Konami rom logo screen out of sync, otherwise all ok?!

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Door olliraa

Champion (296)

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02-10-2018, 07:28

Ran into this weird problem... I have a MSX2+ modded NMS8235 (vdp + bios has been changed) and a Sony BVM20F1E crt connected via rgb scart. When I run e.g. Gryzor with Megaflash SCC+ SD, the Konami logo screen is clearly out of sync. Then when the game enters the actual menus etc. all is fine and looking really, really good. Same happens with e.g. Pengo, the Paxanga logo goes all overt the place, but then all is ok.

I have tested with both RGBs and RGB as both a re available as separate inputs on the Sony. Same result.

Can someone explain what's happening? Is there a screen mode tester somewhere available oO

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Van Guillian

Prophet (3233)

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02-10-2018, 11:21

Perhaps it is related to "white screens".
Try from BASIC "COLOR ,15,15" and check if the image is out of sync.

Van olliraa

Champion (296)

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02-10-2018, 12:51

Guillian wrote:

Perhaps it is related to "white screens".
Try from BASIC "COLOR ,15,15" and check if the image is out of sync.

Ok, will try this evening Smile Thanks!

Van Eugeny_Brychkov

Paragon (1106)

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02-10-2018, 15:08

May help if you show the pictures/shots of the image.

Van Alexey

Guardian (2454)

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02-10-2018, 16:32

What signal did you channel to the C.SYNC input of that SCART?

Van olliraa

Champion (296)

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02-10-2018, 19:24

Quote:

May help if you show the pictures/shots of the image.

Ok, here goes Smile

https://1drv.ms/a/s!ApsnsrBemWnHg8RINDNqsSoZVDtJGw

The last one is the result of the "color,15,15" in Basic. So, there's something fishy with it, right? The Konami logo screen does look really way too good in the image. You can see the deformation of the right top corner though.

Quote:

What signal did you channel to the C.SYNC input of that SCART?

I have a standard scart cable, factory made (as the Philips has a scart in its back). However, there's something weird regarding the CSYNC of this machine.

1. The CSYNC level has always (even before the mod) been way too high (3.xV when it should be ~1.0V). For example the LM1881 sync stripper or Framemeister cannot cope with the CSYNC if it's not "lowered". So I built a scart-to-scart adapter with a potentiometer to be able to set the sync level near the spec. It *seems* to work ok. At least the pot affects the sync in a very noticeable way.

2. After the mod, there was problems with the sync, so I built a filter according to this thread and it seemed to work just fine. However, I only tested it with a crappy crt tv. Before this, I haven't had a chance to really test the Philips with the Sony due to the "retro shelf" being unfinished.

I really thought the CSYNC was ok, but now it starts to look like it really isn't :/

Van olliraa

Champion (296)

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04-10-2018, 09:49

Alexey wrote:

What signal did you channel to the C.SYNC input of that SCART?

Could it be possible, that I actually have the wrong signal as CSYNC? If everything else works, but white bacgrounds (or something like that).

Van Alexey

Guardian (2454)

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04-10-2018, 15:15

If you have a composite video signal connected to CSYNC in SCART, then a fully white screen may affect the synchronization. Especially if the video signal levels are higher than defined by the specs.

Van Jipe

Paragon (1366)

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04-10-2018, 15:49

Van olliraa

Champion (296)

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05-10-2018, 07:40

Quote:

If you have a composite video signal connected to CSYNC in SCART, then a fully white screen may affect the synchronization. Especially if the video signal levels are higher than defined by the specs.

Thanks Alexey Smile This sounds like a viable case here. Only thing that really bothers me is that fact that the white screens don't work even through lm1881, which cleans the sync (without the lm1881 the picture goes totally nuts). So, if the lm1881 produces a "perfect sync signal" as it is told, why does it still not work properly with white?

I really don't know what the CSYNC on Philips back actually is.

Thanks for this Jipe. Seems there has been problems with upgrading Philipses to MSX2+ even way back... The problem is, my Philips is the 8235/00 (made by Kyocera). I have high resolution schematics of the pcb, but comparing those with 8235/19 is probably way too difficult for my level of expertise :/ I'll dig up both schematics (00 and 19) and let''s see what comes out of this.

Thank you guys so far :)

Van olliraa

Champion (296)

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05-10-2018, 08:31

Ok, found it pretty quickly actually Smile

It seems that the 8235/00 is the same pcb as the 8235/19, because it says like this in the manual:

"MAIN PRINTED BOARD FOR: V'G8235/00 from serial no. FF026 1101 0001 onwards
/02 from serial no. FF016 1201 0001 onwards
/19 from serial no. FF016 1201 0001 onwards"

So, the fixes suggested by Jipe should work with my 8235/00, right? I translated the instructions and big G says it means something like this in English:

"delete R102, R103, R104; replace R101 with 120Ohm: connect base of Q15 (connected to R102 / 103/104) to pin 6 of the VDP by 1KOhm. replace LF67 (suppressor) with capa 470uF (Q15 base)"

The last sentence is just gibberish to me Sad

Could someone, who knows his/her stuff regarding electronics look at the high res schematics (pdf, page 1, link below) and comment on this repair job?

https://cloud.uwasa.fi/index.php/s/2UHWAO1vs4Tf26I

The pdf posted by Jipe is here (page 2)

https://cloud.uwasa.fi/index.php/s/wy6OLRTe6i8e9sD

I cannot do the repairs myself, but I have a skilled friend who does this for living. However, I'd need as specific instructions as possible for him to do the job, as he's not into retro computers at all :D

Thanks as always :)

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