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

[Arfa Daily]

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

 

[Vale]

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 ...

http://www.clubdediagramas.com/arch...c-ca-mxkc68-manual-de-serviciopdf-f86697.html

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

 

[Phil Allison]

"Arfa Daily"

The unit has a switch mode power supply (why though?)

** Lower cost and much lower weight - that PSU has to deliver over 500
watts.

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.

** 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.

Heaven knows, there's enough cheap and cheerful examples out there, used
by the million in LCD TV sets.

** Irrelevant what LCD TVs use.

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,

** 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.

2. 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

 

[N_Cook]

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

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.

 

[Phil Allison]

"Nutcase Kook"

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.

** Try operating that switch sometime.

The result is very brief and quite unspectacular.



..... Phil

 

[Arfa Daily]

"Arfa Daily"


** Lower cost and much lower weight - that PSU has to deliver over 500
watts.



** That only increases the expense.

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.

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.

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.

** Irrelevant what LCD TVs use.

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 ?

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

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

Does two jobs:

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

2. 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.

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

 

[Phil Allison]

"Arfa Daily"

Well, if it does at all, not by very much.

** 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.

It's actually not.

** Really ??

How would you know ?

As to them being better for audio work,

** 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.

Well, it isn't irrelevant,

** Fraid it is irrelevant to an audio amp - shithead.

The requirements are very different.

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

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

But the R2KS is a similar part.

http://www.datasheetcatalog.org/datasheets/50/502475_DS.pdf

Also: R2K, R2KN, R2KY & R2M



..... Phil

 

[Arfa Daily]

"Arfa Daily"


** Bollocks.

Yes Phil, very useful comment, as always ...

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

Just goes to show how much you don't know about switchers then.

Just eliminating a switch is a STUPID reason.

That was just one among many ...

** Really ??

How would you know ?

Oh you half baked twat. I was referring to the design of the supply, which
is NOT a simple square wave inverter. Try to read and understand what people
are saying, before you engage your stupid typing fingers.

** 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.

Ha! , and you say WHAT ?

** Fraid it is irrelevant to an audio amp - shithead.

Not sure what that makes YOU then ...

The requirements are very different.

There are differences in requirements, yes, but that does not negate the
basic principles involved.

Do you make this stuff up on your own ? You know, we can all snip bits out
of posts, and then comment on them out of context, but most of us don't feel
the need to try to make ourselves look cleverer than everyone else all of
the time. Every time you get involved in a thread, sooner or later, it
dissolves into you doing just this. Which is a shame, because at first, you
always seem to make some valid and well thought out comments. Then, as soon
as anyone makes the slightest comment or observation back, you start to go
off on one, and then everybody remembers again why they don't get involved
in threads that have you appear in them. Do you actually have any flesh and
blood friends, or have you driven them all away with this bad attitude that
you sport ? Or maybe, in real life, you haven't got the balls to call people
shitheads and worse ?

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

But the R2KS is a similar part.

http://www.datasheetcatalog.org/datasheets/50/502475_DS.pdf

Also: R2K, R2KN, R2KY & R2M



.... Phil

See ? Now there's a good example. A useful comment, like you can make, if
you try

Arfa

 

[Phil Allison]

"Arfa Daily"
"Phil Allison"

Oh you half baked twat. I was referring to the design of the supply, which
is NOT a simple square wave inverter.

** Again - how would you know ?

In professional audio, high powered amps are now commonly using SMPS -
all of them of the simple square wave inverter kind. PFC circuits exist
only on a few of the very largest ( and most expensive) examples and then
ONLY to get the mains RMS current draw down to sane numbers.

Forward converters are seen in a few small powered mixers, the Fender
Passport series is one example - no PFC circuit in sight. These have a 120
/140 volt switch fitted and cause no problems here in 240 volt Australia.

Ha! , and you say WHAT ?

** I say you are lying, pommy idiot.

There are differences in requirements, yes, but that does not negate the
basic principles involved.

** There is no principle involved.

It is a matter of the designers using what is needed and what works best.

They know what they are doing, while smug pommy twats like you do not.

Do you make this stuff up on your own ? You know, we can all snip bits out
of posts, and then comment on them out of context,

** All my comments are fully in context - even when that context comes
straight from the back garden of pixie land.

BTW:

Do you still think that Marshall amps were designed by Jim Marshall ??



...... Phil

 

[Phil Allison]

"Arfa Daily is off with the Goblins & Pixies"

What's that got to do with this thread ?

** Proves my point.



.... Phil

 

[Meat Plow]

Proves my point.

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.

 

[Arfa Daily]

"Arfa Daily is off with the Goblins & Pixies"




** Proves my point.



... Phil

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

 

[Phil Allison]

"Arfa Daily is off with the Goblins & Pixies"

Well actually, that rather proves mine.

** Have to be off with the pixies to think that.

You're in the wrong thread

** You are in this thread and I am talking about you posting absolute crap.

Makes it 100% on topic.



..... Phil

 

[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

" 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