74141 and 7441 Nixie Driver Tester

Dieter's 74141 & 7441 Driver-Tester Project
last update: November-07-2003 (finished)

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As I have dozens of old "unknown condition" 74141 and 7441 driver chips laying around. I sat down and sketched a "super simple" driver- testing circuit to test them all. I also have russian types and "unknown" of which I have no idea if they are 74141 or 7441.

REMEMBER!! 74141, 7441 and 7441A are definitely NOT the same!!!
Check the different truth- charts!!!

Truth Table for the 74141, 7441, 7441A and 7441B Chip

Input				74141	7441	7441A	7441B
D	C	B	A	Output on	Output on	Output on	Output on
0	0	0	0	0	0	0	0
0	0	0	1	1	1	1	1
0	0	1	0	2	2	2	2
0	0	1	1	3	3	3	3
0	1	0	0	4	4	4	4
0	1	0	1	5	5	5	5
0	1	1	0	6	6	6	6
0	1	1	1	7	7	7	7
1	0	0	0	8	8	8	8
1	0	0	1	9	9	9	9
1	0	1	0	none	see note a	0	8
1	0	1	1	none	see note a	1	9
1	1	0	0	none	see note a	2	8
1	1	0	1	none	see note a	3	9
1	1	1	0	none	see note a	4	8
1	1	1	1	none	see note a	5	9

Note a: For BCD inputs A-F the output alternates between 8&2 and 9&3 illuminated together.

You also have to check all the different 7441 / 74141 drivers types- there are:

Type	equivalent to
7441	7441
74141	74141
155ID1	74141 or 7441
155ID1	74141 or 7441
DM54141	74141
DM74141	74141
DM74141N	74141
DM-8640-N	74141
K155ID1	74141 or 7441
KM155ID1	74141 or 7441
NTE74141	74141
SN74141	74141
SN74141J	74141
SN74141N	74141
FLL101	74141
TL74141N	74141
DM5441A	7441A
DM7441A	7441A
FJL101	7441A

Remenber that te russian types are marked like this (orange!):
KM155ID1
or

K155ID1
or

The russian types are either 7441 or 74141, high serial numbers are 74141, low serial numbers are 7441.
The russian types have high "off" voltage (approx 100V), so the efficiency is much better, and the "Blue Spot" problem can not occur (e.g. IN-18)

I also have some data- sheets for the different types:

Block Diagram for 74141:

This one I got from Jan:

Ok, lets go to the Sketch I made for my tester

It's so simple, that there is nearly nothing to explain. Just some words: The 2.7Ohm resistor provides the over- current protection when the test-IC is shorted. the controller drives the 4 PNP- transistors- which drive the control- LEDs ant the inputs of the test- IC. On the right side you also see 10 transistors which only have the job to drive the LEDs and the inputs of the controller. I'll use the very up to date ATmega8515 - so I don't need any reset- circuit, not even a crystal. The button switch switches between the different test modes (I'll explain later) and finally the 3 LEDs show the test results.
The ATmega8515 is totally cool!!! I will use it for all my clocks in the next future because you need no other parts around it!

There will be a free- running mode:

You only have to put in the test-IC. When the green LED lights up, it's a good 74141. When the yellow LED lights up, it's a good 7441. And when the red LED lights up, the IC is defective.

And there will be a single step mode:

when you hold the button for 1 second, you can switch to the single step mode. there you can check output by output and check (in case the IC is defective) which one is defective and maybe use it for a job where the defective output is not used. When holding the button for longer than one second you come back to the free- running mode.

October-16-2003

I got many hints from the Neonixies Gang that in some cases a defective 74141 may leak at the outputs. I never took used 74141 (7441) for my project, so I haven't thought about that this also can happen. I had to change my circuit to this second revision, that works with a Z560M. The Z560M tube is driven with 2mA current. the parallel resistors R38 to R47 add 4mA to the switched on output transistor of the test- IC. The 170V (plus tube and resistors) with the voltage dividers make it possible to detect a too high leakage current in case the IC is defective. In this case the voltage at the cathode is lower than 50 volts (I gave the test IC 20% tolerance as you can see) and the inputs of the ATmega are not high (<4VDC). Moreover I have a good control with the tube whether the test- IC really works. I'll need a stabilized 5V voltage to detect the correct voltage level (>4V) at the inputs of the ATmega. So I added a 7805 IC.

Here is the new circuit

October-31-2003

I've finished the board today.

My other projects took away a lot of time, so I decided to give it to a friend of mine to do the coding.

November-07-2003

Operating Instructions Dieter’s 74141/7441 Nixie Tube Driver Tester

Power Supply
Connect the „GND“- Lead to GND, The +170VDC lead to a power supply +170VDC and the +8VDC to a power supply 7 to 12VDC.

Operating Instructions

Insert Test-IC in socket. Notch pointing to the top. (Switch +170VDC off while you fumble around on the circuit board. If you like electric shocks, just leave it hot
Switch +170VDC power on now
After power up the yellow LED is on, the green and the red LED is off. That means: Tester is ready to start. The Code shown on the row with the 4 red LEDs displays 0000 (all 4 LEDs off). The Nixie should display 0.
Now press the button and click through the truth- table while watching the nixie. Depending to the entries in the table, the nixie should display as follows.

Truth Table for the 74141,7441 and 7441A Chip

Input				74141	7441	7441A
D	C	B	A	Output on	Output on	Output on
0	0	0	0	0	0	0
0	0	0	1	1	1	1
0	0	1	0	2	2	2
0	0	1	1	3	3	3
0	1	0	0	4	4	4
0	1	0	1	5	5	5
0	1	1	0	6	6	6
0	1	1	1	7	7	7
1	0	0	0	8	8	8
1	0	0	1	9	9	9
1	0	1	0	none	see note	0
1	0	1	1	none	see note	1
1	1	0	0	none	see note	2
1	1	0	1	none	see note	3
1	1	1	0	none	see note	4
1	1	1	1	none	see note	5

Note a: For BCD inputs A-F the output alternates between 8&2 and 9&3 illuminated together differently.

If the end of the table is reached, the red and the green LED displays the result of the test.
GREEN continuos light means: The test – IC is a good 74141.
GREEN flashing light (t = 0.5s) means: The test – IC is a good 7441A.
RED means: None of the 2 versions (74141 or 7441A) in the table fits to the test IC. The IC is defective or it’s a 7441 type. Check the chart and compare the displayed symbols of the nixie with the columns- entries.
If you press the button in this “result- state” (Code 1111 displayed) again the code will start from 0000 and the software will reset to a new test (yellow LED on).
If you hold the button down for longer than 1 second you also reset the circuit to a new test BCD „0000“ and yellow LED on.
If you hold the button longer than 2 seconds you switch to the automatic mode.
All display- options of the tests are the same, but you don‘t need to check the IC by clicking through all outputs. The circuit will run free. Each symbol is displayed for 100ms – so you can see the Nixie „running“ through all digits. the yellow LED never will come up. if you set in the IC either the green LED is lit or it flashes. Or the red LED is lit.
If you want to switch back to the manual mode you have to press and hold the button longer than 1 second. When the yellow LED lights up continuously you are back in the Manual Mode.

My friend did the coding this time (had little time)...

and it works:

All are tested now. I really find some old which don't work or leak.
I also found out what I wrote above in the section about the russian tubes.

Note: Please don't ask me for 74141 chips. The ones I have I will use for my next projects.

Project is finished.
Thanks for reading.

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