Digital Test
Weston 1240

Manufacturer: Weston
Model: 1240
Year: 1972
Schematic: (see comment)
Functions: DCV, DCmA, Ohms, ACV, ACmA
Display: NIXIE
Digits: 3.5
Logic: RTL, Fairchild CµL

Benchtop DMM from Weston. This unit was manufactured in 1972, however the model is likely from around 1969-70. The model has auto-polarity but not auto-ranging.

Fairchild CµL (Counter Micrologic) is used for the counter string. CµL was a small series of RTL-class MSI devices intended specifically for decade counter-displays. The series is comprised of 4 IC types: a decade counter, a 4-bit latch, a NIXIE decoder/driver, and a 4-bit binary counter.

The Heathkit IM-102 uses an almost identical circuit design, the IM-102 appears to have been a copy of this Weston model. (The Weston has an additional 914 IC compared to the Heathkit.)

Internal view.

- Unit Log -

Serial Number: 89463
Year of Manufacture: 1972 (Component date stamps of 7104 to 7215).
Date of Receipt: 2013 Oct
State upon Receipt: OK physically, ohms not functional, NEG lamp flaky, POS lamp dim. Black plastic over metal handle fracturing.

Date: 2014 Jan
Procedure: Cleaned. Grease replaced on rotary switch, not replaced on pushbuttons.

Date: 2014 Jan
Symptoms: On all ohms ranges, overrange does not light, any R takes display to 0.
Procedure: Fuse in V/Ohms connector blown. Fuse was 3/16A, replaced with spare 3A located in COM connector due to lack of fuses of appropriate size. All fuses in model are uncommon AGX size, shorter than the standard AGC.

Date: 2014 Jan
Procedure: POS and NEG lamps replaced. Originals were stubby neons (~1/4" long), replaced with more common type (~3/8").

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Early Digital Test Equipment