Nordmende DiVo 3362 Digital Voltmeter

This German DVM by Nordmende has a quite unique design. It uses a mix of TTL and PMOS circuitry for the digital parts (control, counter, etc). It has a dual-slope converter and should be very accurate. It has four range pushbuttons, and a number of function pushbuttons:

• 1, 10, 100 and 1000
• V, Ω and mA
• and an “AC/DC” button

I bought this digital voltmeter on the quarterly NVHR radio swapmeet. A manual came with it, thin but containing enough information. I was really happy to have the circuit diagram, because it had some really unusual components and circuits.

The display consists of two Sperry Panaplex displays: a SP-351 display with 1.5 digit and + and 1 signs and a SP-352 display with two digits. The Panaplex displays are flat, 7-segment neon displays. Like Nixie tubes, they need a 180-200V supply voltage. The DiVo-3362 uses a special 7-segment decoder-driver IC by Sperry to drive the displays in multiplex mode. All the IC's carry production dates in 1973, so the instrument must be from that year. In the manual, the copyright notice is dated 1974.

When I switched on my DiVo, nothing happened except for the “AC” light coming on. I switched it off and removed the top and bottom of the case to be able to measure things. Using a scope, I found the clock oscillator was working and the displays received their multiplex signals. When I looked again, I noticed the rightmost display had come up. It stubbornly kept showing “00” whatever I did with the range buttons and inputs. Apparently, the A/D converter isn't working.

I hoped the other display would wake up as well, but unfortunately, it didn't. I may need a replacement SP-351 display. I'll see if I can find one and then I'll fix the DVM.