Hi everyone,

> I have been experiencing an error signal which  I am unfamiliar with on
> our VG Prism Series II mass spec. If anyone has any information they can
> share or suggestions on how to trouble shoot this problem I would
> greatly appreciate it.
>
> We get a "FAULT electron volt PCB" error signal  when we boot up our
> instrument with HT (high voltage) turned on.  If we boot up with HT off
> we do not get the error signal, instead we get a source filament in
> limit error signal which disappears after a few seconds.  With the
> "FAULT electron volt PCB" error we have no beam. When we boot up with HT

The "source filament in limit" error appearing for a couple of seconds on
source switch-on is pretty normal, as the filament tends to overrun somewhat
as it warms up, then the trap feedback circuit kicks in.

The "FAULT electron volt PCB" error could well be due to a creeping filament
which is sagging and touching the source block.  If you switch the monitor
to read the Electron Volt signal with the fault message displaying, what
does it show?  If you could list /all/ the source parameters as they appear
on the monitor with and without the error, it would make troubleshooting
much easier.

> off, then turn on HT, we do have a beam.  After a few minutes to several
> hours the
> "Fault electron volt PCB" error returns and we lose the beam again.

Hmmm...  This (almost) reinforces what I was thinking, but not 100%.

With the HT off, have a look at your Filament current, which should be
around 3.6A.  Switch the HT on, and see if the Filament current increases
appreciably.  If so, your filament is probably on its way out, and touching
the source block when under load.  If not, let me know and I'll think of
something else :-)

Andrew