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