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A strange problem on a Optel DSM

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A strange problem on a Optel DSM

Post18 Sep 2014, 09:48

Hi friends, some days ago I managed to resurrect an Optel DSM module with the early 5428F oscillator and the flashing display. The watch worked fine for some days, until yesterday it stopped working. I tried to replace the battery, hoping that would be the reason of the problem, but it didn't work. Then, I rotated the crown in the hour setting position, and the module turned on. However, as soon as I released the crown, the module turned off.

That's the issue, basically: if you rotate the crown to the hour setting position, the module works fine, but if you release the crown, it stops working.

I don't know why that module has this problem, honestly. It worked fine for a few days and kept perfect time, until this issue happened. Do you have an idea about the reason, friends? And is there someone, besides Greg Zanoni, who could try to fix this module? So, as soon as I got a good budget, I could send it to someone that could fix it for me. I'd like to have a working module with a flashing display in my collection, and unfortunately I don't have the proper knowledge nor tooling to tinker on these modules, the only thing I can do is cleaning and straightening the contacts.

Thank you for everything.
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Old Tom

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Re: A strange problem on a Optel DSM

Post20 Sep 2014, 16:53

I fished out the circuit diagrams/block diagrams for the SCL5425/SCL5428 combo and stared hard at them for quite a while trying to imagine where your failure could be. I came to the conclusion that the internal minutes setting logic is not functioning correctly and is stuck in a half way state between working/not working. When you engage the hour setting logic you completely bypass the minute set/minute counters and so the display appears. I suggest you have a close look at the selector switch contacts and the protection resistor associated with the switch (small SMD resistor of about 10 meg ohm value).
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Re: A strange problem on a Optel DSM

Post20 Sep 2014, 17:01

Old Tom wrote:I fished out the circuit diagrams/block diagrams for the SCL5425/SCL5428 combo and stared hard at them for quite a while trying to imagine where your failure could be. I came to the conclusion that the internal minutes setting logic is not functioning correctly and is stuck in a half way state between working/not working. When you engage the hour setting logic you completely bypass the minute set/minute counters and so the display appears. I suggest you have a close look at the selector switch contacts and the protection resistor associated with the switch (small SMD resistor of about 10 meg ohm value).


Thank you Tom, I sent you a PM about the problem. I have a couple of spare modules (5428 and 5424F) although they don't work very well (their contrast is very faint). Perhaps they could come in handy to repair this one.

I'm absolutely not an expert on these watches, nor I know how to use professional tools, so I couldn't think about anyone else besides you who could help me to repair it. :-)
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azimuth_pl

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Re: A strange problem on a Optel DSM

Post22 Sep 2014, 17:18

In many cases the Optel modules are fixable with new resistors or other small components that have aged beyond reason.
Old Tom, would you mind posting those diagrams? SCL stands for?
"The first and still only LED watch maniac in the East Block" - www.crazywatches.pl
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Re: A strange problem on a Optel DSM

Post23 Sep 2014, 12:14

azimuth_pl wrote:In many cases the Optel modules are fixable with new resistors or other small components that have aged beyond reason.
Old Tom, would you mind posting those diagrams? SCL stands for?


That's great, so my module isn't lost forever then... Unfortunately I'm not able to repair them by myself, but I hope that there's someone who could help me (as soon as I have a good budget that allow me to pay them for the job, of course). ;-)
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