Harman Kardon 930 lost channel. Hoe to trouble shoot ?

ob.

Normally, blown outputs (is this what you mean by "end"?) will open fuses o r 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 rec eiver has a pre-amp out and in (or tape monitor) arrangement, you can rever se those to see if the problem trades sides. If it uses metal U shaped jum pers, remove them and use RCA patch cords to cross swap.

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.

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.

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.

ob.

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

I also want to point out that soldering as an electrician is probably diffe rent from soldering in a receiver. I recommend getting an old piece of elec tronics to try replacing a component and see if you can do it reliably. Bet ter to find out on a piece of junk. Older circuit boards have a higher fail ure rate due to excessive heat. I had an old Sony board where the pads lift

).

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.

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.

I r

ng

y

r job.

ty

ed output (end) transistors nearly ALWAYS short out and blow fuses. I've re placed thousands over the years.

ifferent 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

tcal).

the

.

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 o ne "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 s ilicon.

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

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 original s are TO-3, try to stick with that and not use the plastic equivalent, I do n'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 goo d. If you got a friend in the US those 2N3773s are not expensive and fit al ot more than just that amp.

So take the outputs out. Short the base and emitter terminals of each as we ll as TR 624 and 604 (?) the bias transistors emitter to collector, if unsu re of the basing just short it all the way around. Not with the outputs tho ugh, the basing is clear enough, the pins are E and B, those are what you s hort. (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 m ay be shorted, if you care to that can be checked with no power using the D VM 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 t he 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 conne ct speakers. There will be much distortion at low levels getting almost cle an as you approach maximum power.

Once it passes that test, remove power and discharge the filters. Remove th e 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 c hecked 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 yo u need the right equipment, either a meter on which you can null the lead r esistance 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 trans istors 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 volt age back to zero and that can exceed the design maximums of the other outpu t in the channel.

If the original AC fuse is not blown use that meter and look for open resis tors all over those output circuits, if anything shorts something has to gi ve. 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 oth er channel then all this is moot and now we are in the preamp. The scope wi ll 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, eit her the top (not grounded) side or the wipers, doesn't matter, if you get b oth channels then the problem is before that. At that point there ain't muc h left. (ain't is a word used only by those with exceptional command of the English language lol)

I r

ng

y

r job.

ty

ed output (end) transistors nearly ALWAYS short out and blow fuses. I've re placed thousands over the years.

ifferent 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

tcal).

the

.

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 conne ctor and the amplifier is the speaker switches for local and remote speaker s. 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 ma ke out if the amplifiers run on +/- 34 or +/- 39 Volts. While the power am ps have twin power supplies, the signal system (AM,FM, phono and tone contr ols) run off the left channel transformer (+B2, -B2) The B3 supply should b e around 20 Volts positive and should have nearly no ripple. You'd see ripp le 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 veri fy normal signal at the 'preamp out' jumpers on the back of the unit. If y ou 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 p reamp 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.

Yup. the mistakes are mistakes, not laziness.

one "open".

I have, but they are usually intermittent.

common speaker protection relay so a shorted transistor on one side will p revent the speaker relay from engaging, rendering both sides mute. Your HK being an older vintage piece may be configured differently.

Actually none at all, there is no protection, no relay, delay or even outpu t current limiting.

It is still a good piece. The outputs are hefty enough to handle a sub 4 oh m real load, looks like a fairly healthy FM as well with the totally shield ed front end. It's not PLL stereo but if it is stable there is no reason it can't perform. It doesn't have the best tone controls of lo and hi cut fil ters but eh, can't have everything.

You missed the sarkasm...

en one "open".

Never saw one, but I did qualify my statement by saying that anything is po ssible. I've lived long enough to know that odd things happen. The only th ing close is that I found a horiz output in an RCA CTC120 (or thereabouts) that was open. That was the first and only high power device I ever saw ope n. I still don't thing Steff has an open output.

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.

put current limiting.

Yikes. I remember a Hitachi receiver in the shop back in the early 80s tha t would destroy speakers whenever it wanted to. Play nice, short loud hum, speaker smoke. Turned out to be one of those weird Hitachi small signal t ransistors with the slanted top. Once every few days it would direct coupl e DC.

here is a tip,

wire an outlet box with a duplex outlet and a switch.

wire the outlet so the two outlets are in SERIES and in series with the switch..

Plug your unit into one outlet and plug a 100 Watt INCANDESCENT light into the other outlet.

Use the switch to turn on/off the power. This makes it easy to turn OFF all the power when you are working on the unit.

Also the bulb will limit the current if there is a fault. If the bulb glows brightly, there is still a fault and this will protect the new parts that you just put in.

mark

Mouser Electronics stocks 2N3772 output transistors from ON Semi-conductor. They run about US$3.50 each in lots of 10 (which will assure you of matchi ng at least four, if not more), and shipping across the Ocean is not so muc h as to preclude that option.

That is a high-powered TO3-case PNP output transistor that is capable of 60

• watts in PP. I will retrofit them anywhere appropriate, and they are very nearly a drop-in replacement for the 2N3055 or equivalent. I state 'very n early' as some devices may require a bias adjustment.

Note that in my experience, one or another of the driver pair often fails a nd takes the outputs with it, or the outputs fail and take a driver-or-two. Do also check for failed diodes - that failure may be invisible - and fail ed caps. As previously noted, comparing channel-to-channel is key.

Yes, that HK Series is worth the trouble.

Peter Wieck Melrose Park, PA

They are NPN , not PNP.

OUtside of that the 2n3771, 2n3772 and 2n3773 are all similar. They are a much higher power than the 2n3055 and I also use them to replace the

2n3055 in most power supply circuits.

possible. "

Well, I have repaired thousands upon thousands and actually have seen them go that way about a half dozen times. It is not common to say the least.

One weird time I had a connection to the base of a horizontal output, IIRC it was an NAP, and that SOB oscillated on its own ! I am initially looking for a sync problem and it was nothing of the sort. Miller effect on steroid s or whatever, I mean how the hell did... ? What's more is it was only a fe w hundred Hz off, and high not low.

hat would destroy speakers whenever it wanted to. Play nice, short loud hu m, speaker smoke. "

I had a Sansui 8900 do that due to a transistor socket. Blew both woofers i n one of the guy's EPIs. I sold him a pair and found out that the polarity of the ones I had were reversed from the original. I mean red to red, black to black, out of phase.

and takes the outputs with it, or the outputs fail and take a driver-or-tw o."

That is the reason for the procedure I described.

The 2N3773 is better in another way, the gain curve. The 3773 still has 35 HFE at 10 amps, while a 3055 drops to 10. At 5 amps the 3773 is 60 and the

3055 is 30. Both of them start around 100 or so at like a half amp.

Absolutely, but I recommend speaker fuses. One good trick to keep the fuses form introducing distortion at high level low frequencies (this is not aud iopholery, it is measurable) is to make a high value bipolar out of like 2

8,200 uFs in series +to+ and put it across the fuse. That only DC or very l ow frequencies will blow it. For this amp all you would need is 35 volt uni ts.

es form introducing distortion at high level low frequencies (this is not a udiopholery, it is measurable) is to make a high value bipolar out of like

2 8,200 uFs in series +to+ and put it across the fuse. That only DC or very low frequencies will blow it. For this amp all you would need is 35 volt u nits.

I agree the distortion is measurable but it may still be audiopholery.

How much are we talking about due to the fuse?

And how much distortion will the speaker itself create at that frequency/ l evel?

m

That has to do with the type of fuse and the current drawn by the speaker s ince it is dependent upon the low thermal mass of the fuse element. The res istance increases with temperature. All it takes is a part of that element to get warm. A large enough capacitor across it will keep that from happeni ng. In fact if you want to risk it to save a few bucks you can get a super high capacitance with low ESR and a lower voltage rating. Of course if the fuse blows then the cap will explode.

level? "

People who care and buy expensive speakers usually get quite low distortion from them. My Boston Acoustics A-150s IIRC were rated 0.7 % which is pheno menally low for a speaker. Really, most of the cheap junk is more like 3 -

5 % at any decent listening level and it is mostly odd order harmonics. How ever with a decent crossover that is just harmonic distortion, the fuse wil l also create intermodulation distortion because all frequencies go through it. I would say that is much more audible.

Lower power ratings don't really help because you would use a commensuratel y lower value fuse and its thermal mass will be less. A slow blow is probab ly better but then it comes down to how much abuse to which you are willing to subject your woofers. Some of them are quite expensive.

Den 2018-10-08 kl. 22:48, skrev Ralph Mowery:

That is correct.. The smaller TO3 ones have small "collers" on them and I noticed that the aluminum coolers dont have to much contakt with the shell of the transistor. The grease have dried out and the aluminum cooler did not have much contakt with the metall casing. I think this is a think for others to have a look at in therir working units. since bad cooling can kill this NPN transistors.

Cleaning and new grease would make wonders I think.