ICL One Per Desk / BT Merlin Tonto
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Troubleshooting : identifying Faults with OPDs
- Common faults with OPD base units, microdrives, modems and ROM packs
- Common faults with OPD mono and colour monitors
- Common faults with Computer One and PCML Teledrives
- Common faults with serial and parallel printers
Common faults with OPD base units, microdrives, modems and ROM packs
OPD base units are fairly reliable, and it's easy to substitute parts from another machine. The OPD carries out a POST (Power On Self Test) routine which helps to diagnose the most common faults. During the self test routine, the OPD checks each sub system (modem, memory, ROM packs) and halts if there is a serious problem.
The most common problem are loose connections, followed by bent pins in the expansion units. 90 percent of faults can be resolved by checking the ROM pack or modem.
A faulty OPD will hang during the POST routine and will present a series of vertical bars in the monitor.
Switch off the OPD and carefully removing the modem and ROM packs and check for dust in contacts, bent pins on expansion cards.
Reattach the modem and ROM packs, and switch the OPD on again.
- Microdrives : Microdrive cartridges have a limited life of approximately 200 hours continuous use, so first suspect the cartidge rather than the microdrive units.
Try removing the outer casing on the microdrive unit before inserting the microdrive cartridge.
It is fairly common to find that one of the two microdrives works intermittently, and this can be cured by first cleaning the microdrive heads with isopropanol alcohol, and if this does not cure the problem, replacing the microdrive units.
- RAM Packs, ROM Packs and Capsules :
Loose connections are the most common faults will OPD expansion units.
- Switch off the machine and carefully remove any expansion units.
- Remove individual capsules and check for bent pins.
Pins can be bent back into position with a pair of fine tweezers, but be carefull not to apply too much pressure!
Common faults with OPD mono and colour monitors
OPD mono and colour monitors contain a switched mode power supply which powers the OPD via a fifteen pin D socket.
We are developing a circuit to enable the OPD to be powered from a PC power supply and run off either a colour television or PC monitor.
OPD mono monitor
OPD mono monitors are 9 inches across, compact and of a simple Phillips design. They are fairly reliable and are straightforward to repair.
If the display flashes, try adjusting the contrast control knob several times, as this sometimes restores the picture.
The majority of faults can be traced to a faulty C10 capacitor in the switched mode power supply, which leads to compaction of the display. It is normal to hear some electronic 'chatter' from the monitor though this can be disconcerting at first!
OPD Colour monitor
OPD colour monitors are 14 inches across and are based on a Microvitec design developed for the BBC and Sinclair QL micros.
The picture quality is superior to the OPD mono monitor and allows one to appreciate the colour graphics capabilities of this pioneering computer. The colour monitor is rarer than the mono monitor and rather large and heavy.
Common faults with Computer One and PCML Teledrives
Computer One
The Computer One disc interface is fairly simple and consists of an enlarged capsule which fits into one of the OPD ROM slots.
The most common fault is caused by faulty connections or bent pins on the ROM pack.
PCML Teledrive
If there is a loose connection between the OPD base unit, ROM pack, Teledrive ROM capsule and the Teledrive, the OPD will reset or report a 'Tdrive failed' error.
Switch off the OPD, remove the ROM pack and Teledrive ROM capsule. Check very carefully for loose connections or bent pins.
The Teledrive ROM capsule needs to be fitted to the rear right hand side capsule role, marked 'J5'. This corresponds to the location in the OPD memory map. Teledrives will not work with early versions of the two slot ROM pack, as identified by the ROM pack serial number.
It is normal for the OPD to report 'invalid capsule' during the power on self test (POST) routine. Remember to switch on the Teledrive a second or two before the OPD, otherwise the OPD will not be able to 'see' the Teledrive.
Early models suffer from a fault in the power supply which can lead to both disc drives locking up.
Common faults with serial and parallel printers
The OPD will work with serial printers such as the Epson FX-80 and ICL thermal printer (OKI-20) . It is possible to connect a parallel printer by modifying a QL serial to parallel printer interface. These can be obtained from RWAP services or from ebay for a few pounds.
The ICL thermal printer is capable of printing in black and white or colour on plain paper with the aid of a thermal transfer ribbon.
It is also possible to print directly onto thermal paper.
The OPD BASIC cartridge contains a program called CONPRIN which controls printer settings.
Details of the OPD printer pin out will be available shortly.
It is fairly straightforward to wire up the three pin serial cable oneself or to modifying a 9 pin serial printer cable.
