[volt-nuts] Fluke 887A replacement Null detector with solidstate chopper

[Robert Atkinson]

Hi All,
I recently picked up a 887A AC/DC differential voltmeter. Unfortunatly it had been dropped, has leaky batteries and is not in great condition. However on oprning the top cover I noticed that Q106, 107, 108 and 109 were missing from their sockets. Therse are the monostable and drivers for the 85Hz chopper. However thay were not inside the unit and the calibration seals were intact.......
I then noticed that PCB 3 which has the null detector lood shiney ans green. It appears that the mechanical null detector has been replaced by a new PCB with a solid state switch. It's marked 887A-4022 P/N812610 (C) 1987 and is obviously a genuine Fluke item. It has a TO8 IC marked [BB] HL805. Obviously a Burr Brown chip, But Ican find no info on the chip or the board.
Has anyone any information on this modification?

Robert G8RPI..