Refurbishment in Progress .. .. .

[Musicmanager]

Hi Etech

The good resistor was measured @ 1k

I'm struggling with the better pics .. if I get close enough to show the detail the auto focus produces a blurred image. I may be able to do better with my microscope camera, but I need time for a setup.

The only part number on the board refers to the manufacturers parts list A4A 130 010 ; There are two logos PCL & Loets. neither of which have turned up anything I could find.

I have to say, I've found so many questionable parts, I'm almost certainly going to look for a complete replacement, so please don't spend lots of time looking for answers that may be irrelevant.

Thanks

MM

 

[Nigel Goodwin]

Looking at the board, it's stuffed full of very old components, probably 70's/80's?, so presumably a fairly old lathe.

I've never used a metal lathe, or even seen one used - at the Grammer school I went to we only did woodwork.

 

[Musicmanager]

I've never used a metal lathe, or even seen one used - at the Grammer school I went to we only did woodwork.

OIC, .. we were never so lucky; we had to walk twelve miles to school for our music lessons and 4 of us shared one violin, but it only had 3 strings .. .. but we didn't complain
I've read about Grammar Schools in books !

The lathe will be quite old, probably early 80's but has been refurbished at some point - lots of new bearings and one leadscrew has been replaced. The fireball spur gear came off easily this morning; the reason it was difficult was it had been pushed onto the shaft too far which in turn had misaligned the tree drive belts and chewed the edges off them which doesn't matter as I have a new set of belts to fit.

The lathe story is quite interesting from what I've researched. The manufacturer is Emco, based in Austria who made quite a name in the hobby market with a range of small machines labelled Unimat SL.
The lathe I have is labelled Unimat PC lathe and it was Emco's effort to get into the CNC market by providing an addon kit to fit steppers etc. I gather the first attempts were a bit of a shambles and Emco used an American company to get it right; they did but only produced a limited number ( around 500, I think ) before deciding to abandon the idea.
The main advantage of this unit over the normal SL range is the tolerances on leadscrews are much tighter, presumably because of the likely stepper motor attachments.

The decision is made .. a new replacement board is to be fitted. At the moment I don't know where to start with that, as you know my knowledge is limited, but I'll get there eventually .. .. .. .

To build, or not to build .. that is the question .. ..
Whether ' tis nobler of the mind to suffer
the slings and arrows of chinese imports ..
Or take arms against a sea of mosfets
and by opposing them - to sleep, perfect
in the knowledge that my lathe works OK

MM

 

[Pommie]

To design your own could be an interesting challenge. A 42V 60W motor is not excessive, is it a brushed DC motor? Only two wires going to it?
So, my vote, take arms.

Mike.

 

[rjenkinsgb]

a new replacement board is to be fitted. At the moment I don't know where to start with that, as you know my knowledge is limited, but I'll get there eventually

I'm guessing the speed control board for the chuck motor? A decent generic controller would probably be OK for chuck speed, but I'd be rather careful with a feed control as probably needs one with back EMF speed sensing to keep it stable at low speeds.

Your original board has a lot of analog stuff so it's possible it may have back EMF sensing?


The four power FETs looks to be an "H Bridge" power output stage, with the two transistors just below them likely the drivers for the P channel mosfets.

If you have an oscilloscope, I'd consider removing the power devices then checking the drive waveforms to all of them & see if they are OK. If they are messed up, a new board is probably the way to go, but if things are OK at that point, it may be worth trying a set of new transistors?

Otherwise, this is the type of thing that may work; it looks reasonably well made, unlike a lot of thing claiming similar specs:

DC 10~50V Max 60A PWM Motor Speed Controller CW CCW Reversible Switch UK | eBay

Find many great new & used options and get the best deals for DC 10~50V Max 60A PWM Motor Speed Controller CW CCW Reversible Switch UK at the best online prices at eBay! Free delivery for many products.

www.ebay.co.uk

This article may also be of interest & it could be worth contacting them to see if they have any technical manuals relating to the machine?

Emco PC & Emco "Basic" Lathes

Emco lathes and milling machines

www.lathes.co.uk

 

[Musicmanager]

Hi Rob

Many Thanks for that .. you've filled in some big holes in my understanding .. .. .. . !

I'm guessing the speed control board for the chuck motor? A decent generic controller would probably be OK for chuck speed, but I'd be rather careful with a feed control as probably needs one with back EMF speed sensing to keep it stable at low speeds.

Your original board has a lot of analog stuff so it's possible it may have back EMF sensing?

Hoping I'm understanding your warning correctly, there is only one motor driving the main spindle; the power feed is achieved with a series of spur gears and an additional toothed belt; It is unlikely that I would ever use this auto feed except perhaps for thread cutting and I would do that without the motor using a mandrel on the main shaft.

All I need to achieve is control of speed and direction of the main shaft.

The ' analog stuff ' is mostly buffers & Op Amps, viz

HEF4050BP M8952 TL084CN HEF4066BP MM74C74N LM324N

I did see the lathe.co article and I emailed 'Tony' a few days ago but no response so far, mind you, the Dr has more patience than me !

I'm going to order one of the boards you suggested and try it - I've nothing to lose save the cost of the board which isn't OTT .. .. .. it looks to do all that I need.

Once again, Thanks very much

MM

 

[Externet]

Is it ?

? ----> https://www.ebay.com/itm/392519657547

----> https://lincolnequipmentliquidation.com/hyl5439e0ae965bd/emco/

----> https://www.surplusindustrialequipment.com/catalog/emco/controls/4896

 

[Musicmanager]

Hi XT

Sadly not .. .. .. .. .

That's one of the more recent versions .. a more sophisticated machine altogether .. .. My Board has a reference A4A 130010

I couldn't afford one of those even if it was broke !

Thanks for looking for it though .. .. ..

MM

 

[Externet]

We at the forum WILL guide you to fix it.

More related
----> https://www.ecosia.org/images?q=emco unimat pc lathe parts control board#

To confirm sanity; wire a DTDP centre-off switch to the motor, with a dimmer in series to ensure there is no hidden issues.
----> https://www.amazon.com/DPDT-Center-Mini-Toggle-Switch/dp/B007Z7OA7K

 

[Musicmanager]

XT

We at the forum WILL guide you to fix it.

Thank you, that thought gets me very excited;
Indeed, I have ordered a set of Mosfets etc to attempt a repair ; however, at the same time I have to recognise that the board is very old and well beyond my expertise which means I'm relying on ETO guys for a lot of help.

I have also ordered a replacement board that will probably do the job nicely.

I've already fixed all the mechanical issues that came with the delivery, so I'm probably well in the £ seats one way or another.

I'm very grateful for your support .. .. .. .

MM

 

[Externet]

Make it !
----> https://www.engineersgarage.com/dc-motor-control-using-h-bridge/

or other flavors :
----> https://www.ebay.com/itm/111832695394?hash=item1a09bf8262:g:kr0AAOSwNKRXiZfR

----> https://www.ebay.com/itm/112632201224?hash=item1a39670008:g:JsAAAOSwVP1iT5ZW

----> https://www.ebay.com/itm/154245598195?hash=item23e9c10bf3:g:b1YAAOSwy11f2IOa

 

[Musicmanager]

Hi Guys

Would someone help me with this please .. .. .. ..

This is the lathe main PCB .. .. based on the advice already offered I have prepared to replace the Mosfets marked with a green dot;
The two transistors (TO92) in the red circle are marked as MPS A43; they appear to be switching the gate of the IRF530's so I thought it would be prudent to replace them also; however, the datasheet states ' .. .. high voltage audio amplifier .. .. ' and unfortunately they are in the unobtainable bin.

I don't know where to start with identifying a suitable alternative .. .. . any pearls of wisdom available please ?

Thanks

MM

 

[rjenkinsgb]

I don't know where to start with identifying a suitable alternative .. .. . any pearls of wisdom available please ?

A ZTX457 is a drop-in replacement for the MPS A43.

Readily available from such as Mouser or RS.

https://www.mouser.co.uk/ProductDetail/Diodes-Incorporated/ZTX457?qs=Ly%2FNF0nuwQ%2F2NhEwCKLrGA%3D%3D

Diodes Inc ZTX457 NPN Transistor, 500 mA, 300 V, 3-Pin TO-92 | RS Components

uk.rs-online.com

 

[Musicmanager]

A ZTX457 is a drop-in replacement for the MPS A43.

Readily available from such as Mouser or RS.

Thanks very much .. on order with RS !

MM

 

[Musicmanager]

Hi Guys

A further update .. .. .. .. ..

I've now replaced all Mosfets, the switching transistors and all the Tantulums

No change whatsoever !

The motor will run, but only in one direction and the speed control is totally inoperative.

I've also now acquire a replacement board which works perfectly, direction and speed, however siting it within the lathe casing is a problem because it is approx. 12mm wider than available space.
I will have to do something creative in siting the board in a separate enclosure outside the lathe case .. .. .. .. .. .

Good innit !

MM