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 8th 18, 03:09 AM posted to sci.electronics.repair
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Default Harman Kardon 930 lost channel. Hoe to trouble shoot ?

On Sunday, October 7, 2018 at 6:58:59 PM UTC-5, John-Del wrote:

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


Yup. the mistakes are mistakes, not laziness.



I've changed many hundreds of outputs over the years, and have never seen one "open".


I have, but they are usually intermittent.

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.


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

It is still a good piece. The outputs are hefty enough to handle a sub 4 ohm real load, looks like a fairly healthy FM as well with the totally shielded 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 filters but eh, can't have everything.

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Old October 8th 18, 05:25 PM posted to sci.electronics.repair
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Default Harman Kardon 930 lost channel. Hoe to trouble shoot ?

On Sunday, October 7, 2018 at 10:09:40 PM UTC-4, wrote:
On Sunday, October 7, 2018 at 6:58:59 PM UTC-5, John-Del wrote:

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


Yup. the mistakes are mistakes, not laziness.


You missed the sarkasm...



I've changed many hundreds of outputs over the years, and have never seen one "open".


I have, but they are usually intermittent.


Never saw one, but I did qualify my statement by saying that anything is possible. I've lived long enough to know that odd things happen. The only thing 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 open. I still don't thing Steff has an open output.


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.


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


Yikes. I remember a Hitachi receiver in the shop back in the early 80s that 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 transistors with the slanted top. Once every few days it would direct couple DC.
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Old October 8th 18, 05:27 PM posted to sci.electronics.repair
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Default Harman Kardon 930 lost channel. Hoe to trouble shoot ?

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



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Old October 8th 18, 07:42 PM posted to sci.electronics.repair
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Default Harman Kardon 930 lost channel. Hoe to trouble shoot ?

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 matching at least four, if not more), and shipping across the Ocean is not so much as to preclude that option.

https://www.mouser.com/_/?Keyword=2N3772G

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 nearly' as some devices may require a bias adjustment.

Note that in my experience, one or another of the driver pair often fails and 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 failed caps. As previously noted, comparing channel-to-channel is key.

Yes, that HK Series is worth the trouble.

Peter Wieck
Melrose Park, PA
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Old October 8th 18, 09:48 PM posted to sci.electronics.repair
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Default Harman Kardon 930 lost channel. Hoe to trouble shoot ?

In article ,
says...

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 matching at least four, if not more), and shipping across the Ocean is not so much as to preclude that option.

https://www.mouser.com/_/?Keyword=2N3772G

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 nearly' as some devices may require a bias adjustment.

Note that in my experience, one or another of the driver pair often fails and 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 failed 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.



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Old October 9th 18, 12:21 AM posted to sci.electronics.repair
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Default Harman Kardon 930 lost channel. Hoe to trouble shoot ?

"Never saw one, but I did qualify my statement by saying that anything is 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 steroids or whatever, I mean how the hell did... ? What's more is it was only a few hundred Hz off, and high not low.

"Yikes. I remember a Hitachi receiver in the shop back in the early 80s that would destroy speakers whenever it wanted to. Play nice, short loud hum, speaker smoke. "


I had a Sansui 8900 do that due to a transistor socket. Blew both woofers in 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.

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Old October 9th 18, 12:36 AM posted to sci.electronics.repair
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Default Harman Kardon 930 lost channel. Hoe to trouble shoot ?

"Note that in my experience, one or another of the driver pair often fails and takes the outputs with it, or the outputs fail and take a driver-or-two."

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.

"Yes, that HK Series is worth the trouble. "


Absolutely, but I recommend speaker fuses. One good trick to keep the fuses form introducing distortion at high level low frequencies (this is not audiopholery, 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 units.

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Old October 10th 18, 04:08 PM posted to sci.electronics.repair
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Default Harman Kardon 930 lost channel. Hoe to trouble shoot ?



Absolutely, but I recommend speaker fuses. One good trick to keep the fuses form introducing distortion at high level low frequencies (this is not audiopholery, 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 units.


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/ level?

m

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Old October 10th 18, 04:45 PM posted to sci.electronics.repair
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Default Harman Kardon 930 lost channel. Hoe to trouble shoot ?

"How much are we talking about due to the fuse?"

That has to do with the type of fuse and the current drawn by the speaker since it is dependent upon the low thermal mass of the fuse element. The resistance 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 happening. 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.

"And how much distortion will the speaker itself create at that frequency/ 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 phenomenally 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. However with a decent crossover that is just harmonic distortion, the fuse will 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 commensurately lower value fuse and its thermal mass will be less. A slow blow is probably 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.
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Old October 11th 18, 07:50 PM posted to sci.electronics.repair
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Default Harman Kardon 930 lost channel. Hoe to trouble shoot ?

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

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 matching at least four, if not more), and shipping across the Ocean is not so much as to preclude that option.

https://www.mouser.com/_/?Keyword=2N3772G

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 nearly' as some devices may require a bias adjustment.

Note that in my experience, one or another of the driver pair often fails and 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 failed 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.


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.



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