Data Precision 2440 Nixie Multimeter -no display can you help find the schematic

[Dana Kitsune]

Hello everyone.

I have just acquired a vintage American 1970's Data Precision 2440 Nixie multimeter.
The issues I am having is that the display is not displaying digits. The decimal places on some ranges light up but no more. When in autoranging mode I dont hear the relays clicking to range hunt.
The fact that the decimal places are lighting indicates that the nixies are receiving high voltage just fine and the fact the relays aren't doing there thing in auto mode makes me suspect that its something to do with the logic side. First rule is testing voltages but there is no labeled test points and the power supply regulator circuit isn't obvious to me, A schematic/service manual would really come in handy.

I have poked around on google but to no avail, I suspect a manual may not be online because of its age. Do any of you have a paper schematic or the service manual you could scan?

Any help in getting this wonderful piece of Nixie test equipment working again would be greatly appreciated

Thankyou for your time

[factory]

Probably the closet free manual available, the 2500 series (extra digit) here; https://josvandijken.nl/elektronica_data_precision_2540a1.php

You should have +180V for the display, +5V for the display logic and +20V for the relays.
The analog circuitry uses +/+15V and -5V.

David

[srb1954]

It may be worth looking for documentation on the Data Precision 245 as well. This is a portable 4 1/2 digit model using Panaplex display rather than Nixies but there may be sufficient similarity in the circuits for it to be useful.

[George Edmonds]

Hi

Over the years I have had a number of Data Precision DVM’s and still have a model 3500 along with a printed manual, which is not immediately to hand as it is in storage.

The entire Data Precision range has proved to be the most unreliable DVM’s that I have owned.

The power supplies are very suspect as they are of a 60Hz design which proved to be marginal on 50Hz, so first check them.

The display side is VERY unreliable, it is basically a chain of 7490 decade counters outputting to 7475 BCD latches which drive 7441 Nixie displays.  At best the 7441 was never a high reliability IC, even worse was that most of the Data Precision DVM’s that I have seen used a Fairchild version, the part number of which I cannot recall, but I think it started off DM.

Shortly after I acquired the model 3500 in about 1980 I started to get failures of the Nixie drivers, as a result I purchased a number of spares which over the time I have used all of my available spares and the instrument no longer works.  I now suspect that most of the Nixie driver IC’s that are on sale are fakes.

I have never had an analogue side failure, so I would suggest that you concentrate on the power supplies first and then the Nixie counter/ drivers.

Interested to hear if you succeed in bringing yours back to life.

G Edmonds

[sarahMCML]

Hi George,

I've had a Data Precision 935 3.5 digit handheld model since 1978, and apart from having to replace the LCD about 20 years ago, it's never given me any trouble whatsoever. It has side keys just like a Fluke 8020, and also has the 200mV ranges etc.
Unfortunately I lost the manual years ago and have never managed to find a replacement online.

[factory]

Hi

Over the years I have had a number of Data Precision DVM’s and still have a model 3500 along with a printed manual, which is not immediately to hand as it is in storage.

The entire Data Precision range has proved to be the most unreliable DVM’s that I have owned.

The power supplies are very suspect as they are of a 60Hz design which proved to be marginal on 50Hz, so first check them.

The display side is VERY unreliable, it is basically a chain of 7490 decade counters outputting to 7475 BCD latches which drive 7441 Nixie displays.  At best the 7441 was never a high reliability IC, even worse was that most of the Data Precision DVM’s that I have seen used a Fairchild version, the part number of which I cannot recall, but I think it started off DM.

Shortly after I acquired the model 3500 in about 1980 I started to get failures of the Nixie drivers, as a result I purchased a number of spares which over the time I have used all of my available spares and the instrument no longer works.  I now suspect that most of the Nixie driver IC’s that are on sale are fakes.

I have never had an analogue side failure, so I would suggest that you concentrate on the power supplies first and then the Nixie counter/ drivers.

Interested to hear if you succeed in bringing yours back to life.

G Edmonds

Not got any Data Precision TE here as far as I know, but I've had very few problems with 7441/74141 drivers in the vintage TE I do have, had more 7490s fail than display drivers.

DM7441N would be National Semiconductor, I've had NS parts fail more often than others, they also made a range of panaplex driver ICs which are quite unreliable. Aren't the Fairchild parts normally labelled with an F, the number and PC code?

As people keep mentioning the 7441/74141 fail often, I've ordered a lot of the Soviet clones to try.
The alternate would be to make an adaptor board with surface mount decoder IC & ten high voltage transistors.

David

[George Edmonds]

Hi

My memories of the exact manufacturer of the 7441 used in the Data Precision 3500 could well be in error as it is now some forty years ago.

I do agree that they also had problems with the 7490’s, the IC failures that I had were probably evenly split between the 7441 and 7490.  I also had a Philips PM6630 counter timer that use the identical 7490/7475/7441 layout to drive the same Nixie displays, in about the thirty years I used it I never had to change one of the driver IC’s.

My own suspicion is that the poor design of the power supply in the Data Precision instrument was the possible real cause of the multiple IC failures that I had, whereas Philips got it right for a 240V 50Hz mains supply.

It was a pity that I finally had to give up with the Data Precision 3500, in its day it was the best DVM that I used, now days, like the majority, I have a HP34401A, it just works.

I still have a Data Precision 2480R, 4.5 digit, LED display, again now unused.

G Edmonds