Fluke 8375A DMM - Part 2

The Fluke 8375A is a digital benchtop multimeter, made around 1973. It supports DC voltage, +/- 1100V as primary function and comes with a module to convert an equal range of AC voltage to an RMS value. As an additonal bonus, it also has a built in current source to measure Ohms from essentially 100µ𝛀 up to 12M𝛀; It does not have built in current shunts however, so current messurement would need an exterman shunt resistor for reference. All of this to output to a 5 digit nixie display with an overflow digit for 20% overflow; i.e. the maximum number should be 120000 with the decimal point set according to the range. The "filter" function is also based on a real analog active low pass filter to even out fluctuations that would be visible to the AD converter. I've seen that as a "digital average" in most modern meters. So... let's see what this little gem has to offer in terms of problems and solutions!

Part two here is the assembly and troubleshooting part. And boy did it have troubles to shoot! The manual for the device came with a very good description of how everythign works; But the schematics had some of the lines and text removed by an automated scanning tool apparently. So it was next to impossible to know where a line is missing from the scan or by design; not to mention that the pin numbers of all the ICs were just blobs of goo at times. But I managed, and since I was fascinated by the design of the AD converter, I'm sharing that part of the troubleshooting process in detail too!

0:00 Intro / Recap / Selection Switches / Front Panel
2:46 Power Supply Dry Test... / 18V Issue
4:02 "All In" Test...
5:42 Power on! / Reduced Test: 18V Good / RMS Unit Fail
7:00 No Measurement? / Solder Bridge! / AD Intro / Better Manual Quality
8:34 AD Function Description
11:00 Analog Storage!
12:15 JK Adapter Boards
13:22 DC Zero Issue #1
14:54 DC Zero Issue #2
16:34 Trigger LED Upgrade / Buttons and Trim Pieces
17:44 Alignment Impressions / Donor PCBs!
19:41 Remote Control PCB / Digital Output Unit PCBs
21:54 Where Is The DC Reference Board? / Threaded Inserts! / Duct Tape Issue
23:45 Lid Paint / Insulation Sheet
25:52 Feet vs. Rails? / IO Test!
27:02 Ohms Fuse! / Summary / Credits / Outtake

Music (in order)

My Train's A Comin' - Unicorn Heads
Nine Lives - Unicorn Heads
Wrong - Dan Henig
Town of 24 Bars - Unicorn Heads
Light Expanse - Unicorn Heads

(YouTube Audio Library)

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