Strange Drive problem

[sneakym8]

I have bought an old (about mid 80's)denford triac, the control is u.s. , infact most of it is missing.
The machine looks like its done little work.
The origional drives and power supply are still ok'ish.
I am probably going to use mach3 on it.But for the time being i am useing cnc zeus to do testing.
The strange problem i am having is if i place any one of the three axis drives in there relative slot, that axis works fine. If i then add any of the other drives the motors whine and control of the motors is unpredictable,this is also the same if i add the third drive. Ihave checked the drive and the logic voltage and both seem fine . Please has anyone got any ideas what might be causing this as all the drives work individualy. The drives are 2 x sd2 1 x sd3.

[Denford Admin]

Very strange

Are you saying the drive and logic supply voltage stays the same each time - with one, two or three drives fitted ?

I'm not sure how (or even if) these cards address themselves, but there must be a way to tell the bus which step/direction pulses to use - maybe there is some cross-talk between cards ?

Maybe Martin can help ?

[sneakym8]

yes
drive voltage and logic voltage remain constant. The output to the motors are dificult to make out on a scope but they change dramatically when i add a second drive , as though they are getting feedback from the other drives.
i have also tried bench testing the drives with totaly different motors and the results are the same. Got me beat at the moment.!!!

col

[Denford Admin]

Have you worked out how the cards are addressed ?
ie, how does the drive know which step and direction it is reading off the bus (I'm presuming thats how it works ?)

Are there jumpers / dip switches to select axis 0 / 1 / 2 ?

Sorry for my ignorance - I just don't know how this system used to work.

It seems logical to me, that the step / direction signals are at fault, if each card works perfectly on its own

[sneakym8]

I have tried removing the step and direction commands from the bus and it still does the same.There are no jumpers or dip switches on the bus. the commands are distributed by the circuit board , there are no options. I have metered the bus for shorts and continuity without the drives in place.

With the drives in place and no motors connected there is about 8 ohms resistance between some of the drives outputs, this is when i meter from one drives outputs to one of the other drives outputs, i need to look further at this and think about whats happening there, i just did this this morning and it didn't seem right , i didn't have much time . maybe i will get some time to lookinto this.

col

[sneakym8]

I got some different drives today, That sorted it.

I would still like to get to the root of the problem some day though.

Thanks for your input..

col

[Denford Admin]

Very strange

I apologise for going down the wrong route with the axis address selectors
Apparently the rack back plane was a "special" with each individual step and direction wired to the appropriate card connectors - not a standard rack as I suspected, where address and data are connected the same to every socket.