Mazak QT20 Gear change to 1 produces spindle to stop and go

Have had this problem for a while but would like to solve it. Haven't seen anything on the forum about it.
First off it is a QT20 (1984) with Mazatrol T-1 Mitsubishi controls

On start up if you are in gear 2 and make a gear change to 1, the gear box shifts ok, but the spindle makes about 1 revolution then stops momentarily and repeats this cycle till a reset is made. There are no alarms however the gear reads "0" on the CRT. This is with parameter SD2 set to 1 (manual shift)
At this point attempting to shift to gear 2 produces Invalid entry.

Changing the SD2 parameter to 2 (automatic) allows the change to gear 2 and there is full operation of the spindle. Gear 2 is read on the CRT.

Gear changing to gear 1 at this point produces the same result of stop and start above.

My work around is to program everything in gear 2 but this limits my capabilities.

Thanks for any suggestions that you could give me.
daveh06033

Probably a proximity switch not seeing gear 1 engaged.Control does not get feedback it expects so inches spindle round a revolution to let gear engage.
This is only a guess but it`s the usual way of doing things.
I think I have schematics for a QT20 but with a T2 control.Will have a look tomorrow if I remember.

U R on it Gridley! Especially if it says gear 0. Control doesn't know it finished the shift. Tweak the sensor a little. If you cannot get there, or have to move the switch a lot, then maybe the shifter is getting engaged enough to jog the spindle but not travel enough to make the switch. In that case you have a mechanical problem with your shifter stroke internally in the gearbox.

Thanks for your response to my problem.

We have checked the proximity switch and it seems to be working ok.
That doesn't mean there could be a problem between the switch and the CPU not getting the instruction to signal the gear change.

Having bought this new in 84 we have all the manuals and are trying to interpret the coded symbols to get to all measurable points of the circuit.

Thanks again.

Dh

I didn`t remember to look at my drwgs.Is there possibly a sensor for both gears?

My elec drwgs which are for a QT20 with T2 show a prox switch for both gears.Prox`s are wired N.O. and change when the gear is engaged.Orient only appears to be used when selecting low gear but I might be wrong as I have not studied it.
Machine Ser no. is 60399

Go to the diagnosis interface page and see if H05 bit 3 turns to a 1 status when you shift to low gear. Make sure that H05 bit 2 goes to a 0 status also. Both should not be "on" at the same time. H05 bit 3 is the input from the low gear sensor. H05 bit 2 is the high gear input. It stands to reason that if they are both on when in low gear then the high gear sensor is faulty or the signal wire is shorted. Also, if the sensor is good as you say, when "on the switch" you see no input from the sensor for low gear, then the wiring back to the cnc must be suspect. Since you say that the cnc display never shows Gear (1), my money is on the sensor or coresponding wiring from that sensor. Drawing shows a limit switch but the electrics show a proximity switch but call it GRL.LS. No matter, the control doesn't care which type it is. As for your SD2 parameter the standard setting is 2- automatic shifting. I'd leave it there and begin troubleshooting the low gear circuit.
Loads of luck, Lee

Leelund,I noticed the limit switch in the parts drawing too,but in the electrical drwg it`s two proximity switches.
I haven`t looked to see if there is an input from the limit switch or why it`s there.Have you?

I don't think there is both a limit switch and prox switch. It's probably one or the other. We no longer have the machine and I'm trying to remember 25 years back. I can't remember what type was actually installed on the gearbox. Anyway it doesn't matter, either one will work as the control is only looking for a 24VDC input when in low gear.
Lee

Thanks to gridley51 and Leelund for all the useful information. It helped us find a problem with the Gear 1 LIMIT SWITCH. There are two limit switches to signal gear change. Previously I mistakenly called them proximity switches. Going to the diagnostic menu we determined that the CPU was working properly which sent us back to the basics- The switches.

Thanks again

Daveh06033