Manufacturer:  | Weston |
Model:  | 1240 |
Year:  | 1972 |
Schematic:  | (see comment) |
| |
Functions:  | DCV, DCmA, Ohms, ACV, ACmA |
Display:  | NIXIE |
Digits:  | 3.5 |
Logic:  | RTL, Fairchild CµL |
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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 introduced by Fairchild in the mid-1960s intended specifically for decade counter-displays.
The series is comprised of 4 IC types:
- the 958 decade counter,
- the 959 4-bit latch,
- the 960 decimal decoder / NIXIE driver,
- the 989 4-bit modulo-16 counter.
The Heathkit IM-102 uses an essentially identical circuit design,
the IM-102 appears to have been a copy of this Weston model.
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"). |