Philips VG8235 - Blurry screen

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Van Meits

Scribe (6446)

afbeelding van Meits

21-07-2021, 23:00


Captured with an elgato hd50s game capture device.

Van sdsnatcher73

Prophet (2241)

afbeelding van sdsnatcher73

22-07-2021, 05:54

Briqunullus wrote:

What? You mean the MSX logo scrolling up? My 8235/00 has it.
The only difference with later models afaik is that only VRAM is reported, not main RAM.

That is the most visible difference indeed, it is the same as all Japanese MSX2’s. But there are more differences indeed, most notably an issue in the memory mapper on the /00 model.

Van sdsnatcher73

Prophet (2241)

afbeelding van sdsnatcher73

22-07-2021, 06:00

Meits wrote:

Captured with an elgato hd50s game capture device.

So the color balance is a bit different and probably the red, green and blue components are not leveled correctly. I am not sure if this a common thing in /00 models or just your /00.

Van Meits

Scribe (6446)

afbeelding van Meits

22-07-2021, 10:19

sdsnatcher73 wrote:
Meits wrote:

Captured with an elgato hd50s game capture device.

So the color balance is a bit different and probably the red, green and blue components are not leveled correctly. I am not sure if this a common thing in /00 models or just your /00.

OmegaMSX told me about it. He knows.

Van Meits

Scribe (6446)

afbeelding van Meits

22-07-2021, 17:40

Pentarou wrote:

@Meits: Why is your ZD1 diode cut?

It was broken. This pic was just before replacement.

Van Meits

Scribe (6446)

afbeelding van Meits

22-07-2021, 18:08

philgood1351fr
I just had a conversation with a tech who always tutors me.
In 8235/00 and 8235/20 12V is necessary for the transistors in the RGB circuitry to switch on. You really do need that 12V. So check and recheck your PSU thoroughly.

Van Pentarou

Champion (396)

afbeelding van Pentarou

22-07-2021, 18:44

Nope, not true (*). If you look at the schematic you'll see that 12V are needed to signal (to) the TV to enable the SCART input/select aspect Ratio, but to enable RGB mode you only need 0~3V to SCART pin 16.
RGB output transistors/RGB enable signal (/YS) are powered by 5v and driven directly by the 9938.
However 12V are needed by the daughterboard that sits on top of the video section, so maybe it's true that you really need 12V.

(*)8235/00-02-19 has a very different RGB output section, and DIN/International versions (all revisions EXCEPT French versions) need 12V for CVBS.

Van philgood1351fr

Rookie (23)

afbeelding van philgood1351fr

22-07-2021, 21:28

Hi friends, very grateful for your tremendous help. Sorry for the delay but busy day at work.
So here are my mesurements :
With disk and main bord not connecterd : 0v (no tension)
With disk only : 2 v
With board only : 1.9v

The PSU is noisy (hear the tension inside). and the measures inside shows 0v on three cables and 8.8v on the blue one.
What do you think ?
Can we provide only the 12v with another source lije a PC PSU for example or there's a risk doing it.

Van Meits

Scribe (6446)

afbeelding van Meits

22-07-2021, 21:40

In my case the noisy (more whining) psu was caused by a dead zener diode. But it did not even switch on with that diode being broken. But diodes are easy to measure anyway.

Van philgood1351fr

Rookie (23)

afbeelding van philgood1351fr

22-07-2021, 22:01

OK. Can you be more precise as I'm not electronic friendly...
What Zener do you mean ? between the PSU and tje yellow cable ? do you have a picture of it and the way to check it ?

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