Philips PM2421 Digital Multimeter

This PM2421 is the first Nixie multimeter I acquired. I wasn't yet able to fix it. But it is a nice piece anyway.

The PM2421 is a digital multimeter. The case is apparently intended to be placed on a shelf, although it does have a tilt support for bench use. Its display has 4 nixies. The digital circuitry is based upon TTL.

A look at the digital circuits from the top.

I bought this meter in spring 2001 on the Veron radio amateur flea market. The person who sold it, told me it had been used at a school. No documentation came with it, and I haven't found any yet.

When I tried the meter, it gave an overload indication and it behaved somewhat strange. When I switched ranges and flipped the switches on the back, it sometimes gave a 0 readout, as it should when no input signal is connected. Apparently, something is wrong with the switches or with the autoranging circuitry. But as I did't have any documentation, I balked at the idea of analysing the circuits.

A look at the analogue circuits from the bottom.

So this is the first nixie multimeter I bought, but not very useful yet. The perspective of fixing it has improved since in March 2008 I received a mail from a fellow nixie admirer that he had the service manual for me. I borrowed and copied it, so now I could start. In the mean time it is a nice thing to look at, isn't it?