recap on Sony STR 6046A

Dan75

Member
2018-06-27 6:43 pm
Hi,
I am cleaning a seventies receiver, bought at a thrift store.It is a Sony STR-6046A. I noticed that 2 electrolytic caps are starting to bulge.
Because of this I de-soldered them and googled them for specs. Nothing found so far. I think because they are that old, there is no info to be found on the net in
form of data sheets. So I am trying to understand what is important to look at when one has components that are without specs provided and are to be replaced.
Would like to replace them and maybe the rest mas well ( of the same series).


Note; I do not have the correct service manual for this type receiver. The one I have (from the internet) does not have the same layout so therefore I do not know if I can use it in any way.


thanks

Dan
 

Dan75

Member
2018-06-27 6:43 pm
Sorry, noticed I missed adding some needed info. The caps are old blue Nichicon caps 25V 220uF (only other info is H7322) and 35V 330uF (H7314) No further info on temp or other.
Positions are C807 and C808 on the PCB.
Other similar series caps in different values are on the PCB and the power supply maybe best to change them as well?
 
In my experience as electronic industrial repairman, I suggest to unse Nichicon as a first trade, and Jamicon as second. Jamicon are very good devices, in my experience. 105°C is recommended. Values nearest the original (Say, 47µF for 50µF) and voltage equal or sligtly higher than original (Say, for a 12V unit, use 16V but not 35V units).
 

mikeAtx

Member
2019-11-17 7:44 pm
I'd go to mouser or digikey and start looking. They will likely have the exact size/voltage you need. But it may be physically smaller. I usually try to match the can size and more importantly the lead spacing. You may end up with a higher voltage cap when you match the physical size of a 70's cap.
 
As a rule of thumb, it is suggested not to take capacitor rated voltage much beyond 3 times the actual sustained voltage in operation. (So 35 V on an actual 12 V would still be deemed feasible.) Otherwise leakage current may not be able to repair imperfections in the dielectric layer to a degree sufficient for the part to withstand full rated voltage.

The question, of course, is whether you actually need this. Few caps are actually taken out and re-used, and even if so the question is whether some gentle reforming couldn't bring them back enough.

In theory, higher voltage rating = thicker dielectric = higher thickness even in imperfect spots = less leakage. Now there's this whole pesky εA/d business, so if your dielectric layer is twice as t h i c c and makes up most of platter spacing d, you'll need close to twice the area for the same capacitance, which brings with it correspondingly more imperfections, so there's not quite as much benefit as you'd think. Still, I'd think the higher-rated part from the same series would generally be winning out in leakage under the exact same circumstances. I don't really see how the opposite could be happening. (ESR is a slightly different kettle of fish, it generally hits an optimum at some point.)

IMO it is a good idea to go slightly higher than stock voltage rating at least. Back in the day the spread in caps' actual sustained voltage was much greater due to less tight process control and hence more imperfections, and they had to derate the parts substantially to hit an acceptable failure rate. On the flipside, this could have meant that you could have cherrypicked parts that would have sustained a multiple of their rated voltage (I remember some mid-'70s device where documentation stated a factor of 3!), and an average part might still have sustained substantially more than rated. That's not so much the case these days, now that better control of imperfections has effectively made caps substantially smaller (or rather permitted less derating). Some stingy manufacturer actually used somewhat underrated caps in the '70s and got away with it, this definitely wouldn't fly these days.

I wouldn't fret about temperature rating too much in most spots except notoriously warm places, and if so do read the fine print (datasheet) - a cap rated 105°C at 1000 hours is probably not a great deal better than a 85°C. Likewise, there a few spots in an audio amp that need ultralow ESR, so there usually is little point in anything more extreme than Panasonic FM or FC series. Ultralow ESR parts tend to have higher leakage and as a result shorter life in undemanding environments. In some small coupling caps you may even be tempted to go with a low leakage series.

Re: cap manufacturers, you are generally good to go with Japanese ones (bought from major parts distributors for greatly reduced risk of counterfeits). Nichicon, Panasonic, United Chemicon, that sort of thing. There's a few good American and Euro manufacturers left as well. Taiwanese brands can be at least good second-rate, like Rubycon.
 
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Dan75

Member
2018-06-27 6:43 pm
Thank you all for your input. And "sgrossklass" for your extensive and interesting reply. Didn't know that Rubycon was Taiwanese. I had to order some 1uF caps for my turntable, my supplier was out of other brands in this rating. Thought they were up there with Nichicon and Panasonic. But maybe that was yesteryear??


I had a feeling that Panasonic FC would be ok, and therefore already ordered some Panasonic FC , FM series caps yesterday.
Most are of somewhat higher voltage than the originals. But I am only replacing the blue Nichicon caps, I am leaving the rest of them in place. They look ok to me, although to be fully sure I have to measure them which I am not going to.
Thanks everyone for help on this one. Have the next one on the backburner already as when I picked the unit off the ground a piece of a ceramic cap flew out. I don't know the specs of it yet as it blow completely to pieces and therefore I cannot measure it anymore. It has the marks on it though but I can't make cookies out of it. Only thing I am sure of it's a Matsushita cap but at what rating....? The service manual on ths one is such a bad copy that is is hard to read anything.
 

Dan75

Member
2018-06-27 6:43 pm
So, I finally finished the recap of those caps, cleaned the outside of the unit and after a good visual inspection turned on the little Sony.

At first I thought one channel was faulty as the left side almost had no volume at all, but it turned out that the speaker terminal is not what it should be.
After reconnecting the wires again volume was the same on both channels except there is one issue. It seems there is a hum in the left channel.
Does anyone have a clue what to look into? I've made a video on it, I could post it if anyone wants to see it


Thanks a million
Dan
 

Dan75

Member
2018-06-27 6:43 pm
Did a few things and I think it was in the speaker terminal. There is no hum anymore on the left. This little Sony was somewhat neglected and smoked (nicotine that is :)

What still is, is a hiss that is present form both speakers at equal strength, and is heard even with the volume set to zero or completely counterclockwise..
It only goes silent when the speaker terminal A is switched off and set to terminal B.

Hiss is present on both terminals, doesn't matter if I connect the speakers to A or B.
 

Dan75

Member
2018-06-27 6:43 pm
That's what I was thinking. It is indeed audible when nothing is playing. If I put on a cd (Dave Brubeck - Take Five) then the sound is amazing (imo) and the his is not to be heard. But, I am not an experienced audiophile :)

I think it's just because it is an old build style receiver it occurs.
Thanks so much for your input