To recap or not to recap...

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

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  1. KM1H

    KM1H Ham Member QRZ Page


    Ive repaired two flat screen TV's for that reason as well as several PC monitors from CRT to flat screen.
    Also had to rebuild one of the several "control" boards in a 06 Volvo S60 which was thankfully totaled about 6 months later by a deer with no human damage. That car turned into a real lemon around 120K.

    I suppose one has to actually turn things on once in awhile to understand the capacitor issue and the specific circuits impacted:D

    Carl
     
  2. KA9JLM

    KA9JLM Ham Member QRZ Page

    Replacing all of the caps is the 12 gauge shotgun method.

    Sometimes only a BB gun is needed to hit the bad ones.
     
  3. K0OKS

    K0OKS Premium Subscriber QRZ Page

    Definitely I replace all the caps with high ripple, like the smoothing caps after the rectifier. Also, I replace any caps next to voltage regulators, transformers, power transistors, or any other sources of heat. These are known causes of capacitor failure, and caps are cheap and easy to replace. Other parts that fail from lack of cap replacement may not be.

    Anyway, don’t ya know, like a car after a new tank of gas, a radio with new caps receives and transmits at least 12% better! :D
     
  4. KE0ZU

    KE0ZU Ham Member QRZ Page

    I've owned and used almost exclusively old to Very old transmitters, receivers, and test equipment for decades, and I have always practiced the "if it aint broke, don't fix it" approach, and so far so good, maybe a half dozen electrolytics, and a fair number of paper caps and composition resistors.

    Thats not to say I haven't done wholesale replacements, but only in 2 or 3 instances.

    NOW, If you are talking about consumer electronics, just start in the lower left, and finish in the upper right corner.:)
     
  5. W1BR

    W1BR Ham Member QRZ Page

    There is no one shoe size fits all answer.

    I have several pieces of high end HP test gear that was made in the 1960s and earlier. Almost all of them have no problems with aging electrolytic caps. And to be brutally honest, recapping a HP 141T would cost much more than what working units are selling for!

    One the other hand, I have a Tek 497P spectrum analyzer and a Tek 2467B scope that both required a complete recapping due to leaking SMD electrolytic and axial lead tantalum caps. In some cases the leakage cause damage to multilayer PCB boards. Even the film caps Tek used for AC line bypassing were cracked and showing signs of stress. If you want to deal with a destroyed A5 board in your Tek 2465B, go for it... used replacements are around 150 bucks if and when they are available. This is gear that sold for megabucks in the mid 1990's.

    I do shotgun vintage consumer radios that have paper caps... leaky audio coupling caps can cause dramatic increases in current drawn by the audio stages; replacing push pull out transformers and power supply transformers can be expensive--most of those sets were not fused! I bought Capacitor Wizard and DE-5000 to test caps for leakage and ESR. After a short period of time I figured out it was just as easy to change all of them if several were showing signs of aging. I use Denon vacuum solder removal tools, so it is a pretty trivial task on end to do that sort of work; but it might be more a daunting for the average ham's workbench.

    Experience is the best gauge for what needs to be done for a particular piece of equipment. Most have track records for failures that are well documented.

    Pete
     
  6. AD5MB

    AD5MB Ham Member QRZ Page

    if it is big enough to make a mushroom cloud, replace it.
     
    KI4AX likes this.
  7. K9STH

    K9STH Platinum Subscriber Volunteer Moderator Platinum Subscriber QRZ Page

    Methinks that anyone who has ever had to clean up a radio that has had an electrolytic capacitor explode would automatically replace all of them in any "boat anchor" unit. Shorted paper capacitors are not usually quite so messy when they go. But, still a pain in the posterior to clean up after one has given up the ghost.

    Since I work on equipment for others, as well as on my own things, and since people want to have the longest equipment life possible, I do replace all paper capacitors, electrolytic capacitors, and silver-mica capacitors that have more than around 75-volts applied. Doing so adds only a very small amount to the bill and having those capacitors replaced is good insurance.

    In high school, the physics teacher decided to have a 1-semester "electronics" class and asked me to be his student assistant. We had a lot of parts from old television chassis, etc. Those parts included electrolytic capacitors that had the wires coming out of the same end. Several of the students (I definitely was NOT one of them) would "appropriate" those capacitors and then plug the wires into an AC mains outlet in a classroom or in the hallway. Usually, between 15-seconds and 30-seconds (just enough time for the person to get away) the capacitor would explode sending bits of metal, paper, and smoke into the room plus a very offensive odor.

    We "knew" who the miscreants were but could never catch them. After the first semester, the school board shut down the class because of the capacitor "bombs".

    Glen, K9STH

     
  8. WA9SVD

    WA9SVD Ham Member QRZ Page

    I have a KnightKit TR-106 (6 Meter AM xcvr.) OTHER than the power supply caps, should I be concerned about replacing other caps? Probably not used since the late '70's.
     
  9. K9STH

    K9STH Platinum Subscriber Volunteer Moderator Platinum Subscriber QRZ Page

    SVD:

    I had to replace several capacitors in my TR-106 that I restored several years ago especially in the AGC circuit.

    Glen, K9STH
     
  10. KD8WU

    KD8WU Ham Member QRZ Page

    Ask 10 hams and you get 12 different answers.

    If this were mine; repairing I would just replace what's bad, project/restoration rig I would lean towards changing them all especially if it's been in storage for several years. https://passive-components.eu/get-the-lowdown-on-shelf-life-and-storage-of-capacitors/

    I've restored a few TS-830's, they have like 104 electrolytic caps. Very first thing, change all the electrolytics, do the band switch repair, replace a coupling, clean and lube pots and switches, and go from there.

    You do have to watch for things like engineering changes where something use to be a disc cap then changed to an electrolytic. Also on the '830 there is one cap that the polarity on the PCB is wrong ( https://forums.qrz.com/index.php?threads/ts-830s-capacitor-polarity.462406/ ) and that wrongness is supported by the polarity on the schematic (when you dig deeper into the schematic you see that that point IS tied to a (-) supply and that cap IS installed properly, although it is opposite the marking on the board.)

    If you're comfortable doing that, go for it. You have nearly 150 small projects. LOTS of before pictures, hand drawings, and notes.


    Have fun,
    Bob - KD8WU
     
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