Electronics > Metrology

Datron 1281 Repair/Maintenance

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leighcorrigall:
Hello, members.

Many of you are familiar with this 8.5-digital 1281 Datron/Wavetek multimeter manufactured in England, but there does not seem to be a dedicated repair/maintenance thread on the EEVBlog.

I am going to post about my experiences with this unit and I invite others to join in as well.

TiN has a great work-log https://xdevs.com/fix/d1281/ where most of the material is already available for servicing this unit.  :-+

EDIT: rigrunner also has a repair thread for the Datron 1271 https://www.eevblog.com/forum/repair/datron-1271-repair/, which shares many similarities to the 1281. In fact, most of the boards are nearly identical to mine with the exception of the DC board.

The unit I have seems to be manufactured around 1987 to 1996, based on the date codes of the integrated chips. I would say that the unit is from 1991 until I know more. The last calibration was performed on 2017-10-04 by Pylon and expired on 2018-10-04. Calibration seals were unbroken on the calibration lock, and on the screws which secure the top and bottom covers. The battery that sustains the calibration data measures 3.7 V. The previous owner was the Hydro-Québec Research Institute. All options (True RMS AC Converter, 2- and 4-wire Resistance Converter, Current Converter) are included in the unit. The vacuum fluorescent displays are bright and in good condition. The firmware appears to be the latest version (400918-3.12B 10May96, 400918-3.12A 10May96).

The unit was tested (Section 4-30 of the User's Handbook) and inspected (with a Keithley 238 and some precision resistors) prior to purchase. Most of the ranges measured seemed to be decently accurate compared to what I had available for testing at the time. There were some major offsets at the lower ranges as expected for an instrument out of calibration.

Test -> Full Test (select the appropriate ^ arrow below the menu)

OUTPUT: REQUIRES INT. SCRE. CAL. 2105

Test -> Fast Test (select the appropriate ^ arrow below the menu)

Sometimes the fast test is successful. The following errors have occurred:

2.7.3.1 True Zero Checks (possibly because of old electrolytic capacitors)

OUTPUT: "FAIL: DCV 2181 List" - 2181 Noise (standard deviation ≤ 5 μV)

OUTPUT: "FAIL: DCV 2182 List" - 2182 Magnitude (-250 μV < mean 100 mV Zero < +250 μV)

Already, I am very impressed with the documentation available for this instrument.

When I got back to my hotel, I foolishly left the instrument running for several hours to warm up so that I could test it when I got back later that evening. After learning more about the functionality of the instrument in the hotel, I pushed a few buttons and the display information scrambled. No smoke or bad smells, although concerning. The unit was still responsive in that I could somewhat understand what was going on from some of the fragmented information presented and I knew that the unit could switch into various modes. At this point, I turned the instrument off not knowing if it would ever come back. Fortunately, the unit functioned properly the next morning.  :phew:

To be continued ...

mendip_discovery:
Ask to see if they have the old certificates to build a spreadsheet of its history.

leighcorrigall:

--- Quote from: mendip_discovery on November 28, 2021, 04:50:12 pm ---Ask to see if they have the old certificates to build a spreadsheet of its history.

--- End quote ---

Who is 'they'? I might be able to get calibration information from Pylon. Right now, I am trying to get the unit to operate without errors.

leighcorrigall:
After considerable effort and help from TheSteve, I have compiled a list of aluminum electrolytic capacitors throughout the instrument. A comparison is made between the Wavetek Service Manual, me, and TheSteve.

Note:

-> TheSteve was able to acquire a more recent Wavetek unit in mint condition with factory seals. This may suggest that the selected capacitors in his unit are more suitable for the instrument. My unit is likely to have been refurbished a few times during service so the capacitor specifications may deviate from the original design.
-> Some of the capacitor identifiers are difficult to read or have been mislabeled in the service manual. I have done my best to identify these capacitors. One way to tell from the bill of materials is to look for CAP AE (capacitor aluminum electrolyte) in the description. I was able to determine the unknown labels this way along with inspection of various reference pictures from my unit and TheSteve's.

The current part shortage made it difficult for me to order selected parts. Some parts have to come from eBay. Most of the items will be delivered sometime in mid-December. Better than nothing, I suppose. The cost was about 120 CAD.

leighcorrigall:
Since the unit had suffered from an issue related to the digital board, I decided to check the taps. The taps have been identified in the attached images along with labels that correspond with the tap number.

TP503 is the reference for all others:
VRef_2.5V (TP201) = +2.46 V (+1.6 % error)
+11V_UNREG (R307, R517) = +11.65 V (+5.9 % error)
-14V (TP501) = -13.86 V (-1 % error)
+45V (TP502) = +46.8 V (+4 % error)
-14V_2 (TP504) = -14.15 V (+1.07 % error)

There seems to be noise on some of these references, specifically +11V_UNREG and -14V_2. The noise is likely caused by the aged capacitors which have been ordered. Apart from the line regulation, it seems the voltage references are in good shape.

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