19-10-2011, 11:27 AM
OR.. and this is always a beaut.. back in days gone by when a resistance was needed to be absolutely precise they used to fit a long carbon composition resistor and then stick it on a bridge and file away at it until it was spot on the required value... In a precision piece of test equipment this is probably what you have, and may have soaked up loads of damp over the years and be the cause of your problems..
Best approach now would be to trace out and draw your own schematic (with values) and see where it lives in the circuit. My guess would be in one leg of the bridge or the oscillator timing circuit..
Another thing to check is the speed the oscillator is running at, either problem could be causing the 40% off reading. Somebody who has a calibrated working example should be able to help with accurate voltage readings for the test points lurking within.
Best approach now would be to trace out and draw your own schematic (with values) and see where it lives in the circuit. My guess would be in one leg of the bridge or the oscillator timing circuit..
Another thing to check is the speed the oscillator is running at, either problem could be causing the 40% off reading. Somebody who has a calibrated working example should be able to help with accurate voltage readings for the test points lurking within.
