Capacitor Question.

[KG4CGC]

Can a bad cap act like a short?

[VE7DCW]

A bad capacitor can become shorted......... I have seen it in electrolytics and in ceramic disc types in B+ circuits in my Yaesu FT 101ZD......... all age related,that I need to acquire a re-cap kit for that transceiver :yes:

[KG4CGC]

Thank you. Have a radio that suddenly makes the PS go into protection mode. It's an old radio so yeah, it's probably age related.

[N8YX]

Tantalum capacitors love to fail in "shorted" mode, often taking out associated circuitry. If your rig incorporates them - typically as TTL supply de-spiking and post-regulator filtering - I would look into replacing the lot.

[K7SGJ]

The easiest first place to start, in my opinion, is to look at or disable the overvoltage protection circuit found in the output circuits. The most simple, is a zener that is reverse biased right across the out put. If that goes TU, it will act like a short on the output of the supply, and "crowbar" the supply into failsafe, causing the supply to foldback to near zero output. If the supply is fairly old and you plan to keep it and use it, I agree with the others and shotgun all the elect and tants. Once done, be sure to clean, exercise, and readjust any internal controls. They will affect output, meter calibration, and any safety circuits.

[w0aew]

Can a bad cap act like a short?

Like a short what?

[suddenseer]

May your electrolytics never go dry. When it comes to the old stuff, I always re-cap before re-tubing. Except for the boob tube.

[HUGH]

Some of the "suppressor" caps consist of a resistor in series with a cap, these generally look like 22 to 220ohms when they short. The plastic film types usually melt and shrink locally so no apparent short but when they do fail it's quite entertaining watching them gradually turn into a wrinkly blob (no, not that).

[ka8ncr]

Tantalum capacitors love to fail in "shorted" mode, often taking out associated circuitry. If your rig incorporates them - typically as TTL supply de-spiking and post-regulator filtering - I would look into replacing the lot.

I recall many a tantalum cap doing just that in the early 90's. Used across the power supply rails, it usually caused fire and smoke.

[AA1LL]

Yes any type capacitor can fail shorted but you can usually force them (or any shorted failed part) open by putting enough current through it. It's not pretty but it works.

[WØTKX]

https://www.youtube.com/watch?v=gouMnKavDI4



https://www.youtube.com/watch?v=gouMnKavDI4

[kb2vxa]

There is a way to clear shorts in electrolytics BUT there is a trick to it and it only works SOMETIMES. That's why I never bothered, replace it and you have a NEW electrolytic. (;->) As far as other parts are concerned forget it, force enough current through a transistor and you let the magic smoke out of just about everything if it doesn't explode in your face first. I had that happen quite accidentally I must say, getting hit with bits of epoxy traveling at extreme velocity is just a BIT painful.

Oh you can get even better fireworks putting things in the microwave that really don't belong there, a CD is about the most spectacular of all. Just be sure to put a small glass of water in with it to absorb excess microwave radiation so you don't burn out the magnetron and no more than 10 seconds, if the plastic melts you have a small disaster on your hands. The stink is just awful and just when you think it's gone you have another thing coming, coming every time you turn on the microwave for the next month, it's baaaAAAaaack. It's bad enough if the wifeoid catches you putting junk in the microwave, you may talk yourself out of trouble, but if she discovers her microwave is haunted by the ghost of a dead CD she'll KILL you!

[KG4NEL]

Used to scare the crap out of people in high school discharging their 1 farad car stereo caps with a screwdriver... :)

[kb2vxa]

At the now defunct RCA Institute we'd charge HV oil filled caps and toss them, HERE, CATCH! Leaving them charged on the shelf was fun too, until the instructor made us wrap bare wire across the terminals after HE got zapped... heh heh heh. Periodically he'd remind us, "Get your kicks from sex, NOT electricity." Firkin killjoy.

The bang from a 1F cap is nothing compared to the fireworks the Chief Engineer on my last job made with his jockstrapped test jig. We were making inductors for electric railroad locomotive power inverters rated at 2,000 amperes and he was looking for a way to test inductance with that crazy DC bias. Stan, you MUST be kidding! He wasn't and built some crazy contraption with a huge capacitor bank and the mother of all SCRs all strapped together with copper bus bars to zap it with a pulse, how he planned to measure inductance was all Greek to me, literally. After several mean explosions that scared the shit out of everybody and the same number of VERY expensive SCRs he gave up. Meanwhile I was running an experiment of my own, I found inductance measured at 1KHz didn't change a bit from 0-200ADC so the whole lot ended up on the Wayne-Kerr analyzer using 1KHz @ 1mA 0DC the easy way. Then the plant manager came up with one crazy mock on his last name that cracked everybody up, "What is a Plevis and what useful purpose does it serve?"