Denford Software & Machines

First time posting here, so here goes.
I am a technician in a school, here we have a microrouter v3 (black box with denstep/baldor control board).
this machine had been working fine up until last wednesday when out of the blue it stopped mid way through a program, went back to the home position, the motor kept spinning but really slow. I stopped the machine using the M codes on VR milling and thats where all problems started to arise. Machine became unresponsive so was closed off using the software and turned off and both PC and router were restarted. No connection can be found on Comm 1. PC went through the motions trying to find mint on comm 1 but to no avail.
what ive tried thus far
1. opened the black box and powered it up, red seven segment display comes on showing 'L' for about 3 secs then '8'
Sprint 800 board shows led showing 'on'
2. checked all fuses F1 through to F6, all fine.
3. changed PC and re-installed software, made no difference
4. removed eprom from denstep board and re-seated it
5. tried 'Mintman' in denford folder on PC to try and find Mint on Comm1 - no difference
6. tried finding machine using VR Milling, using 'search for machine' by right clicking on real machine icon.

Machine has had an upgrade to the newer porter cable router motor.
Sorry dont really know what else to try, any help would be greatly appreciated. the last time this happened it landed us with a bill for over £1000, Baldor board replaced and Sprint 800 board replaced.

It does sound like the RS232 on the Denstep may have failed. Can you check the RS232 lead to make sure?

Thanks Martin for the reply, I forgot to mention, the RS232 cable had also been replaced to a direct cable labelled 'Lindy, Denford Link Cable' this was in place of the original two peice cable that was supplied with the machine. I have checked the connections with a meter and they seem ok.

I presume the Eprom is version 2.1 or 2.0 Beta?

Yes, version 2.1

It may be worth making a direct 9 to 9 pin baldor lead otherwise it sounds like it's the Denstep card.

how do i go about getting this repaired, can a repair of this sort be done on site or a replacement board sent to try and cure this problem.
What would cause this to happen, and is there anything that can be done to prevent this happening again, as this is the second time.

I notice that there are two boards on the main control board at the top, can these be split or does the whole thing have to be taken out as a unit