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Thanks for the hep they were backwards. I had assumed that the flat side should have matched up with the board. I'm surprised that everything works since the board was falling apart when I was desoldering it. (PCB's weren't meant to take that much heat.)

Hey Tony,

I have been having some troubles with my V2 thermometer lately. It had been working great for the last 2 years, sitting on my entertainment stand. Lately I've noticed that the temp display would 'lock-up' and stick on an incorrect temp. The display would still switch from K, to C to F and H properly, but not update the temperature. I picked it up and blew the dust off of it, this made several of the elements on all the tubes light up. I unplugged the power, disassembled the case and thoroughly cleaned all the dirt and dust from the board, reassembled and all seemed well. A few days later the same thing, temperature not updating. This time I tried unplugging the external sensor I had made, but the temperature didn't change to a higher value as expected. (I got lazy and never swapped coil L1 for the smaller one ). I removed the power cord then plugged it back in, only the last 2 tubes would light. the first 3 still lit, but only for the transition effect, also the 3 decimal points on the left 3 tubes would all flicker. Pulling the power cord again and plugging back in a second time, nothing would happen, like no power. I didn't have much time to mess with it this morning, so I left the power cable out and went off to work. I came home and plugged it in only to have it work fine. Seems to me the controller IC is starting to give up after running for a few days. I did see your post about a batch of faulty ICs. Your thoughts?

Update

Today the temp display locked up again. After cycling the power cord, the thermometer no longer powers up at all, so at least I have an issue I can chase. Ill take it apart and begin checking voltages this weekend.

I've not known a faulty processor to cause problems like this up to now though it's possible and if it's 2 years old will be an earlier batch with 16f1847s. The 3 numeric tubes not displaying is usually the DHT11 but could be the PIC not reading the sensor if it is faulty. Could you measure the voltages on all pins and let me know?.

Even with an external sensor connected, will a fault with the internal sensor still cause this?

It could as the software expects to see it at all times even if it's just displaying data from an external sensor.

Hi Tony,
I wondered if you could help with a problem I'm having with my thermometer.
I have mine on a timer, so it switches off during the night and while I'm at work.
This morning when it turned on, the second last (celcius) nixie was the only one lit up. It also wasn't lit correctly, like all of the symbols tried to come on at the same time.
This has happened a couple of times before and disconnecting and reconnecting the power has always worked.
Not this time. After reconnecting the power, none of the nixies light up.
The LEDs are working correctly and I can tell that the IR sensor is getting it to change modes, but nix on the nixies.
I've tried different power supplies, but I can't make them work.
Any ideas?

Can you remember if the LEDs worked correctly when the single tube lit up? if so then the pic would be OK and the problem is on the HV side. You'll need to go back to the tests after fitting L1 - check the voltage across the pads for C6, there should be 180-200v there.
If not, see if L1 or T12 are getting warm. If the voltage is OK and given the fault description, it might be the KM155ID1.

Hi Tony,

I'm pretty sure the LEDs were lit up.
I'll dismantle it and check the points you mentioned.
Thanks,

Hi Tony,
I'm measuring only about 3 volts at C6b and nothing at C6a (mine is a v1.11a PCB).
L1 and T12 are stone cold.
I've re-soldered everything and still not working properly.
I have noticed that the LED under the 4th nixie (D5) isn't working either.
For some reason, I can measure continuity across D5 (12 ohms), which shouldn't be there.
That LED connects to the middle leg of T8 and pin 1 of IC1, doesn't it?
Would that provide a clue?

It shouldn't be related to the no HV fault but as it's the same tube that had a problem and was the last to light, it can't be ignored.

What is the voltage on pin 1 and pin 9 of IC1?. A shorted D5 would not on its own stop anything working except the LED itself.