Re: Tektronix 2430A occasionally fails some tests

Goran Parezanovic
 

My experience with similar problem as described was that one of the sense voltages coming back to power supply was around 5 % lower that what it was supposed to be ( I think it was 8 V ). The sense voltage goes through 1 ohm resistor in the power supply and the voltage drop through 1 ohm resistor causes regulator to reduce voltage ( in case that there is a short somewhere through 8 V supply ). So my 8 V was draining some small amount ( 5 % ) of current more than max. designed for and from the sense voltage drop the 8 V supply would drop to few percent down and therefore the calibration would fail. I tested components (as far as I could ) but couldn't find what is taking extra current. At the end I decided to reduce the resistor of 1 ohm in feedback branch - I replaced it with 0.9 ohm same watts and everything worked fine since ( 2 years ). Occasionally I open it and check that the voltages are still the same ( since I was a bit nervous playing with the circuit designed to limit the current ) but so far all is good.

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