Help identify 80's era 28-DIP IC (marking ME-47538E G70250-1)

[benj38]

Can anybody help identify this part?
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Thanks in advance,

[fzabkar]

Could it be an OTPROM or mask ROM?

Can you identify IC2? If so, then this should enable you to identify the pinout of the mystery IC.

The fact that there is a similar "ME-" part number on the transformer would suggest that this a custom IC.

[srb1954]

With the number of tracks between the two ICs it definitely looks like IC3 is the ROM for microprocessor IC2.

Since IC3 is in a CERDIP package it was probably produced in relatively low volume and is a mask ROM rather than an OTP ROM. The pinouts of mask ROMs sometimes differ from standard EPROM and OTP ROM pinouts so you may need to trace out all the relevant tracks to fully identify the chip function.

[fzabkar]

I notice that some of the chip's I/O pins connect to resistors. This would be unusual for a ROM.

Also, the crystal is in a strange place.

[CaptDon]

What is the unit from, who made it? Any online service / user manuals with schematic?

[benj38]

The microcontroller IC2 is an Intel P8050, which is from the MCS-48 series. It also carries an ME prefixed part number.

The board is from a Mettler analytical balance. I am certain Mettler have never produced their own IC's and I very much doubt they have had custom ICs made for them. I bet that IC3, like IC2, is a standard part that just got a custom part number printed on it.

No schematics or service manuals available anywhere as far as I could find.

[fzabkar]

https://en.wikipedia.org/wiki/Intel_MCS-48

8050 -- 4K x 8 ROM -- 256 × 8 RAM

I think that U3 is probably a peripheral of some kind. The P8050 has a mask ROM, so U3 is unlikely to be an additional ROM.

I don't think we can progress until we know the pinout.

Could it be an ADC?

Does the balance store any user defined settings in nonvolatile memory?

Can you help us to put the part in context? Can you tell us the part numbers/markings of all the other ICs? Can you tell us what is connected to the 20-pin header? Can you point us to a user manual?

[benj38]

The balance model is AE163. There is an operating manual online, but no service manual or schematics I could find (but I would love to have the service manual if anyone has one!)

I know for a fact that the firmware is not stored in the microcontroller IC2, and thus IC3 may be a mask ROM.
The reason I know that is the following: moving the whole board from a model AE163 balance to model AE160 balance makes the AE160 behave like an AE163 in terms of the available menu options, but moving only IC2 does not have this effect, i.e., one still sees the AE160 menu options.

BTW, notice that to the left of the microcontroller there is a DIP-14 chip marked ER1400. This is a 1400 bit EEPROM. The other ICs are comparators, op-amps, and voltage regulators.

The 20 pin header goes to a daughter board that controls the microbalance weighing cell (no digital ICs there), and to the front panel keys and display (VFD type).

The operator manual indicates no user data that can be stored in non-volatile memory except for a single calibration number, but I would suspect that factory calibration may also store some linearity correction factors in such memory.

Unfortunately, the balance belongs to a friend I was visiting, and I do not have access to it now, so I can not analyze the pinout etc. at this point :-(

[m k]

My guess is that they are both MCUs.
U3 is 8021 and a main thing.
U2 is a peripheral thing and includes a character generator.

[fzabkar]

There must be a DAC or ADC somewhere. I know Intel had RAM+IO and ROM+IO ICs in those days, but they were 40-pin chips. If one were to implement a successive approximation ADC, then U3 would need to perform the function of a DAC, and the external comparator would compare the (amplified?) output of the load cell against the DAC output.

The crystal is in the right place for an 8021 (pins 15 and 16).

ER1400 datasheet:
https://www.tautec-electronics.de/Datenblaetter/Schaltkreise/ER1400.pdf
http://www.bitsavers.org/components/gi/_dataBooks/1983_GI_Electrically_Alterable_Non-Volatile_Memory_Handbook_1983.pdf

Operating Instructions:
https://neurophysics.ucsd.edu/Manuals/Mettler%20Toledo/AE163_manual.pdf

MCS-48 Family (8021 on page 147):
http://bitsavers.trailing-edge.com/components/intel/8048/9800270D_MCS-48_Family_Users_Manual_Jul78.pdf

The resolution of the balance seems wrong. Is it really 0.1mg?

Maybe the external components comprise an integrating ADC, in which case C7 could be the precision capacitor.

[benj38]

The resolution is not wrong. It is indeed 0.1mg which is typical for analytical balances. In fact, it even has a range of 32g with a resolution of 0.01mg.

As far as I know, the basic operating principal of an analytical balance is to exert a compensating electromagnetic force to the measured weight, with an optical sensor detecting when compensation has been achieved. I believe that most analytical balances of that era measured the electromagnet coil current using a precision resistor to turn it into voltage, followed by an ADC. The resolution of the 32g range would indicate an ADC with at least 22 bits.

Does the above shed any light?

BTW, another clue may be that IC2 is in a socket, while IC3 (as all other ICs) is soldered.
Also, the second line of marking on IC3 says G70250-1. Can it be that the "-1" indicates a speed rating?

[fzabkar]

I can't see how you can get 22 bits out of U3. Therefore, ISTM that the ADC must use an integrating topology. In such a case U3 would only need to function as an interval counter.

https://en.wikipedia.org/wiki/Integrating_ADC

Converters of this type can achieve high resolution, but often do so at the expense of speed. For this reason, these converters are not found in audio or signal processing applications. Their use is typically limited to digital voltmeters and other instruments requiring highly accurate measurements.

Maybe there is a clue here?  ME-47538C is a DIP-28 TI part (CF72602).

Mettler Lab Balance Scale PM6000 Internal Circuit Board ME-34127:

https://i.ebayimg.com/images/g/b74AAOSwmRBdMv5t/s-l1600.jpg
https://i.ebayimg.com/images/g/xcoAAOSwKDddMv5p/s-l1600.jpg
https://www.ebay.co.uk/itm/293158808579

FWIW, here is the datasheet for a TI CF72306 teletext data slicer:

https://www.blunham.com/Radar/Teletext/PDFs/CF72306dataSheet.pdf

It is part of TI's ASICTEXT Custom Family. I guess that corresponds to the "CF" prefix in the part number.

[benj38]

@fzabkar I think you correctly identified the part as a TI CF72602 chip. Thanks!

As you can see in the following image, it clearly shows a CF72602 chip in the position of IC3 in a board that looks extremely similar, if not identical, to the board in my original post.


Unfortunately, I can find no information on this part number 

[fzabkar]

If you compare the writing on IC3 against the ER-1400, particularly the "5" in the date code, I think you might agree that the "E" part was possibly made by General Instruments. That would also account for the "G" in "G70250". Perhaps GI and TI second sourced a similar custom IC?

[ace1903]

Thinking what ADC were available at that time and that precision range I remembered that I used ICL7135 for one hobby project.
There was another similar IC but different interface but I can not remember well part number.

You can check your device against pinout of ICL7135 especially crystal pins and capacitors needed for conversion.
If that isn't a match I would recommend searching Burn Brown, National instruments and Linear Technology old ADCs.
Even if it is marked with TI chip can be rebranded or made by license from other source.