Nixie clock runs too slowly

Thread Starter

RobMendell

Joined Mar 15, 2019
21
I am looking to get a nixie clock repaired. The clock itself is in great shape and the nixie tubes are all good (I got the clock on eBay), but it runs too slowly. I believe there is a bad potentiometer or something. There is an adjustable pot for the speed, but it is ineffective. The clock is this one: http://www.mapsevoli.com/. I live in Chicago (USA). Any ideas on who can repair this? The manufacturer has been unresponsive for nearly a year, but before they went AWOL they suggested that a shop could repair it with a couple of hours of work. Thank you!
 

Thread Starter

RobMendell

Joined Mar 15, 2019
21
crutschow: I don't have a schematic, but I may be able to get one.

MrChips: I am not an engineer. I am a clock owner.

The circuit board seems to be easily accessible by design.
 

dl324

Joined Mar 30, 2015
11,262
Any ideas on who can repair this?
Not without a schematic.

AC powered clocks should use line frequency for timing. If it's AC powered and has it's own timing circuit, replacing that with something derived from line frequency will be more accurate.

If you wanted to go crazy, you could connect a microcontroller connected to WiFi so it can update time against a time server periodically. That's what I'm doing for a clock I built. I never have to set the time manually (after I configured the microcontroller).
 

AlbertHall

Joined Jun 4, 2014
10,234
The link provided says it is powered by a 12VDC wall wart and gets its timing from a microcontroller with a crystal.
If its time error is small then it might just be a case of tuning the capacitors around the crystal. If the error is large (say greater than 1 minute per day) then maybe the wrong crystal has been fitted.
 

JohnInTX

Joined Jun 26, 2012
4,209
upload_2019-3-15_16-28-43.jpeg
From the website. Zooming in on this picture shows what looks to be an 18pin PIC (alongside the High Voltage warning) with a crystal oscillator trimmed by C7 (the little red screw thingie). It's DC powered so the PIC oscillator likely does the timing and C7 trims the speed. C7 might be broken. Or, it just takes a long time to see what the effect of trimming the oscillator is without a frequency counter. All things being equal, try large adjustments to see which way it runs faster/slower then trim using smaller adjustments. It will take a long time to get it dialed in.

Alternately, the chip next to the PIC may be the timekeeper and the PIC just handles the user setting and display interfaces. Hard to say without a schematic.

What are the numbers on the crystal (the oblong silver component between the PIC and C7) and what is the part number of the PIC and the chip next to it?
If you can get a schematic, that would be the next step.
Watch out for high voltages on the PCB.

Good luck and welcome to AAC.

EDIT: I see some others have the same idea.
 

AlbertHall

Joined Jun 4, 2014
10,234
The adjuster should be able to cover that. Does the adjuster make no difference at all or it does adjust the speed but not enough?
Can you take a good close-up picture of the adjuster?
 

MrChips

Joined Oct 2, 2009
21,664
Trimming the crystal oscillator by adjusting the trimmer cap will take a lot of trial and error adjustments over many days if you do not have the right test equipment. We're talking about looking for 1 second drift in 12 days for 1ppm stability.
 

JoeJester

Joined Apr 26, 2005
4,316
a minute in two weeks means your clock is off about five parts in 10 to the minus 5th. That should be well within the adjustment of that trimmer capacitor.

You will be making minor adjustments, weeks apart, as MrChips described. If you had a frequency counter, that would be better. Are you running fast or slow?
 

Thread Starter

RobMendell

Joined Mar 15, 2019
21
I wrote this to the manufacturer years ago:
"I did some experimenting. The problem seems to actually be that the screw in the red square does not appear to affect the speed of the clock at all. After making tiny adjustments and letting the clock run for hours with no change in the result (comparing to an atomic-synced clock that shows the seconds digitally the nixie goes ever-so-slightly too fast), I spun it tighter several full rotations… and the seconds still go slightly too fast. No matter how that screw is rotated, the clock gains/loses approximately two seconds a day."

They replied:
"If the variable capacitor has been rotated around full rotations, it may now be broken and may need to be replaced.
http://www.digikey.com/product-search/en?keywords=SG2010CT-ND
There is a part on the board labeled C10 you can replace to help with the speed of the clock. You can order the part from Digi key to replace on your board:
http://www.digikey.com/product-search/en?keywords=PCC220CNCT-ND
You might need to use one of the Samsung substitutes if it's not available. We do not have any repair technicians on staff any longer. It would be a couple of hours of work for us to sub-contract this out to someone local [to us] to replace for you. It would be more cost effective for you to find someone local to do this work."

I do not know where to turn.
 

Thread Starter

RobMendell

Joined Mar 15, 2019
21
The trim pot doesn't seem to affect the speed, so I think that is probably the culprit. Again, I'm not an engineer. I'm a clock owner.
 

AlbertHall

Joined Jun 4, 2014
10,234
And just to complicate the adjustment that trimmer looks like the sort that go round and round - no end stop ( though the note from the manufacturer seems to deny that).
If it is as I think then through a full rotation the capacitance will go from maximum to minimum and then back to maximum again. Therefore turning it more than 180 degrees is unnecessary.
Check the timing.
Turn the adjuster about 30 degrees.
Check the timing.
Repeat until you have turned it a total of 180 degrees and then you will know just how much adjustment is available and also a good estimate of where to start the fine tuning.
Using only the clock timekeeping, to get accurate time is a slow iterative process and be aware that it still won't be spot on.
 

Thread Starter

RobMendell

Joined Mar 15, 2019
21
Upon looking back on my notes, it seems the clock ran faster than it should. Would faster mean one thing and slower mean another?

My first tests were small like that (partial turns) but when that didn't affect the speed, I turned it more.
 

AlbertHall

Joined Jun 4, 2014
10,234
Upon looking back on my notes, it seems the clock ran faster than it should. Would faster mean one thing and slower mean another?

My first tests were small like that (partial turns) but when that didn't affect the speed, I turned it more.
The adjuster should be able to make it run too fast and too slow and somewhere in between about right.
 

MrChips

Joined Oct 2, 2009
21,664
I wrote this to the manufacturer years ago:
"I did some experimenting. The problem seems to actually be that the screw in the red square does not appear to affect the speed of the clock at all. After making tiny adjustments and letting the clock run for hours with no change in the result (comparing to an atomic-synced clock that shows the seconds digitally the nixie goes ever-so-slightly too fast), I spun it tighter several full rotations… and the seconds still go slightly too fast. No matter how that screw is rotated, the clock gains/loses approximately two seconds a day."

They replied:
"If the variable capacitor has been rotated around full rotations, it may now be broken and may need to be replaced.
http://www.digikey.com/product-search/en?keywords=SG2010CT-ND
There is a part on the board labeled C10 you can replace to help with the speed of the clock. You can order the part from Digi key to replace on your board:
http://www.digikey.com/product-search/en?keywords=PCC220CNCT-ND
You might need to use one of the Samsung substitutes if it's not available. We do not have any repair technicians on staff any longer. It would be a couple of hours of work for us to sub-contract this out to someone local [to us] to replace for you. It would be more cost effective for you to find someone local to do this work."

I do not know where to turn.
You do not need to turn the trimmer more than half a turn.
Can you turn the trimmer any number of turns clockwise and counter-clockwise? (Answer should be yes).
Does it appear to tighten or slacken either way? (Answer should be no.)

Depending on the design of the trimmer cap, trimmers are usually two half-discs laying one on top of the other. As you turn the trimmer through one half-turn (180°) the cap will be set from minimum to maximum capacitance.

Hence find the position that gives you the most time loss in a day. Make a note of the position and the time loss.
Find the position that gives the most time gain in a day. Make a note of its position and time gain.
This will give you a starting point to find your best position for best time keeping.

Remember, the total adjustment of the cap is only half a turn.
 

Thread Starter

RobMendell

Joined Mar 15, 2019
21
Of course I had the same thought, but the pot doesn't seem to be good anymore. Rotating it a little or a lot doesn't appear to make the clock run at a different speed. Maybe I just need to get with someone who knows how to hook it up to a meter and see the results.
 
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