Project: Heathkit GC-1092A digital clock

Starting to tackle some of the projects that have been stacking up on the workbench. First one up is a Heathkit GC-1092A digital clock (serial number 00433). This was part of a collection from KB4NNM (SK) that was donated to the club earlier this year that’s been sitting on the workbench waiting for me to have time to get to. Decode Systems has a very useful page on Heathkit clocks.

Heathkit GC-1092A digital clock
Heathkit GC-1092A digital clock

Aside from a bit of dust and a few scratches and scrapes on the case, it’s in pretty decent condition. The clock works well, although the numbers flicker sometimes, especially when handling the clock. Haven’t tested the alarm capabilities yet. Setting the clock and alarm is done with a bank of switches on the bottom of the clock. A helpful sticker shows how to set things with the switches.

Setting switches for the Heathkit GC-1092A clock
Setting switches for the Heathkit GC-1092A clock

Removing 4 easily accessible screws from the bottom lets you take the top of the case off, revealing a fairly densely populated (for through-hole components anyway) circuit board and a big chunky transformer. Sitting in center stage is the brains of the operation, a MOSTEK MK5017AA clock chip (the white ceramic IC package in the center). There’s some corrosion on the heat spreader for the IC, but operation doesn’t seem to be affected.

Heathkit GC-1092A main circuit board and transformer
Heathkit GC-1092A main circuit board and transformer

The underside of the board has two large filtering capacitors, and the setting switches and speaker are attached to the case below the board.

Below the main board of the Heathkit GC-1092A clock
Below the main board of the Heathkit GC-1092A clock

The front panel contains the 3 2-digit 7-segment display units (Beckman SP-352). There are also a couple of 555 timer chips on the board, but I haven’t explored the schematic enough to know what they’re doing. Probably something related to the alarm function.

Heathkit GC-1092A display circuit board
Heathkit GC-1092A display circuit board

I’ll need to do some more research and studying the schematic to see if I can figure out the display flickering problem. Closing this clock back up and putting it back on the pile for now.