So, who's the king of finding data sheets ... ?

I have a JVC hifi on my bench. Brand new, purchased by a British soldier from a base somewhere else - possibly an American one, I seem to recall being told. Oddly, for modern equipment, it has a voltage selector switch, which was of course set to 120v, when he applied 240v UK power to it ...

The unit has a switch mode power supply (why though?) which is one of the old style designs where the front end has two main filter caps, and the input voltage is configured by how you jigger the connections of the reccy and the caps. That is where the back panel voltage selector switch is connected. Even more why though ? I would have thought that if you were going to bother putting a switcher in a junky piece of hifi that was for worldwide use, you would have used a design with an efficient PFC front end, that makes it universal in terms of input voltage. Heaven knows, there's enough cheap and cheerful examples out there, used by the million in LCD TV sets.

Anyway, that aside, the bridge was twatted, as were two diodes?? , one across each of the filter caps. These devices *look* like diodes, and the symbol on the board is for a diode, and they're called D34 and D35, but I can't recall having seen diodes in this position before. Voltage sharing resistors, maybe. The type number on them is R4KL, and that's where the problems start. All of the usual suspects - Datasheetarchive, Allicmall etc deny knowing anything about this device. I can't seem to find any references to the it on the net, other than lots of people on groups and forums, also trying to find data. An admittedly brief trawl of some of those postings, didn't seem to turn up any definitive answers. Some seem to be calling the device a "transient suppressor" so maybe it's some kind of avalanche diode ? Appears to be used in some monitors as well, so I'm surprised that it is so difficult to turn up info.

Anyway, I've replaced the bridge, removed the short circuit whatever-they-ares, and fired the supply up in isolation. It runs quite happily without the "diodes" as you might imagine it would, and the output voltages seem reasonable.

Apparently, the owner is being posted to Afghanistan or some such at the weekend coming, and wants to take the hifi with him, so my back's against the wall a bit on this one. In case of the remote possibility that anyone has a service manual for the item, it's a JVC MX - KC68 or CA-MXKC68 depending on whether you have it listed by system or model number.

Any help then, please lads. TIA

Arfa

Reply to
Arfa Daily
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Just register and download. Spanish is not a problem, isn't it?

Reply to
Vale

"Arfa Daily"

** Lower cost and much lower weight - that PSU has to deliver over 500 watts.
** That only increases the expense.

The PSU in that JVC is likely to be of the unregulated kind - ie a simple square wave inverter.

These are far preferable for audio amplifiers and cheaper to make too.

** Irrelevant what LCD TVs use.

** That type is an "avalanche " diode that is specified to zener breakdown at a particular voltage - like 200 volts.

Does two jobs:

  1. It sacrifices itself and goes short to protect the electo when some idiot does what your customer did.

  1. It prevents reverse polarity current from flowing into the electro ( via the load) during the switch on surge period - this is only an issue for 120 volt use when the circuit is acting in voltage doubler mode. Any diode with adequate voltage an current ratings is OK for this.

.... Phil

Reply to
Phil Allison

end,

TV

etc

references

?

so

Have you put any volts on the low volt side to see if there is life still left in that side?

Before returning an Orange combo back to its owner yesterday I disabled the user operatable 120/240V switch, it only takes one UK drunk/ moron who thinks they can improve or repair an amp by moving everything moveable. All the elfin safety stuff around these days and they're still allowed to deliberately make those glaring fire safety hazards.

Reply to
N_Cook

"Nutcase Kook"

** Try operating that switch sometime.

The result is very brief and quite unspectacular.

.... Phil

Reply to
Phil Allison

Well, if it does at all, not by very much. Many switchers now have a 'universal' PFC front end, based on a single chip, one cheap FET, and a small piece of magnetics. Having this would save on the cost of the rear panel voltage selection switch, having to fit that switch, the wire that connects out to it, the plug and socket on the board that connects to it, two whatever-they-are 'diodes' and one high voltage smoothing cap. Also, the cost of the warning label about using it on the wrong voltage, and the warning sheet in the box. Apart from this, it would slash the standby power consumption, which is why many manufacturers have adopted this scheme in the first place.

It's actually not. It's a fairly sophisticated design, apart from the stupidity of not being universal on its input voltage. As to them being better for audio work, just last month, Elektor magazine did some lab tests to assess whether off-the-shelf switchers could be used to replace linears in some of their well respected and time-tested designs. In every case, the THD figures were worse.

Well, it isn't irrelevant, because these are now being built by the million, and they have driven the development of cheap, sophisticated, and above all efficient power supplies more than any other consumer or industrial product has, in the civilized world. LCD TV manufacturers - including JVC themselves - have developed the techniques of front end PFC usage to the point where it is absolutely standard in their products, so why do they bother to go back to an old technique of an inefficient voltage doubler front end, for one of their audio products ?

I too felt that it probably was an avalanche diode. Do you have any data on the device to support that contention ?

Agreed on the purposes if the device is, as suspected, an avalanche diode. The unit is never going to be used on 120v, so I am going to leave the switch disconnected anyway, which places the unit firmly in the 240v bracket, meaning that in theory, the two diodes are not required. The supply works absolutely fine without them, and I have seen plenty of examples over the years, where there are just voltage sharing resistors in that position.

Arfa

Reply to
Arfa Daily

"Arfa Daily"

** Bollocks.

A 500 watt PFC corrector is a lot of extra circuitry for which and no need or benefit exists.

Just eliminating a switch is a STUPID reason.

** Really ??

How would you know ?

** Preferable to either flyback or forward converters and cheaper to make at the high power levels needed.

Try learning to read what has been written.

** Fraid it is irrelevant to an audio amp - s*****ad.

The requirements are very different.

** There is no data on the net, as you well know.

But the R2KS is a similar part.

formatting link

Also: R2K, R2KN, R2KY & R2M

.... Phil

Reply to
Phil Allison

"Arfa Daily is off with the Goblins & Pixies"

** Proves my point.

... Phil

Reply to
Phil Allison

On Thu, 01 Jul 2010 20:33:22 +1000, Phil Allison ??o??:

You have to have a point in order to prove it. In this case you didn't and you used the thread to discredit and insult -as usual- now run along and fix some amps and leave the chatter for the big boys.

Reply to
Meat Plow

Well actually, that rather proves mine. You're in the wrong thread altogether for that one, but of course, stupid headed as you are, you hadn't even noticed, had you ? What a plank ... :-)))

Arfa

Reply to
Arfa Daily

"Arfa Daily is off with the Goblins & Pixies"

** Have to be off with the pixies to think that.
** You are in this thread and I am talking about you posting absolute crap.

Makes it 100% on topic.

.... Phil

Reply to
Phil Allison

" Snip snip .... Context ? What's that ? ... Proving points or on topic ? ... What were we talking about ? ... Which thread am I in ? .... Which group am I even posting my stupid headed comments in ? "

Is that how the voices sound, Philip ? Dear oh dear. Back to the quack for you, I fear, to try to see if they do stronger meds you could get yourself on .... :-)))

Arfa

Reply to
Arfa Daily

It looks like the elephant tranquilizers no longer work for Phil anymore. :(

--
Anyone wanting to run for any political office in the US should have to
have a DD214, and a honorable discharge.
Reply to
Michael A. Terrell

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