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

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Van RetroTechie

Paragon (1563)

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01-05-2010, 20:13

PS.: if this doesn't produce some sensible readings (meaning: you don't know how to measure a resistor value, you don't know how to count / how pins of a connector are numbered, or how to read a schematic / datasheet), I'm gonna give up on this thread. Read: it won't work, just get a 'pro' to help you or buy a replacement machine. Crying

Van sp4

Master (214)

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01-05-2010, 20:59

RetroTechie, I've told than i've found an idea for repearing the original msx keyboard.
The original keyboard is maden with a two thin superimposed menbranes: when its contact buttons is broken, is possible to replace them.
My idea consist to use the two thin contacts menbranes for made the master for reproduce
the keyboard in double face printed-circuit.
I've solded in component side the reed contacts for replace the contacts button: under each button i've put a little magnet for close the contact-reed when i press it.
I've cold that my idea reed-keyboard.
Reed-keyboard give more press button sensibility than the normal microswitch.

Van sp4

Master (214)

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01-05-2010, 23:39

Well, i've maden the measuring than you've asked at me:

step 1- R1-4=399ohm

step 2- R43pin-3(+12v)=10Mohm

step 3- R1-45pin=0,2ohm about 0ohm (<1ohm typically)

step 4- R48pin-50pin=14,95Kohm

RetroTechie, what do you think about that ?

Van RetroTechie

Paragon (1563)

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02-05-2010, 00:46

To follow the path, look to the master, follow the master, walk with the master, see through the master, become the master.
You are here ---------------^ Wink

(Read: I give up). Nice idea for the keyboard though (thx), I've been looking myself for a durable replacement for those not-so-durable keyboard foils. Currently doubting between a DIY 'something' based on a capacitive effect, or find a cheap supply of low power, 5V/12V-operated Hall sensor IC's... :-? Or find a (new) keyboard for sale that uses mechanical switches, place those on a cut-to-size backplane (eg. the metal plate that was behind the MSX's keyboard), and glue the MSX keycaps on top of those switches (buying loose switches sounds more logical, but is likely more expensive than buying a keyboard that uses 'em).

Van sp4

Master (214)

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02-05-2010, 15:22

RetroTechie, vg8020 is come back at life !!!
I've disconnected power-supply board and i've check it for test all its component with the multimeter.
The component are all right, but i've saw than the ground wire was disconnected from
power-supply board. I've solded it in the printed-circuit and i've connected all periferal, switching on the power-supply i've could watch the presentation screen of Microsoft and i could see the pressed key in the screen(it's all all right).
The problem was the ground wire disconnected.
Thank you very much RetroTechie and Eugeny !!

Van RetroTechie

Paragon (1563)

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02-05-2010, 18:33

but i've saw than the ground wire was disconnected from power-supply board.
Eugeny suggested that 3 pages back (and matched your voltage measurings). Thx for determining that disconnected ground wire on the 8020 won't fry it... Smile2

Van Gregory

Master (177)

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14-07-2021, 13:23

RetroTechie wrote:

Click the link above for VG8020/00 service manual... :P I also have service manual for VG8020/20, but unfortunately in dead tree format only. The missing info you'll need is S3527 pinout, you can find this in S3527 datasheet or other service manuals. If you're going to repair it, exact routing of the clock signal is something you'll have to check anyway, schematic or not.

The only significant difference in 8020 models is S3527 vs. discrete 8255 PPI + soundchip (and maybe ROM contents for different country versions?). AFAIK differences between 8020/20 and 8020/40 are very minor, if any.

Would you consider selling the VG8020/20 service manual?

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