Electrolytic Caps
Question for anyone who can answer it…
When electrolytic caps eventually fail due to aging, will they ever fail in a shorted state? That is, a state of being conductive?
This is going back to the Atari 1050 floppy drive I mentioned before. I’ve pulled the mainboard, removed all socketed ICs, and disconnected the electromechanical bits of the board. The short is still there, so I know that the problem is somewhere on the board. As it was working fine the last time I tried it (a number of years ago) I’m guessing that the failure is in a part which degrades with age.
There are some rather large electrolytic caps on here, including some smoothing ones which are (likely) located right after the LM7805 and LM7812. I figure if these have failed shorted, they could cause the problem that I’m seeing.
I’ll probably try pulling them tonight or tomorrow and seeing if the short(s) go away. If so, I might just replace all of them. There are only nine, so it shouldn’t be too expensive to try, and I need to place a Mouser order for other stuff already.
(And no, I can’t find a schematic for it, unfortunately.)
YES. Electrolytic’s especially will leak and or short. I believe its mostly due to the elecrolytic liquid or oil drying up over age. I’ve also experienced caps shorting when the voltage exceeds there maximum rating. But then those were mostly on purpose. They make great firecrackers!
These haven’t leaked nor bulged, and the drive worked last time I tried it. Also, it has been stored indoors since its purchase, so I can’t help but think it’s a problem with something aging. I just wish I could find a schematic for the board.
When electrolytic caps eventually fail due to aging, will they ever fail in a shorted state? That is, a state of being conductive?
Yes indeedy.
Oh, and a “short” that you measure on a board could possibly be normal current flow through some portion of the circuit (resistors, semiconductors, etc). But if you are reading actual zero ohms, it’s probably a short. Desoldering and testing the caps off the board is the only way to be sure.
OK, just read your previous post about a dead short. Definitely some component has failed and power supply electrolytics are usual suspects in these situations. Regulators can fail as well, though they are designed not to fail in such a way, I’ve seen it happen. But first pull the caps and see what you get.
I’ve got the board stripped down to just all the board-level stuff. As it hadn’t been a problem before I’m going to remove the large (I presume power regulation) caps first. I just have a hunch it’s in them. Before the bridge rectifier I see the normal AC, and after there’s about 7VDC. However, both the LM7805 and LM7812 seem to get really hot.
I’ll know more tomorrow… I just got home and it’s a bit too late to work on it tonight.
Oh, and yes. 0-1 ohm, with the meter just beeping solid.
A x0xb0x with one of your panels just hit youtube from AHMW 2007
Ha! Wow! Thanks. :) It’s really neat to see one out and about for once. :D