high voltage and resistors

Resistance value increases and then it finally goes open.

....... Phil

I think that Phil's answer is only correct for carbon composition resistors and for carbon and metal film resistors, all of which are vulnerable to the ozone produced in corona discharges along the length of the resistor. The ozone will react with carbon to produce a partially oxidised surface layer in the first instance, and probably carbon monoxide in the longer term, while metal films will be oxidised to less conductive metal oxides.

Metal oxide resistors, commonly used for high resistance parts, don't oxidise and are not vulnerable to the is particular mechanism.

In general, non-thermal maximum voltage rating for resistors are determined by arc-over and creepage distances.

The particular 0805, SMD ones in the URL he posted are " thick film ", ie "cermet" or "metal glaze" types with a voltage rating of only 150 volts.

Do try to make your posts relevant some day.

........ Phil

First of all: thanks for the replies

As to using bunch of resistors in series - this is for rev2, now I have to make do with what I have without hacking the board too much. What I do not know is if resistance voltage coefficient can jump at some point (it needs to be negative to explain what I am observing). ... I do not wan to experience premature hair loss due to excessive tugging... ... P.S.: the relevant area of the PCB is clean and dry...

Phil Allis>

" The output does not want to go above 460V or so."

Work on that for a bit.

....... Phil

Since cermet and thick film resistors are all made by silk screening a metal-oxide/glass slurry onto the alumina surface, then firing it to fuse the glass, your degradation mechanism is irrelevant in those two cases, and pretty slow for metal glaze resistors, where the metal particles are similar protected by fused glass.

How does your foot taste? I used to claim that you knew your electronics - and you did catch me out a day or two ago - even if if you social interactions were on the sociopathic side of barbaric, but now you are putting the electronics into question.