HP 5971A MS: low ionization gauge pressure and odd noise

[sirpatty79]

Hello all,

I maintain an HP 6890/5971A GC/MS system where I study and am stumped concerning a recent problem. Recently the MS stopped collecting data and the log displayed the following messages (paraphrased):

Diffusion pump is too hot
Diffusion pump is too cold
System is in VENT state
Run Error: 1101,"(RUN:RDY ON;): Mass spec fault during acquisition : 417"

The detector manual and error code search didn't provide much insight. I noticed the MS was making an unusually loud noise and that the pressure reading on the ionization gauge controller was ~10^-3 torr, about 100 times higher than normal. The diffusion pump fan is functioning and the noise seemed to come from inside the rear of the MS. Upon checking the vacuum status, the pressure was normal (50 mtorr). I'm assuming that the pressure value in the vacuum status window is the foreline pressure, while that from the gauge controller box is the source pressure? Anyway, when I tried to vent the system the program seemed to be unable to complete the vent cycle. I'd really appreciate any feedback on possible causes/remedies for the problem. Thanks.


-Pat N.

[Sielemann]

If the pump reports being too hot and too cold it sounds like a sensor problem...

You say that you were unable to complete a vent cycle - not a pumpdown cycle ?

I would vent the system and first replace diffusion pump fluid. If that doesn't help it may be the heater/sensor of the pump that is broken. I had a similar problem (system reported diffusion pump too cold and remained in Vent state) and ended up having to replace the entire pump (I had a spare and parts for this MS is hard to come by).

Hope this helps.

[Don_Hilton]

Can you describe the sound coming from the MS? It's been a while since I've touched a 5971, but I don't recall much in the way of moving parts near the back of the MS. Could it be the fan turning, but having some kind of problem?

With the description, even if the fan is having a problem, there is clearly something else going on.

From the pressure reading in the MS, the diff pump does not appear to be working properly.

[sirpatty79]

Can you describe the sound coming from the MS? It's been a while since I've touched a 5971, but I don't recall much in the way of moving parts near the back of the MS. Could it be the fan turning, but having some kind of problem?

With the description, even if the fan is having a problem, there is clearly something else going on.

From the pressure reading in the MS, the diff pump does not appear to be working properly.

I'd describe the sound as a whirring (?). It does sound like you
might think a malfunctioning fan rotor would. The sound did come
and go, but even when present the fan was blowing air well. Yes it seems that the diffusion pump is either not turning on because if a faulty sensor or because the pump is broken.

-Pat

If the pump reports being too hot and too cold it sounds like a sensor problem...

You say that you were unable to complete a vent cycle - not a pumpdown cycle ?

I would vent the system and first replace diffusion pump fluid. If that doesn't help it may be the heater/sensor of the pump that is broken. I had a similar problem (system reported diffusion pump too cold and remained in Vent state) and ended up having to replace the entire pump (I had a spare and parts for this MS is hard to come by).

Hope this helps.

Thanks. I'll try a pump down again to be certain this won't help and replace the pump fluid.

-Pat

[HbJ]

I don't know the 5971A itself but I've worked quite a bit with diffusion pumps and have seen a 5973 with similar symptoms.

The root cause might be a creeping fan failure: As the diff is air-cooled, it relies on a minimum stream of air to ensure condensation of the pump fluid. If this stream fails, the diff overheats and is shut down.

The noises you hear point to a defective bearing (the factory mounted, praised Papst fans (now EBM Papst) are actually junk).

So I'd go for a fan replacement (and cleaning the air path) first.

[sirpatty79]

Thanks all for your responses. We sent the MSD to a repair facility that ended up replacing the diffusion pump.

-Pat