First tube won't light up

stoffi
Posts: 6
Joined: Tue Jun 18, 2013 12:20 pm

First tube won't light up

Post by stoffi »

Hi.
I just finished my thermometer, and thought i checked everything, but sadly I
didn't notice that the first tube won't light up before after i finished asembling
the case around the printboard.

the thermometer seems to be working ok otherwise, although maybe showing a
bit low temperature. (not confirmed yet.)

where/how should I proceed in troubleshooting(faultfinding?) this tube?


(Also, the "dot" in the top of the last tube (rightmost) came loose while soldering
the tube to the printboard, I'm not sure what it is supposed to do, but the tube seems
to work fine with the "dot" just laying on the "top plastic" inside the tube.)
Tony
Site Admin
Posts: 953
Joined: Tue Jul 24, 2012 8:05 pm

Re: First tube won't light up

Post by Tony »

Does the LED under the faulty tube light up?.

The 'dot' is a getter pellet, they sometimes do come loose and as long as it stays on top of the mica washer it'll not cause any problems. It should be too big to 'escape' from there.
stoffi
Posts: 6
Joined: Tue Jun 18, 2013 12:20 pm

Re: First tube won't light up

Post by stoffi »

Yes the led under the faulty tube lights up.
Does that mean there should be power to the tube?

(good to get confimed my assumtion about the getter pellet)
Tony
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Joined: Tue Jul 24, 2012 8:05 pm

Re: First tube won't light up

Post by Tony »

The tube is being switched on if the LED is lighting up but for some reason the HV isn't being applied or possibly the tube itself is faulty. Check the transistors and resistors next to it (T1 and T2) are in the right places and there are no solder bridges. Check the voltage at pin 1 of the tube (one with the white ceramic paint inside, right at the back of the tube) which should read around 150-180V.
stoffi
Posts: 6
Joined: Tue Jun 18, 2013 12:20 pm

Re: First tube won't light up

Post by stoffi »

Oh no!
this is so not cool!

I was unlucky, and shorted something with the testleads of my multimeter.
I think maybe it was two pins on tube one.
Now, the tubes displays several digits at the same time, although changing modes
as usual. (scramble doesn't seem to work that well)

I measure 37VDC on the working tubes, and 173VDC on the first tube.

Have I fried the driver IC? (most probably)
May it have been the faulty part all along?
Tony
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Joined: Tue Jul 24, 2012 8:05 pm

Re: First tube won't light up

Post by Tony »

This is probably going to get complicated....
Shorting two of the nixie cathode pins shouldn't damage the driver IC2, they can usually survive far worse. The short was probably between a HV pin and the LED, damaging the pic or the anode pin and something else, damaging the switching transistors. At this point the easiest solution would be to send it to me for repair - if it's the pic I would need to supply a replacement anyway.
stoffi
Posts: 6
Joined: Tue Jun 18, 2013 12:20 pm

Re: First tube won't light up

Post by stoffi »

I was afraid of something like that.
But!
I have had another night of whiskies and soldering, and have finished my second kit up to
the first test.
(I also have put som "shrinkwrap" (don't know the english term) on my testleads to lessen the
chanse of something similar happening in the future. :oops: )

would it be safe to move over one, or both of the IC's?

Tracing back the steps I did, (measuring topside) I find it unlikly that D1 was shorted, but rather
T1, if not two pins on the tube. (if not T1, both R3, and C6 is connected to T1. if I'm not mistaken)
If I shorted C6, then several transistors should be broken, no? (is it not connected to several transistor-colletors?)
Shorting the emitter of T1 (I'm assuming it is closest to the tube, should do no harm, since it's already
connected, right?

If I shorted R3, it is connected to the base of T1, and T1 may be broken?

Anyways, to say it short, would it help to try and swith over IC's between the kits?,
or is there little point in that, and I should send it to you?
Tony
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Posts: 953
Joined: Tue Jul 24, 2012 8:05 pm

Re: First tube won't light up

Post by Tony »

That certainly would make eliminating them easier.

When you have the second board working try the suspected damaged ICs in it. I will be surprised if IC2 is faulty but I suppose there has to be a first time.

Let me know the results, if they both work OK then it's in the switching transistors.
stoffi
Posts: 6
Joined: Tue Jun 18, 2013 12:20 pm

Re: First tube won't light up

Post by stoffi »

I have (finally) finished the second kit.
after testing the IC's from the defect kit, I see that IC2 is broken. (IC1 seems ok)
With the broken IC2, all tubes light up in the new kit,
so it is not a faulty IC2 that was the reason that the first tube won't light up in the first kit.

PS:
In the new working kit, I have an A letter which flickers slightly (in the last tube)
when the power is supposed to be turned off the valve.
To a lesser degree, this also happens with the '4' letter in the first tube.
I have put a short video of it below.
I am wondering to which extent this is normal?
I can't find any solder-bridges, and I have searched especially thorughly around the IC's, and all the tubes.

http://dump.no/files/b56a6341dfae/thermometer.mp4
Tony
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Joined: Tue Jul 24, 2012 8:05 pm

Re: First tube won't light up

Post by Tony »

I am surprised at IC2 dying that easily. The tubes shouldn't flicker at all, usually I've found it's caused by slight leakage around the switching transistors, the nixies will light faintly even with microamps. Clean off any flux residues in the area of the transistors next to the flickering tubes, I would try one at a time and observe the effect it has.
From the voltage readings on the first kit I'd guess the nixie itself is at fault. Annoying as they're all tested before being packed but maybe that one didn't like being put to use after a few decades of sleep.
If you can unsolder it (just cut the legs off and remove them one at a time) I can send you a replacement IC2 and nixie or you could buy them from a local supplier and I'll pay for them. Alternatively you could send the PCB back for me to replace them.

Congratulations on being the first with two new faults ;)
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