[time-nuts] Re: Faulty HP 10811D

[frank.stellmach at freenet.de]

The thermal fuse on the top board often fail after many years, w/o overtemperature event, just by ageing.

You might replace it with a short.

Check the oven current, if it’s very low or zero, then it would be the thermal fuse in first place.

If it’s a few mA, and maybe the oven won’t get warm, then it might be the NTC which is glued inside the oven mass.

I once had a 10811 with intermittently open NTC.

I drilled it out, used a standard precision NTC, I think 100k, placed it into the bore hole with some thermal paste, and trimmed the oven set point (written on the XTAL, or the oven mass) according to the manual, but taking the different NTC characteristic into account.

The oven still works like a charm.

Frank