Elektronika 7 (soviet clock) stuck - does not advance

Thread Starter

kriksis

Joined Feb 23, 2016
27
Hello!

Far fetched, but maybe someone is familiar with electronics from this era and geographical origin? Also, sorry if I've opened this in wrong forum.
Last year purchased an Elektronika 7 wall clock - sort of vacuum tube clock made in early 90s. When I got it, opened it up, cleared the dust and was checking for any obvious issues - found none. Caps looked good, boards and ICs all in one peace and no burn marks to be found. Crossed fingers and plugged it in - all worked like a charm. There are three buttons on it - all worked correctly.
Then it sat until last week. There is an battery compartment, where if you supply 9v, the clock remembers the time when turned off. I wired in a 9v battery and hooked it up in my shed so that when lights are turned on, the clock also turns on. First three days it worked fine, only issue was that it had been slow and was few minutes behind each day (I thought it's an old clock from ussr, - this to be expected). Also I suspected, my 9v battery maybe not sufficient since originally it required 6 x 1.5v C type. Then came the yesterday - I turned on the lights, clock turned on also and time it was showing was few hours off. After about 15 minutes I noticed, it was not advancing - minute counter stayed at one value. I pressed the button for minutes - nothing happened. Hours also did nothing. The third button resets the minute counter to zero - pressing it did that. But that was the last successful input I got. Between there is a separate nixie tube, which blinks 'counting' seconds - that does not blink anymore. Except, when pressing and holding the minute reset button - then it sort of lights up, and stays lit until released.
Unfortunately I did not have time yesterday to check anything and was hoping to gather some materials today, before trying to diagnose it tonight, but internet remains silent about such issue - at least with my google kung fu.
I'm planning, to first, remove the battery I put in place. Then check the input buttons with multimeter - maybe something is stuck and being pressed all the time, blocking the clock from advancing.
Other than this, it is made with some logic chips (which are beyond me to diagnose) and a quartz crystal for the clocky bit.
Basically my question is (I apologize if this is long winded for this forum) - has anyone had to deal with such clock? Are there usual suspects? Could I have broken it with the inappropriate battery?
Adding a picture with the clock (source - google)

Best regards
 

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Yaakov

Joined Jan 27, 2019
3,737
Just a note: the capacity of 6 C cells is enormous compared to a PP3 style 9V battery which is effectively 6 AAAA cells.

Perhaps the battery is just dead and the clock won’t run without it.
 

Thread Starter

kriksis

Joined Feb 23, 2016
27
Just a note: the capacity of 6 C cells is enormous compared to a PP3 style 9V battery which is effectively 6 AAAA cells.

Perhaps the battery is just dead and the clock won’t run without it.
Thanks for info! That will be the first thing I will do - remove it and see if it helps. The clock runs without battery - just when turned off it resets to 00:00. But maybe there is some logic verifying if battery is in fact present.
 

Yaakov

Joined Jan 27, 2019
3,737
Thanks for info! That will be the first thing I will do - remove it and see if it helps. The clock runs without battery - just when turned off it resets to 00:00. But maybe there is some logic verifying if battery is in fact present.
It’s certainly the first troubleshooting step I’d take. I hope it’s that simple. Though from what you say, it would have to be the battery has enough left to maintain the time but somehow not run the clock (circuit) and when the battery is present the clock doesn’t use the line voltage to run it. An odd set of things, but first things first…
 

Yaakov

Joined Jan 27, 2019
3,737
One nore thing: if the battery doesn’t prove to be the culprit, the next thing i would do is find the crystal oscillator and check/replace any caps actually in that circuit.
 

Thread Starter

kriksis

Joined Feb 23, 2016
27
One nore thing: if the battery doesn’t prove to be the culprit, the next thing i would do is find the crystal oscillator and check/replace any caps actually in that circuit.
The crystal sounds like a possible cause, yes. Just that I'd expect it to do weirder things, than to simply refuse any inputs from buttons. Some sources have documented the replacement of it, but then it behaved different than what I am experiencing.
Regardless, thank you for the advice! Removal of battery will definitely be the first thing I do. (It's behind the backplate, thus I did not do that already)
 

Thread Starter

kriksis

Joined Feb 23, 2016
27
One nore thing: if the battery doesn’t prove to be the culprit, the next thing i would do is find the crystal oscillator and check/replace any caps actually in that circuit.
Hello! Well, so far I've done:
1. Removed the battery
2. Changed the only electrolytic capacitor on the logic / Crystal board
3. Changed the cap after the rectifier, for good measure
4. Tapped on all the ICs
5. Checked for any suspect connections and tried refitting connectors
6. Inspected all the pcb lines and components visually
Nothing has forked thus far. Except got some different behavior - now the second indicator does not come on no matter what I press. And hour section is stuck at 01 instead of 00 as it was before.
Next, I would like to change the crystal. Unfortunately I don't have an exact one, - could I use other crystal from, like generic wall clock?
I assume they all oscilate at the same frequency, no? Thing I'm not sure about is the other parameters, like voltage needed to make it work. Van it differ?
 

Ramussons

Joined May 3, 2013
1,098
I don't think it is the clock. Normally, all the displays are in a Multiplexed mode, and a clock failure will normally result in a particular segment of the display brightly lit. Does not seem to be that in this case.
I think the clock divider chain has failed at some stage or some "Hi" voltage point has failed.
 

Thread Starter

kriksis

Joined Feb 23, 2016
27
I don't think it is the clock. Normally, all the displays are in a Multiplexed mode, and a clock failure will normally result in a particular segment of the display brightly lit. Does not seem to be that in this case.
I think the clock divider chain has failed at some stage or some "Hi" voltage point has failed.
Hello! From the things you mentioned, I don't really understand how the voltage point failure could be the issue. Like, some logic bits don't get the power needed for them to operate?
I can try to poke around with multimeter, but I am not really a diagnostics guy if I don't have schematic in front. Even with that, I would have trouble, but at least I'd have a chance.
 

Thread Starter

kriksis

Joined Feb 23, 2016
27
From a guy in YouTube: "I've done nothing and it still does not work".
Basically was hoping it would be something I can easily change or check. That leaves me with transformer outputs and if the power get to the boards. If that will not be the cause, I'll accept the defeat and look for a donor. Almost all tubes are in good condition (bright and evenly lit) and the enclosure is in acceptable condition. So I'd likely take all the black magic ussr chip boards and swap those. Best case, I'll have two non working clocks. :D
 

Ramussons

Joined May 3, 2013
1,098
Hello! From the things you mentioned, I don't really understand how the voltage point failure could be the issue. Like, some logic bits don't get the power needed for them to operate?
I can try to poke around with multimeter, but I am not really a diagnostics guy if I don't have schematic in front. Even with that, I would have trouble, but at least I'd have a chance.
What I mean by the Hi point is that there may be some pins of the IC tied to HI to enable the chip to count or shift or whatever. If the Hi voltage bus has failed, the IC's may get inhibited. Since there is no schematic, all these are guesses.
 
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