Hioki 3237 5.5 digits meter teardown

[coromonadalix]

Just grabbed this on Fleabay, i was curious  of its internals

199999 count Bench DMM

Dac : Burr Brown  ADS1250U     20 bit ??

Next to it  IC22 :  An OPA2277        10µV, 0.1µV/˚C, High-Precision, Low-Power Operational Amplifier

Reference : An LT1027     thks @AVGResponding    Very Low Drift: 2ppm/°C Max TC Precision reference with extra-low drift         
                                                                           For sure not the LM199 399 or even an LTZ1000  loll   

Main Cpu : Renesas H8S/2134F        Web says : Microcontroller for Office Equipment Applications

Eeprom i think  :  8 pins Soic    3771    if someone find a datasheet   i could try to read it ?
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ADC clock :  An EXO 3 clock module  18.432 Mhz  ??

Precision Resistor : Caddock 1776-C4

Display Drivers : 2x  TD62083F  8CH DARLINGTON SINK DRIVER

The front panel plastic is very thin / brittle, i dont think it would survive some impact,  sure its now yellowish

Under the pcb i only see some transistors, no other ic's,  i dont want to dismantle more than this

For sure they have put the cpu far away from the front panel ??

[coromonadalix]

Reserved

Seems more an ADC on steroids than a real meter ??

They exist as 3237, 3238, 3239    way overpriced for what they are ...


I did start a thread about Hioki calibrations ... but never got any responses

No schematics

Just some user manual and code snipets : Labview C# C++ Mathlab Python VBA

[dobsonr741]

The Manual - no schematics however.

[Martin72]

no schematics however.

Hioki also consistently does not give out anything, and if the devices have not been manufactured for ages...

[coromonadalix]

some of theses 3237  goes down to 2001 

[AVGresponding]

Just grabbed this on Fleabay, i was curious  of its internals

Reference : ?    have to check  For sure  not the LM199 399 or even an LTZ1000  loll   

The reference is the LT1027. Bit of a strange/old fashioned choice, but then that's Hioki...

https://www.analog.com/media/en/technical-documentation/data-sheets/1027fcs.pdf

[coromonadalix]

Maybe they tried the best bang for the buck in thoses days

Haven't found a thing for the 8pins soic ic,  i do think it's an eeprom for the cal constants or more ??

OK Works so far  with Termite,  null modem cable

As per manual

*IDN?
HIOKI,3237,0,V1.10

So far,  nothing is shown on the rs232 port when the meter boot's up

[coromonadalix]

you have +8v and -8v symetrical supply (ic71 and ic72) and +5vdc (ic74) coming from the xformer secondaries / blue wires
around 7vdc for the 2 small xformer wires who goes on a rectifier bridge, and regulated (ic75)   at 5vdc  for the cpu section

blue wire pin 1 and 2 = 4.8 ohms
blue wires pin 3 4 5 =  3-5 = 14 ohms,    3-4 or 4-5 = 7 ohms
two small yellow "ish" wire = 0.9 ohms


some front pcb section ground is not common with othe meter ground sections, that's normal,  you have to know where your probing is grounded

[AVGresponding]

I thought RS232 needed +/-15V or so?   

I bet even with the somewhat odd choice of reference, it has pretty good performance.

[Kleinstein]

RS232 could be just OK with +-8 V, especially modern parts usually already accept +-5 V.  The old PCs used +-12 V.  New designs often use max232 or similar charge pumps to run of 5 V and create a voltage a bit under +-10 V.

[fzabkar]

Eeprom i think  :  8 pins Soic    3771    if someone find a datasheet   i could try to read it ?
                                              0026     
                                                343

MB3771 power supply monitor:
https://www.mouser.com/datasheet/2/100/002-08511_MB3771_Power_Supply_Monitor-931495.pdf

[coromonadalix]

could be that one   THKS

if it is, i dont see on the pcb  where the calibrations would be stored, unless it's directly in the mcu ?

 

[fzabkar]

H8S/2138 Group, H8S/2134 Group,
H8S/2138F-ZTAT™, H8S/2134F-ZTAT™,
H8S/2132F-ZTAT™
Hardware Manual
Renesas 16-Bit Single-Chip Microcomputer
H8S Family/H8S/2100 Series

https://www.renesas.com/document/man/h8s2138-group-h8s2134-group-h8s2138f-ztat-h8s2134f-ztat-h8s2132f-ztat-hardware-manual

I think I can see a NiCad (?) battery on the PCB. Maybe the settings are stored in RAM???

[coromonadalix]

no sorry  loll  the green one is a capacitor ... or a mov  due to its thickness,  but an input part  you see a line of resistors / voltage divider

and the black round thing 5A1 marking is the buzzer, had to put a tape on it,  very loud    loll