Data Precision 245 multimeter information needed

[anachrocomputer]

Today, I received a parcel containing a very fine Data Precision 245 multimeter. I bought it with the hope that it had a Panaplex display, and I was not disappointed! The Panaplex digits are smaller than I've seen before, and in fact the whole meter is smaller than I expected. It's a lot smaller than a Fluke 8010, say. The date codes inside are 1977 and 1978. I've seen scanned manual pages that are dated 1974. But there's the thing: I can't find a complete manual on-line.

So my questions are these: Does anybody know of an on-line scanned manual for the Data Precision 245? Is there a schematic available anywhere? The NiCad battery pack is missing (I'd rather that than if it was present but corroded!), so I need to know the polarity of the connections to the PCB, which are two springy contacts. Can anybody show a photo of, or describe, the battery pack contacts? I expect it'll need about 8V or so, given it's a six-cell pack.

Any help with getting this fine old meter working will be greatly appreciated!

[lowimpedance]

I found one of these meters in some junk to be tossed at work and sadly it was indeed toast. Also with it was the operators 'leaflet' and a calibration cert. So that seems to be all there is available for this unit.
I cannot find any schematics either.
Attached the operators booklet in case you have not found it yet.

[coromonadalix]

here ya go   its for the 248 model, but should have some similarities:

http://www.download-service-manuals.com/en/manual.php?file=Dataprecision-8210.pdf

better than nothing ??

[coromonadalix]

oh  i add this   found on the web :

You can search on ebay using +data +precision and you might find a manual. The 1450 was basically a repackaging of the handheld model 245. It's a 4 and one-half digit meter with 100% over-ranging. The basic DC accuracy is around 0.05%. If you get a manual for a model 245, the schematic will be nearly identical except for the line power supply. Data Precision always included the basic schematic in their manuals.
The displays are a beautiful gas discharge type display, but they do burn out, so don't leave them powered up when you're not using the meter. This was an era when nixie tubes were popular for displays, and before LEDs were cheap enough for this market.
The great thing about the 1450 and the 245 is the nearly infinite input impedance on the 1V DC range. The other ranges have 10 MOhm impedance. Another innovation of this design is the auto-zero feature. There is no zero adjustment pot. If the meter doesn't zero automatically on the 10 VDC range open-circuited, then the circuit is not working correctly.

[anachrocomputer]

Thanks to both who replied! I now have those PDF documents and I've been able to get the meter working. The manual for the model 248 revealed the polarity of the battery pack -- in fact, the 248 looks like a re-implementation of the 245 using LEDs instead of Panaplex displays. The 245 design dates from 1974, but the 248 is nearer 1978. They look like they share the same case design and battery pack (6 cell AA NiCad).

So, with a Farnell bench supply rigged up to the battery terminals, I switched on and... it worked! It's drawing about 100mA from the PSU at 7V or so (simulating a somewhat run-down NiCad pack). The meter flashes the +/- polarity indicator when the battery voltage drops below about 6V, which makes sense as a low-battery warning. The auto-zero feature on the 10V range appears to work.

Testing with a 1k Ohm, 0.02% resistor gave a reading of 1.000 on the 10k range and 0.9997 on the 1k range. Not bad! And the DC voltage and current ranges seem OK, too.

Photo shows the meter under test -- note that the red crocodile clip is on the battery terminal, but it isn't shorting with the range switch, it just looks like it is!

Thanks again for assistance rendered, and I'll update with any further progress!

[coromonadalix]

glad to see it working

[anachrocomputer]

So, for my next question, having got the meter working with a bench PSU, is about the input connectors. There are the usual two input sockets on the side of the meter. They're smaller than 4mm (everything about this meter is small), so I expected them to be 2mm. But they're not! 2mm plugs fall out. A 3mm drill shank will not fit into them, but a 2.5mm will, and is slightly loose. The sockets are plain brass bushes with no springiness to them -- any springy contact must be part of the plug.

Does anyone know the correct size for plugs to fit this meter? I think I can get 2.5mm banana plugs, would they be worth a try?

[Bill158]

Does anyone know the correct size for plugs to fit this meter? I think I can get 2.5mm banana plugs, would they be worth a try?

I use Pomona 3690 for my DATA PRECISION 248 and they fit perfect.  So your answer is 2.64mm.

Bill

[gwerl]

I also have a Data Precision 245.  It mostly works, definitely needs a replacement wall wort (which my information says is 8.7 VDC @ 160 ma) and new NiCds in the battery pack (which will require some plastic surgery as the batteries are in a glued-together plastic carrier).  It's principal problem is in zeroing.  When in X1 DC mode the display slowly climbs until it over ranges.  Shorting the test leads together brings the reading down fast to about 20 mv on the X1 range, after un-shorting the leads the reading again climbs to over range.  In X10 DC the meter will turn on indicating several volts but eventually settles around 20 mv or so.
In checking waveforms, the digital signals (phase 1/2/3+/3-/EOC) all seem present and correct.  Measured known DC voltages (against another meter) indicate correctly after subtracting the residual "zero" value.  Further investigation (by O-scope probe) shows that this offset appears to be due to a charge on C17.  When in X1 the nearly infinite input impedance does not discharge this capacitor (unless the test leads are shorted), on other ranges the capacitor appears to discharge through the "input range" select voltage divider.   Given the otherwise correct measured voltage indications on the 245 I do not suspect the A/D converter or the tri-phasic "zero" circuitry (matching the charges on C19 and C20).
I am wondering about the switching FET's and whether one might be not fully switching allowing some small charging current to C17.  There is no help on these FETS in the Data Precision manual, they are listed with internal part numbers and designated by "yellow", "green", "white" or "blue" types.  The FETs carry a Teledyne trademark.
Might anyone have any better insight into the design of the 245 or replacement FET types?

MORE INFO:
After more inspection I found a tiny capacitor (C45) Buried on the board that was damaged somehow.  Looks like it provides the discharge path to C17.  The schematic says "FSV"  (Factory Selected Value?).  Any idea what this value might be?  The manual for the Data Precision 248 lists a similar part (C18) at 1-4 pF, although that schematic is hard to read.