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Hi All,So I have this H/K A402 that I've used for a few years now (at least 4) without major incident (apart from yearly cleaning/lubrication) - not bad for a 30 year old piece of equipment!
Anyway, this past week my phono section (which I use regularly) appears to have died in the left channel. I've done the usual - swapped left/right channel, changed between phono 1 and 2, etc. and it appears that the left section is just dead.
Has anyone else experienced this and fixed it? The path of least resistance here is to just buy a separate phono stage, but I thought I would just see if anyone has a common problem/solution handy.
Thanks again...
Edits: 07/15/07 07/15/07Follow Ups:
If the electrolytics are 30 years old, it could be that. H-K used electrolytics for coupling at the input and output of the phono stage in many of their designs. They go bad before the other electrolytics (dc use) because they have only a millivolt ac voltage across them so they do not stay formed.
I suspect them only because the exact thing happened to me when I bought a NOS factory sealed Citation 21 which was 16 years in the box unpowered.
You've probably checked the obvious but have you changed cartridges?
I know you tried swapping channels but generally problems start at the cartridge and work to the phono section.
Just want to make sure it's not something like a loose connection etc.
Nowave
You didnt tell us if its just the phono section or is it that way on the aux or cd player? This is important so we know if its a phono section problem or a preamp/power amp problem.
Sorry, Yes - I'm not seeing the problem in any of the other aux or tape inputs - it is strictly isolated to the phono section, and while I don't have anything else with which to test the phono section, swapping left and right leads from the turntable keeps the sound on the right side.
Thanks for asking for clarification - I should have included that - any ideas?
Nowave
From of the sound of it you have a failed semiconductor..Many solid state phono sections start with an op amp for each channel and it looks a little square thing with eight legs on it,4 per side..This is a actually a buffer they go bad internally and wont pass the signal.
You may have a transistor for the input also and that could be open or shorted but you need a voltmeter to check this stuff and if you know how to use one I can walk you thru it but if not your kind of screwed.
I've used a mutlimeter plenty of times, but not lately. If you know the topology and physical layout, that would be great.
I haven't seen any opamps for this thing (it's from 1975-77) so it's definitely a transistor-based circuit, and taking the case off, it looks like a separate board from the phono amp. I just don't know enough about general phono amp (or amp of any kind) construction to really focus in on where to look.
Thanks - if you can provide a littel more info based on this (I know it's vague) - I might be able to resolve it relatively easily.
Thanks!
jason
A smallish-value capacitor with one lead held between thumb & forefinger & other lead touched to the Base lead of transistor should produce an audible hum from loudspeaker if circut is conducting. Same result when cap lead is touched to center terminal of input jack if entire following circut is OK. IOW begin @ input jack & each successive transitor until you do hear a hum; the preceeding stage that produced no hum should then be thouroughly checked. An aged electro-chemical constructed capacitor in that stage may also be the culpret rather than the transistor = a $1 replacement from a local Radio Shack discovers. The only problem with this procedure is knowing WHICH transistor lead is the Base vs Emitter & Collector = an HK schematic is useful (as with any diagnostics).
Ron
Thats a good point..When you mentioned the signal tracer in your title it made me get mine back out..Boy what a fun thing that was and its a heathkit tube unit I built back in junior high in 1973.Boy how time flies.
He could also use his meter and check for the .6v turn on base to emitter but then as you say he has to know where the base emitter is and many units didnt have silk screened boards.
I assume it's phono-specific.
I wonder if it could be dirty contacts?
Unfortunately, since there is another gain stage for MM phono, something could well have failed in one channel :-(
I haven't thought of a clever way to troubleshoot. When I have phono section problems, it's usually cable-related. :-)
all the best,
mrh
Ah, has been pointed out. I should have looked at the model # before posting, instead of going strictly on memory.
It's an HK A-402 (not 410). Not sure what I was thinking...
nt
all the best,
mrh
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