I need help fixing my Nixie Clock!

Thread Starter

Lorne Allaire

Joined Apr 17, 2017
26
I built a DIY nixie clock from a kit several years ago. It worked then and has been working ever since until up until a few days ago when I was cleaning it. The wire going from the adapter to the pcb broke off and must have touched something it shouldn't have. Now the tubes don't light up. I tested power levels and all the IC's are getting 5V and the TP1 is getting 212 VDC. However, all three pins on the J3 connector are not getting any power. I don't know enough about electronics other than the basics and can't read the schematics very well to decipher where the problem might be. Can someone suggest what component might be causing the problem from the attached schematic?
 

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JohnInTX

Joined Jun 26, 2012
3,892
I assume you're operating from an AC source. Check the anode and cathode drivers.
Also check the PIC to see if it is operating and generating the multiplex signals.

Since you have anode volts (albeit a bit high, see R24), you should be able to get something out of the tubes if they are being multiplexed. Be sure J3 is intact.

If you scope RB3, RB4 and RB5 you should see a high going strobe with roughly 1/3 duty cycle to sequentially drive the anode drivers on a pair of tubes.

If you don't get that, the PIC may not be running. Check MCLR (1) for 5V.

Check OSC2 to see if the oscillator is running - it should be 4MHz.

RA4 is the 60hz timekeeping reference. That should not exceed 5V or you may break the PIC. Scope it to see. Maybe if the timekeeper input is not active, the tubes are blanked. That would depend on the firmware. If an AC wire came loose and contacted something close, maybe it contacted the top of zener D9 and smoked it. Unfortunately, that input is the only one on the PIC without an input protection diode to Vdd so it's easy to smoke it on overvoltage. It is also the input TOCKI which drives TMR0 internally and I would expect that is used to derive a 1 second signal from the pin. Depending on your firmware version - see the note - it might be going into a mode that depends on the smoked input.

It looks like the LEDs D30 and D31 are status outputs. The notes in the bottom left corner seem to indicate some functionality. If the LEDs aren't installed, the pins may still wiggle as described.

Verify that the volts on AN0 is something that would not excessively dim the tubes. The code disables dimming when AN0 is >4.7V so that might be something to try.

Worst case, you could verify that the ABCD pins on one of the 74141's are some BCD number then momentarily ground one of RB3-RB5 and see if you get a pair of tubes lit. If the PIC is socketed, even easier.

The FAQs here have some things you can try:
http://www.nixieclocks.de/english/faqs.html

Cool clock! Hope you can get it running.

Good luck!
 
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MrChips

Joined Oct 2, 2009
19,728
Once you have confirmed DC voltages with a DMM, +180VDC at TP1 and +5V at IC3 pin-3, the next step is to look for signals using the oscilloscope.

Look for 5V pulses at R20, R21, and R22.

Similarly, look for pulses at IC3, and IC4, pins 3, 4 ,6, and 7.
 

Thread Starter

Lorne Allaire

Joined Apr 17, 2017
26
Is there anyone here who would be willing to repair my nixie clock? I’m afraid my electronics knowledge is not strong enough to fix on my own. It’s frustrating because it’s like listening to my French speaking in-laws and can only pick up a few words here and there, the rest is over my head.
 

Dodgydave

Joined Jun 22, 2012
8,569
Is there anyone here who would be willing to repair my nixie clock? I’m afraid my electronics knowledge is not strong enough to fix on my own. It’s frustrating because it’s like listening to my French speaking in-laws and can only pick up a few words here and there, the rest is over my head.
Ok if you're familiar with an Oscilloscope, you can test the voltage points to see if the psu is ok,,second step is to check the PIC chip to see if it's giving out pulses to feed the tubes, pins 15-18 and 24 -26 ,and if the crystal oscillator is working...
 
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