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The Memotech MTX Series




Using an HD9800 (or GBS-8x00) With A Memotech 80 Column Card


As described on my MTX Video page, the colour output from the Memotech 80 Column board is RGB video similar to the IBM CGA adapter, it uses TTL level signals and has a horizontal sync rate of 15.7 kHz. This is incompatible with modern VGA monitors which typically have a minimum horizontal refresh rates of ~30 kHz and uses analogue RGB signals where the voltage varies between about 0 and 0.7VDC. Since CGA compatible monitors are no longer readily available and, even if they are, tend to be long past their prime, an alternative solution is needed.

In order to be able to use the 80 Column board with a modern VGA monitor, signal level conversion and video frequency up-scaling is required. The GBS-8200 or HD9800, both available through ebay, are one option for converting between CGA and VGA. I purchased an HD9800 and my experiences with the HD9800 are described here. I will only discuss the RGB inputs that are relevant to the Memotech 80 Column card output, I will not cover the Component Video ("Y", "Pb","Pr") input.


There isn't any! - At least, not supplied with my board, there was some limited information on the item page on ebay, but it was by no means comprehensive - or even adequate. I have found a couple of different versions of the manual on the internet, including this one and this one.

Features and Specification - (from the ebay advert)

  • Latest & official HD9800V.5 HD-Converter Board using a SAMSUNG IC.

  • Supports CGA/EGA/VGA/YUV Component Signal Input

  • Supports VGA Output (640 x 480, 800 x 600, 1024 x 768, 1360 x 768)

  • CGA/EGA/VGA signal auto scan (15KHz, 24KHz, 31KHz)

  • YUV Component signal auto scan (480i, 576i, 720i, 1080i, 480p, 576p, 720p, 1080p)

  • On Screen Display (English and Chinese)

  • Supports image position control & image zoom control

  • True digital 24-bit A/D converter for true 16.7-million colour conversion.

  • Supports ALL types of VGA monitors (CRT, LCD, PDP, Projector, etc)

Input Power 5VDC +/- 0.5v (2A) P7 or P9
Input signal
14.5kHz - 16.5kHz
23.5kHz - 25.5kHz
30.5kHz - 32.5kHz
Auto scan
P3 or P11 or P10
30.5kHz - 32.5kHz
Auto scan
P10 or P11
30.5kHz - 32.5kHz
Auto scan
P10 or P11
Auto scan
Auto scan
Output signal
P4 and P13
User controls Input Switch, Image Zoom, Image Position,
Output Resolution ,R\G\B gain adjust.
Menu Key


Board Layout

This picture is of an earlier version of the board, but the location and function of the various components is the same as the HD9800, some of the English translations from the original Chinese are "interesting" to say the least!

Package Contents

My board arrived from China in a padded "Jiffy" bag, without even the "luxury" of a box, even so, it arrived undamaged and made it through UK Customs without attracting import duty or VAT.

In addition to the board, the package contained two cables; a short length of a red & black pair of wires, terminated with a 2-pin connector at one end, intended to provide power from an external 5VDC supply to the "P9" connector on the board. Power can also be provided through "P12", a 2.1mm, centre positive power plug. I elected to use this connection, the board has a power consumption of around 10W (2A @ 5VDC), so I also purchased a 3A "wall-wart" from ebay.

The other cable is a short length of coloured wires, terminated with an 8-pin connector at one end, intended to connect the signal input to the "P11" connector on the board. When you place your order, you can choose to have a 5-pin cable to connect to the "P3" connector instead, but this connector does not have a vertical sync terminal. "P10" is a standard 15-pin VGA connector, the corresponding cable must be supplied by the end user.

Cable Schedule and Input Port Connections.

There are number of input connectors at the bottom of the board, including 3 for RGB - "P3", "P10" and "P11", each of these expect the same signal input types, and in fact, are actually just connected together, but the "P3" connection does not have a "VSync" input.


Wire Colour Function P11 P10 P3
Red Red 1 1 1
Green Green 2 2 2
Blue Blue 3 3 3

H-Sync or C-Sync

4 13 5
n/c   5 - -
Yellow V-Sync 6 14 n/c
n/c   7 - -
Black Ground 8 4-8, 10, 11 4


Video Output from the 80 Column Video Board (FDX/SDX)

The connections to the 80 Column Board installed in the FDX are shown below :-

Connecting the 80 Column Card to the Converter

As with most things Memotech, the connector for the 80 Column board RGB output is non-standard, do not attempt to use a 9-15 pin VGA adapter to connect the FDX 9-pin connector to the converter's VGA input - a custom cable is required.


FDX 9-Pin Connector Pin-out


80 Column Board signal

1 Red
2 Green
3 Blue
4 Horizontal Sync
5 Vertical Sync 
6 Ground
7 Sync
8 Light Pen Input
9 Audio Out



Getting Started
When the converter is first switched on, the immediate problem is that the menu system is in Chinese and some of the manuals that I have managed to locate, do not mention this minor detail. It's actually easy (when you know how) :-
  • With the output from board connected to a VGA monitor - normally you'll be using "P4"
  • Make sure that you have at least a 5V/2A power supply connected
  • Press the Menu button on the board to show the On Screen Display (OSD) - it will probably be in Chinese
  • Use the up or down button to move the cursor in front of the entry 4
  • Press the Menu button and the language menu will be shown
  • Select entry 1 and validate with the Menu button
  • You should now have the menus in English.






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