Dear Joost,

In regards to your second problem, I also had a similar one with my
5-year-old Optima where the FS1 fuse (5A 250V) on the HT motherboard would
blow repeatedly. Initially the problem was very sporadic, could run for a
day or so and then all of a sudden the current would rise and then the fuse
would go. I checked my source installations so many times I could reassemble
the whole thing in my sleep! It turned out that we had a problem with
overheating causing excessive current on the source controller unit. We
never actually isolated the faulty component(s) but for safety's sake,
replaced the large capacitor (40V, 10,000uF), the bridge rectifier and the
two transistors associated with it. These were ordered from the factory in
Manchester, England by the service engineer. The total value of the parts
was no more than about 200$ (Cdn) compared to the one-day charge (1800$) for
a service call from Micromass! Wish I could have solved it on my own.

I hope this helps.

Diann Whitehead
Canada Customs & Revenue Agency
Laboratory & Scientific Services
Ottawa, Ontario
Canada


----- Original Message -----
From: Joost Van Haren <[log in to unmask]>
To: <[log in to unmask]>
Sent: Tuesday, June 06, 2000 6:50 PM
Subject: [ISOGEOCHEM] Optima and Prism questions


> All,
>
> I have two questions regarding the mass spectrometers that we have. I'll
> give a brief history on the problem and the attempt to solve it.
>
> 1) the penning gauge on our VG Optima from one day to the next did not
want
> to start up. Prior, I shut down the system electronics and the source
> controller without switching off the penning gauge. When I started the
> system back up the penning gauge did not want to start again (reads 1e+3).
I
> cleaned the gauge and measured the pins on the cable comming from the
> Utility PCB. According to the drawings pins 2 and 7 have to form a closed
> circuit to enable the penning gauge. When I switch the penning gauge on on
> the computer screen that does not happen. This leads me to believe that
the
> penning gauge enable circuit on the Utility PCB is not functioning
properly.
> There is an IC and a Transistor in that circuit that could have gone bad,
> however, we cannot find those in the states. The # for the IC5 is SPH610-2
> and the TR1 is 2N7000.
> Is my assessment correct and if so does anyone know where I could get
> replacements for the potentionally bad parts?
>
> 2) We also have a VG Prism II which has not been behaving well. On and off
> over the last month a Electron volt PCB fault comes up on the screen and
> with that the source current is off scale and the filament current is 4.4
in
> stead of 3.8. Finally last week the instrument was running fine over the
> weekend the source fuse blew (the 5X20 mm, 5A 250V ceramic fuse). I
replaced
> the fuse and ever since the fault has been coming up again. I also have
> taken the source apart 3 times over the last month to make sure that
> everything is put back perfectly and I have not been able to find anything
> wrong in the source itself. Has anyone had this problem with this
instrument
> and if so do you have any suggestions where the problem might be?
>
> Thanks very much,
>
> Joost
>
> Joost van Haren
> Senior Research Specialist
> Columbia University
> Biosphere 2 Center
> 32540 S. Biosphere Rd.
> P.O. Box 689
> Oracle, AZ 85623
>
> Voice:  520-896-5018
> FAX:    520-896-6214
> [log in to unmask]
>