I have a jameco clock kit, the digits are ghosting - Page 1
Forum section: electronics / repair

author: CoopedUp
author_rank: Regular Contributor
timestamp: May 08, 2020, 12:51:20 am
content: I have posted about this clock before, but it has a new problem. before the clock only displayed intermittently, but now the digits are ghosting so if a digit is supposed to be off its is a dim combination of all of the other digits. any thoughts?

author: greenpossum
author_rank: Frequent Contributor
timestamp: May 08, 2020, 12:58:25 am
content: Model number, pictures, schematics if you have them?

author: George Edmonds
author_rank: Frequent Contributor
timestamp: May 08, 2020, 01:12:33 am
content: HiMy gut reaction is power supply-power supply-power supply, in the absence of further details and schematicsGeorge G6HIG

author: CoopedUp
author_rank: Regular Contributor
timestamp: May 08, 2020, 01:26:35 am
content: its a je725, the picture is back when it wasn't working the first time but it was just a broke trace. it still shows the time its just harder to read

author: floobydust
author_rank: Super Contributor
timestamp: May 08, 2020, 01:54:28 am
content: Ghosting is due to the digit driver staying on and overlapping when the next digit is switched on.I have seen it happen a little with older silicon (1972) MM5314 clock IC's or if the mux oscillator is way too fast. With C2 0.01uF /R9 100k should give about 2.3kHz. You broke a cap before? It might be bad or the trace open.I posted JE-725 clock schematic here:https://www.eevblog.com/forum/repair/jameco-digital-clock-kit-turns-off-then-back-on-later/msg2934256/#msg2934256There is a way to add extra inter-digit timing pause with the MM5314 running nixies. It's in the app notes.

author: WattsThat
author_rank: Frequent Contributor
timestamp: May 08, 2020, 02:33:54 am
content: Is that thing reallyinside a sauna?

author: CoopedUp
author_rank: Regular Contributor
timestamp: May 08, 2020, 07:22:56 pm
content: no its a log home hahahaha

author: CoopedUp
author_rank: Regular Contributor
timestamp: May 08, 2020, 07:24:43 pm
content: Quote from: floobydust on May 08, 2020, 01:54:28 amthis sounds about right, ill look into this

author: CoopedUp
author_rank: Regular Contributor
timestamp: May 08, 2020, 09:05:30 pm
content: I have replaced all the mux stuff and the traces involved and its still not working right

author: floobydust
author_rank: Super Contributor
timestamp: May 16, 2020, 04:05:13 am
content: Is the ghosting happening on all digits and the right digit ghosts over to the one left of it?I think you've got an old clock IC or there is a design issue where the CD4049 digit buffer is slow with the clock IC. It's ion-enhanced depletion-mode PMOS and I have to think if that really works well at all with a CD4049. MM5314 clock IC sources only 0.3mA and sinks 5-25mA meaning it is slow to turn digits off here.I used MOSFETS instead of the TIP31 and get ghosting with an old clock IC but not a newer one.

author: envisionelec
author_rank: Frequent Contributor
timestamp: May 21, 2020, 08:43:38 pm
content: It's likely the MM5314 - and is a typical failure mode that I've seen in the past.

author: floobydust
author_rank: Super Contributor
timestamp: May 24, 2020, 01:11:08 am
content: It's a design quirk of the Jameco clock- to run PMOS into a CD4049UB buffer. With the old PMOS slow edges and mushy logic levels, the CD4049 doesn't clean that up much at all and you get digit driver overlap.With no pulldown it takes forever 400usec to go below 2V.I thought the digit ghosting could be fixed adding by adding six 47k pulldown resistors (pins 3,5,7,9,11,14 to GND). That did clean up the logic 0 level but still a tiny bit of ghosting.Adding the pulldown somehow weakens the output drive so it seems to make things slower (if you go lower value, to say 10k).The MM5314 datasheet is depletion-mode PMOS, +VSS and VDD=0V so I read that wrong - so sink is source and source is sink for output current specs with my NMOS convention I'm used to... I see about 2mA source and 0.5mA sink. With the datecode 1972 IC, about 2usec digit overlap depending on temperature, digits displayed etc.If there was a 4049 compatible IC powered at 15V with better gain, that could fix it too.