SVI738 upg. MSX-2 + 128kb V-Ram + PAL/NTSC + RGB

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Van LS120

Expert (105)

afbeelding van LS120

15-03-2017, 10:14

did any of you guys get any further on this??

Van LS120

Expert (105)

afbeelding van LS120

09-06-2017, 12:03

hey Xiny6581 im looking ti do the 738 upgrades in my pc plus have a 256kb mapper i'm trying to sortout... would love some good picks of the upgrades and wires used etc..

thanks

Van Hanzugam

Supporter (4)

afbeelding van Hanzugam

05-05-2022, 00:26

Xiny6581 wrote:

Okay so here we go. I finally got some time to unscrew the floppy, to take a look what's there.
Here's the pic Smile

Best regards,
Xiny6581 ._,

Hi! Another bump of old thread.

I also have already converted one of these motherboards from MSX1 to MSX2 (Thank you for your help Nyyrikki!), but for the next one I would like to add the clock circuit function too.

It is not easy to figure out the cuts and wires required for SVI-738 V2.1 motherboard clockcircuit componets.

Also let me point out there are errors in sviombouw.pdf ("PROJEKT OMBOUW X'press SV.738 MSX-1 tot "MSX-2"-machine" article commonly found here https://hansotten.file-hunter.com/uploads/files/sviombouw.pdf:

Page 4: “C20 680 ohm (weerstand tussen pen l en 18 van IC 20)”
Page 6: “C 20 680 ohm (weerstand tussen pen l en 18 van IC 20)”

C20 is an error. C62 is the correct component location.
C62 is located near IC20 which is the main clock chip location.
The real C20 is under IC22 which is part of video RAM circuitry.
Page 6 sentence is in the middle of english translation and it is not translated.
Page 6 typing C 20 may have created more confusion when doing searches with CTRL+F and trying to find more info about C20.
There is no info how the 680 ohm resistor should be assembled since there are no VIAs to install it, but it looks like it is meant to be stuck and surface mounted between IC20 socket and C20 to make it more visible than soldering it on bottom side of the motherboard.

Today I saw Xiny6581's picture (found by Google) of the floppy drive area http://www.6581.org/msx/underthefloppy.jpg I immediately got answers for many things that have puzzled me.

The picture verified me:

What kind of crystal can replace a three legged XT2.
How is the second 680R is assembled between IC20 pins 1 and 18 by postioning it physically between C62 and U20.
That D4 minus is pointing up.
That R50 resistor and diode are really parallel (piggy backed) and R50 minus is pointing right.
What kind of three legged VC2 compoment to look for.

I can see U19 pin 1, D3 top foot and C62 left foot have exess solder in them, which probably indicates they have wire soldered on bottom side of the motherboard.

Xiny6581 Could we please have a picture from the bottom side showing added wires or anyone else how has clockcircuit working?

I'm about to release better instructions how to do these conversions but I would like to double check everything and one picture from the bottom side would make it way easier.

Van sdsnatcher73

Prophet (3203)

afbeelding van sdsnatcher73

05-05-2022, 10:01

What is meant is not C20 but IC20, you are supposed to install a 680ohm resistor between legs 1 and 18 of IC20 (directly).

Van Hanzugam

Supporter (4)

afbeelding van Hanzugam

06-05-2022, 17:26

Thanks, it is an error anyway worth correcting. Smile Lucky that nowadays marking chips with U-letter is more common than with IC to avoid probability of confusion with missing I-letters.

Can you clarify these two wire positions too:

** Connect with wires:
- C 62 to connectpoint D4 and R50
- D3 to R51 (ground) (fig.2)

This fig.2 is way too blurry to reveal anything else than the cut. So should the wire to C62 be conneted closer to edge of the motherboard or the other foot of C62?
There is a factory track between D4 silkscreen plus (up) and R50 left foot, is this were the other end of this wire is supposed to be connected? Since D4 and R50 both have one diode after conversion the wire would connect on minus side of both, right?

D3 to R51 (ground)
Should this wire be connected to D4 silkscreen minus or plus side?
(ground) is meaning R51 foot that is closer to D3 since that is connected to the motherboard common ground, right?

A picture of bottom side of clockcircuit converted SVI-738 V2.1 motherboard would tell me more than 1000 words, but I understand there is some work to open one 'Xpress to see under motherboard.

Van Hanzugam

Supporter (4)

afbeelding van Hanzugam

07-05-2022, 17:25

Figured this out myself
"- D3 to R51 (ground) (fig.2)" for new instructions I will describe this with "Cut track on bottom side between D3 minus feet (closer feet to the front edge of motherboard) and R50 ground feet (closer foot to the edge of the motherboard)."

Now I got it that the banana shaped black drawing in (fig.2) wanted to indicate a wire connecting between the track coming away from D4 minus feet and R51 ground feet. No reason to even use wire here, but just peel solder mask on the fat track going under R51 and bridge R51 to that ground track or make the cut as close to the D4 minus VIA as possible and bridge it to above fat ground area. All these on solder side = bottom side of the motherboard.

There was zero help on the schematics for this since clockcircuit part is missing in these scans: https://hansotten.file-hunter.com/uploads/files/svitechref.pdf
I believe they exist in the Techical Manual, but have not found that yet.

"C 62 to connectpoint D4 and R50" I believe means that because C62 VCC feet closer to the edge of the motherboard is already connected to D4 silksceen minus feet which is closer to the motherboard front edge. Then my logic tells to connect that feet of C62 to another end of D4 which is also connected to R50 feet that is closer to D4. There would be no point connecting the other non-VCC feet of C62 since that one has no changes made when the other one had earlier itself cut away from VCC track. Is this right?

Van Hanzugam

Supporter (4)

afbeelding van Hanzugam

08-05-2022, 00:11

Page 6 of https://hansotten.file-hunter.com/uploads/files/sviombouw.pdf tells us to:

Connect with wires:
- IC50 pen 27 to IC31 pen 5 (A14)(fig.3)

BUT (fig 3.) on page 8 of the same old document tells us to connect IC31 pin 14. Actually this is not written in the picture, but I have triplechecked that it is really pin 14 track the arrow presenting a wire is pointing at. Even if someone had counted pins incorrecly from solder side (without seeing pin 1 markings) it could only be pin 4 and NOT pin 5 with any counting method.

Looking IC31 LS244 in the schematics tells:
IC31 pin 5 is 2Y3 and connects to CARTRIDGE SLOT pin 25 which is A14 signal.
IC31 pin 14 is 1Y3 and connects to CARTRIDGE SLOT pin 20 which is A10 signal.

Which one is wrong the text (again) or the figure?

Also is this part of MSX2 conversion or clockcircuit modification?

Van lkpalwa

Expert (114)

afbeelding van lkpalwa

09-05-2022, 16:25

info about RTC, even if you dont have the one with default none added component, you can make it your one by using info from here: oO oO oO
https://www.infodocmsx.com/_files/ugd/a61f9d_1a354ea96e20405...

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