Saturday, July 25, 2015

Clock repair

Just a quick repair post today. The clock/timer on our stove has been starting to make a low hissing/squealing noise that was very quiet but sounded a little like the gas was on, which makes me nervous, and also the display has been ghosting.




This was pretty clearly a bad capacitor issue, acting exactly like the filtering was going out on the power.

I took a peek at the caps under a magnifying glass and discovered that one of them had some splooge around its base. I desoldered it and put it on the parts tester (I love this thing, it's ridiculous how useful it is).



It's supposed to be a 47uf cap, at 50v, which should have a 0.5 ohm ESR. It's measuring 150 ohms and only 38uf.  So there's yer problem.

I only had 25v caps in the bin but I tested the circuit and only saw about 2 volts across the cap so I just went for it, and it's fine now.  Gotta love the easy ones.

The weird bit is that these were 105*C Nippon Chemicon caps. The stove is 20 years old at this point but I'd have thought that in a relatively benign environment like this they'd last longer than that.

The vacuum fluorescent display is getting a little weak. When it decides to go, I guess that'll be an opportunity to build a whole new unit.  Maybe I'll put an ESP8266 in it and have it get the time from an NTP server :)

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