Old Panel Readout\Panel Meter Identification TIL306/7

[Infrared_Fred]

Hello!
About a year ago I ordered a large box of vintage LED displays from someone on Ebay and included among assorted displays were two nearly identical circuit assemblies that appear to be some sort of panel meter.  The assortment of displays included a single unused (or else previously socketed) TIL306 LED display, which is a seven segment LED display + IC counter + decoder and two circuit boards that had identical looking displays to the unattached one, other than dirt and gunk on them.  It is also possible that they are a TIL308/309 but....whatever.  The circuit boards have the digits in a +-3.5 digit format with three integrated displays and one passive +-1  overflow display.  ICs visible on the front board are 2x 555 timers and a 7474 D-Flip Flop, which I am pretty sure goes with the overflow display based on TI schematics I have read.  There is a second board with a bunch of ICs, but the only part numbers I can read are a LM308 precison op-amp since they are on the inner side of the circuit board.  There also is a precision 10 or 25 turn potentiometer most likely for calibration.  There does not appear to be any manufacturer's logo or identification, although there is a rather difficult to read 62?44A and Made in USA printed on it.  Googling the 62?44A with various numbers for the unreadable one only gave real estate listings or other useless results.  If they are panel meters I am much interseted in using them as is, but for that I would need a pinout or such information, since none is given.  I could take them apart but I wnated to ask here for identification help before I did that since I am a newbie and I don't want to damage them.  Hopefully the pictures below are helpful--please let me know if they are readbale or if you want any differnet angles or anything like that. Thank you so much for you time and your help!

[Infrared_Fred]

I am trying to post more pictures but it isn't working for some reason.  Here is try three.

[Infrared_Fred]

More pics...

[Infrared_Fred]

The final ones.. I am not rrying to spam but it wont work otherwise.

[CaptDon]

Not sure exactly who made those, there are so many to choose from. I serviced a bunch of panel meters from Simpson, Non-Linear Systems and several others that were in our locomotive simulator panels at the GE locomotive factory and the guts were all very similar. They were all built to the same 'DIN Cutout' dimensions. Most were internally 0-200mv D.C. with scaling resistors for voltage or shunts for current. They all used transformers for line input and typically 12vac output for the circuitry and therefore you could safely measure voltages that may or may not be related to earth ground. For instance you could use a 0-200vac meter to measure leg to neutral on a 3-phase 208 source while also powering the panel meter from the source, or either of the other two phases. If you had a higher scale the internal isolation would allow you to measure leg to leg of a 208 circuit while powering the panel meter from leg to neutral (for a 120vac input rated meter and perhaps a 0-400vac scale. They are handy.
I have seen similar meter guts to yours also inside digital panel thermometers.

[CaptDon]

B.T.W., those T.I. 7 segment displays with the built in logic are worth their weight in gold, specifically the ones that incorporate the decade counter and latch logic. I used them in a piece of medical gear I designed back in the mid 1980's and they saved a huge parts count although they were expensive. One T.I. device saved the board space of a counter, latch and driver. They were excellent as readouts for signal generators and I think they could go at least to 15mhz.

[Infrared_Fred]

Thanks for the information!  Do you know of a place you could point me to find the pinout or another way to detemine that without damaging it from improper connections?  I did find a panel meter which at least had a 15 connection card edge connecter made by NLS and a front potentiometer, but the ones I have seem to be a different model and the two sides of the 15 posistion edge connecter appear to have connections that differ from the other side's connections for a total of 30 connections and most postions do seem to be connected.  I would guess that many of them might be a parallel BCD output since the counter/display ICs have that as a feature and I don't neceserrily see any other particular reason for a big 24 pin ribbon cable connecting a display board to the base board when all the counters and such are integrated on the front board.
The device itself is a https://www.weschler.com/wp-content/uploads/2018/05/NLS-RM-350-Data-Sheet.pdf. 

[Terry Bites]

 I chucked out few of these Texas Instuments Fossils in the bin recently. Silly me.

[Infrared_Fred]

Can anyone help with the pinout please?  Thanks!

[CaptDon]

Not knowing the original manufacturer or model it is impossible to give you the pinouts. At best you can reverse engineer it by tracing back to the I.C.'s and see if it goes to the I.C. inputs or outputs. Since the 306/307 series was 5 volt based at least you can put 5vdc at probably an estimated .2 amps and light the thing up and go from there.

[Infrared_Fred]

Okay, I will try that.  Thanks!

[Infrared_Fred]

I disconnected the front panel from the back to get a closer look and this is what I got.  I have not had a chance to do any work on the pinout but I thought these pictures might be helpful.  Grand Total Count is 1x each: DTL NAND,  DTL NOR, TTL 7490 Decade Counter, TTL 7404 NOT, LM709 Op amp; 2 each: AD308 op-amp , 7474 TTL D-Flop 1 on front board 1 one on back, LM555 Timer, CMOS 4016B analog switch; 3 each TTL LED TIL306 counter decoder. 
In total I am guessing this might be a autoranging V/F based panel meter,  probably the AD308's are analog, the LM709 is used as comparator?  on the bsack of the front board is 71-0569505 and on the back of the back board is 71-0618803.  Any ways, thanks!

[Neomys Sapiens]

While I certainly understand if you loathe to perform such operations on such rare components, depending on your tool fit you might consider to desolder one of the displays. The bottom side might hold a clue. Although that's a wild guess, the TI datasheets do not hint at that.