just take a pair of RCA cables and switch left and right. If the problem switches to the other channel then all this is moot and now we are in the preamp. The scope will come in VERY handy if that is the case.

If it does go to the other channel a mono switch would be nice but I do not wee one. In this case you can just short the volume controls together, either the top (not grounded) side or the wipers, doesn't matter, if you get both channels then the problem is before that. At that point there ain't much left. (ain't is a word used only by those with exceptional command of the English language lol)
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Old October 8th 18, 02:49 AM posted to sci.electronics.repair
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Posts: 471
Default Harman Kardon 930 lost channel. Hoe to trouble shoot ?

On Sunday, October 7, 2018 at 1:06:45 PM UTC-7, Steff wrote:
Den 2018-10-07 kl. 03:24, skrev :
On Friday, October 5, 2018 at 8:54:11 AM UTC-7, Steff wrote:
Well just lost a channel at my Harman Kardon 930 Vintage geek as I am I
want to keep my great Reciver and repair it..

What I done sofaar

Check Fuses ( They are OK)
Moving the speakers between the channels left-Right And A and B speaker
outlets.

With this info I understand that the left Channel is ALMOST dead turning
the balance to Left channel I can hear a faint OK sound. (Like the tiny
transistors trying their best before the end power transistors do their job.

My conclution.

1 Not enough power to the end transistors on the left channel.
2 Broken End Trasistors (two 2SC897 according to the scematics)
3 End of preamp broken on left channel.


Most likely End transistors..

Is my thinking OK or did I miss something ?

I am a beginner in HiFi electronics but have basic skills in electricity
as an electrician for 25 years and do know how to solder..


You got some very good advice already. Just want to point out that failed output (end) transistors nearly ALWAYS short out and blow fuses. I've replaced thousands over the years.

I also want to point out that soldering as an electrician is probably different from soldering in a receiver. I recommend getting an old piece of electronics to try replacing a component and see if you can do it reliably. Better to find out on a piece of junk. Older circuit boards have a higher failure rate due to excessive heat. I had an old Sony board where the pads lifted too easily with a 700° tip but were OK with a 600° tip (Metcal).

I like old HK gear and would prefer to hear you have it working again.



I love HK products and specially the older septon ones. So giving life
to my old 930 have high priority for me as well. Mu dad buy it new and
had some JNL speakers with it.. I got is when I left home in 1979 as a
19 year old and it have been with me ever since, so ofcourse I will try
to keep it alive. Best Amp I ever had. I did have a Sansui that was OK
but still this one is the best.

I also have an oscilloscope and multimeter så I will try to separate the
pre amp from the poweramp and se if the prombel is located in the power
amp for sure. I already order some effekt transistors to prepare to
change them since i Still belive it is in the "end transistors"
I found 3 off them in Italy for a decent price (25 USD for 3)

So thanks so far for all advise I keep updating until it works hopefully
with all you guys help.

Sorry for my English My native language is Swedish so bare with me please..



Hi Steff,

Your English is way better than my non-existent Swedish.

So you have a scope and meter and are way ahead of the game. Most folks
don't realize they also have a test generator called their computer. I make test signals frequently with Adobe Audition 3. Audacity is free and works as well.

I would bet money the output transistors have not failed. I got the service manual from HiFiEngine and noted the only thing between the speaker connector and the amplifier is the speaker switches for local and remote speakers. There is no 'protection' or fault detection or relays

The first thing to do is verify all the power supplies are good. I can't make out if the amplifiers run on +/- 34 or +/- 39 Volts. While the power amps have twin power supplies, the signal system (AM,FM, phono and tone controls) run off the left channel transformer (+B2, -B2) The B3 supply should be around 20 Volts positive and should have nearly no ripple. You'd see ripple with your scope set to AC coupling and turn up the sensitivity to 50 mV per division. I would expect it to be 0-5mV.

If I had it on the bench I would run a 1KHz signal into AUX 1 or 2 and verify normal signal at the 'preamp out' jumpers on the back of the unit. If you want to test tone controls you can generate a 'chirp' (frequency sweep) in Audacity and observe the output on the scope. I predict no problems at preamp output. With no speakers connected (speaker switch off is
the same thing) there should be sound on the headphones even if the speaker fuses are blown.

Good luck and let us know.





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