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Capacitor Polarity

I was having trouble with CDs skipping on the factory radio in my 94 Trans Am. I pulled the radio out of the car and took it apart, intending to clean the lens and adjust the tracking (if needed). While it was apart I decided to check ESR on the electrolytic capacitors. On the (Sony) CD main control board there are half a dozen 4.7uF @ 6.3v cap's. The ESR on all of those measured quite high, so I want to replace them. The problem is that I can not tell which lead is + and which is -. There is a polarity stripe on one end, but both leads come out on that end. These look like a black plastic surface mount tantalum chip except that instead of having a wraparound terminal on each end, there are 2 wire leads coming out of one end. They are actually made up of a radial lead aluminum can inserted into a hole drilled into the cube shaped plastic body. I pulled the can out of the body on one of them, but there are no markings on the can to indicate polarity. How can I determine the polarity of the capacitors? The level of disassembly needed to get at these parts does not lend itself to powering the unit up and measuring voltage accross the cap's.

Also, Are there any adjustments on this particular CD transport? I do not see any pots.

TIA, Paul

Reply to
Paul
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At least some if not all of those caps should have the negative leads at ground potential, so use your multimeter on Ohms or continuity setting and find out which lead is negative that way, no need to power the unit up. Or simply visually trace the cap lead to the ground plane on the PCB.

Morse

Reply to
Morse

...How can I determine the polarity of the capacitors? The

Thanks, But none of the 6 caps of this type seem to be grounded on either side. I guess I'll try to find non-polar caps small enough to fit (3mm x

5mm), unless I get other suggestions.

Paul

Reply to
Paul

What do you consider to be a "high" value for ESR on these caps ? 4u7 at

6.3v will likely have a correct ESR value of 15 ohms or more. You should also be careful when replacing small electrolytics like this, that you only replace with exact like for like. On many Sony HiFi CD players from a few years ago, the CD servo board had several small caps of very similar description to the ones you have there. One in particular used to leak. If you tried to replace these caps with anything other than the original low voltage surface mount types, the servos would never work again.

Arfa

Reply to
Arfa Daily

Should not matter. Measure each lead, using ground as a reference. The more positive lead is the positive side. Or, the more negative lead is negative side. If one is pos. and one neg., then pos. is pos.

Hope that helps.

Reply to
Charles Schuler

The ESR measures 50 ohms on my meter. Typically fresh 4.7uF caps measure about 2 ohms on my meter.

Thanks for the warning that generic replacements might cause trouble. So far, no luck finding original type replacements from Mouser, etc. Don't suppose you can point me to a source???

Paul

Reply to
Paul

Arfa

Reply to
Arfa Daily

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