RGB Video Fix NMS 8250/55 for GBS-8220

By GodzIvan

Rookie (21)

GodzIvan's picture

20-06-2021, 22:01

The GBS-8220 + LM 1881 does not synchronize with the video signals, because the video output of the SCART (pin 19) has no correct signal at 15Khz, fault of the IC302 delay circuit. it is solved by removing the JI309 bridge, connecting the pin 3 of the JI309 to the test point TP301

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By Pentarou

Champion (375)

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20-06-2021, 22:36

What happens if you switch to 60Hz mode?

By GodzIvan

Rookie (21)

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21-06-2021, 01:00

this fix brings out the video signal on pin 19 of the scart. 50hz and 60hz will work

By Manuel

Ascended (17945)

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21-06-2021, 07:46

What exactly does this solve? I am not aware of issues with the 8250 scart output.

By Meits

Scribe (6395)

Meits's picture

21-06-2021, 11:49

Manuel wrote:

What exactly does this solve? I am not aware of issues with the 8250 scart output.

It does have some nasty jailbars.

By Pentarou

Champion (375)

Pentarou's picture

21-06-2021, 12:40

GodzIvan wrote:

this fix brings out the video signal on pin 19 of the scart. 50hz and 60hz will work

Good to know. I asked because the MC1377 has a pin to select PAL/NTSC, but it isn't connected in the 8250 (according to the schematic of the service manual).
I experienced funky results when feeing a a 60Hz signal into an MC1377 device set to PAL.

Meits wrote:

It does have some nasty jailbars.

According to the first post it's needed when using a GBS8220, no jailbars mentioned.

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BTW. The Analogue/Video PCB has an interesting feature:The SCART socket can be set to either (Euro) SCART of (JPN) RGB21 by moving the jumpers. When set to 1-3 it's SCART, when set to 1-2 it's RGB21.