I have resurrected a long unpowered CNC lathe with an 820T control, having managed to obtain back ups from a long ago user (phew!)

The 820T control is I think a very early one - the machine is build date June 1989. MD 157 (controller type) shows just 21 so I assume it's an early software release as otherwise there would be two more digits

EVERYTHING works except M19 spindle orientation. I am assured that this function was certainly previously enabled and working. The format used is:

M20 (Enable Spindle Drive)

M19 S180 (orient at 180 degrees)

But the system just hangs with the green Run light on

Can someone please explain to me how the loop is closed between the spindle encoder (which works, I can see the angle of rotation under DIAGNOSE) and the MENTOR spindle drive.

I know that the spindle encoder goes to the measuring card 6FX1121-4BA01 and that this card gives the analogue signal to the Mentor Drive but that this is NOT the fault as I've tried a spare.

The Spindle Drive is apparently fully working as not only can I run the spindle CW or CCW at whatever speed I want, and can cut threads reliably and repeatably.

Is there anything else I can monitor or measure ?

. . .this is just so frustrating - so near and yet so far !

That is very encouraging :)

The back up that I have includes:

TEA1

TEA2

PCP

ASM

as well as tool offsets, R params etc. My PCA alarm file comes from a similar vintage lathe by the same manufacturer.

I have back ups from another lathe from this manufacturer (Beaver) who's M19 definitely works as I got the owner to try it, and I've been through the files comparing with mine and accounting for differences but haven't spotted the culprit :(

If anyone knows the specific address and bit I'd be eternally grateful - Beaver (now demised) definitely paid up for this option.

If anyone can please explain what the ASM file is I'd be grateful - it looks like hex machine code?

Thank you for taking the time to help me - much appreciated :)

Maybe I am misleading both you and myself. The control 'hangs' when I issue:

M20

M19 S180

But it is actually hanging on the M20  and never getting to the M19. M20 on this lathe is 'Enable Spindle Drive' by which I assume they mean close the control loop, as the spindle runs M03 /M04 functions correctly without an M20. There is a 'spindle enable relay' but it is set on when the control goes ready.

When I give it an M20 under MDI the green light stays on, but looking at Q100.6 (Spindle Servo Enable) and Q100.7 (Spindle Enable) in the PLC under DIAGNOSE they both change to a '1' from previously being '0'

At this point the spindle is NOT being held in position by the servo, I can freely turn it by hand.

Now a few assumptions (dangerous I know!) I assume that the M20 is implemented in the PLC software as it is not a Siemens standard M code. I have the PLC program from the other lathe, but am slightly concerned to load it as the lathe does have differences - it's a smaller machine, less travel, has a parts catcher (I don't), has no gear change (I do) etc so I'm afraid of doing damage with the wrong PLC program - also I notice in the TEA1 files MD12 (Designated User RAM Area) is '3' in mine and '1' in the other case)

If only I could convert the 'PCP' back up files to ladder logic just maybe I could see what is happening (or not happening!)

Again many thanks for your time. I'm having difficulty finding the meanings of the various PLC Q words and bits - the details re 100.6 & 100.7 came from references in other texts - is there a definitive list somewhere that I can down load, as I cannot find the Read In Enable bit in any of my documentation :(

I'm attaching pictures of:

A/ the MDI code on screen

B/ the MDI code on screen when run has been pressed and M20 executed (but not ended?)

C/ Q100.6 100.7 set after this first run

Picture #3

(It seems that only 1 picture per message is allowed !)

OK I have found a document "6ZB5 410-0DM02 SINUMERIK 810 GA3/820 GA3" that gives a table of PLC QB meanings, but that is for a GA3 - I think mine is either GA1 or GA2 (nothing marked on the controller label and MP157 just says '21' - are they going to be the same?

On the chance that they are QB87.5 is marked 'Read-In Enable' for channel 1 - sure enough before I run the MDI code M20 it is set to '1' and afterwards is set to '0', but when I try and change it to '1' (having put in the password) it stays at '0' and the M19 S180 isn't read in :(

So (again assuming) the PLC must be writing this bit back each cycle to a '0' ?