I have bought some
nasty Chinese 1.3Ghz video transmitters and receivers (due to a lack of alternatives). As a rule I usually whip the case off such items just to check the construction, usually the machine assembled bits look fine but anywhere a human has been involved (connectors, shields, thru hole parts, bodge wires, etc.) the quality can go down hill dramatically. On one of the receiver tuners there is a component missing, looked like it had been knocked off the board. On opening another identical tuner it looks like a capacitor, I have removed it and tried to measure it but the capacitance is so low I am looking for a way to verify it.
I measured it using one of
these by Phil Rice VK3BHR and it comes up as 0.6pF, it is repeatable but god knows how accurate this meter is at this level of capacitance. (Buying a 0.6pF cap and checking it would be a fair comment)
I considered buying a Mastech MS5308, I know overkill for one measurement but it doesn't look like the accuracy would be the best.
This post is the nearest I can find, it is just a breakdown of the official spec not an actual test.
So the question is what tricks are there to figure out the value of this capacitor given it's potentially low value ? I have a digital scope, multimeter and other basic equipment.
This simple Femto Farad circuit looks interesting.
I also realize that there is potential for this value to be a calibrated/compensated for value but I don't know enough about tuner topology to figure that out so I was going for the get it as close as I can and try it approach. Plus the only trimmed component I can see in the tuner is an air cored inductor and in several tuners the trimming looks very similar, which granted may be a good or bad sign. Good - the construction is so tight the trimming is all similar, bad - they just make it look like they trimmed something but the device never gets powered, granted the latter is more likely.