Digital Test
Fluke 1900A

Manufacturer: Fluke
Model: 1900A
Year: 1976
Schematic: MF
Max. Rate: 80 MHz
Display: LED
Digits: 6

Counter with Auto-ranging feature.

Internal view.

Units with the battery option require NiCd batteries to be present for operation. Shown here is a unit modified with a simple shunt regulator to substitute for the batteries. The transformer used with the battery option does not supply sufficient overhead voltage to allow use of a standard series-pass regulator. See battery substitute schematic.

Also in the above unit, the power connector had shorted and blown a hole in the PCB. A standard IEC power connector has been installed in its place.

- Unit Log -

Serial Number: 2328047
Year of Manufacture: 1979 (IC date codes of 7903-7945).
Date of Receipt: 2012 Oct
State upon Receipt: Functional. Line power version (no batteries).

- Unit Log -

Serial Number: 1263-C
Year of Manufacture: 1976 (IC date codes of 7248-7629, mostly 1974).
Date of Receipt: 2012 Oct (customer repair)
State upon Receipt: Counts in Total mode but does not update in Frequency mode (no gate or sample cycle). Power receptacle had previously shorted out, burning large hole in PCB. This unit has the battery option.

Date: 2012 Oct
Procedure: Sampling problem traced to bad U5 4011 IC, some gates (1-2-3, 4-5-6) are 'weak'/inadequate gain. U5 replaced. Functional.

Date: 2012 Oct
Procedure: Modified for use without batteries by substituting a shunt regulator for the batteries.

Date: 2012 Oct
Procedure: IEC socket installed to replace original receptacle.

Date: 2012 Oct
Procedure: Overflow LED not lighting. Works after resoldering.

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Early Digital Test Equipment