X2 Mini Mill - eBAY Item number: 7619672293

Actually the X2 isn't the best mill to convert. It has rack and pinion feed to the Z and a weird spring loaded lever system to support the head. The motor board on this one can be suspect if you live in an area where the voltage can rise to 250 or close as it's rated at 220 v
Since the introduction of the longer table and screw on the X1 that machine actually has larger travels than the X2.
About the only thing going for the X2 is the fact it has a larger motor than the X1 but as the electronics are flawed it's a moot point. -- Regards,
John Stevenson Nottingham, England.
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Given that I ordered the X1 (Dad's birthday) just before I saw the X2 on eBay, that's good news!
Regards
Steve

That's the cheapest for a while - they usually go for a little more, perhaps £350 - he sells one every week - and they aren't such a great bargain, even at the cheaper price.
Add £60 for delivery, and the price is now £370 to £410 delivered.
Chester will sell you one for £450 delivered, and while their after-sales service isn't all that hot it is getting better. AET will sell you one for £490 delivered, but that's "prepared" and comes with some accessories which is worth a bob or two on the price. Warco charge $455 delivered, machinemart don't seem to sell them any more.
Known problems include the FET's exploding when the voltage is too high - I think AET replace them; - Chester replace the whole circuit board on the C3/Conquest lathe (which has many interchangeable parts with the X2/Conquest mill), and perhaps Chester do something similar on the X2. Dunno about Warco.
The FET's are about £3.50 each BTW (not £35 as I was recently quoted!)
The Z axis on the X2 sucks too, I haven't seen one with less than a mm of play.
However, that's getting off the point - you have some kind of after-sales service, guarantee and backup with the big boys, and for the sake of £50 or so, is it worth it? - perhaps, but it isn't the great bargain it might seem.

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Known problems include the FET's exploding when the voltage is too high - I think AET replace them; - Chester replace the whole circuit board on the C3/Conquest lathe (which has many interchangeable parts with the X2/Conquest mill), and perhaps Chester do something similar on the X2. Dunno about Warco. The FET's are about =A33.50 each BTW (not =A335 as I was recently quoted!) -- Peter Fairbrother
My X2 (Chester Conquest) has just expired, so what are the FET's ? where can you buy for =A33.50 each and are they a easy fit. I think that all for now.
Mike Cole

The FETS (field effect transistors) are black rectangular transistors about 12 x 9 x 3 mm with three legs which will be mounted on an aluminium heatsink.
The AC mains input is converted to DC by the rectifier(s), and the FETs then control how much DC goes to the motor. The FETs are the main output switches/controllers, and they are specced for 220V ac input, not 250V, so can blow.
Actually that's just an assumption - and it may well not be true. The US 110V boards also have FET problems, so it may not be solely a voltage issue. Maybe it's bad FET's? Snubber or reverse diode problem? But if you stick in a FET with more magic smoke afaict in practice it seems to work okay thenceforward, so that's what I'd do.
I don't have an X2 so I can't say for sure whether it's an easy fit or not, plus the boards vary slightly between different X2's and C3's. I do have a Chester C3/Conquest lathe and I just looked at that - it has the replacement circuit board I mentioned, and it doesn't use FET's at all, it uses SCR's instead, so that's not much help as a guide.
Which leaves a question - does the Conquest mill have the improved circuit board, like the Conquest lathe? I will assume not, but I may be wrong and/or they may have changed it over time.
The FETs would be fairly easy to exchange if you have any electronics experience, but you will have to do some desoldering and soldering and you might have to mess around with heat-transfer compound (used to improve the transfer of heat between the FET and the heatsink) and/or uprated components which are of slightly different size.
Some other issues - first I'd make absolutely sure that the problem is the FET's - likely but by no means certain, for example the brushes in the motor can go, the wiring can go, the switch, as well as several other things - even the potentiometer which controls the speed can go wrong. Checked the fuse?
Of course the FETs may have small blackened holes in them where the magic smoke escaped, look carefully, in which case ..
Second, when the FETs blow it is quite possible that other components are damaged by the transients. I'd check the circuit generally before just replacing the fets and plugging in - although others might not, and apparently people don't usually bother.
Third, this is mains equipment and dangerous, are you confident you can do it safely?
I'll look out a source for the FET's - £3.50 is the correct-ish price for a suitable FET, rather than for any particular FET.
LMS do fets for $4.95 : but I can probably choose something better for you, those are for US voltages.
It would be a help if you could tell me the numbers on the FETs so I can choose a better specced one. Probably they are IRFP-460 / IRFP-460A, but not definitely. There may be several black packages attached to the heatsink, it may say FET or MOSFET on the board to identify them, or just send all the numbers. If you are stumped send me a photo of the inside of your controller and I'll point out the relevant bits.
BTW some boards have two fets, some only have one. Just to make life more interesting ..

Yes, we "repair" the boards. Originally, over two years ago when we first imported them, we cleaned, adjusted, lubrated, incorporated a captive drawbar sytem on the X2's, and sent them out to our customers. Out of the first 10 we sent out, about 4 boards blew within about three to six months. I do not understand the electronics part of this, so I will explain it simply according to what I have understood from David - our electronics bod.
There are two MOSFETS on the board. Each one is good and "genuine", and correctly rated at 500V. This means each one can handle upto 250V in real terms, before it blows. In each of the four blown boards, the first MOSFET has blown, and the second is OK. However, the second does not kick in. Can't explain why.
In our own workshop, we have measured voltage supply above 250V. Highest measured 263V so far !.
We repaired various boards with various MOSFETS, and we finally settled on 1x1000V IXYS MOSFET IXTH14N100 - Farnell Part No.61602954 cost =A316.40 per piece, when we last checked. There may be a cheaper alternative - better or worse I cannot say, but dare we take the risk?...NO. In the repair process, the 2x500v mosfets are removed, and the new 1x1000v mosfet is soldered into the second slot.
Since then, all boards have been repaired before the machines which we prepared were sent out, and everything in this repect has been fine so far...touch wood.
I have brought this to the factories attention, given them a "free" MOSFET, but for their own reasons, they are not prepared to supply the X2 with the new 1x1000v MOSFET, even though we were prepared to pay the higher cost.
We have stopped selling the X2 now - this being one of various reasons. We are however continuing to support our existing customers who have X2's, and we may sell "repaired" boards at around =A3125.00 inc.vat and carriage, starting next month, along with various accessories and spare parts, in a similar manner to LMS. (Customers who have purchased an X2 from me and who are reading this message can rest assured that they can buy spares from me at a reduced rate - if outside warranty).
Please note, C3 is not equal to The Conquest lathe. C3 is equal to the Super Conquest. Both C3 and Super Conquest have overload protection so chances of MOSFETs blowing on them are far reduced. On them, the speed limit control part of the circuit is more likely to blow (mainly from abuse...knowingly abusing/testing the lathe as I did...can't tell you how....or...unknowingly - fat chance) before the MOSFETs blow. The Conquest, CL300 etc, have no overload protection, and the MOSFETs on them are more likely to blow in similar manner to the X2 boards. Looking at the demand, we might consider repairing these boards too!, even though we do not sell these lathes.:)
Ketan.

Hi Ketan,
Two possibilities - one, if the fuse has blown then the failed MOSFET has likely failed short and is shorting the other MOSFET - or two, if the fuse is okay the failed masfet's gate has failed short, and the short is stopping the second MOSFET's gate getting any control voltage.
In both cases simply removing the failed MOSFET should restore function. You don't really need two MOSFETS.
Fair enough - but 1000v seems a bit of overkill to me, and 14 A seems just a little skimpy. The original FETs are rated at 20 A each, 40 A overall.
Perhaps a pair of 900V 9.5A STW9NB90 MOSFETS at £12.50 for five from would suffice better?
Half the total "on" resistance so should run cooler, plenty volts, and a bit more current - at £5 the pair ...
But I'd understand if you didn't - you have a record of success with the more expensive MOSFET.
I have a standard Conquest, with a "US-made circuit board", which does not use MOSFETs at all.

I can see why - but it did have a niche, so it's sad in a way.
Is there anything else available between the X1 and the X3, at around the £500 mark?
Something with a bit more oomph! than the X1, and less money than the X3, with a non-round column?

Hi Peter,
What you said for the MOSFETs makes sense. We just didn't want to take any risks at the time, and we settled on the one which I mentioned earlier, after testing one or two others. I cant recall if we had tested the one you suggested. If anyone tries out the FETs which you are suggesting, and if it all works fine, do put the post on to help others.
For the Conquest lathe, it looks like we wont be repairing boards if the American boards are fine. (What a shame Anthoney).
Thanks, Ketan.

Peter,
It had / has a niche. There were technical issues such as circuit board, table size (width), limited table travel, restricted Z movement, rack & pinion movement, some of which restricted sales. The main thing it has going for it is the motor. Commercial reasons such as competition was just a minor issue. If and when we come up with an alternative to the X2, you will hear about it, but there are no plans for us to introduce a replacement model in the near future. For the time being, we will concentrate on working with independent companies and persons to provide more accessories for the Super X1L - long table version and X3.
Ketan.

I found my FET's and the only numbers on them are K790 with 2A on one and 6k on the other.Things like the brushes and fuse are fine and a relay and power light still work. I also remembered I have a old control board off a another scrap conquest, I might have a go with fitting that. As I work in Chester I could allways go to ChesterUK and see what they say. There open day is coming up in a couple of weeks.
Mike Cole

Mike That's a 2SK790 FET, N channel, ratings are 500V, 15A and 150W max dissipation, Rds 0.29 Ohms. It's listed as obsolete but can be found for anywhere between £3.00 and £16.00 in the UK. The other codes (2A and 6k are likely to be batch or date codes). Martin

So why would these go rated at 500V 15A ?
. -- Regards,
John Stevenson Nottingham, England.
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Back EMF when stopping the motor might kill em, but then I've never seen those controllers, so cant say
Wayne...

Not entirely certain, 500V is certainly enough to cope with up to 350V RMS supply so it's unlikely to be a supply overvoltage issue. Provided that the device is correctly heatsinked and driven correctly, it should not fail as often as they apparently do. I'm not familiar with the circuit, but if there's a switch somewhere in the high voltage DC supply it may be that a high voltage spike is generated by interrupting the current to the motor or, possibly, due to poor contact in the motor's commutator; of course, if there's a correctly sized suppression capacitor across the motor, this shouldn't happen. Martin

Yes - I was wondering about that too.
Done a bit of googling into the how and why of this, and afaict it seems the US 110V ones tend to fail short-circuit, so either the fuse blows or the motor goes at full speed, while the 220 V ones fail open-circuit, so the motor doesn't turn - the latter could well be a gate insulation failure, the gate insulation fails short and that also stops the second FET's gate getting any control voltage so the motor stops even if one FET is still good.
Looks like an overvoltage problem in the UK, and an overcurrent/overheating problem in the US models. But I haven't studied the circuit either, and am just guessing.
Mike wrote:
What Martin said.
Does sound like a FET failure.
Be a bit careful if you decide to swap the FETs - they are static sensitive devices. In theory you should ground the equipment through a resistor, and wear a grounding strap. You also shouldn't use a vacuum desoldering tool, as they can generate static.
In practice however a little care is all that's necessary, I blew one about 20 years ago, when they were more sensitive than they are now, and haven't blown one since even though I almost never use a grounding strap (only when the equipment is worth £1,000's)
Modern power MOSFETs almost all have electrically insulated cases, so you don't have to worry about electrical insulation between the FET and the heatsink - but it would be a good idea to use some thermal paste between the FET and the heatsink.
And maybe drill some cooling holes, especially if you have a 110V model.
It may well run on one FET - all you would have to do is remove the broken FET, but it will be hard to tell which one to remove. Don't swap just one fet though, swap a pair if you will be using two fets.
If you are stuck I can fix it for you. That way I can also look at the circuit etc, and tell you if I guessed right about what has happened. :)
Maybe swap the fix for some scrap conquest bits, plus ?? either way?

It may well run on one FET - all you would have to do is remove the broken FET, but it will be hard to tell which one to remove. Don't swap just one fet though, swap a pair if you will be using two fets.
If you are stuck I can fix it for you. That way I can also look at the circuit etc, and tell you if I guessed right about what has happened. :)
Maybe swap the fix for some scrap conquest bits, plus ?? either way? -- Peter Fairbrother
Hi again Peter Some good news, I have swapped over the control boards and the old one seems to work. But not tried it under any load or lenght of time yet. If you would still like to have a go at the other one I sure would like to have a spare board just in case. The conqust bits I have are the box section column with its fittins, rack stay and clamp thing at the bottom.
Mike