GenRad 1657 RLC Digibridge

For a while now I've been after a LCR meter but I wasn't sure what to get - now I'm always a sucker for older test gear; so, in the end I saw this on Ebay and decided to buy it.

It's quite an early piece of test equipment and apparently it was the first ever digital bridge meter.

As you can see from the PCB build style and the white ceramic 6503 processor with a date code of 1977 it's pretty vintage stuff.





I had to hook up some temporary 'croc' clips but I will order a proper set of kelvin clips when I get time.

It was sold with a display fault which turned out to be a problem with one of the 7 SEGMENT LED drivers; So I ordered some replacements and fitted them,  that seemed to fix the 7 SEGMENT fault but it was still glitchy for some reason;  I then noticed one of the range LEDs was dull,  so I replaced that too;  after that the display seemed to work fine!

I checked out the power supply; the 5V rail was slightly under but looking at the datasheet for the 5V regulator it was still within the manufacturers specifications.

I measured some CAPs, and it seemed great;  I then measured a few Inductors and it gave sensible results.

Below are a few pictures of the internals;  notice the very large smoothing CAPs on the power supply.

The above pic shows how the display board fits to the main board.

The above pic shows the white ceramic 6503 processor;   the other white package to the right of the CPU is a precision 25 Mhz crystal oscillator.

The two chips to the left of the CPU are ROMs;  one of the ROMs provide the code to run the CPU;  and the other provides the sinusoidal waveform data which is fed into a DAC.

The display board and the row of 9 driver chips;  one for each of 7 SEGMENT displays.

Whilst de-soldering and removing one of the LEDs, the LED literally fall apart.