Multiplier Voltages Jumping Around?

[mburleson]

Hello!

My woes with resurrecting our Thermo LTQ continues. I've sent more stuff out to be tested and found them to be okay. Here is an image they took with my parts showing all the correct masses:


Yesterday, I did an extended dive while directly infusing the cal mix for this system. I noticed that even with the voltages cranked to the max, I saw no noise whatsoever - it was the cleanest yet bounciest mass I have ever seen. Here is a video showing this:

https://drive.google.com/file/d/1wsMEuq ... sp=sharing

I tested continuity across the dynodes – they were good. Video is here:

https://drive.google.com/file/d/1vmESif ... sp=sharing

The last thing I tried, and the one that has caught my eye is that I set the EM voltage for EM1 & EM2 to -500V and tested the voltage output through the cables with my multimeter – I noticed the voltage was all over the place much like the signal!

Video showing jumping voltages on multimeter is here: https://drive.google.com/file/d/1u-ePnF ... sp=sharing

LTQ Tune display recording is here: https://drive.google.com/file/d/1HvZ2SV ... sp=sharing

Thoughts on the jumping voltages? The software never showed the voltage jumping around like that.

I tested our electrometer PCB by following a document from Thermo that says if you touch the anode, you should see an increase in baseline. Here is that:

https://drive.google.com/file/d/1BPSyZO ... sp=sharing

[JMB]

My knowledge of electronics and electrical engineering is severely limited, so I have to take a very simplistic approach, namely:

1) a loose connection (either a ground or a power input) is acting as a make-and-break contact,

2) my experience with cleaning quadrupole rods shows that any piece of dirt/lint etc on the metal surface can cause electrical problems (arcing ??)

Is it possible that the surface of the electron multiplier has just deteriorated enough (that it is no longer electrically continuous) during a long period of non-controlled storage?

Regards,

[mburleson]

My knowledge of electronics and electrical engineering is severely limited, so I have to take a very simplistic approach, namely:

1) a loose connection (either a ground or a power input) is acting as a make-and-break contact,

2) my experience with cleaning quadrupole rods shows that any piece of dirt/lint etc on the metal surface can cause electrical problems (arcing ??)

Is it possible that the surface of the electron multiplier has just deteriorated enough (that it is no longer electrically continuous) during a long period of non-controlled storage?

Regards,

Thank you for your input!

I checked each cable going to the power supply and didn't see anything suspicious and they all showed continuity.

I've wondered about cleaning the quads due to dust and such, so I'll try that again.

It certainly was possible, so I popped in some new (sealed) horns and saw the same. I even found a new power supply on eBay and tested it - same result. I'm beginning to suspect it could be either the power module or the board that would do the communication/processing - the LTQ Digital Board.

I'm planning to make a separate post, but I have been wondering if our low pass filter PCB could be bad? That's one of the only PCBs I have not replaced during my time attempting to resurrect this thing.