Replacing resistors in VIM box

Had my THC VIM box go down on me after a year of not so hard use.

Langmuir provided excellent customer service and after diagnosis quickly sent me a replacement.

Once my table was up and running again with the new box, I decided to look at the old box and find out the problem. Looks like the R8 position resistor has burnt up - there is no visible sign of damage, but an ohm meter across the posts shows there is no connectivity leading to an open circuit.

Has anyone taken the effort to replace a faulty resistor? Furthermore does anyone know what’s causing these to burn up so that I can prolong the life. I don’t want to be in this same situation in a year!

I don’t think that it is worth losing Langmuir support over a $50 VMI box. This is your box to work on, and I am sure you are entirely competent to ensure it’s repaired correctly.

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100% I agree.

But I now have a working box under warranty which will stay that way, I will not touch.

The non working box, I’m still in possession of. Hence wondering about replacing the resistors.

I’m basically thinking long term here - in 10 years time in the event Langmuir no longer provides support etc.

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Repair it and test it to make sure it works. Then put it in the box and on a shelf some were. When the new box goes bad put on the repaired one. Just keep in mind after setting for a few years it still may not work again. It has happend to me and I see this all the time.

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My plan exactly. But I’m wondering if any one has repaired / replaced the capacitors, and if so what did they use? New to the this afterall!

There was a guy posting about this recent too. He found the replacements online. I’ll see if I can find it.

There should be numbers on the capacitors.

Mine died about 6 months after purchase. Here are my notes from my fix.

These four resistors are merely a voltage divider with a little nuance in they don’t share a direct ground.


I don’t remember much and can’t guarantee the accuracy of my notes. I think R8 calcs are wrong. For some reason, I had a bunch of 5 band resistors. The photo here is after my fix that’s worked for the past 3 years.

I’d recommend that you measure the resistors on your board and start there.

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curious to know what cutter you were running when the VIM went out?

also just fyi, the RAW voltage side is still good as it is on it’s own circuit. i wouldn’t put to much effort on fixing the divided voltage side.

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Holla2040 - thanks for the notes and the pics. Looks like the same one went down for me as for you.

It was the Razorweld that Langmuir sells setup specifically for this application. I’m also aware the raw side is still functional - and have replaced the box under warranty.

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Good to hear. I was under deadline and needed this working, so I hacked it. I mean fixed it.

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