QXL.WIN 

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Original Sinclair QL related hardware.

Manufacturer: Sinclair.

Item Name: ZX-83 Motherboard / Pre-production QL system.

Estimated Rarity (1 - 10): 10

Related Software: None.

Notes:

WANTED: The missing 3rd of the ROM data, see here for more info.

There is a lot of text on this page so I'll put a couple of pictures first, before going on about it!

Obvious differences between this system and the production QL's include...

Case related:

• Case lacks the 3 rear ventilation holes (the first 1200 or so production models were also of this style).
• Case lacks serial number and the raised Sinclair copyright text on the bottom.
• The metal keyboard plate has a hole intended for the keyboard membrane connections, instead of the usual rectangular cut-out. 

Heat sink:

• Earlier style metal heat sink (the first 1200 or so production models were also of this style).

PCB differences (obvious ones, there are no doubt others):

• Upside-down 74LS04 chip stuck to IC17 - which seems to act as a slight delay for the clock signal to the ZX8302 chip.
• 7806 6v voltage regulator added next to the SER1 port which feeds the ZX8302 - it seems the pre-production ZX8302 chip required more voltage than the other chips.
• The ZX8302 chip is ceramic with gold plated pins. Apart from a hand-written sticker, it has no markings.
• Capacitor C39 is mounted to the side to allow better access to the very short microdrive connection cables.
• The connections to the microdrive units are hard-wired (soldered) onto the main PCB. Microdrives are disconnected at their own 'daughter' PCB.
• An extra inductor and another capacitor are mounted behind the power socket (and also connected via a wire to C39).
• A few transistors are fitted the opposite way to that which is indicated on the silk screen.
• The IPC chip is an Intel D8749H with UV erase window.
• PCB is 'hard-wired' via 0 ohm resistors in jumper positions JU1 and JU6 to only accept 2x 16k EPROM chips.
• The pinout of the expansion port is different and not compatible with any QL expansion cards. It has the main 5v rail connected to pins 32A and 32B. Due to the way that all expansion cards connect pins together, any card would send higher voltage through the 5v rail and would very likely cause damage.

Visible date codes:

• 1983, 50th week - on the PCB.
• 1983, 24th week - on the CPU.
• 1983, 34th week - on the left 27128 EPROM chip.
• 1983, 33rd week - on the right 27128 EPROM chip.
• 1982, 29th week - on the ASTEC modulator.
• 1983, 17th week - on the main 7805 regulator.
• 1983, 33rd week - on both microdrive 7805 regulators.
• 1983, 5th week - on the added 7806 regulator.
• 1983, 27th week - on a couple of 74x logic chips.
• 1983, 36th week - on another couple of 74x logic chips.
• 1983, 40th week - on the MC1377 chip.
• 1983, 30th week - on both the microdrive ULA chips.
• 1984, 20th week - on the ZX8301, AKA CLA2310. NOT ORIGINAL, I had to replace this chip and the broken one was also non-original.

Hand-written stickers:

• The ZX8302 has a sticker with 'ZX8302 S1 #35' - revision number 35?
• The left EPROM has a sticker with 'BASIC 0000 13-2-84' - indicating it was programmed on the 13th Feb 1984 and that it contains the first 16k (hex 0000 to 3FFF) of the OS.
• The right EPROM has a sticker with 'BASIC 4000 13-2-84' - indicating the date it was programmed and that it contains the second 16k (hex 4000 to 7FFF) of the OS.
• The Intel D8749H has a sticker with 'BLOWN' - to indicate the Sinclair firmware had been written to it. I added a small piece of electrical tape over the UV window.
• The ASTEC Modulator has a sticker with 'D?0' - indicating perhaps that the manufacturer was likely Thorn EMI Datatech and that it is build standard 0?

Functionality:

Upon purchase in December 2024 the machine was very clean. The previous owner had invested a lot of time in cleaning what started off as an utterly filthy QL, and he'd done a very good job! After cleaning, he purchased an RGB to SCART adapter and a new keyboard membrane (the original had disintegrated) and powered it up, but got nothing much on screen.

My hunch was that the ROM situation, with it's 2x 16k chips wasn't complete and that this machine would have originally required a 'dongle' to be able to boot successfully. After closer inspection, I was able to confirm that it was configured for 2x 16k ROMs, i.e. 32k total, and as any QL fan will know, 32k was not enough space for the operating system (QDOS and SuperBasic). I removed and read the internal EPROMs and showed their contents to QL gurus on the QL forum - the data was unlike any previously known ROM version, but was definitely incomplete. The missing ROM code would have originally been contained on the external 'dongle' that had been sold separately by the previous previous owner in spring 2023.

The next step was to burn three EPROM chips containing a later complete ROM OS version, but split into three 16k parts just like the early production models would have been configured. The first and second part were installed in the motherboard sockets and I made use of the ROM dongle included with my factory test jig to house the third 16k to total a complete 48k ROM. Upon power-on the result was just a black screen with coloured random horizontal moving dashes! I wondered if I'd made a mistake creating the EPROMs, but decided to dig out my spare QL chips and try swapping some out in case any of the socketed chips were faulty. The first I always try is the ZX8301 (CLA2310) as this one seems to be the one that dies most easily, and that was indeed the case! With a known working ZX8301 the pre-production QL started up with the normal tweed pattern followed by the familiar 'press F1 or F2 screen'. I have no idea how many other ZX-83 Issue 2 QLs exist, but this could possibly be the earliest working QL.

I haven't tested the microdrives yet, as the connections between the main PCB and the microdrive daughter-boards seem even more flaky than the production models and the cables visually don't seem to be making a secure connection with the sockets, so that's a can of worms for another day

PCB images:

Case detail, heat sink and microdrive PCB:

Page on QL Wiki: there isn't one, but Urs Koenig has published some great info on QL build standards etc: https://www.sinclairql.net/build_standards.html

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