Clock problem

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5 years 5 months ago - 5 years 5 months ago #3220 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: 5 years 5 months ago by kay486.

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5 years 5 months ago #3224 by Nomotron
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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5 years 5 months ago #3226 by cf8m
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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5 years 5 months ago #3228 by kay486
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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5 years 5 months ago #3229 by Nomotron

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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5 years 5 months ago #3230 by kay486
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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5 years 5 months ago #3231 by Nomotron
Sounds like the K155 then. There really isn't much else in the design which could cause the symptom IMHO.

Jon.

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5 years 5 months ago #3232 by Ty_Eeberfest
tl;dr version: I agree with Jon - replace the chip.

Verbose version:
Clearly somehow the "6-bus" is finding a (relatively) high resistance path to ground that shouldn't be there. A couple things that might be interesting to know but most likely are just wasting time: 1) What happens if you remove all but one tube - is there still a ghost 6 on the remaining tube? 2) What happens when a 6 is supposed to be displayed - does it look normal?

Look into it later when the dust is clearing off the crater.

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5 years 5 months ago #3235 by Dr pepper
Run the clock with the driver chip unpluggeg or unsoldered, if no6 still shows its a leak on the board, if all is blank then its likely to be the chip.

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5 years 5 months ago - 5 years 5 months ago #3271 by kay486
Ok, ill finaly have the time to mess with it. Pete suggested that i should try cutting the output for the 6 cathode first to see if the problem remains. It seems like a logical thing to try out before changing the whole ic.
I just need somebody to confirm wich lead is the 6 out. Im always wondering how the schematics describe the ics, like if its shown from top or from the bottom.
As i think, the 6 out would be the pit that is third from the bottom on the left side (just look at the attached picture to see what i mean)

and by the way, is the MH74141 (by tesla) the same as the K155ID1? Does somebody have any experience with the tesla one, (because it would be much easier for me to get new ones)?


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Last Edit: 5 years 5 months ago by kay486.

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