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MSX2 VG8235 black screen

By AxelStone

Prophet (2764)

AxelStone's picture

09-09-2016, 21:14

Hi everybody, I was using today my VG8235 playing Hinotori and suddenly the image turned black. It sounds and MSX works, but no image. It was connected using a SCART cable connected to AV1 input of TV. I've tried same cable with my HB75P and it works fine, so it's not cable or TV. I've tried monitor output from philips but still black screen, so it must be something internal.

Any idea? Thanks.

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By RetroTechie

Paragon (1563)

RetroTechie's picture

09-09-2016, 22:45

Which exact type VG8235? (8235/...)

Symptoms suggest a failed +12V line. Do you have a voltmeter to check? (for example on the back cartridge slot).

By AxelStone

Prophet (2764)

AxelStone's picture

09-09-2016, 23:04

How can I check the voltage with the cartridge slot? It's /20.

Thanks.

By RetroTechie

Paragon (1563)

RetroTechie's picture

10-09-2016, 02:47

Going with the pcb layout from service manual here:

With back of the machine facing you, take this picture of a cartridge slot, and (in your mind) rotate 90 degr. counter clockwise. Power pins are near the right side of the slot then.

If your voltmeter includes continuity, then -with MSX powered OFF- you can verify that pins 41 and 43 (GND) are connected. Same for pins 45/47 (+5V).

Then -with MSX powered ON- black pin of voltmeter goes onto a "GND" pin, red pin of voltmeter goes onto one of "+5V", "+12V" and "-12V", and record the readings. Just be sure not to push contacts inward against opposite contacts, or make short circuit via voltmeter's test pins...

By AxelStone

Prophet (2764)

AxelStone's picture

11-09-2016, 18:43

RetroTechie wrote:

Going with the pcb layout from service manual here:

With back of the machine facing you, take this picture of a cartridge slot, and (in your mind) rotate 90 degr. counter clockwise. Power pins are near the right side of the slot then.

If your voltmeter includes continuity, then -with MSX powered OFF- you can verify that pins 41 and 43 (GND) are connected. Same for pins 45/47 (+5V).

Then -with MSX powered ON- black pin of voltmeter goes onto a "GND" pin, red pin of voltmeter goes onto one of "+5V", "+12V" and "-12V", and record the readings. Just be sure not to push contacts inward against opposite contacts, or make short circuit via voltmeter's test pins...

Man at first shot, +12v line has gone. I hace verified it a cartridge slot and directly from power supply and it gives about 2v. How can I repair the power supply? Thanks.

By AxelStone

Prophet (2764)

AxelStone's picture

11-09-2016, 21:00

Ok problem found: Voltage Regulator STK7561A not working, 12v output doesn't work. I've just bought a replacemente.

Thanks for your help.