NMS 8280 RGB output vertical lines/quality

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Por donluca

Expert (69)

Imagen del donluca

06-05-2020, 14:46

So... the solution is to use pure sync instead of composite? Looks like a doable job, just tap the sync signal somewhere and route it to the scart connector (and cut the trace/desolder the point with composite).

Por Grauw

Ascended (9071)

Imagen del Grauw

06-05-2020, 15:19

In the case of the Panasonic FS-A1GT that was the problem. The problem there seems to me that either on the board or in the cable there is interference from the composite signal with the RGB signals.

However I don’t know if it is the case here... I’m no electronic engineer but in essence what you see is a signal stability issue, in sync with the video signal because the bars are straight, and it seems to me that electrolytic capacitors or power supply or interference problems could all cause this.

Por shaiwa

Champion (384)

Imagen del shaiwa

06-05-2020, 16:42

Well, did some googling about the v7040 chip today and found out it was also used in the Sega Master System 1.
They have a mod but i dont go that far on the nms, the bars stay a "feature" then ;)
See some talk on the sms forums about modified cables with some extra resistor and elco, not sure if thats for the same chip because some use a CXA chip.
@Grauw, you may be right, could also be a design flaw we start to see now LCD and scaling is more used.

Por donluca

Expert (69)

Imagen del donluca

07-05-2020, 15:23

Alright, moving away the MSX from my CRT monitor solved two issues:

The 60Hz slight horizontal shake and a diagonal banding which appeared occasionally on the screen while the FDD were accessed.

It might be placebo effect, but it looks like the vertical jail bars are also way more faint.

If I want to keep the MSX on top of the monitor I think I'll need to create something akin a shield... maybe a layer of wood with aluminium foil glued will suffice?

Por Grauw

Ascended (9071)

Imagen del Grauw

21-05-2020, 17:35

I just watched this video on a jail bar repair of a ZX Spectrum 128K, and I particularly liked the side-by-side oscilloscope section at 9:58 where it showed really well how on that machine the jailbars originate from noise on the 5V power line.

Por Daemos

Paragon (1718)

Imagen del Daemos

21-05-2020, 17:55

If the 5 volt has some high frequency component the only way to clear it is by building a pie filter. That means putting the 5volts through a inductor that has bypass caps on both sides acting as a good low pass filter. 1milli henries accompanied with two 47 uf caps should do the trick. Low frequency noise needs bigger caps and bigger inductors.

Allthough calculations show that 1 millihenries will not be enough it usually removes noise fairly effectively.

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