• You can now help support WorldwideDX when you shop on Amazon at no additional cost to you! Simply follow this Shop on Amazon link first and a portion of any purchase is sent to WorldwideDX to help with site costs.

Talk about replacing your dried out capacitors

Robb

Honorary Member Silent Key
Dec 18, 2008
11,432
3,651
323
Silicon Valley CA, Storm Lake IA
Local new radio operator asked me to fix his first sideband radio. A Uniden PC 244, which is similar to the Cobra 146 GTL which he bought from a flea market for $35. He was told that it worked. It did, in that it turned on, received, and could transmit. However poorly. In fact, all modes had a nasty oscillation heard when TXing.

So I throw it on the bench and open it up and then test it for vital signs. Driver/final bias were waaaay off scale and couldn't be adjusted to specs. The loop osc freq's varied greatly from ch 1-40. At first I suspected that the AN 512/balanced modulator IC had failed, so it was replaced. No dice. So I then suspected that the mic amp was oscillating due to a bad cap. SO, I started checking caps . . .

Hmmmm; this cap is showing half its rated value. And this one is one third its value. Wow; this next one shows up as a diode. The next shows up as two opposing diodes! So I replaced each one that showed up bad - which was all the ones I'd pulled and checked so far. Uh oh; how far is this going to go? What I found was unlike any radio I've ever recapped.

With the exception of just three caps out of thirty-four, they were ALL bad. Regardless of their rated voltages too. Most often I have seen that the 10v caps are the first, best suspects for failure. But not this time; regardless of voltage they were testing bad. Surprised that it worked at all, given what I'd found. Even more surprised that this condition didn't take out other parts too.

The nasty oscillation went away when I found and replaced a cap that was so dried out that it read 'open'. Two hours later it was finished. Then the entire radio was aligned to specs.

Have a similar experience?
 
Last edited:

In this case thinking it was the environment that it was used/stored in that made these caps as bad as they became in the radio that I'd made this thread about.

Its not as thought it was the age of the radio so much that I blame for this situation. Though age is a big factor too - then made worse by the environment conditions. I have my own PC 244 that I'd refurbished awhile back, that was mfd in the same time frame, and it had only a few bad caps. I don't see how using/not using a radio affects the amount of electrolyte in the cap, as much as great environmental shifts in temperature and humidity that have the mechanical means to deplete the electrolyte volume.

Thoughts?
 
Last edited:
I don't see how using/not using a radio affects the amount of electrolyte in the cap, as much as great environmental shifts in temperature and humidity that have the mechanical means to deplete the electrolyte volume.

Thoughts?
It is not so much the amount of electrolyte that changes, but rather the condition that it is in.
By using the capacitor you are keeping the electro-chemical purpose of the electrolyte in action, if they sit for a long enough time with no voltage/use the internal constituents of the chemicals used can change.

Electrolytic capacitors are different from other capacitors. They rely on an oxide layer that forms on the aluminum plates as an insulator to handle the high voltages - the oxide forms from current passing through the electrolyte. When an electrolytic capacitor sits for extended periods of time, that oxide layer slowly disappears, dramatically reducing the voltage capacity.

I cannot recall any suggested shelf life numbers, but six years is unlikely to be a problem; 20 to 30 years IS a problem. I suspect 10 years sitting is enough to begin causing some problems with a few individual components. Just firing up a device every five years or so is probably enough to keep the capacitors formed, but I'm mostly guessing on that.

"New" capacitors that are "old" can be reformed before being put into use, but if they have gone bad from sitting in an existing circuit, applying power can both damage the caps (even exploding them in rare cases) and other items in the circuit. A lot depends on just how much of the oxide is still there. If the caps are not too far gone, I have seen cases where the circuit had initial problems when first put back into use, but the capacitors actually reformed themselves before anything else was damaged. In these cases, multiple power cycles with very short 'on' times can be beneficial in trying to bring things back to normal.
source: tivocommunityDOTcom/community/index.php?threads/do-capacitors-go-bad-if-unused.491454/

I would agree that humidity can wreak havoc on radios, as long as the radio is in use though I think the capacitors would hold up well, even in a humid climate.

Caps from the capacitor plague expanded and popped (& lost electrolyte) in short order because of a certain (undisclosed in factory) inhibitor being left out of the (stolen) formula.
Not all capacitors will swell when they fail, but it can happen to just about any electrolytic cap (even the best of quality) after enough time.

I have had a few mobiles CB's come back to life and function properly after a simple re-cap.
 
Last edited:
  • Like
Reactions: Robb
I have had caps blow up inside of the older tube rigs like my gemtronics gtx 5000. Its most always the ac caps that go first. So i just replace them all before i even power up the radio.
 
  • Like
Reactions: LeapFrog
It is not so much the amount of electrolyte that changes, but rather the condition that it is in.
By using the capacitor you are keeping the electro-chemical purpose of the electrolyte in action, if they sit for a long enough time with no voltage/use the internal constituents of the chemicals used can change.


source: tivocommunityDOTcom/community/index.php?threads/do-capacitors-go-bad-if-unused.491454/

I would agree that humidity can wreak havoc on radios, as long as the radio is in use though I think the capacitors would hold up well, even in a humid climate.

Caps from the capacitor plague expanded and popped (& lost electrolyte) in short order because of a certain (undisclosed in factory) inhibitor being left out of the (stolen) formula.
Not all capacitors will swell when they fail, but it can happen to just about any electrolytic cap (even the best of quality) after enough time.

I have had a few mobiles CB's come back to life and function properly after a simple re-cap.
Great info and thanks for that link. No doubt that when a cap has gone too far it might not ever come back. Rather not bother with any possibility for a future failure point and just change them all out.

Back to the bench to recap two Cobra 2000's, Emperor 5010, PC 66, and a Galaxy 88 . . .
 
  • Like
Reactions: LeapFrog
Calculating costs using shop rates for time and parts, how much did it cost for this $35 "special"?
It was for a local/new operator. I did the job for free. He needed a break. Guy has two jobs, two kids, and too much to do. He and his wife both dig the radio now, It sounded superb on his end and mine on SSB when we first talked today. These PC 244's are very stable radios; one of the most stable I've seen and worked on.
 
Last edited:
  • Like
Reactions: 2RT307 and kaos513
It was for a local/new operator. I did the job for free.
Good for you. I just hope you are able to impart to the owner how much time and effort went into getting that radio to a usable state. Too much disrespect out there by appliance operators. That $35 radio will cost more than the purchase price if they are to be used on a daily basis.
 
Last edited:
This is the first thing I do if the radio is 10 plus years old. No sense chasing voltage differences.
 
This is the first thing I do if the radio is 10 plus years old. No sense chasing voltage differences.
Dunno about 10 year old radios. But most of the best, classic, and desirable radios are almost 35-40 years old now. I can tell you for a fact that I've never been wrong by recapping them. Because I go thru the caps I've taken out and tested them, and many are no longer holding their values and some have failed outright. Don't know of any 10 year old radio that I worked on that needed recapping. That is a Snake radio maneuver - lol.

Klondike Mike:
I had the extra caps for repairs, so I had the supply. I took two straight hours to do that job; then another 40 min to align. Any shop would have charged ~$80 for recapping/parts included plus another ~$50 for the alignment for a SSB radio. That would be my price - anyway.
 
Last edited:
Ouch Rob.... LOL . I am just a hobbyist, not a tech. I too mostly repair the 80s and 90s vintage Cobra/Uniden that need new caps and various other wear items. I do a lot of mobile rigs from dump trucks, semi and farm tractors in my area that take vibration, big temp swings and seasonal powered off time.

I have found myself chasing voltages down the rabbit hole too many times to find cap problems. I make it point to inform my customers and or friends that an $18 upgraded cap kit will be a benefit for longevity and performance. Do I force on them? Of course not. But highly make my point if the radio is 10 yr or plus older in the conditions they use them.

I should mention I live Iowa, the corn/bean state. Much implement equipment out here, farmers and such.

Also, did you know it is highly recommended that you should replace your 110v outlets every 7 yrs? NEC, ( National Electrical Code), suggestion but not required. Just my $.02
 
Ouch Rob.... LOL . I am just a hobbyist, not a tech. I too mostly repair the 80s and 90s vintage Cobra/Uniden that need new caps and various other wear items. I do a lot of mobile rigs from dump trucks, semi and farm tractors in my area that take vibration, big temp swings and seasonal powered off time.

I have found myself chasing voltages down the rabbit hole too many times to find cap problems. I make it point to inform my customers and or friends that an $18 upgraded cap kit will be a benefit for longevity and performance. Do I force on them? Of course not. But highly make my point if the radio is 10 yr or plus older in the conditions they use them.

I should mention I live Iowa, the corn/bean state. Much implement equipment out here, farmers and such.

Also, did you know it is highly recommended that you should replace your 110v outlets every 7 yrs? NEC, ( National Electrical Code), suggestion but not required. Just my $.02
Didn't mean anything by it, just saying that a 10 year old radio isn't really a candidate 90% of the time. If anything, it may have a single bad cap due to factory defective cap. I would try to isolate a problem to a circuit and then check the caps with a tester first rather than selling them a cap job. Would think that a lot of the problems you might face would be due to poor solder joints, since you are dealing mostly with lots of vibrations.

Not a tech either - just a hobbyist that fixes and aligns radios for fun and very little profit - if any.

Iowa - eh? Family still has a farm in the NW corner near Storm Lake. Beautiful farm country. Been there more than a few times on family business.
 

dxChat
Help Users
  • No one is chatting at the moment.
  • dxBot:
    Tucker442 has left the room.
  • @ BJ radionut:
    LIVE 10:00 AM EST :cool:
  • @ Charles Edwards:
    I'm looking for factory settings 1 through 59 for a AT 5555 n2 or AT500 M2 I only wrote down half the values feel like a idiot I need help will be appreciated