Clock problem

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7 years 1 week ago - 7 years 1 week ago #3220 by kay486
Clock problem was created by kay486
Hi there,
i had this clock from PV electronics for about a year. I have decided to change the tubes from Z566M to ZM1040 but i must have messed up something on the circuit so now, i have the ghost number six displayed on all of the tubes, no matter whats on the rest, even when there is no real six displayed anywhere. Its less bright than the normal numbers, but its brighter than normal ghosting (the clock had tiny bit of ghost numbers since it was new, but its almost invisible, andthe tube gets the ghost number only from the tube after it to the left, thast due to the multiplexing i suppose and ist not a big problem)
The six is displayed even when im in the menu and there should be completely blank tubes.
So id like to ask you, does anybody have any ideas what could be wronk with the clock? Have i shortened something i cant see?

Look at the attached .pdf file for the schematics. The photo shows the clock in while its in the menu and the minutes should be completely off.

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Last edit: 7 years 1 week ago by kay486.

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7 years 1 week ago #3224 by Nomotron
Replied by Nomotron on topic Clock problem
I imagine one of the output transistors in the 74141 driver chip (IC4) has started leaking. Try replacing the chip.

Jon.

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7 years 1 week ago #3226 by cf8m
Replied by cf8m on topic Clock problem
HI i would have a good look to see if their is any solder bridges first B) or you could send pete a Email i have just put one of the kit together useing the same type of tubes and it works fine

regards
steve

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7 years 1 week ago #3228 by kay486
Replied by kay486 on topic Clock problem
Yeah, i already spoke with pete about this yesterday, but he was too busy to look more into it, so i posted it here in the meantime. I too though that the 74141 would be the problem, but he said its unlikely. The clock i have uses the russian K155N is it possible that these are less reliable?

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7 years 1 week ago #3229 by Nomotron
Replied by Nomotron on topic Clock problem

kay486 wrote: Yeah, i already spoke with pete about this yesterday, but he was too busy to look more into it, so i posted it here in the meantime. I too though that the 74141 would be the problem, but he said its unlikely. The clock i have uses the russian K155N is it possible that these are less reliable?


Don't think there's a general reliability issue with the K155, but individual chips can always fail. In fact the Russian chips are generally held to have higher breakdown voltages than genuine Western 74141 and therefore perform better with respect to ghosting.

A couple of other possibilities... It's possible the symptom could be created by a solder bridge which somehow creates a high resistance path from the cathode 6 line to ground or some other current sink.

The other idea is that the new tubes are more sensitive than the old ones, and there always was some leakage on cathode 6, but only now can you see it. Can you change the tubes back to the old ones and see if it goes away?

Cheers,

Jon.

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7 years 1 week ago #3230 by kay486
Replied by kay486 on topic Clock problem
I checked the board for any bridges and found nothing, also its not a problem with the tubes, i tried out several tubes with the same rsults, in fact you can see in the picture one ZM1040 tube on the hours position, the rest are Z566M.
The possible bridge was my first guess, but as i said, i found nothing, and also i really dont see a reason a bridge would occur while i was changing the tubes. I have to admit the clock was powered so idk what i should have shortened with my hands. That would leave only one option, something is permanently demaged due to some shortage i caused.

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