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FRG-7. Replace Electrolytic caps...or leave well enough alone?

Discussion in 'General Electronics Chat' started by cdnpont, Apr 20, 2017.

  1. cdnpont

    cdnpont New Member

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    Hello again Electro Tech,

    I have a question about replacing Electrolytic capacitors,

    I've picked up what turned out to be a sweet, early model Yaesu FRG-7 to compliment my now working again (thanks guys!) RF4800. Got it for a song, was really dirty to the point it would barely function. But after a thorough cleaning it looks 9/10 perfect and works pretty well.

    On a whim, I'd bought a $15 eBay kit from KK4HXJ to replace all the electrolytic caps, but now I wonder if it's worth messing with, to my untrained ear, what seems to be a fairly decent functioning radio. Some internet talk suggests to always replace all 30 year old electrolytics...some say don't mess with them unless they show visible signs of failing, or testing can show a degredation. Mine all look like new, with no bulging, leaking or corrosion , even under a magnifier.

    The one thing I do wonder about is this; if the volume is turned up past 1/2 way, a slight, steady and fine crackle is heard, getting more prominent as I increase output further. But it's not like a dirty pot or blown speaker might sound. Did not change after 2 cleanings. Could this be a cap gone or going bad in the amp section?

    Anyway, there is only 15 caps to easily replace, do I go for it and at worst see maybe slight performance improvement, or do I leave this original frog well enough alone?

    Any thoughts appreciated,
    Cheers and thanks,
    Mark

    [​IMG]
     
  2. cowboybob

    cowboybob Well-Known Member Most Helpful Member

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    If your comfortable doing the swaps, I'd say go for it.

    I might suggest, however, starting with the PS caps first. Then re-check for the "crackle" and proceed if need be.

    CBB, K4NFF
     
    • Agree Agree x 1
  3. Colin

    Colin Member

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    Sometimes all the electros will be faulty to some extent, depending on the product. It really depends on who made them.
    Spray the pots with "cleaner" by screwing a hollow shaft over the shaft of the pot to make them new again. One of the first things you will notice is background "hum" if the main filter electros are dry.
    In general, if an item does not work or "plays up" - - - change all the electos !!! But you have to know which items I am referring to.
     
  4. dave

    Dave New Member

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  5. cdnpont

    cdnpont New Member

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    I'll take your advice bob and maybe start with the power supply caps just to see if rids the crackle.
    I did a very careful Deoxit spray and blowout of all the pots Colin. Wrapped in paper towel, it was unreal what came out of them. I think it was a smokers machine. No discernable hum at all from the FRG, but the same can't be said of my RF4800, on AC it was terrible. Silent on a 12v dc adapter or car battery. Didn't come with an adapter, so I found a old switching 12v/3.2a cable box adapter that works cool and silently. Huge difference. I suspect the big caps on the PS on that one might be tired. Cheers.
     
  6. crutschow

    crutschow Well-Known Member Most Helpful Member

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    My general motto is, if it ain't broke, don't fix it. :rolleyes:
    Sometimes in the process of preemptive "fixing" it you will damage something else that's an even greater problem to fix.

    I have a Dynakit Stereo 120 audio amp I built circa 1970 (one of the early, well-designed solid-state audio amps) and I've only had to replace one electrolytic coupling caps since, although another may be going bad since sometimes the sound distorts some in the right channel, but a whack on the amp cures it (so far).
    Otherwise it still works great with a solid clean sound, and I'm not going to touch it unless something fails permanently.
     
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  7. Mikebits

    Mikebits Well-Known Member

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    I use to work at a Ship Repair Facility (SRF) as a technical liaison. Our task was to assist shipboard personnel in repairing malfunctioning electronic equipment (specifically Meteorological equipment). Anyways, what our group had discovered was that 99% of most problems encountered were exacerbated by the ships personnel attempting to repair the faulty equipment. That is to say, the attempted rework and repair usually introduced additional problems with the equipment, errors like solder splash, poor solder connections etc.
    This is not to say that the repair people were bad at their jobs, rather the inherent nature of performing rework/repair poses the risk of inducing more errors on a circuit board/assembly.
    It is therefore my reason to agree with Crutschow. If it ain't broke, don't fix it.
     
  8. KeepItSimpleStupid

    KeepItSimpleStupid Well-Known Member Most Helpful Member

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    It's always a toss up and it may depend on a lot of things. If you have a schematc and can look at the power supply ripple, that's a good start. The supplies that supply negative voltages affect more things, You have to be careful replacing stud=ff that may alter the circuit such that aligning is necessary.

    The X, Y and Z caps on the power line might tbe worth looking at.

    You can see the effects of a scratchy pot on a scope.

    An overheated voice coil can cause scratyness, but you can also mechanically feel it. You scratcyness may also be clipping. Check for any excessive DC voltage on the speaker voice coil.

    In my professional life, the negative supply caps were the most sensitive and measuring ripple usually identified them. The degradation was accelerated by heat.
     
  9. KeepItSimpleStupid

    KeepItSimpleStupid Well-Known Member Most Helpful Member

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    I fixed one after everyone else tried. probably in the early 80's.
     
  10. Nigel Goodwin

    Nigel Goodwin Super Moderator Most Helpful Member

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    I concur, "if it ain't broke, don't fix it".

    The main area where electrolytics fail is in switch-mode PSU's, where they fail high ESR.

    It's pretty rare for them to fail other than that. I wouldn't blanket change them in a working item, unless they showed physical signs of failing.

    If you do replace them, make sure you use high quality ones, and not cheap crap ones.
     
  11. schmitt trigger

    schmitt trigger Active Member

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    a Yaesu FRG-7 !! And looks great too!
    I used to salivate over those, but could never afford it.

    About your question: once had a piece of equipment which was doing just that. It was a transistor which had developed leakage. But could be as well be a leaky coupling cap.
    Do you have access to a scope?

    Most importantly, do you have the schematics??
    If so, could you please share, and we can give you some pointers.
     
  12. cdnpont

    cdnpont New Member

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    Thanks for all the reply's,

    Now you've got me thinking.

    The static sound I describe really isn't a big issue, unless at somewhat beyond 50% volume, which there never seems to be a need to be at. And I'm also using a Bose Bluetooth speaker from time to time on my radios, which really sounds far better than the stock speaker.

    The caps that came in the kit are all from china, indeed cheap, but the fellow that sold them claims he's never had any issue from anyone in all the years he's sold them, and stands behind them. He also claims he tests every cap to ensure it's in tight spec, + - 1%. Is there really such a thing as a "Good" cap anymore? Like everything else, aren't all of these components just coming out of china now?

    I love to tinker, but I have to agree somewhat with the philosophy of "If it aint broke....". The boards, for the most on this radio are really packed tight, and as such the solder points, except for the ones at the large PS caps are very close. So perhaps I'll just change the 3 or 4 that are easy and have a listen. I do feel I have the skill to fine solder, but perhaps I'll wait a while. At least I have the parts now.

    I'm new and just getting into this, so I don't, and likely will never have a scope. Although I'd like to someday have the tools and skill necessary to at least attempt an alignment on a vintage radio myself. I'm trying to learn as much about theory as I go along, and this will take me a while, as I'm really more of a mechanic.

    Besides the fun of vintage, the part I'm really enjoying about this, is experimenting with different antennas. I have a remote 5 way switch and a tuner, and am trying all different stuff. It's really a lot of fun.

    Cheers,



    [​IMG]

    Here's a link to a great page of FRG-7 illustrations and info,

    Schematic divided in four,

    Schem Pt1
    Schem Pt2
    Schem Pt3
    Schem Pt4
     
  13. Nigel Goodwin

    Nigel Goodwin Super Moderator Most Helpful Member

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    Well that's a load of crap from him, electrolytic specs are VERY wide tolerance, often +50%/-25% - you don't get 1% electrolytics :D

    You certainly get good caps, and VERY bad caps.

    I would advise Panasonic or Rubicon as good ones, and CapXon as absolutely useless ones - although there are plenty more useless ones as well.

    I wouldn't blanket change the caps unless I was using good quality ones, and not at all for the purpose these are been used (unless they are leaking or bulging).
     
  14. cdnpont

    cdnpont New Member

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    My mistake, I went back and read his ad, and sure enough he doesn't mention tolerance. Not sure why I had that in my mind...

    Some are Chenxing, some are Nishicon brand. Not exactly confidence inspiring.

    I closed the cover and will ponder this more.....
     
    Last edited: Apr 21, 2017 at 11:28 AM
  15. cowboybob

    cowboybob Well-Known Member Most Helpful Member

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    It is, indeed, fun.
     
  16. cdnpont

    cdnpont New Member

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    Thanks for all the expert suggestions guys. I really do appreciate it.
    I am leaving well enough alone. The unit works well enough not to risk disturbing it.

    Cheers, Mark
     
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  17. Mosaic

    Mosaic Well-Known Member

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    The thing about don't fix it if it ain't broke isn't necessarily a good approach when it comes to Vintage electrolytic caps and battery backed items like NVRAM.
    Vintage Electrolytics WILL eventually fail and leak and destroy your PCB traces via corrosion. Also, watch out for battery backed items which carry critical config. or cal data. Items like Dallas NVRAM & RTCs are rated for 10 years ..., they usually last for 15+ but when they go they often take the device function with them.
    Thus like changing the oil in your vehicle's engine, you can do prev. maintenance before damage occurs.

    Go after all electrolytics in the PSU section as they tend to run hotter and fail first. If you don't see any leakage under the caps then the rest of your device is prob. ok. If you do find a leaky cap, well further investigation is required.
     

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