Need Help!- Fanuc 15 M Problems

[titanmachining]

I have a Toyoda FA550 with a Fanuc 15 MA control.
I received the machine DOA.
First, replaced the Fanuc Input Unit which was not operating
Now,
I hit the "on" button on the input unit.
The 2 amp fuse on the Fanuc Power supply (F34) in the IO rack blows then the input unit shows the red alarm LED. This will reset after hitting the "off" button.
I first removed all of the 24V input and output connectors from the IO cards to see if that helped. Replaced fuse, same thing happened.
It is still has all of the AC wires connected.
I understand wiring and some electronics but not the control.
Any help on what, where to test from here?
Is the 2 amp fuse on the 24v side or something different altogether.
Thanks,
TME

[memoryman]

Sounds like the i/o unit is defective.
give some more info on the i/o rack.
We have a rack available; I may have the diagrams for that too.

[cncserveng]

Try removing the 24v wire from the unit, power on and see if you get the unit up without a blowing the fuse, if yes there will be lots of PLC errors on the screen.

If the fuse blows with only the I/O board connected, then I agree it has probably shorted out.

If not, you can connect inputs then outputs one by one, or check every input and output to ground using a multimeter on Ohms, this might show a short and save on fuses.

Its long winded I'm afraid.

[titanmachining]

Thanks for the help. The I/O board had a bad relay on it.
Got that fixed.
Also had a bad servo amplifier, got that fixed.

NOW...

When I give a M3 command, I get an Alarm 28 (Spindle Drive Unit Alarm) on the control and AL-15 on the spindle drive.
The control also says OT399 S-Spindle error
Where do I start testing?
Sounds like a output relay problem.
I have the ladder logic but I don't know which command fails.
The error is pretty vague.
Is there any more info I can get from the control or the spindle drive?
Thanks