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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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#1
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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 ****ted, 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 |
#2
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So, who's the king of finding data sheets ... ?
"Arfa Daily" ha scritto nel messaggio news:mHpWn.93263$tH4.24979@hurricane... 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/archi...df-f86697.html Just register and download. Spanish is not a problem, isn't it? |
#3
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So, who's the king of finding data sheets ... ?
"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 ****ted, 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 |
#4
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So, who's the king of finding data sheets ... ?
Arfa Daily wrote in message
news:mHpWn.93263$tH4.24979@hurricane... 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 ****ted, 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. |
#5
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So, who's the king of finding data sheets ... ?
"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 |
#6
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So, who's the king of finding data sheets ... ?
"Phil Allison" wrote in message ... "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. 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. Heaven knows, there's enough cheap and cheerful examples out there, used by the million in LCD TV sets. ** 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 ? Anyway, that aside, the bridge was ****ted, 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. 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 |
#7
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So, who's the king of finding data sheets ... ?
"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. Well, if it does at all, not by very much. ** ********. 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. 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. ** 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. Heaven knows, there's enough cheap and cheerful examples out there, used by the million in LCD TV sets. ** Irrelevant what LCD TVs use. Well, it isn't irrelevant, ** Fraid it is irrelevant to an audio amp - ****head. The requirements are very different. Anyway, that aside, the bridge was ****ted, 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. 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/data.../502475_DS.pdf Also: R2K, R2KN, R2KY & R2M ..... Phil |
#8
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So, who's the king of finding data sheets ... ?
"Phil Allison" wrote in message ... "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. Well, if it does at all, not by very much. ** ********. 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 ... 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. ** Really ?? How would you know ? Oh you half baked ****. 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. 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. Ha! , and you say WHAT ? Heaven knows, there's enough cheap and cheerful examples out there, used by the million in LCD TV sets. ** Irrelevant what LCD TVs use. Well, it isn't irrelevant, ** Fraid it is irrelevant to an audio amp - ****head. 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 ****heads and worse ? Anyway, that aside, the bridge was ****ted, 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. 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/data.../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 |
#9
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So, who's the king of finding data sheets ... ?
"Arfa Daily" "Phil Allison" 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. ** Really ?? How would you know ? Oh you half baked ****. 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. 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. 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 ****s 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 |
#10
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So, who's the king of finding data sheets ... ?
"Phil Allison" wrote in message ... "Arfa Daily" "Phil Allison" 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. ** Really ?? How would you know ? Oh you half baked ****. 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. 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. 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 ****s 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. No they're not. You've done it again in this reply. The context only comes directly from Pixie Land in your stupid head, as every sane person on here knows ... Do you actually know the meaning of the phrase "in context" ? Or come to that, even know the meaning of the single word ? No ? I thought not .... You do it all the time in every thread that you get involved in. You ignore anything that you can't refute and snip it out. Then you take everything else, cut out anything that fixes the context, and then post one of your ill thought-out stupid-headed replies, usually with some offensive comment attached. If I'm smug, then sobeit. It's because I know how much better I am in every regard than you. **** ? Well, I really think that you have got that one tied up all on your own, Phil. BTW: Do you still think that Marshall amps were designed by Jim Marshall ?? ..... Phil What's that got to do with this thread ? Now run along, take your meds, and go to bed in a nice dark room for a few hours, until those nasty voices in your head stop talking to you ... Arfa |
#11
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So, who's the king of finding data sheets ... ?
"Arfa Daily is off with the Goblins & Pixies" Do you still think that Marshall amps were designed by Jim Marshall ?? What's that got to do with this thread ? ** Proves my point. .... Phil |
#12
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So, who's the king of finding data sheets ... ?
On Thu, 01 Jul 2010 20:33:22 +1000, Phil Allison ǝʇoɹʍ:
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. |
#13
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So, who's the king of finding data sheets ... ?
"Phil Allison" wrote in message ... "Arfa Daily is off with the Goblins & Pixies" Do you still think that Marshall amps were designed by Jim Marshall ?? What's that got to do with this thread ? ** 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 |
#14
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So, who's the king of finding data sheets ... ?
"Arfa Daily is off with the Goblins & Pixies"
Do you still think that Marshall amps were designed by Jim Marshall ?? What's that got to do with this thread ? ** Proves my point. 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 |
#15
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So, who's the king of finding data sheets ... ?
"Phil Allison" wrote in message ... "Arfa Daily is off with the Goblins & Pixies" Do you still think that Marshall amps were designed by Jim Marshall ?? What's that got to do with this thread ? ** Proves my point. 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 " 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 |
#16
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So, who's the king of finding data sheets ... ?
Arfa Daily wrote: "Phil Allison" wrote in message ... "Arfa Daily is off with the Goblins & Pixies" Do you still think that Marshall amps were designed by Jim Marshall ?? What's that got to do with this thread ? ** Proves my point. 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 " 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 .... :-))) 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. |
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