Since I was curious and there aren't many pictures available on what's inside a Datron 1271, I decided to void the Fluke cal stickers from 2005 and take a quick peek inside.
The 1271, like most good HP DMMs, is split into Inguard and CPU compartment. But in contrast to HP, they decided to split it crosswise, instead of lengthwise, so that the ADC board sits in front of the CPU board and takes about 2/3 of the space available on the top section.
Front terminals are connected via flat-flex cable to the left front corner of the ADC board. All boards are dual layer PCBs, as far as I can tell. A nice feature are the retractable front terminals (for instrument protection during e.g. shipping) that can be extended by pressing the 'TERMINAL RELEASE' button on the back. Interestingly, the input switching JFETs use no PTFE/Teflon isolators commonly found in other, similar DMM, like HP-3456A. Instead, low leakage parts are guarded by PCB traces. Only 3x 3.3M resistors (probably 10M 1000VDc divider) are placed on Teflon isolators. Guess you have to keep the PCB especially clean in this one.
LTZ1000 is inside the black epoxy box, on which I didn't dare to fiddle to get it removed. (any idea whether is is solid cast epoxy or a removable box?). A LM399 reference is placed next to it, along with some metal canned precision resistors.
Like most medium to high end DMMs (except HP3456A and Keithley 196), this one also uses a lot of unobtanium, like that big DIP40 ceramic CLA3722 chip on the right side of the ADC board (ADC controller?). A few more custom DIP16 ceramic CLA3106 chips are also found on ADC board. As a nice feature, all chips are socketed. Datecodes are around 1988.
CPU board uses a huge DIP64 68k (which kinda runs hot @16MHz, judging from the brown marks on the label) and a total of 5 EPROMs (which I have to backup some times). Cal data is most probably stored in battery buffered SRAM, hence the lithium battery on board (last replaced in Nov. 2008, according to Datron sticker on the back). The PLCC socket with metal clamp hosts a CLA3721, more unobtainium
. A common TMS9914 is used as GPIB controller. All other parts are common 74-logic along with one PAL10L8. Like on ADC board, all chips are socketed.
Bottom section consists Option boards on the front section inside inguard/below ADC board and 2 really big toroid transfromers below the CPU board on the back.
Option boards are (left to right):
Opt030: Current converter, AC/DC current from 100uA to 1A full scale in 5 decade steps;
Opt020: 2W/4W Resistance from 10Ohm to 1GOhm full range in 9 decade steps; Several special modes available in config menu, such as High Ohms (10M to 1GOhm), low current measurement and TrueOhm (for in circuit measurement with diodes... in parallel with resistor)
Opt010: High Speed true-RMS, AC voltage from 100mV to 1000V full scale in 5 decade steps.
All option boards use several (custom?) CLA3106 chips along with one gold capped CLA5532 chip on tRMS board. As usual, all chips are socketed.
I uploaded these and some more pics at TiN's Xdevs FTP in higher resolution
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