Denford Software & Machines

I have a 1994 Harrison M280 trainer. When I went to view the machine it was working ok. Now it has been transported and installed in my workshop. On turning the machine on the screen displayed some info on the operating system, then memory check and below that it said previous bootup (i think!) failed, starting in default mode. It then restarted and came up with the same message. It did this several times and then nothing. After reading the previous problem with the same model of machine I checked the voltage at the floppy drive and found it to be about 4.3v. Turning the pot to maximum produces between 4.5 and 4.8v. The input on the control transformer is connected to 20 and 420 terminals on the input. According to the manual should this be 0 and 420. It is a 3-phase machine. Also the gold mesh screen on the rack power supply had been removed and was in the bottom of the electrical cabinet. The seven bit display on the control board shows nothing but does flicker when the power is turned off. Even with these problems it was still working originally.

I guess that you need to look at the Mains voltage coming in to the machine & work from there. Is it possible that the input voltage is low. Without looking at the electrical drawings it does sound strange that the transformer iw wired accross the 20 & 420 tappings. From memmory the control transformer should output 110 volts to the fans & the 24 volt DC power supply. The 110 should then feed in to the computer power supply. It could all well be down to the 0 going to the 20 volt tapping.

I turned the machine on again today and the seven bit displayed showed an L. I think the monitor may not be working properly. Is it possible to plug in a normal computer monitor to check? The transformer is meant to give out 110v for the control system and this also feed to the power supply unit for the rack. I checked the voltage and the transformer is giving out approx 53.5v between the 0 and 55v terminals.

The "L" on the seven segment LED display is correct. When the software is up & running it should read as a "8" with the E-stop button. This means the control is powered up & initalised.

The monitor is a standard SVGA monitor so you can easily unplug the 15 way heigh density plug from the computer break out pannel on the rack & fit a standard computer monitor.

The machine is now displaying on the monitor. When turned on it goes through it's memory checks and the says "previous boot incomplete-start using default mode" then below this it says "keyboard error" and then it restarts itself. I have got another normal keyboard plugged in to the socket in the back. If I disconnect this it still says keyboard error. I have tried disconnecting the nachine control pad but it doesn't seem to matter which or both of the keyboards are plugged in it still says keyboard error.

Keyboard error , usually means a stuck key somewhere .
so check your keys , especialy the more often used ones

it's a pain but the best way is with a multimeter across the contacts of each key , as they may be more than one , and in the absence of a diagram etc . disconnect the keyboard from the pcb as well .

it may well clear it's self with a aerosol switch cleaner sprayed , so as to be able to get inside the keys .

Dave

also their may be other switches connected as if they are keyboard switches etc , hence why when you unplug the origional keyboard you still get the same error .

other than that it would appear to have a faulty pcb , difficult to trace without a diagram .

but the chances are it's a short across the keyboard wiring / switch contact matrix etc

sorry i can't narrow it down any further .

if you have the wiring diagrams for the machine , that would make it easier to locate

The "Keyboard disconected" mesage is displayed because the computer thinks that the qwerty keyboard is not plugged in. You can try the keyboard in the socket on the breakout board on the rack. under normal useage the keyboard is not requiered but if you need to re set the computer bios then it is. Some machines had a special bios eprom fitted that had the correct pc settings stored on it as default. It may also be worth trying a different qwerty keyboard.
It now sounds like the voltage to the pc is too low. It needs to be 5 volts or it does a continueos re boot like you are seeing.