Unfortunately, I haven't been able to get the problem to repeat. I tried slowly unplugging the parallel port cable as the router was moving, it gave a very different reaction, so I doubt its loose cables. I am leaning towards the 203Vs going into shutdown mode due to excessive heat, as I don't have the motors turning to 'standby mode' when things aren't running, so they're at full power when standing still (which would explain why it happened when I wasn't cutting, and the machine was just idling, but under power). I can't really imagine it being a voltage issue, even though I went with the higher voltage motors, the power supply I have, and the Caps used, should be providing more than sufficient power. Any other ideas? I'm going to track down an IR thermometer to get some temperature readings off the Geckodrives some time this week.

Do you have the Geckos on a heatsink? Pretty sure the book says anything over 3 amp needs a heatsink and make sure you are using a good thermal compound like Arctic Silver Arctic Alumina to transfer the heat properly and will not run when heated.

Heat sink does sound like a prime candidate. When starting off "cold" how long does it take for the problem to manifest itself. Can you touch the Geckos and do they feel hot. Hope you find the problem. Harbor Freight sells a thermal sensor for $89.99 take off %20 with a coupon.

There is picture of the panel layout in post #75. There is what appears to be a modest heatsink. There is another picture of the of the outside of the case and no apparent ventilation holes. If the panel is oriented in the case the way it appears in the picture, I could see the heat accumulating at the top of the panel and maybe overheating one of the top two drivers.

Again just wild speculation, but things to consider.

Looking here as DB found.
Solid heat sinks will not dissipate your heat rapid enough. You need the surface to thin out for the heat to travel or else you are just making a hot plate to cook with. I do not see any thermal compound out to the edges either. It may be there but a complete thin layer of surface coverage is crucial. Any air gap and even metal bolted tight together will not transmit heat efficiently. Reference is here. A finned sink would be better also. Types of heat sinks here. You also want the sink to dissipate the heat outside the box not in. For a quick test, use a high cfm fan and have it directed so the air is flowing both in back of the plate and in front. See if the problem lessens. Just my opinion and I hope you understand that. Hope you get it figured out.

Boy I am slow at reading, I would not be so concerned about box ventilation unless a through the box heatsink is not getting enough out. A sealed box is always cleaner than a vented one. I run 6.3A on 2 of my 203V and have no box ventilation but the box is 24" x 36". If you do use a through fan design, get the filter media with a tactifier already on it or by a small bottle of tactifier and spray the one side of the filter in the direction of air flow. This will help attract the smaller particles that normal would travel through the filter media.

Al brought up a good point about grounding, if you are using a bulkhead connector on the side of your box to connect your LPT cable. Most of them ground out to the case when you attach them. If that is the scenario, you may have a ground loop because your computer LPT is already creating the ground path for stray currents from the metal shield that is on the back of the computer. Something else to try.

Thanks for all the suggestions, everyone! I've been out of town for a few days, so I haven't been able to test anything just yet, but I am thinking that it is a heat related issue. I did forget to put thermal compound behind the drives when I put them on. They'll be getting a coating of arctic silver this afternoon, then we're going to turn the fan off and see if I can get the problem to replicate more quickly.
As for the grounding issue, the LPT cable is attached to an ungrounded plastic through connector, so it is not grounded out to the case. It took some doing to find one of those, but I was able to finally.
I think the issue is, as most of you have pointed out, heat related. I'm going to take a look at modifying my design for my heat sink, possibly to mounting each Geckodrive on a finned heat sink or something of that nature, if the thermal compound doesn't do the trick (which it very well may).
Thanks again for all the suggestions. Off to run some torture tests!

Zouave, and your power supply specs is? (vdc,va,vac).
What wiring system? (Unipolar, Bipolar Series, Bipolar parallel).
dont know your confiuration.

for your drivers, you know the resistor config?

1. 1A – 7.8K
2. 1.5A – 12.8K
3. 2A – 18.8K
4. 2.5A – 26.1K
5. 3A – 35.25K
6. 3.5A – 47K
7. 4A – 62.67K
8. 4.5A – 84.6K
9. 5A – 117.5K
10. 5.5A – 172.33K
11. 6A – 282K
12. 6.5A – 611K
13. 7A – OPEN

After a very busy spring, I'm finally getting back around to this project. Just ordered a large heat-sink extrusion from http://www.heatsinkusa.com/, I'll report on how it works once it gets here.

I have a large heatsink on my control box and never had a problem...good luck.

I followed the plans.
5 geckos drives on a 1/4" thick x 4" x 20" piece of aluminum on 2" standoffs. Sealed box with internal circulation fan located behind it.

No issues...ever.

Well, the saga continues with further mysterious results... I've checked my cable connections, all were tight and clean. I've run a solid ground wire from the heatsink to the DIN bar (as grounding for wires coming into the control box and the wires from the BOB terminated on the heat sink). I've also acquired a large heat sink that will be mounted on the side of my box, as others have done, once some basic machining is completed on it (cutting in a slot for a rubber gasket to seal against the box) and drilling and tapping holes for the Geckos.
Symptoms I've noticed at this point:
LEDs on the BoB out immediately after errors appear.
High frequency buzz from the motor that most often loses control.

Possibly related is that after the latest error, I started up the computer & MechMate, and the X-axis had reverted to running the same direction instead of opposite directions (being on opposite sides of the MechMate). Upon test motion, gantry tried to twist off the tracks (boy is this thing stout!) but was unable to. No damage to machine, corrected axis slaving setup, and cut project without issue.

Is this sounding like a computer issue, suddenly?

When you say errors, what are the errors specifically?