ORAC CNC lathe

[Tim Lewis]

Has anyone got a spare Digiplan CD20 driver board for my 1983 ORAC lathe? I would like to keep it in its original condition.
Hope someone can help.

Regards

Tim Lewis

[seaman77]

Do you want to send it to me and get it back repaired? I am talking about the drive alone.
You will not have to pay anything...just post a photo of the drive
to help me see that yours is the one i have in mind.

cheers

dimitri

[angel-tech]

his drive has the four leds on one end.

[seaman77]

IS THIS THE ONE?

[seaman77]

...Can you see any of the leds illuminated? If it looks dead you have no choices but to do the following...
The drive consists of two levels/2 boards the one carrying the leds on top of the base board or mother board.
Try to remove the top aluminium heat sink held in place by 6 philips screws.
Then, remove the additional two screws from the board with the leds and gently pull this off to separate it from mother board.
Now do the same with the good drive and first swap the led boards(they are interchangeable /absolutely equal circuits.)
Maybe now you are about to notice that the good drive is out of order. This means the faulty board is the one carrying the leds.
Otherwise the fault is located at the lower board. The one with the power transistors.
Now that you know which board has failed make a visual check with the aid of a magnifying loop x30 and search for any blown capacitors or diodes, transistors etc even for broken coper traces on the underside . If you see nothing, take a multimeter and test all diodes and transistors. If no results yet you should start removing integrated circuits very carefully until you see the board resembling the one at the attached image. For an operation like this you need a low wattage soldering iron and blow air when the solder is in liquid state to completely remove solder.Desoldering pump is not good here.If you can now move the IC with your fingers it means you can remove it. But if force is needed to do this and you continue, you are about to destroy some of the coper traces on the component side under the IC you are working with.

Better try to do this first on a board of a failed transistor radio to gain confidence with such stuff.
When the component is removed and the area still warm get an old tooth brush soaked in alcohol and quickly remove any debris caused by the desoldering process..
Now is time to go to Maplin's and get all the iC sockets needed and solder these in place of the IC's. With the aid of a beeping multimeter carefully test every single resoldered point for continuety. I forgot to tell you to also buy all the IC's consisting this circuit. Besides it is about time after so many years of service to replace them. I'd also replace every single electrolytic and solder sockets for all transistors and diodes fort easy servicing in the future. It is a good idea to proceed placing back all the old IC's and start replacing with new one by one so at the end you will know which one failed. On mine, it was the CD40106BE

Good luck

Dimitri

[Tim Lewis]

Hello

Thank you for the replies - all are very helpful.

The boards I have are the same as that shown in the photograph. The label shows:
Prod. No. CD20
Mfg. no. 1245-029
Serial no. R3-957P/47

The Tested label shows 4.4.84 so I assume that this board has been repaired previously.

I have separated the two boards and checked for dry joints and visibly damaged components. I re-soldered joints which looked suspect particularly a couple on the driver transistors. Unfortunately this did not cure the fault so I would appreciate help from someone who has dealt with these boards previously. I can send the board and will pay repair costs and post packing etc. Please advice address etc.

Thank you for your help.

Tim

[seaman77]

Hey Tim,
Please swap the top boards and attach the faulty driver board first onto the good one's socket. Do not reassemble the bulcky heat sink yet. Only screw in the 2 philips screws to secure the board in its natural position and establish perfect contact. Insert the drives in their respective sockets on the rack and power up.
We must first know on which board is the trouble..Tell me which l.e.d.'s are glowing.If possible send an image of what you see.
Please remember to swap X and Z axes as well.
And don't worry we'll fix that. This happened to my Orac more that twice.
Do you have an air compressor?

I am here to help...If your drive won't be recovered then you will have to send it to me OK?

cheers...Dimitri

[seaman77]

...And I forgot to tell you. Do not touch anything if you forgot to take pictures of it and save them. At least one megabyte each.
So first you take shots and then you start removing things OK?

regards

[Tim Lewis]

Hello

Thanks I'll do this swap and let you know the result. Of the four LED's that are mounted vertically the top one is green (not on) - it is the second LED from the top that is on when the machine is powered up. Yes I do have a compressor!

Regards

Tim

[Tim Lewis]

Hello

I have identified that it is the smaller board that is faulty - the one which is mainly populated with 4000 series chips. There are no visible faults. Could you please advise a procedure from identifying faulty components - or - is a case of trial and error. Are you aware of any particular chip which is prone to going faulty?

Thanks for your guidance.

Tim Lewis

[seaman77]

Well yes!
Test the CD40106BE first.
If you can purchase a brand new equal chip try to place it on top of the suspected one using slight pressure and taking care to keep all pins of both chips perfectly aligned. Read about how to handle CMOS chips.
Use foam tape to keep the new chip securily in place. I am not sure if we have static electricity issue here. If you can guarantee secure contact among the two try to avoid the tape.Then place the board back to the drive and power up.
If the drive still refuses to run the stepper you must use a more elaborate approach.
I propose you solder colored insulated wires...(there are nice multicolor ribbon cables found in most electronic stores like Maplin or Digikey)...on every single pin of the suspected IC. Make these wires long enough to allow you terminate them on a prototyping bread board. Alternatevly you can number these wires and insert them in the bread board in an order coinsiding the pin numbers of the particular chip where pin #1 is the far left lower line of pins as you are looking at the IC from top.This will allow you to insert Led's at every logic IC output.To power the bread board you can use a Li-ion battery charger rated at 4.7vdc 1000mA.
If the experiment shows inadequate power use the 5 volts found in an old desktop computer power supply.The board has been removed from the rack and you are doing totally bench work now.
At this point you can download the datasheets of every single chip found on this small board, so you can check the levels of input signals for the IC under test.You will probably find four or six equal gates in the same chip. If one has failed replace that chip.
To be able to do all this you must be able understanding the truth tables found in data sheets of logic IC's and that is a child's play. You do not need to have knowledge of combinational logic at all.This is mainly for engineers and PCboard designers. Just copy the truth table.
This is the beauty of the electronics of the eighties. I mean you can place hands on them.
If you locate the faulty chip this way better try not to disolder the chip which contains risk. Get a dremel a rotating shaft anyway and cut the chip's pins to remove it trouble free.
Sorry, I forgot to tell you about a time base present on the small board and this is built around a 555 timer. Please do not do anythithing before you make sure its output pin3 delivers pulses to the circuit.
Only if that frequency is high you won't be able seeing anything. In such case you must connect a higher value electrolytic capacitor (try experimenting with values starting from 4.7 up to 16mF in place of the polarised tandalum capacitor connected by the manufacturer (Parker)between pin 6 and ground. Doing so you must remove the existing capacitor as you clearly understand. Or you can use a frequency divider. You can build one on the same prototype board using the 74LS90 IC's
And..here comes another way to locate that beast.
You can take impendance measurments of selected output points of the good board, record them and do the same on the faulty one. This way you can compare the values and from the point you notice a significant difference of impendance you can follow the route of that test point and narrow your search around the components related to this finding.
I know what a headache it gives you when working this way.
That is why I prefere to remove the chips first, solder the apropriate DIP sockets in place of the chips and proceed with the insertion of the new IC's . This way you eliminate the risk of damaging any of the sensitive CMOS chips.
You can not imagine how easy your life will be when you are done with the insertion of the sockets. I usually do this even for transistors and diodes whenever/wherever the circuit allows me.
Before starting better take shots of the PCboard of around 1.5Mbyte and have this image covering the whole screen of your laptop so you can instantly locate the area where you are working with...

Wish you good luck for the moment and feel free to contact me If you feel I can be of more help to you.

cheers

Hello

I have identified that it is the smaller board that is faulty - the one which is mainly populated with 4000 series chips. There are no visible faults. Could you please advise a procedure from identifying faulty components - or - is a case of trial and error. Are you aware of any particular chip which is prone to going faulty?

Thanks for your guidance.

Tim Lewis

[Tim Lewis]

Hello

Thank you for this detailed procedure. I have used the technique of cutting pins off a chip and soldering a DIL holder onto the stubs but with only one or two chips. Suspect I will need to check that the increased height does not interfere with the other board when they fit together. I have a bench power supply so I will set this up to provide a temporary supply. I think the best way forward is to buy a set of chips and replace each in turn starting, as you suggest, with the 40106. I can check the output of the 555 using an oscilloscope. I'll earth myself for good measure when working on the board. Will have a go and keep you informed as I progress.

Best wishes

Tim Lewis