Help checking voltage on Nixie Clock please.

[wheresthetubes]

Hello, I'm building a nixie clock from a kit, and I now need to check the voltage before I continue. I have to set my multimeter to a dc setting and check the 5v supply, then the 170v supply, which I asume is the HV (high voltage?) tab on the circuit board.

1) I'm unsure what setting I should put my multi-meter on, from the pic of my meter can someone advise the setting?

2) Where on the circuit board should I place the test prongs, in what order? I've posted pics of the three points on the board that are the testing points (5v,GND, and HV which I believe is the 170v supply).

3)There is a variable resistor on the circuit board which I have to tune to get the optimum voltage to drive the nixie tubes (170-180v). Do I need to disconnect the power supply to tune safely, or is it ok to tune whilst powered up?

4)There are 4 electrolytic capacitors, presumably these will still hold some charge when mains is disconnected. I've been told to discharge these (when mains off) by using an electricians flat blade screwdriver. How is this safely done?

I'm fairly new to electronics, though have had some recent successes. However I've not used my multi-meter to check voltage yet, so a detailed response would be greatly appreciated.
Best regards, John.

[julie_m]

1. Set meter to 20V range.
2. Black probe to 0V -- leave it there.
3. Red probe to 5V. Check reading.
4. Reset meter to 200V range.
5. Red probe to HV. Check reading.
6. Remove both probes. Switch off meter.

You can adjust the variable resistor while the device is powered, as long as you're careful and use a non-conductive tool.

To discharge a capacitor, apply the tip of a screwdriver so it joins the two terminals together. It will spark. This doesn't actually do the screwdriver or the capacitor any good .....

[Al (astral highway)]

Originally Posted by wheresthetubes

1) I'm unsure what setting I should put my multi-meter on, from the pic of my meter can someone advise the setting?

2) Where on the circuit board should I place the test prongs, in what order? I've posted pics of the three points on the board that are the testing points (5v,GND, and HV which I believe is the 170v supply).

3)There is a variable resistor on the circuit board which I have to tune to get the optimum voltage to drive the nixie tubes (170-180v). Do I need to disconnect the power supply to tune safely, or is it ok to tune whilst powered up?

4)There are 4 electrolytic capacitors, presumably these will still hold some charge when mains is disconnected. I've been told to discharge these (when mains off) by using an electricians flat blade screwdriver. How is this safely done?

Hi John. Great that you're tackling this project. Take it a step at a time and you should be okay, but do watch your personal safety.

1) The setting you need is picture left. There is a V followed by three dots capped by a bar and then 200. This means 200 volts DC and is the range you need.

2) Switch the meter to this setting. Leaving the black probe in contact with GND, touch the red probe to HV. The meter will instantaneously give you a reading.

3) You can adjust the trimmer potentiometer while the circuit is operational. Do not hold the sides of the board. A small screwdriver should be fine.

4) This is potentially risky if you are not experienced. You need to know what you are doing. What this means is that with the underside of the board turned upwards, you place a screwdriver directly across the two electrolytic caps in the power supply, right where they are soldered to the tracks of the board. As you're shorting the caps, the energy in them is instantanously dissipated as heat and light - it makes a hot arc when you do this.

The danger to you is in turning the board upwards. You can accidentally touch the HV and ground simulataneously, giving yourself a shock.

So take care! Don't hesitate to ask for more help if you need it.

[wheresthetubes]

Many thanks for this advice. I have to check the 5v supply first, so I assume I put the black probe to GND and the red probe to the 5V first, is this correct? But I think I have to put meter onto 20v setting first? Then put meter up to 200 setting as you've described and check the 170v supply? Regards, john.

[Al (astral highway)]

Originally Posted by wheresthetubes

... I assume I put the black probe to GND and the red probe to the 5V first, is this correct? But I think I have to put meter onto 20v setting first? Then put meter up to 200 setting as you've described and check the 170v supply?

John, this is exactly right. To check the 5V output make sure you've selected the DC option with the three dots and a solid bar above it, followed by 20V. Then switch to 200V as you describe.

Good luck,

Al

[wheresthetubes]

Many thanks to the both of you for your help. I just tested and got no reading, but diagnosed fault to dry joint on one of the three solder tags on the power socket. A bit of solder and I got the reading I wanted, after a little adjustment to the variable resistor. Think I'll plough on now and get on with the next bits, best regards, John.

[Al (astral highway)]

Originally Posted by wheresthetubes

Think I'll plough on now and get on with the next bits

Well, good luck and keep us posted on progress.

Al

[wheresthetubes]

Hello all, well here's my completed nixie clock. It actually took me a week on and off, in between mundane house chores etc. The kids didn't get a lot of help with their homework. It also took me a little while because of the design. I utilised the long fly wires on the In-8-2 nixies so that they stand well proud of the case. The case is about 60 years old, and used to house an oil stone which had worn out. A little time with a chisel and stanley knife allowed the circuit board to sit snugly inside.

The only problem I had was with the timer chip, incredibly small and fiddley to work with. Threading the long fly wires through the holes in the top of the case and ensuring they were in the correct holes of the circuit board wasn't much fun either.

In the 2nd posted pic, you can see a large Mullard RG4-3000 valve. Its my intention to gut this somehow (without breaking the glass hopefully), then drill holes in the underside and place it over the nixie tubes. I'd then mount it on the case somehow. Its an idea I got from a website that shows many completed nixie clocks, either an American or Dutchman did this, can't remember which. It looked very effective with the nixies operating from inside a large valve, and this Mullard valve is just the right size at 300mm long. I'm not completely sure how to gut the valve so I might need some help with this.

Anyway, I'm pleased with the clock. Ok, so its a kit, but its still going some from a relative beginner like me. I guess thats why I'm trying to make the case distinctive.