My (VERY COOL) Digital Clock needs some help

[dbmurphy]

Thanks Tom,

I will report the results of my measuring, and wanted to answer the big question first.

Having sorted this out time to see why the hour digit no longer rolls over- does it roll over when you use the setting switch?

The clock works fine (aside from the non-working segments) and the hour rolls over during setting, AND while time keeping. What is actually happening is that after some time, while the clock is working/heating up..... the hour doesn't roll over any more either on its own, or via the setting switch.

I have a probe, so I can do that testing. What is the best way to check the caps? Scope, DMM, some other cool secret test ;)

Also I really need to identify a replacement Transistor for the SPS6725s

[Old Tom]

I think I would start testing by having a cold clock and turning it on. I would then probe (and note whats happening) the 7410 by the regulator bottom left and the 7490 (tens of hours counter) top right in both setting and run modes. I would then wait for the fault to appear and recheck to see where the count signal is disappearing or counter not counting- to me it is a toss up between the 7490 or 7410 with my money being on the "hot" 7410.

House marked transistors are a pain- I suspect it is an ordinary Silicon transistor (not a darlington) with a gain of about 60-100, most likely NPN and capable of switching 500+mA so I would still go with something like a 2N3704.

[dbmurphy]

That sounds like a good plan Tom - Thanks a lot.

I will start on this right away, so stay tuned for the results. I also greatly appreciate the help with identifying the replacement transistors. I have tried several (darlington) with no Joy, so I'll try the 2N3704, and report back.

Cheers,
Dennis

[jk1966]

Sorry to resurect this zombie thread but here's another of these clocks if someone wants a project:
http://www.ebay.com/itm/321063099100?ss ... 1558.l2649