To recap or not to recap...

Discussion in 'Radio Circuits, Repair & Performance' started by WM4MW, Feb 14, 2019.

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  1. K0OKS

    K0OKS Premium Subscriber QRZ Page

    Remember, changing caps is not a repair technique at all. It is a maintenance technique.

    Really both, of course, but shotgunning caps is not a good troubleshooting technique.
     
    K7TRF likes this.
  2. KM4YTW

    KM4YTW Ham Member QRZ Page

    The audio board usally does a little better with new electrolytics . I usally replace the filter caps on 30 plus years old radios. But anything else has to show a problem before I touch it.
    73
    Km4ytw
     
  3. W2ILA

    W2ILA Ham Member QRZ Page

    You may want to do more research on your particular rig to see if any problems might relate to specific poor quality caps.
    This winter I did recap my Swan MKII power supply after comparing notes with other owners who measured leakage in their original PSU. The amp worked fine but no sense putting extra strain on a 50 year old rig. The Kenwood TS850 had some leaky capacitor problems on the CAR board that do damage to the PCB. My 1984 Nissan has a known electrolytic capacitor problem on the compass PCB. These all relate to how the the components chosen during manufacture have aged.
    Do the research and focus upon known problem areas if there are any.
    73
     
    KB0MNM, K6LPM, N1OOQ and 1 other person like this.
  4. K6LPM

    K6LPM Ham Member QRZ Page

    Yes, do your homework.
    Look for obvious signs of impending doom. Look for bulging caps, consider the caps function and look around where a cap is placed. Is it near excess heat?
    I wouldn't shotgun all the electrolytics just for maintanence sake.
    At least not for the complete rig. Certainly not a s/s rig.
    It depends on the circuit. Obviously the the power supply filter caps are going to be the susceptable and the greatest candidates for routine consumable replacement.
    Why not routinely test capacitors? Is it not routine to check your oil level in your car?
    Well it's easier to check your oil level for sure.
    To fully test a cap usually requires removal out of circuit. That is likely why many folks will just replace them with age, instead of testing. Also, to fully test a cap, especially for leakage at full dynamic load and voltage is beyond most neophyte hobbyists.
    For myself my concerns are aging dried PS filter caps in vintage tube audio gear w/their output transformers being stressed. My vintage gear has a greater chance of catastrophic failure to their vintage iron. The transformers being the heart and soul of the audio gear I regularly service.
    I first determine if the caps are not fully functional by listening for hum and/or looking at ripple on a scope. I check the published ps voltages versus actual circuit voltage I look for bulged deformed caps .
    I know they make specialty test gear that let's you test and measure esr and the like in circuit.
    I am curious how others test caps in circuit especially electrolytics! Educate me!
     
    KB0MNM likes this.
  5. KB0MNM

    KB0MNM Ham Member QRZ Page

    I have diagnosed then repaired a few of those older radios which I knew had old filter capacitors just by listening to the characteristic hum of the audio, and a few that would work for a while until the power supply warmed up ( and these were solid-state rigs- mostly 20 or more years old ). If you were dealing with a GE commercial business-band receiver, I would say replace the two larger electrolytics if you can find values that are close and fit in the radial positions on the PCB ( there were stacked PCBs for tone decodes in these half-loaf-of bread brown boxes ). Since you are working on a Kenwood radio instead, I suggest that you consider doing what I did- look closely at the cost of components that match exactly both the schematic and numbers on the parts ( same maker or get specs and do better within reason ) before removing any parts. Then wait until you have at least two-thirds of the electrolytics needed on-hand before opening the equipment a second time. Finally, I always replaced no more than two at a time- making sure that the polarities were noted on the PCB- not on the solder traces. A good red permanent marker ( unless the PCB is red ) can save a great deal of agony. One thing to remember- getting carried away with replacing filter capacitors can leave you blind to other problems- was the equipment hit with a huge surge that crystallized most of the solder joints or caused a rectifier to fail? Some full wave-bridges will power a circuit well-enough on three good diodes- until the electrolytic caps give out- and a hum is usually evident before failure. Replacing the caps without checking the diodes carefully ( in a bridge is more difficult ) can lead to premature failure of the same capacitor(s). The hum can also be caused by ground loops, but that is a different story- more likely to be seen by musical instrument amplifier repair folks than radio repair ( the audio folks deal with miswired microphone cables and amplifier combinations )- yet your mileage may vary.
     
  6. KA3JRT

    KA3JRT Ham Member QRZ Page

    In any tube audio amp which uses RC coupling to the output tubes, the coupling capacitors are a major problem; if they get leaky, the bias on the tubes will be upset. Many of the "classic"amps used a selenium rectifier in the bias supply, which is another troublemaker. I routinely replace these components in any tube amp that crosses my bench; diodes and capacitors are cheaper than tubes.

    For working on solid state or hybrid rigs, an ESR meter is a good investment. I use the Anatek Blue model, a Sprague Telohmike, and a Sencore LC-53; each one has its merits.
     
  7. KM1H

    KM1H Ham Member QRZ Page

    The Kenwood hybrids from the TS-520 t0 830 series are known for PS electrolytic problems for their tube circuits.
    The early all SS TS-130, 180, etc are known for bad electrolytics in the external PS.

    The TS-930 and 940 have a high failure rate on the AVR board which takes out lots of other parts.

    Those are only from actual experience, Ive no idea about others and my TS-950SD has been fine so far.

    Carl
     
    WQ4G likes this.
  8. W8AAZ

    W8AAZ Ham Member QRZ Page

    I have not had issues with electrolytics in solid state ham rigs. Most of my old radios are collecting dust or used just occasionally, anyway. People go nuts with replacing caps. The problems in old vintage tube gear do not translate to identical issues in solid state gear that I have seen. Old tube radios, I shotgun all paper caps and electrolytics. I have an old KDK rig I use as a monitor and they are supposedly all full of bad caps from reputation. Mine works fine as-is. I have not seen bad caps in Japanese made stereo gear going back to the 70's receivers. Not that there are not any, just I have not had issues. However I did have leaky caps in a very high end exotic US brand of stereo eqt. and I shotgunned alot of caps as they were all the same size, brand as the leaked problem cap. My FT-101 plays fine with what are apparently the original caps. But it is a backup, a for-fun radio. Tantalum caps in solid state are a different matter, they will blow up, smoke, short out and damage stuff. The little colorful ones that is. The milspec and high grade commercial, not so much. Replacing all the caps in a 20 year old Japanese radio seems time consuming, and futile. And alot of the caps you find now are not as good, anyway. Some old tube stuff like broadcast receivers are not fuse protected. Some stuff has over rated fuses. Modern stuff should be fuse protected and if the correct fuse is installed, that should avoid nearly any catastrophe in the power supply. Figure out why the fuse blew, not just stick in another or uprate it!
     
    N1OOQ likes this.
  9. K9STH

    K9STH Platinum Subscriber Volunteer Moderator Platinum Subscriber QRZ Page

    Not amateur radio related: "Modern" flat screen television sets are notorious for electrolytic capacitors going bad after a couple of years. Most people just throw away the set and purchase a new one. However, if one looks at the circuit board, there are going to be a number of the electrolytic capacitors with swollen tops. Those are the cause of the set no longer working.

    Replace these capacitors with higher voltage versions that are available very inexpensive from places like Mouser (many cost less than 20-cents). Total expenditure is normally less than about $10.00 and the television will operate for a long time.

    Glen, K9STH
     
    KM1H and K6LPM like this.
  10. K6LPM

    K6LPM Ham Member QRZ Page

    I have recieved several monitors this way!
     

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