[stuarth]

Not the correct diagram I’m afraid. It shows a 20k/V version of an SBC 851.

The diagram shows a separate AC/DC switch rather than AC and DC ranges at different positions of the main switch, 2AA cells rather than 1, 4 Ohms ranges rather than 3, and different current ranges. Resistor values will be different.

However, assuming a reasonably conventional circuit with a universal shunt, and comparing the front panel picture in post 3 with the resistor values visible in the attachment to post 15, we can hazard a guess at the missing resistor value.

The resistors at the top of the picture are obviously the voltage range resistors, and unsurprisingly are undamaged. These resistors show that this is a 20k/V meter (for DC).

Resistors close to the missing resistor have values of 143, 1430, and 1.41 Ohms

Unless I’m very much mistaken, these are the universal shunt resistors, and the missing resistor is between the 30mA and 300mA switch positions and should be 14.3 Ohms. The resistors between the two pots are 2840, 274, and 27.4 Ohms. These would match up the resistance ranges seen in post 3 with current ranges of 0.3mA, 3mA, and 30mA. There is no 0.3mA range on the main switch, but the top of the 1430 Ohm would give that range for the highest resistance range.

If this theory is correct, DC voltages will read high by 20 to 30%, current ranges of 30mA and below will read very high, and current ranges of 300mA and above won’t read at all.

If you just short the stub ends of the missing resistor, the voltage ranges should read correctly. If you fit a 15 Ohm resistor, the resistance ranges should be OK, but the 30mA current range will read a bit high. Adding a 330 Ohm resistor across the 15 Ohm resistor should give near enough 14.3 Ohms.

Then again, I might be very much mistaken!

Stuart