SVI.738 Xpress

Spectravideo SVI.738 X’Press

The SVI.738 is a very special MSX computer. It was presented as a MSX-1 computer with 80 column display facilities. Also a quality CP/ M 2.2 system was delivered in the box.
It is a ‘portable’ machine with dimensions slight bigger than a modern notebook. Ofcourse in those days LCD screens were not available so it needs a television or a monitor. But the carrying bag is really convenient.

Under the hood it was a surprise: the video chip is the V9938, and in fact it was nearly an MSX-2. Missing was enough memory, the clock IC and the MSX-2 BIOS ROMS. Many X’Press machines were converted later, for example in the Netherlands by the CUC and in Denmark by Henrik Gilvad. Missing was the memory mapper (external memory mappers do function though if you change the slot address of the cartridge connector. Note that several revisions of the motherboard exist, the first were having space reserved on the print with notes where to place the clockchip.

Manuals


The SVI.738 X’Press Technical Reference Manual circuit diagrams in PDF format.

The SVI.738 X’Press User Guide pages in PDF format.

SVI.738 CP/M 2.2 and MSX-DOS system disks

The Spectravideo SVI.738 is a special machine: it comes standard with CP/M 2.2 and MSX-DOS. The system disks contain the usual files and utilities and also special utilities to exchange files between the two operating systems.

Here you can download the SVI.738 CP/M 2.2 and MSX-DOS system disks including the tools to recreate real floppy disks. Another image of the MSX Systemdisk here

SVI.738 system disks stickers scanned by Gerrit Dijkstra

Clock circuit diagrams design notes for the SVI-738 X’Press (Henrik Gilvad and other scandinavion designers)

Sources of Termtype and Sysgen , the SVI.738 Xpress CP/M utilities, commented by Luis Claudio Grosso

Disassembled and commented source of the SVI.738 utilities Editfkey and Loadfkey , made by Luis Claudio Gross

Disassembled and commented source of the SVI.738 DUMP utility , made by Luis Claudio Gross

The dutch original text of the SVI.738 CP/M bios patches I designed for C.U.C. Computer Info, which appeared as a long series.

Louis Claudio Grosso has updated his information on the CP/M BIOS of the Spectravideo SVI.738 X’Press.
Not only the source of the BIOS is now available but also a program to write the boot information to disk.

Henrik Gilvad even made the X’Press into a MSX2+ with internal memory mapper. If you know how he did that: please mail me!
Dan Derpaux send me this info how to do the SVI.738 MSX-1 to MSX2+ conversion!

SVI.738 MSX2+ ROMS (dump made by Bjoye Skjoldhammer) some part is not correct alas. I do have such a MSX-2+ myself so i should dump it soon!

The instructions to convert the SVI.738 to MSX-2
New and in english, combined the CUC dutch (translated) info and the danish/finnish info

The international SVI.738 MSX-2 Roms (thanks JP Grobler) without clockchip

The international SVI.738 MSX-2 Roms (CUC version) with clockchip

Add an RGB connecter to the SVI.738

Change slot settings for MSX-DOS 2, SCC, etc

Second diskdrive for the SVI.738

Reset button for the SVI.738

Improve sound for FM-PAC, SCC

Internal SVI.738 32K static RAM (contributed by Dan Derpaux, translated for the Syntax magazine)

Another MSX2 conversion

Louis C. Grosso did, independent of the conversions above, also an update of the SVI.738 to MSX2, without clockchip. The videorams are updated as in the other descriptions, he modified the MSX2 ROMS of a DAEWOO MSX2 computer and placed them in EPROMs with the following circuit

No picture

This SVI.738 was equiped further with a 720k internal drive, and a 360k 5 1/4 external drive, no memory mapper.

Here are the EPROMs, here are the utilities to format the 5 1/4 inch floppy drive.

The SYS02.BIN is the system rom and the EXT02.BIN is the sub rom. The original roms belong to a DAEWOO TPC310 sold in Argentina under the brand ‘TALENT MSX2’ model TPC310

The roms were patched for the following:
– Skip all the RTC access to avoid system hang during startup.
– Make the logo screen indicate 64k main ram instead of 128k.
– Program a 2 PIAs based memory mapper I never constructed.
– Translate the error messages to English (copy the English messages from the original SVI rom over the DAEWOO Spanish messages).
PS. The EXT02.BIN rom also contains the TURBO BASIC compiler that works also in MSX1 mode.

RTC circuit diagram by Henrik Gilvad

Spectravideo SVI-738 MSX2+ Mod

14 september 2013, the following text by kilroy-71

I have two Spectravideo SVI-738 computers. One in mint condition for my collection and one for daily use. The SVI-738 is perfectly suited to be modified as it has plenty of room in the case for modifications and there are also many instructions available to do various mods. It is originally a plain MSX computer but it comes with the V9938 videochip available in MSX2. It is therefore often referred to be a MSX1.5. I planned to upgrade it to a real MSX2, by exchanging the original 16K VRAM to 128k and replacing the ROM-files with MSX2 ROMs. But then I found out that Nyyrikki had managed to do a MSX2+ of his SVI-738 (Home made weird MSX2+) so I decided to contact him and ask how he had done the conversion. He kindly offered his help and the modification described here is done using his instructions.

The mod consists of doing the following:

  • Exchanging VRAM with 4 x TMS4464 chips
  • Exchanging the V9938 with a V9958 chip
  • Exchanging the Main ROM, Disk ROM and RS-232 ROM (I do not think that the disk ROM is necessary to change, but I wanted full 720k floppy support)

I have also done the following mods at the same time

  • Exchanged the internal 360k drive with a new PC drive to be able to use 720k
    disks.
  • Exchanged the very stiff and easily breakable flat cable between the keyboard and the motherboard.
  • Exchanged the wires between the motherboard and the power supply with cables usings Molex connectors to make it easy to separate the PCB:s
  • The FM-PAC-, SCC-mod to make the sound with these extensions to work properly

VRAM Exchange

The VRAM on the motherboard is easily exchanged by desoldering the four TMS4416 (IC22-25) and soldering back IC-sockets and adding two 0.1uF capacitors (C17 and C18) in front of the IC sockets. Then place the four TMS4464 circuits in the IC sockets. Start the computer after the VRAM is in place and check that the computer starts normally.

ROM Exchange

This is the more tricky part, not only do we need to desolder IC49 (RS-232 ROM) and put a socket in place, but as the new ROMs are of different size and with different contents than the original ROMs we need to do some additional modifications.Some address lines missing; A13 and A14 which need to be connected on the EXT/RS232-ROM (previously just RS232-ROM). The original ROM was 8k (IC49 2764), but the new ROM is 32K (27256). I chose to connect the A13 line on the underside of the PCB to A13 on IC50.

The A14 line was connected to A14 on the Main ROM (IC51).

Next problem is that we need to change the inverted output enable (/OE) signal to IC49 to make it work properly. The combined EXT/RS-232-ROM that I used had the RS-232 ROM in the upper half of the ROM (address #4000-#7FFF) and the EXT-ROM in the lower half (address #0000-#3FFF). The original RS-232 ROM was activated by /CS1 and the /SLT30 (slot select) signal. The problem is that the combined output is only activated for the memory range #4000-#7FFF. This means that the EXT-ROM will never be visible. The trick Nyyrikki uses here is to use A15 combined with /SLT30 as the /OE signal to IC49 as A15 is low in the memory range #0000-#7FFF. So what needs to be done is to disconnect the /CS1 signal from pin 10 on IC62 and replace it with A15. I did this by cutting the trace to pin 10 on IC62 and taking the A15 signal from IC40. (The cut is marked with a red circle in the picture below)


The disk ROM (IC50) was originally a 16K 27128, but the ROM I used was a 27256. The A14 line on the 27256 controls which half of the 27256 ROM is used (when only using 16k) and it is originally connected to VCC on the motherboard. The Disk ROM needs therefore be placed on the upper half of the ROM or alternatively on both the upper and lower half to make it work with both high and low signal on A14.

Start the computer when everything is soldered and in place and test that it starts up correctly.

V9938 Exchange

The V9958 chip must be prepared before it is connected to the IC37 socket. Pins
4, 21 and 27 are bent upward. Then connect pins 4, 20 and 27 together with a
wire that are soldered to the pins. These are connected to ground through pin
20. Solder also a wire between pins 21 and 58. This connects pin 21 to 5V.

FM-PAC/SCC-mod

This is simply done by replacing the 4k7 R2 resistor with a 150k resistor so
that the sound volume is lowered. Here is before…

and after…

Disk Drive Exchange

I found a PC TEAC floppy drive in my stuff that had a jumper for setting DS0/DS1. I changed the jumper to DS0. The floppy cable in the SVI-738 is very short and pin 1 on the new floppy drive was on the wrong side so I needed to exchange the cable to a longer one. I used a normal PC-floppy cable, but connected the drive using the B-drive connector, thus avoid using the twisted
part of the cable that cannot be used with the SVI-738.

An inconvinient thing with the original floppy drive is that the screw holes are not in the standard locations. I mounted the floppy on a frame from a PC that I cut and tried to drill holes at the correct locations, but I did not manage to do it properly. So what to do? Yes, hot glue to the rescue! It works, but I do not think that it will hold the floppy in place for very long. I plan to take two steel plates and drill holes in the right locations and mount them between the floppy and the stands.

The original floppy drive was a little bit higher so there is a gap in the case
now, but it looks ok anyway.

Keyboard Cable Exchange

The cable between the keyboard and the motherboard is known to break easily and it cannot be disconnected either. I wanted to have the possibility to disconnect the keyboard when working with the motherboard so I replaced the cable with a 50-pin SCSI cable. I desoldered the old cable and soldered a straight male 22-pin header on the motherboard. Then I soldered a similar on the keyboard PCB. Don’t do this!

The problem is that it makes it impossible to close the case. Use instead a 90 degree angled connector.

You can also take advantage of the fact that the keyboard has been opened and clean the gold plated parts for all keys with alcohol:

Here is a picture of the backside of the keyboard:

And here is everything connected:

Power Supply Cable Exchange

As I was exchanging the keyboard cable, I decided to also exchange the power supply cables. I use two PC power T-connectors that I had. I wanted to use the
correct color coding so I switched some of the wires.

Final Touches

Now everything is connected and the computer is ready to be run for a final test.

Push the power switch and wait:

Great! Lets try the keyboard and the floppy:

Excellent! We are done! Or wait a minute… There is one last thing, the MSX2+ logo…

That is better!

TODO

First off is to add a Real Time Clock-circuit to the motherboard. My SVI-738 is of the older model so it has already a part of the PCB dedicated to a RTC.

… and then I would also like to add an internal memory mapper. Unfortunately I have not found any instructions how to construct one, especially for the
SVI-738.

Credits

All credits for this mod goes to Nyyrikki. Thank you very much for all your help and your patience answering my questions!