Research an electric schematic of the mother board for msx vg-8020

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Por sp4

Master (214)

imagem de sp4

20-04-2010, 21:14

Hi, thank you for your reply: have you the schematic of the mother board and the components
than you have described in this answer please?
I'm searching in hans otten's site, but it's very difficolt, there isn't nothing about it.

Por Leo

Paragon (1236)

imagem de Leo

21-04-2010, 16:13

Yes he has removed most ofthe contents recently , it is bad luck for you.

You say your computer is VG8020 , but the motherboard is VG8235/00 , VG8020 is an MSX1 with 64kb ram , and VG8235 is an MSX2 with disk drive and 128kB ram : they are completly two different computers.
Which one is yours ? ( maybe a photo can help )

Por RetroTechie

Paragon (1563)

imagem de RetroTechie

21-04-2010, 16:50

@sp4: e-mail sent...
Thank you RetroTechie, my msx model is exactly vg-8235/00. I have maden any measurement inside it: i have tested the ck-pin of CPU z80, its frequency is 0 Hz,(it's strange) i have maden it with keyboard unconnected. I think than the problem is in the ck generator.
What do you think about this problem ?

Confuses an MSX2 for an MSX1, and then proceeds to report that Z80 clock signal is missing.... Smile2 Just out of curiosity: what equipment did you use to determine that? Logic tester? Scope? Frequency counter? Asking because most MSX users don't have that kind of equipment, but if you do that might make repair a lot easier.

Missing clock signal might sometimes occur if VDP clock output is damaged, this eg. may happen when a cartridge is inserted / removed with MSX powered on. Knowing what happened to it when you/previous owner last used it, might shed some light on this.... If that is the problem, you can choose between replace videochip, or hook up an independent 3.58 MHz clock signal. I'd try that first to confirm the problem, and because exchanging a (non-socketed) V9938 isn't exactly an easy/foolproof job (aside from needing a known-good replacement VDP).

Btw. have you checked supply voltages, are they all within normal range?

Por Jipe

Paragon (1499)

imagem de Jipe

21-04-2010, 18:26

yes i have a PDF with schematic of 8235/00 size 5222 ko

i can send it if you give me a e-mail

Por sp4

Master (214)

imagem de sp4

21-04-2010, 18:54

Hi, in the case bottom is whoten vg8235/00 , but over the black cover' s slot-cartrige it's whoten vg8020: i think than the real name of the mother board is vg8020.
The color of case is silver, the color of the keyboard is black and its house production is philips.
Leo, what's your opinion ?

Por sp4

Master (214)

imagem de sp4

21-04-2010, 19:00

Hi Jipe, my email is: newbie75@libero.it.
Thank you again for your interest.

Por sp4

Master (214)

imagem de sp4

21-04-2010, 20:38

Thank you for your PDF Jipe, but it's not vg8020 schematic: it's very different than it (for example; vg8020 hasn't floppy drive integrated).If you give me your email, i'll send you vg8020 photo.

Por sp4

Master (214)

imagem de sp4

21-04-2010, 20:46

Thank you for your PDF Jipe, but this schematic it's not compatible with vg8020 for example: vg8020 hasn't floppy drive integrated. If you give me your email, i send you vg8020 photo.

Por RetroTechie

Paragon (1563)

imagem de RetroTechie

21-04-2010, 21:05

Oh please, what a ridicilous discussion:

VG8020: MSX1 (logo says "MSX" ), gray bottom, silver-like top, fixed keyboard (not sticking out from the bottom part), 2 cartridge slots on top with (single) black cover lid, no RGB (SCART connector), no built-in floppy drive, power switch on the right, reset button at the back.
VG8235: MSX2 (logo says "MSX2" ), fully grey case, keyboard can be adjusted in height & sticks out a bit on the sides, 1 cartridge slot on top (with auto-closing cover lid), 1 cartridge slot on the back (usually with no cover, sometimes a holder), RGB (SCART) connector, built-in floppy drive, power switch at the back, reset switch at the top (next to power/FDD LEDs).

This is so obvious Crazy on the inside the differences are even greater. So which is it? Or post pix of case + label somewhere.

Por Jipe

Paragon (1499)

imagem de Jipe

21-04-2010, 21:07

i have the schematic of 8020/00 too but your MSX is a very strange engine

look a VG8020

http://www.system-cfg.com/detailcollection.php?ident=257

if inside your MSX you find a VDP V9938 is not a MSX1 but a VG8220

VG8220 is the same to a 8020 but is a MSX2 with no drive inside and 64K ram only

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