resistors can be sensitive to all kinds of stuff..
try repairing a keithley electrometer.. you'll be tearing your hair out ...
i had one fith a fried input. the dual j-fet in there is solid unobtainium... ( i have the last three ones in existence , so if anyone needs one
![Grin ;D](https://www.eevblog.com/forum/Smileys/default/xgrin.gif.pagespeed.ic.QVVz6XIT20.png)
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and the resistors are all glass fused .. there is one 100 Gigaohm resistor with 1% tolerance. get a greasy finger on its outer body and kiss it goodbye ...
you can't even clean that sucker with alcohol...
If you have to solder anything in this circuit you need to wait 4 hours before doing the calibration to make sure there is no more thermal gradient...
the service manual of these machines is actually funny to read...
required equipment :- tera-ohm meter ... whathefu ?
do not touch the body of the resistor to avoid contaminating it....
when you adjust the zero balance ater touching the trimpot you need to wait several minutes ( suggested : 15 minutes ) to let the input settle. the fact you poked a trimmer key ( one of those plasitc trimmy pot turners ) through the calibration hole and touched the trimmer has created enough charge differential to upset the input stage ... this needs to disperse first ...
they are an absolute pain to repair...
oh , and keep one hand in your pocket ... the whole input stage floats between -200 and +200 volts.... no touchy !
i have one . maybe i'll do a teardown. it is very interesting equipment. this thing is so sensitive it can actually count electrons...
And capacitors... those suckers also have very funny properties... microphony for example : tap on a ceramic cap and it produces voltage. becasue its dielectricum is actually piezo material.... send ac current trhought them and you can hear it ....
solder them so the dielectricum goes above curie point ( 147 degrees C for the barium based dielectricum in classic x7r style caps ) and the capacitance 'reset's. it will drift to a rate of 1 to 2% per year ....
So forget about using these in a precision oscillator or filter. the fact that you soldered it in means you can wait 4 or 5 years for the sucker to stabilize ...
so it;s funny to see people trying to make superstable oscillators and use class-ii caps as part of the timing element...