fv1620
Active Member
New & it was the same make as originally fitted.
I thought it was going to be corrosion or Afghan dust inside between the internal earth connection to the case, which is held tight by the insulated pillar for terminal 1. It was a bit tedious to dismantle, but it seems that the resistor has gone a bit high to the winding that exerts a permanent force to pull the need towards Empty, was lacking power allowing the winding that draws the needle to Full to gain dominance.
I thought it was going to be corrosion or Afghan dust inside between the internal earth connection to the case, which is held tight by the insulated pillar for terminal 1. It was a bit tedious to dismantle, but it seems that the resistor has gone a bit high to the winding that exerts a permanent force to pull the need towards Empty, was lacking power allowing the winding that draws the needle to Full to gain dominance.
fv1620
Active Member
Not worth it, but I like finding out how things work (or don't). Tedious to get inside by drilling out the three locking indentations then progressively prising away the bezel. Even if I replaced the offending resistor, I would never fully trust it again, the mangled bezel would look grotty and besides I have a new one that works fine. But without buying it I wouldn't have twigged how these dual winding gauges work, every indication from circuit diagrams suggest it is simply a single winding gauge.
I was wrong in my original description there is one resistor that feeds both coils. The second resistor is in parallel with Full winding to dampen the pull sensitivity. This is an E96 Series of resistor ie has 6 colour bands & initially I had read the value in the wrong direction! It is 1% tolerance & 50 ppm temp coefficient.
I was wrong in my original description there is one resistor that feeds both coils. The second resistor is in parallel with Full winding to dampen the pull sensitivity. This is an E96 Series of resistor ie has 6 colour bands & initially I had read the value in the wrong direction! It is 1% tolerance & 50 ppm temp coefficient.
fv1620
Active Member
Further investigation reveals that both resistors are within tolerance. Even so, if the 220 ohm resistor was off tolerance it would not have been critical as it supplies both windings. The purpose of the two windings is that it makes the gauge read independent of voltage variations. The culprit appears to be a tiny amount of corrosion on the inside of the metal case that should press against the earth strip on the coil frame. The internal desiccator seems not to have done its job properly. I intend to clean this up & see if it works, so you may well have been able to sort it : )
