Fixed a clock radio, but is capacitor choice ok?

[mc349iii]

I've got a 20+ year old Hitachi Clock Radio which is mains powered.   I had noticed that the LED 7 Segment digits were becoming dim and then they started to flicker.   

Opened it up and it has a transformer based supply and I instantly noticed a bulging capacitor which seems to be connected across the supply feeding the main IC  (it only has the one!).    It was 15V 440uF,  of course I didn't have that value,  but I measured the voltage across the old one and it was 9v so I instead I picked the nearest I had which was a 10v 220uF to try and that seems to have fixed things just fine.     I clipped off the old cap's leads and soldered the new one directly onto the old leads, so I didn't even need to remove the board.  So a very easy fix.

Does my choice of cap pose any risk?  Should I be ordering a closer match to the original?    Will it just be a longevity issue?

[tunk]

The measured 9V might be an average, i.e. the max could be more than 10V.
What's the voltage with the new capacitor?
A worst case would be that it blows up. If you have an oscilloscope you could check.

[NivagSwerdna]

10v 220uF

Your device probably was failing due to its actual capacitance reducing to a level it could not function correctly.  You clearly have found a level that works but with reduced headroom so as you say the longevity could be an issue.  Normally you would aim for a value that had the same capacitance and equal or greater voltage rating.  16V 470uF would be ideal and cheap on ebay.  If you exceed the voltage rating on a capacitor all bets are off and it could fail quickly... so "do you feel lucky punk"?

[madires]

I'd go for a 16 or 25V 470µF electrolytic. When replacing filter caps choose one with the same capacitance or little bit more. The voltage rating should be 20% higher or more than the maximum voltage.

[mc349iii]

I do have a scope, but tend to shy away from waving it anywhere near mains powered stuff.        I tend to stick with Arduino USB battery bank powered things.

[mariush]

I agree... go for higher voltage rating, 16v or 25v should be fine.

As for actual capacitance, I doubt the circuit is very picky..  470uF should be perfect, but it will probably work with as little as 270-330uF just fine.

You could also parallel 2 capacitors ... 2 in parallel means double capacitance, same voltage rating.  2 in series means half capacitance, double voltage rating.

[mc349iii]

Thanks all.   Just ordered a 16V 470uF replacement.  20p each from eBay (in a pack of 10).