Varian pump controller electronics

[Peter Apps]

Hello all

This may be something of a long shot, but I am putting my faith in the assembled expertise of the forum.

I have a Varian 320MS in which the turbopump controller and one of the two 24V power supplies suffered blown varistors as a result of my boss messing with the electricity.

I have fixed the 24V supply by replacing the varistors and the MS system control software starts OK and runs through the startup to the status screen that shows 'No vacuum" and plausible values for the various zone temperatures.

However, as soon as a hit Pump Down on the Analyzer control screen the new varistor in the pump controller blows, and takes the 4A fuse with it. The controller is a TV 401/301 NSF C.U. model 9698979M002, and the varistor is at RV3 between live and ground. The replacement is rated 270V, if the original was the same as at RV4 (neutral to ground) then it was 275V. Power comes from a UPS showing 230V output, measured 227 V at the socket between live and ground and between live and neutral.

The pump controller draws power from the power board at the back of the cabinet, presumably something there is malfunctioning to generate a voltage spike on pump start up.

Does anyone know where the fault might lie ?, and any diagnostics I can run to find it.

I am more or less stuck with going the low cost component swap route since the same boss who messed with the electricity is distinctly reluctant to spend any money on fixing things. In any case, it does not make sense to put in a new pump controller if there is a fatal fault elsewhere that will kill it as soon as switch it on.

Have a great weekend.

Peter

[Peter Apps]

In a triumph for the empirical experimental approach I now find that the new varistors I got are too low voltage, so they just blow as soon as they see mains power, even when they are the only component in the circuit.

So the question is now simplified to; what varistor do I need with mains volts at 230 V and a 4A fuse in series ?

Does anyone know what the original varistors are at RV3 in the controller ?

Peter

[uzman]

Hi Peter ,

I think varistor code RV3 ( or RV4 ) is not the varistor voltage code , they are numbered to locate them in the circuit diagram.

Inspect a good varistor ( if any ), there must be some codes on it to locate the correct one. Google may help to find the right voltage.

You may try a varistor around 350 volts for a starter , or even you may try without a varistor to test your system for a short term.

[Peter Apps]

Thanks Uzman

You are right the RV3 and 4 are just the circuit board locations.

At RV4 the surviving varistor has 275 on it, and Google turns up three possibilities for which voltage this refers to; AC max, varistor voltage or clamp voltage. I was too conservative and took it to be varistor voltage when it is probably max AC voltage. The new ones have 275 on the label, so superficially they are the same as the original.

The lowest varistor voltage I can find with a max AC voltage safely above the 230V mains is 390 V, so I am going to try to get hold of some of them - logistics here are a nightmare.

Peter