Schneider Euro PC restoration research notes

The Schneider Euro PC

The Schneider Euro PC is a compact IBM PC-compatible computer released in 1988. A documented example has an Intel 8088 processor, 512 KB of RAM, integrated CGA/MDA graphics and a built-in double-density 3.5-inch floppy drive. The case also provides access to a single ISA expansion slot. (LinuxJedi restoration notes)

One unusual feature is that several machine settings are controlled through the BIOS rather than by the large collection of configuration jumpers common in other PCs of the period. The BIOS can be used to select options such as CPU speed and video mode. (LinuxJedi restoration notes, Homecomputer Guy)

There are reports that Commodore may have contributed to the design, but I have not found a primary source confirming this. One of the restoration articles explicitly describes it as an unverified rumour, so I will not treat it as established history. (LinuxJedi restoration notes)

First concern: the motherboard battery

The rechargeable setup battery is one of the first areas that must be inspected. Multiple Euro PC restoration reports describe either a dead battery or leakage and corrosion around the battery area. One owner found visible PCB corrosion and a machine that produced only a continuous error tone. Another removed the battery before the visible damage became serious. (Old Machinery, LinuxJedi restoration notes)

The battery is not only used for the clock. It also preserves the BIOS configuration. One report notes that without a working battery the machine may be unable to retain the configuration required to boot from the floppy drive. (Old Crap Vintage Computing)

A published Euro PC I modification replaces the original rechargeable NiCd battery with a CR3032 holder. In that particular machine, diode D3 was removed to interrupt the charging path. The author also found that resistor R16 still had to remain connected for the machine to start normally. This is useful evidence, but it is one owner's implementation rather than a universal instruction for every board revision. (Homecomputer Guy)

Before fitting any non-rechargeable cell, I will need to identify the motherboard revision and verify the charging circuit. A normal lithium coin cell must not be exposed to the original NiCd charging current.

Display and BIOS access

The Euro PC provides CGA output on a nine-pin connector. One owner measured approximately 15.7 kHz horizontal and 60 Hz vertical synchronisation and used a CGA-compatible display path or scaler. The same report warns that a blank screen can also be caused by the BIOS video configuration rather than a failed motherboard. (Old Crap Vintage Computing)

The documented BIOS shortcut is:

Alt + Ctrl + Esc

The internal video option and the startup video mode therefore need to be considered during diagnosis. I will not assume that a machine with no visible picture is electrically dead until the display connection and BIOS state have been checked.

The non-standard floppy-drive connection

The internal floppy arrangement is not a normal 34-pin desktop-PC installation.

LinuxJedi describes the floppy signals as conventional but the connector pinout as specific to the Euro PC. The smaller ribbon also continues to the external floppy connector. (LinuxJedi restoration notes)

Another documented machine contained a Sony MP-11W-58S 720 KB drive with a smaller ribbon connector, making a direct swap with a standard PC floppy drive impractical. This identifies one known factory drive, but it does not prove that every Euro PC was fitted with exactly the same model. (Old Crap Vintage Computing)

A published conversion adapts a standard 34-pin PC floppy drive to the Euro PC's 26-position connection, of which 25 positions are used. The modification was tested on a Euro PC II and is described by its author as probably applicable to the original Euro PC. It requires cutting ground tracks and changing the way power reaches the drive. The author explicitly warns that an error can damage the Euro PC II power converter. (MCbx floppy-drive modification)

For that reason, I will not copy the conversion blindly. Before deciding on an internal replacement, I need to record:

the exact motherboard revision;
the original drive manufacturer and model;
connector orientation;
cable continuity and pinout;
the voltage requirements of the proposed replacement drive;
and any differences between the Euro PC and Euro PC II.

A VOGONS repair report describes connecting a Gotek to the external floppy connector and obtaining both 5 V and ground from that connector. This may be a less invasive option, but it is still a community report that must be checked against the service documentation and the actual machine before connection. (VOGONS repair notes)

The keyboard processor problem reported by other owners

The main specialist repair I am researching concerns the keyboard processor.

In the Classic Computing forum report, a Euro PC developed intermittent keyboard faults. Some keys eventually produced strings of incorrect characters. The author socketed the suspected IC and exchanged it with the corresponding IC in a working Euro PC; the fault followed the chip. (Classic Computing forum)

The Schneider-marked part ZC86115P was identified as a mask-programmed Motorola MC6805U2. Because its program is fixed during manufacture, a blank generic MC6805U2 is not a direct replacement. (Classic Computing forum)

The forum discussion also clarifies the terminology. Although the part was initially called the keyboard controller, another contributor notes that the controller function is integrated into the FE2010A. Schneider calls the MC6805-family part the keyboard processor: the microcontroller performing the job that would normally be handled inside a separate PC keyboard. (Classic Computing forum)

The documented MC68705U3 alternative

The Schneider service schematic includes two keyboard-processor configurations:

a mask-programmed MC6805U2 ROM version;
an EPROM-programmable MC68705U3 version.

The schematic also shows different solder-jumper settings for these alternatives. This is important because it means the MC68705U3 was anticipated by Schneider's own board design rather than being only a later hobbyist substitution. (Schneider Euro PC service manual)

The Classic Computing repairer reports that firmware was recovered from an original working processor, programmed into an MC68705U3 and successfully verified. The replacement then worked in the Euro PC. The post includes two downloadable archives:

EuroPC-KbdCtrl-MC6805U2.bin.zip
MC68705-Prog4.ino.zip

The same post explains that the MC68705U3 contains a bootstrap loader and that the required 12-bit counter and source EPROM in the programming arrangement were replaced by an Arduino Mega 2560. (Classic Computing forum)

A later VOGONS report independently describes the same overall approach: change the relevant motherboard jumper, use a programmable Motorola 68705 replacement, build the Motorola programmer board and connect it to an Arduino Mega in place of the source EPROM. (VOGONS repair notes)

This shows that the repair has been completed successfully by other owners. It does not yet prove that the same repair is required or directly reproducible in my case.

In particular, the published reports refer to an MC68705U3, while the devices I ordered are marked MC68705U3S. Before attempting to program one, I still need to establish from original Motorola documentation whether that exact suffix is compatible with the device, programming method and Euro PC board configuration described in the sources.

I also need to verify:

that the ordered devices are genuine, blank and functional;
that the firmware archive is complete and unmodified;
whether the firmware is specific to a keyboard language or board revision;
the exact solder-jumper state required by my motherboard revision;
and the original Motorola programming documentation on which the community build is based.

This article intentionally does not reproduce a programmer schematic or programming procedure. That stage will only be documented after the original device documentation and the published hardware have been checked independently.

Possible external-keyboard workaround

The VOGONS report also describes using an external XT keyboard while the internal keyboard was unavailable. The author warns that not every keyboard labelled XT or XT/AT is suitable because the Euro PC requires the correct keyboard code set. (VOGONS repair notes)

This could be useful for diagnosis, but an external keyboard working or failing would not by itself identify whether an internal-keyboard problem is caused by the printed key sheet, the matrix wiring, the keyboard processor or another circuit.

Software and ROM resources

LinuxJedi provides a recovered Schneider Euro PC DOS 3.3 disk image. It is described as a 720 KB double-density image from a UK-specification Euro PC. The same download page provides a Euro PC BIOS 2.08B image patched for the year-2000 date problem. (LinuxJedi downloads)

The restoration article also provides backups described as a 27256 BIOS EPROM and a 2764 character ROM. These may be useful preservation resources, but I will compare versions and checksums before writing any image to hardware. (LinuxJedi restoration notes)

What is known so far

Based on the available documentation and repair reports:

the Euro PC is a compact 8088-based PC with integrated video and a built-in double-density floppy drive;
the rechargeable motherboard battery is a known age-related failure and corrosion risk;
BIOS configuration retention can affect successful startup and floppy booting;
the internal floppy interface uses an unusual connector and pinout;
a standard-drive conversion has been demonstrated on a Euro PC II, but it is not automatically proven safe for every Euro PC;
an external Gotek has been used successfully by another owner;
the original Schneider keyboard processor is a mask-programmed MC6805U2;
Schneider's service schematic provides for an MC68705U3 EPROM version with alternative jumper settings;
firmware and an Arduino Mega sketch have been published by a repairer who completed the replacement successfully;
and another owner has independently reported using the same general replacement method.

What is not known yet

For my own machine, none of the following has been established:

whether it currently starts;
whether its battery has leaked;
whether the power supply is safe;
whether the floppy drive works;
whether the keyboard has any fault;
whether any keyboard fault, if present, is in the key matrix or the processor;
whether the motherboard revision matches the published examples;
whether the MC68705U3S parts are suitable replacements;
or whether the archived firmware matches my machine.

Planned first inspection

The first practical stage will be documentation and inspection rather than modification.

I plan to record:

the case model, serial number and country/keyboard version;
the motherboard part number and revision;
the existing keyboard-processor marking;
the positions of the keyboard-processor solder jumpers;
the battery type, voltage and condition of the surrounding PCB;
the floppy-drive model and cable orientation;
the power-supply model and unloaded output voltages;
and the part numbers and checksums of the installed ROMs.

Only after that inspection will I decide whether the machine needs a battery repair, a floppy replacement, a keyboard-matrix repair, a replacement keyboard processor or none of those.

For now, this project consists of research and parts gathering. No repair result is being claimed.

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