Qdisk v4

QL_CST_FLoppyController

A clone of some version of the CST's Floppy Disk Interface for Sinclair QL

History

CST was one of the main manufacturer of add-on for the Sinclair QL computer, this include backplanes, memory expansions and disc interfaces.

The Disk interface evolved over several version, with enhaced compatibilities in each version.

• Issue 1 - I can't get information about this Issue on internet.
• Issue 2 - This version use ROM Revision 1.13 (C) 1985, of 8Kb, Nicolaos Doukas draw the schematic an create a clone. Is possible to upgrade Issue 2 to ROM 1.16 if isolate the PIN 3 of IC3 (74LS03).
• Issue 3 - This version use ROM Revision 1.16 (C) 1984, of 8Kb, new clock circuit and 1 missing track on the PCB (and this is the reason you need to isolate pin 3 on Issue 2)
• Issue 4 - This version use ROM Revision 1.18 (C) 1986 /1.19 (C) 1987, diferent circuit, increase the ROM size to 12Kb (use a 16Kb Eprom chip), now include RAM disk driver in rom, this version use a scrambled ROM, so when read with a external device, you can see the code.

Version 1.19 of ROM is missing in action, other version area available to download here: https://dilwyn.theqlforum.com/qlrom/index.html

Has been seen version of Issue 4 with, the top/botton cooper tracks interchanged, this help to reverse engineered the complete board.

Nowday I have draw and test the PCB of Issue 3 and 4, they are in separate folders, including, manuals and and ROM image.

The Board

It use the standar stugart conector, so a plain cable can have up to 2 disk drives, that shall be correctly configured as DS0 and DS1.

It use a WD1770 disc controller, and is expected that will be compatible with WD1772 (not checked), WD1773 is not compatible.

Thanks to Derek_Stewart and techy of qlforum.co.uk for providing the pictures that allow me to capture the schema.

A interactive bill of materials for each board is available here:

• https://alvaroalea.github.io/QL_CST_FLoppyController/ibom_3.html
• https://alvaroalea.github.io/QL_CST_FLoppyController/ibom_4.html

WARNING: Use good components!

During testing we found that bulk unknow 2N2222 transistor seen to work, but have hard compatibility problems with other boards.

Using a wellknow source transistor eliminate the incompatibility and work correctly with other passthrough boards. Be aware if you use a external or internal RAM expansion, a Qbide with passtrough or a backplane that allow several boarda.

Recreated Boards

Issue 4

Issue 3

Original Boards

Issue 2

One of the few images available on internet, noted the transistor near the edge conector, 3 resistor on top of the PCB, two of this near the crystal, and the resistor array near WD1770 is called R4 (SIL)

Issue 3

The transistor has been moved, the 3 resistor has been replaces by array R1, and the resistor array near WD1770 is called R2 (SIL)

Issue 4

Complete new PCB, note The right one, with top/botton layer correct, but without silkscreen, and the left, with silkscreen but top/botton swapped (and exposed tracks under heat disipator).