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Broken CNC milling machine

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AdeV:
Well... I think I've found the problem with my main CNC milling machine....


There are 6 capacitors, and whilst only one of them has actually caught fire, all of the others are in an advanced state of decay, or have already burst. So... 6 new caps it is. Off to Farnell I go!

I'm just grateful it's not the computer board that's let go... although I need to check it for fire damage, as it sits right over that capacitor, and there's a properly big sooty mark on it... plus I found some blobs of solder on top of one of the orange components (you can actually see it in the picture, 2nd one along), which doesn't bode well.

awemawson:
Well at least you found it before the shop burnt down  :clap:

It all looks horribly familiar.

The orange components are triggering (pulse) transformers driving the thyristors. Are the burnt capacitors Rifa ones like these? (RFI suppressors)

AdeV:
Hi Andrew,

Yep - they're identical in every way!

I've got 10 on order from Farnell (£12.70+VAT)... unfortunately I missed the cut-off for next-day delivery, so it'll be next week before I can fit them. However, I'll pull the board out tomorrow for a good clean up.

I'm just hoping the burnt one didn't take out the resistor above it, as I can't find a like-for-like replacement, nor can I find any reference to the existing part(s) to buy an equivalent...

awemawson:
When I was replacing mine, I dug about on the internet investigating the failure mechanism. Apparently these things are designed to 're-heal' after break down discharge from spikes, and can be expected to be subjected to many many spikes in their life time.

I've gone though all the circuitry in the Beaver lathe and replaced every one of them, even if they look pristine.

AdeV:

--- Quote from: awemawson on February 08, 2019, 07:20:37 AM ---I've gone though all the circuitry in the Beaver lathe and replaced every one of them, even if they look pristine.

--- End quote ---

I will probably do the same to the Bridgeport now... although before I do I'll get it back up and running.

Removed, after much unscrewing, the drive board, unsoldered the caps. The burnt one has taken its trace off the back of the PCB, but fortunately its very simple, so a straight wire bridge will replace it easily. The blackened resistor, remarkably, is still pin on 33.3 ohms! So I'll re-use that, after cleaning the soot off it.

Now I just need to wait for the caps to show up, and it can all go back together again  :thumbup:

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