All in one rev 4.2 clock issue

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2 months 1 week ago #12646 by PhillV_76
Hi all,
Started a all in one clock a while ago, due to many commitments never got round to finishing it.
Have started back on it again. My issue is the following:
At start up, tubes count from 0 - 9 as expected, hold button down @ 88:88:88 holds for a sec then counts what I guess is voltage reading is 02:46:00 then goes back to 88:88:88 for approx 5 seconds then display is all blank.
Tried pressing button incase tubes were blanking, no change, tried resetting, goes through same start up and back to blanking. Removed LDR incase that was an issue, no change.
Checked HV , but it reads 11.2 V no high voltage, when I check HV while tubes are counting, all tubes go blank and still read 11.2 V. Have tried several different power bricks from 9V to 12V , there are no solder joints, no shorts etc, is it possible something has just worn out over time.

Thanks.

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2 months 1 week ago #12647 by Ty_Eeberfest

PhillV_76 wrote: Checked HV , but it reads 11.2 V no high voltage, when I check HV while tubes are counting, all tubes go blank and still read 11.2 V.
Thanks.


I could read that a couple ways - let's make sure I understand. If you can see the tubes counting then obviously the HV is good at that time. So are you saying that if you try to read the HV while the tubes are visibly counting the HV dies and the tubes go out as soon as you touch the meter probes to the board? But if you don't try to read the HV then the tubes do the whole counting and calibrating routine properly and then blank out when it switches to time display?

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

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2 months 1 week ago - 2 months 1 week ago #12648 by PhillV_76
After another reset attempt I'm now reading high voltage perfectly which tubes are counting and calibrating, but then after calibration they still go blank and I get 11.2V again ???
Last edit: 2 months 1 week ago by PhillV_76.

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2 months 1 week ago - 2 months 1 week ago #12649 by Ty_Eeberfest
The HV dying when you try to read it seems really strange. This may be a dumb question, but do you have your board standing up on screws / stand-offs so the solder side isn't touching the table? And if it is touching the table are you 100% sure there is nothing conductive (cut off leads?) underneath the board? My reasoning is that when you touch the test point the board is pressed down a little bit.

It would be interesting to know if the MOSFET gate drive (the "HVD" signal on the schematic) is going away when the HV dies. HVD can be checked at pin 1 of the MOSFET or pin 15 of the Atmega. Ideally you check it with a scope and see a continuous string of pulses when it's running and ground when it's not. If no scope available you can try reading it with your meter. Probably something like 2V when running and a pretty solid 0V when not running.

Look into it later when the dust is clearing off the crater.
Last edit: 2 months 1 week ago by Ty_Eeberfest. Reason: minor typos

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2 months 1 week ago #12650 by PhillV_76
Hi, the board is on standoffs so it's raised up, I've checked the underside of the board and it's clean, I'll try checking the pin with my meter shortly and let you know what it reads.

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2 months 1 week ago #12651 by PhillV_76
Just checked across pin 15 on atmega, I get 3V while in calibration mode solidly, after button press it drops to 0.01V

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