Fluke 5440B - 1000V range broken

[e61_phil]

Hi,

the 5440B from "a friend" has a problem. It is unstable in the 1000V range.

If I select 275V it is rock stable (measured with HP 3458A). If I go to 276V (next range) the voltage begins to change in the range of a volt. If one goes higher in voltage (~700V) the 5440B sounds like an overloaded switching power supply and resets a couple of seconds later.

The HV selftest stops with „FIL B/OUT BRDS FAULT CHECK +1100V RANGE“. I doubt that this is the problem, because 275V are stable.

Does anyone know such behaviour?

Thanks
Philipp

[TiN]

I doubt that this is the problem, because 275V are stable.

Maybe Fluke knows better?
I'm not familiar with 5440B, but in 57x0A PA in 220V range using another set supply rails (+/-250V) instead of high voltage, to limit the thermal dissipation. After all these calibrators are linear devices, so heat is an issue. If 5440 use same idea, than kV range would be powered from other rails than lower range.

[e61_phil]

In the 5440B there is only a +/-30V and all the rest comes from the controlled HV transformer.

[TiN]

Ok, my bad then. Check if high voltage generated properly.

[RobK_NL]

the controlled HV transformer.

And there's the crux. The +/- HV rails are controlled by a bunch of triacs to suit different ranges of output voltage. Guess which part of the control circuitry is malfunctioning in your friend's 5440?

The service manual has all the info needed.