Broken CNC milling machine

[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 

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]

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

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 

[AdeV]

Mutter grumble... 

So - replaced all the caps  cleaned up the boards  returned and re-wired  and things lit up kinda like they should do  - but no spindle action 

When I powered up this time, the first thing the machine requested I do was replace the buffer batteries... so - whilst I had it all powered up, I did exactly that: 3 shiny new Duracells to replace the ones which are 8 years past their "best before" date  . And now the damn thing has lost all its parameters & switched to German! Argh! It's not a disaster, I have the parameters saved on the computer, but buggered if I know how to switch it into English until I find the manuals. Annoyingly, I think the spindle problem MAY be the phases are out of order in the plug - this is the first time I've tried to use it (well, excluding the time it caught fire a few weeks ago), and I recall I had to switch wires in the plugs of both the normal mill and the lathe, in order to fix a phase difference between my old & new workshops...

So... once I work up the Round Tuits to figure out the parameter re-load... I'll have a go with the phase wires the other way around. Oh, and try to figure out why the shiny new batteries have decided not to work properly.

TBH, I'm getting closer to think it's time to re-fit this mill with some updated electronics/controller.

[awemawson]

Parameter 92 for most early Heidenhains

[AdeV]

Hi Andrew -

I discovered that earlier, reading a post on the CNC Zone forum + downloading the TNC151 service manual. It's hardly obvious about the setting!

I suspect I'll have to type them all in this time, as I can't find my serial cable, or the laptop with the TNC Server program on it (!), so that should keep me busy for an hour or so tomorrow!

[awemawson]

TNC server is downloadable from Heidenhain or I can send you a copy

The cable is straightforward and again I can send you details, and if you've lost your back up there are default values for most Interact versions floating about on the web.

[AdeV]

Thanks Andrew - I've got copies of the software floating about somewhere... the cable, well, I think I have enough D-subs to build another one, if not, it's no big deal, I can buy the bits readily enough.

So last night I printed the parameters out, and this afternoon I typed them all in... Couldn't get any useful response from the machine... so I powercycled it "just in case". Back to German!  Typed the parameters (all 263 of them!) again... this time I got it to home in, so progress! Went for a spindle start, and CLACK! Tripped breakers everywhere.  Switched it on again... German again! 

The batteries I've put in all test good, so I'm not sure why it's having such a hard time with them. I reckon I've got another 2 or maybe 3 parameter-typing sessions left in me before I lose my rag... so I've come up to the office for a think and a

Now... I do recall this machine being particularly hard on breakers, I had it on a "C" type at the old place (i.e. it'll take a substantial surge over-current before it trips), whereas it's on a "B" breaker now, which won't help. Plus, in my efforts to get life out of it, I've turned all the knobs to 11  so maximum ramp, maximum stab, maximum current limit.... so that might be causing some issues  For my next parametric session, I'll try turning it all down again & see where we go. Also I need to dig out a laptop to plug into it, if I don't have to type the parameters every time, I can have a few more goes at getting it working 

Anyway... I think we're nearly there, just need to get everything warmed up properly and the pentagram the exact right shape, fingers crossed "just so", and the old girl will breathe again!

[awemawson]

You shouldn't lose parameters if a breaker trips

The 'replace batteries' message has cleared has  it?

I ask because it's not impossible to put the batteries in wrong polarity. iirc it's positive outwards on a TNC151 but on my TNC355 they are in a tiny tube buried inside the control and even worse to see !

[AdeV]

You shouldn't lose parameters if a breaker trips

The 'replace batteries' message has cleared has  it?

I ask because it's not impossible to put the batteries in wrong polarity. iirc it's positive outwards on a TNC151 but on my TNC355 they are in a tiny tube buried inside the control and even worse to see !

I'd not expect to lose the parameters on a battery change, no: However, that's what's happening. Polarity is correct. The only thing I can think of immediately is the little plastic housing is somehow stopping the batteries from connecting properly... It's the same on the TNC151 - a thin tube with a plastic insert that carries the three cells.

[awemawson]

But if that's the case the 'change batteries' message will persist 

[AdeV]

The battery message doesn't come up if there's no batteries in it... either that, or it comes up in German (there are a couple of messages).

[AdeV]

Bit of an update...

Purely by chance, I tried the batteries I was putting in the mill in another device ("The Exterminator!" fly killer, since you ask  ), and it worked, but then didn't..... Hmm... A little investigation suggested one of the terminals wasn't making a good contact; so I scrubbed it with a sanding block, perfect.... Just put them back in the mill, typed all 263 parameters in (luckily, about a pageful of them are zero!), held my breath and powered down.... and back on. It came back in English! Yay!! So that's one of the jobs off the list.

I've also managed, courtesy of another group, to grab a copy of the diagnostics/setup manual for the KTK drive - so maybe tomorrow, I'll have a crack at adjusting my drive board using the given procedure to see if I can get it to spin up without tripping all of the electrics off...

If that doesn't work, somewhere in the Atlantic Ocean (er, hopefully still on a boat!) is a replacement drive unit, with the thyristor board & the control board all in its box. Obviously I'll replace the big fat capacitors before I try to use it, and if THAT doesn't work, then at least I will know where the fault lies... finding a replacement for that board, however, is likely to be an excercise in pain - apparently they're rarer than hen's teeth (and the thyristor board was rare enough!) I don't really want to go down the road of buying another entire machine just to get one board out of it; but without knowing what the electronical magic that's needed to drive the spindle at the appropriate RPMs, at this time I don't know what I'd replace it with if I did to a LinuxCNC (or similar) retrofit.  If I do get it going, though, I want to find a replacement for the CRT, which is getting very dim in its old age.

[awemawson]

Every year, a few days before Christmas, I replace the batteries in my TNC355 with brand new Industrial Duracells only bought from RSComponents, and update the 'Batteries Changed XX/XX/XXXX' label on the outside.

Why that particular brand and that particular source? Because there are so many fakes about it's about the only way of making sure you buy what you think you are buying, and the application is too critical to take chances !

[AdeV]

These are Duracells (they call them "Simply Duracell", I assume to differentiate them from all the miriad of spin-off names which mean the square root of bugger all in real life), probably bought on a whim in Aldi.... This is the first time I've changed the batteries since I bought the machine about 4-5 years ago - I actually can't remember when I bought it! Next time, hopefully in another 4-5 years, I'll remember the trouble I had and make sure the contacts on the cells are clean *before* I power it off!

[awemawson]

Google Duracell reliability and leakproofness, and the only ones that come close to the 'original' Duracells are the 'Industrial' ones.