Debugging battery drain

[ennui2342]

Hi all,

I picked up a lovely non-working Sankyo 515 which, with some effort, I managed to get functional again.

However, my D cell battery is draining to .3v in a couple of days and the clock stopping. Debugging this is a bit beyond my electronics expertise, so is there any tips you could give for me to find the cause? How does one do root cause analysis on this kind of problem?

Thanks for any help.

-Mark

[Johan de Jong]

Hello Mark,
that is a strange problem. I have a 515 and it runs for a few months now on its first battery.
Have you checked that the light is off and the alarm is not engaged?
Is there any dirt from battery leakage that could cause a short circuit?
If not then I would disconnect light and alarm and measure which is still conducting.
It is really unlikely the problem is in the clock movement itself. This is a DC motor that is switched on every minute by a reed relay and that is either conducting or not, not something in between.

[ennui2342]

Thanks Johan. There isn't a short from the light or alarm that I can tell, but it's a good call. I'll disconnect one at a time and try with some new batteries see if I can narrow it down. My version isn't a reed relay - it's two metal contacts closed by a cam. Maybe I should strip that down - there could be dirt between the blades.

[Johan de Jong]

Oops, have to admit that I never actually opened the movement of my 515 and just assumed it would be the same as for a 535 I also own. But looking back at pictures I made when working on this one I see even there my memory was wrong: the 535 also uses a cam operated metal contact, just like you described. I got it mixed up with a Tamura movement that does use a reed relay.

Hope you can find the cause, sorry about the confusion!

[ennui2342]

So I got a power supply for xmas which allowed me to look at what's happening. The motor which kicks the mechanism, draws very little when free from the mechanism, but when engaged with the gears the current draw is 0.25A at 1.5v (nothing else connected like the light or alarm). At that rate it's not surprising the battery isn't lasting long. I've oiled everything I can oil to no improvement in the current draw. Do you think this is the end of life of the little motor and I should give up, or are there other things to try?

[ennui2342]

Finally cracked this one. The metal contacts were the problem - always touching and making the motor work against the mechanism constantly. Somehow they'd got bent out of position and after a lot of fiddling, managed to get them back working against the two cams so that the motor is off most of the time and just knocked on to give the kick.