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Luxman LV-105 hum
Luxman LV-105 hum
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Old 3rd February 2018, 10:34 AM   #11
Depaj is offline Depaj  France
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I order all my parts from mouser Nichicon FG, ES, Panasonic FM/FC and elna silmic II. I don't think there's anything to worry about there
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Old 28th February 2018, 10:13 AM   #12
Depaj is offline Depaj  France
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I might have found something.
Although I have the right schematic (LV105 not the U version) there are some major differences with what I actually see on the board (for starters the protection circuit is on the main board and not on a separate one as the service manual says).
There were 2 diodes that were eaten up by the brown glue that were marked D7305 and 7306, I didn't think any further and replaced them with an equivalent of the 1s2462. Now it turns out the part numbers are also different in the manual and on the board and D7305 and D7306 weren't 1s2462 at all but what I believe are zener diodes (marked 12C3) and are in place of R7385 and R7386 (8.2K in the service manual) going to the cathodes of the tubes. Can anyone tell me what diode this is and what I can replace it with ?

20180228_115808.jpg

lv105.jpg
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Old 28th February 2018, 05:40 PM   #13
mjona is offline mjona  New Zealand
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For an example of a Zener diode look at an angle of 10 o clock from the red circle on your second image see ZD7309 which is defined by the symbol as well as the prefix.

The datasheet for 1s2462 describes these as a general purpose rectifier in a hermetically sealed miniature glass package - the sort of package shown in your first image.

If your replacements have equivalent or better specifications than 1s2462 and are oriented as the board overlay indicates, the only other thing to check here is to ensure there are no cold solder joints.
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Old 28th February 2018, 06:47 PM   #14
Depaj is offline Depaj  France
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Hi!

I know what a zener is , the schematic shows an 8.2k resistor but instead there was this diode from the picture that was shorted (in the red circle on both channels). I mistook it for one of the 2 1s2462 diodes because the marking on the board corresponds but not the implantation in the circuit. The only marking on the diode is 12C3, I googled it but the results aren't very conclusive, I found one that shows this as a 13.8V 1/2W but as I can find this nowhere else I'm not sure.
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Old 28th February 2018, 09:39 PM   #15
mjona is offline mjona  New Zealand
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From this link you can see this being a 12 V zener. It could well be this drops the same voltage from where it is sourced as an 8k2 resistor. HZ12(C3) NTE Equivalent NTE5021T1 ZENER DIODE - 12V ... - Wholesale Electronics

I downloaded the comprehensive service manual and looked at the component lists to identify HZ12 (C3) listed. I see from downloading the pdf from the link the replacement has a 1% tolerance rating.

Last edited by mjona; 28th February 2018 at 09:47 PM.
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Old 28th February 2018, 09:47 PM   #16
Depaj is offline Depaj  France
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That does seem to make sense. I just measured the voltage across the diode I installed as a replacement and it was about 80v, no wonder the amp wasn't happy, I don't see how the 63v cap that is in parallel didn't even get hot. Maybe it did do some damage so I might just go ahead and replace it again (it was a new one already). I have some Vishay BZX55 12v 1/2W on order for another project, I'll just add 2.

Last edited by Depaj; 28th February 2018 at 09:50 PM.
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Old 1st March 2018, 01:38 AM   #17
mjona is offline mjona  New Zealand
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Just thinking aloud a bit about this - the parts list shows HZ12(C3) or RD15E-B2 as zener options for designated part no. ZD1307. The parts list gives D7305 and D7306 designated part numbers as 1s2462 or 1s2463.

According to the pcb R7385 is a resistor but in the parts list I don't see a resistor or a zener diode with the matching type number 7385. It seems some circuit changes had yet to be documented when the service manual I referenced was published.

If the voltage applied to your diode was 80 volts, substituting an 8k2 resistor in place would result in a negligible drop in the voltage seen by C7307. Nominally limited to 63 volts it many have withstood higher voltages to a point - but not at 80 volts in the long term.

There is only one HZ12(C3) in the parts list - ZD1307 in another part of the circuit. This component would have been in the parts inventory and convenient to use to replace R7385.
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Old 8th March 2018, 12:32 PM   #18
Depaj is offline Depaj  France
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I guess that's exactly what they did, I replaced both with vishay BZX85 12v zener diodes and the amp is hum free, the relay stays nicely closed, bias has been set and it now sounds pretty good. Thanks for the help !!
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Old 12th March 2018, 03:54 PM   #19
Depaj is offline Depaj  France
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I did some tests today with the new tubes in, it sure seems healthy now, it got up to 105W into 8ohms (rated for 80W) , both channels driven at 1kHz and there still wasn't any clipping. I didn't want to push it because my dummy load is only rated for a 100W. It does get quite hot even with no signal with those 45mV of bias so it will need some space to breathe. It sounded very nice through the headphones and will do some tests later on my B&W DM4.
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