Datron 1081 Teardown and repair

[MaxFrister]

Good ideas.  I've been focused on getting the meter working and so I have not spent much time calibrating.  I've done most of the digital board adjustments but I skipped over reset signal.  I'll go back and check that one.

I think it is possible that the calibration constants were okay but not being read correctly over the bus.   Of course once I pulled the ics that was no longer true.

I have no idea what to make of the noise on the long logging run.  It correlates with the HP meter so it may be external to the Datron.  There seem to me to be 3 possibilities: source reference noise, AC power problems, or external EMI. 

As for EMI, I am in range of a couple of military installations and they have been known to take out the local cable TV.  As the US is prepping for war with China, Mexico, North Korea, Canada, Iran, and/or Australia who knows what they are doing this week.

I'll setup both meters to read a shorted voltage tonight.  That will take the voltage reference out of the equation and disconnect the 2 machines from each other.

[MaxFrister]

The overnight logging of shorted meter inputs is much prettier.    There is only minor deviation with temperature and no 50ppm excursions.   I still don’t know what that happened in the previous run.  I’ll set it up to run that experiment again.

For the Datron, the settings are “F3R4T2C1A3” with a side of “K1L5”.  That translates to DCV, 10V range, normal triggering, low-pass filter on, and block averaging with the block size set explicitly to 1.

The temperature sensor is programmed to behave like a GPIB instrument so it is trivial to use here.   The sensor is a Dallas 1-wire sensor.  I have a fancier BME280 sensor but I can’t seem to find it.  Somehow I never lose the boat-anchor instruments.

I’ve attached the logging script.  It is about as simple and dumb as can be. 

[MaxFrister]

After years of working nearly flawlessly I pulled it for calibration and some upgrades.

• Every once in a while it fails to boot properly.  It is very intermittent and only happens in cold weather so it has been difficult to find.
• The cal key is missing.  While it is pretty easy to open up and jumper, I'd like to fix it.
• The external trigger connector is missing
• Maybe add some of the missing options

The options on the Datron 1081 were:
Option 10:     True RMS Converter
Option 20:     Four-wire Resistance conveter
Option 40:     Selectable Rear/Reference Input
Option 50:     IEEE 488/GPIB
Option 52:     Remote trigger
Option 70:     Analog Output
Option 80:     115V 60Hz Line Operation
Option 81:     115V 50Hz Line Operation
Option 82:     115V 400Hz Line Operation
[No option listed for 230V Line, presumably no option meant that]
Option 90:     Rack mounting.

My unit had 10, 20, 50, 80.  I'm going to try to add 52 and 40.  I'd add 70 but I can't think of any use for it.

There were also some accessories:

PRT 100    Platinum resistance thermometer Probe(100R)
CS1:          Current Shunt Set
HVP:         High voltage probe
1501:        Deluxe Lead Kit
Someone is selling something that might be CS1 on ebay for crazy money.  If anyone has these, it would great to see pictures.