VG8235 and OSSC -> wobbly lines

Prophet (3951)

17-03-2020, 05:48

Hi guys. I’m wondering if anyone else has experience with the VG8235 in combination with an OSSC. I really like the VG8235 but cannot seem to get a perfect picture using the OSSC (latest firmware). The lines seem to be moving left/right a few pixels (maybe even just 1) between lines. I think it is a horizontal sync issue (but not very good on video technology, so could be mistaken).

So here are my questions:
1. I’ve tried 2 VG8235’s, both have this on my OSSC. Has anyone else experienced the same?
2. If so were you able to tune the OSSC (through it’s many settings) so you got a stable image?
3. Does anyone know (or able to deduce it from the schematics) why the VG8235 is different intrusion aspect to most other MSX’s with RGB output? I have not seen this on any other machine, I’ve used FS-A1ST/GT, NMS8220/45, HB-F1XV, CX-7/11, YIS-503-II. All have rocksteady image on OSSC.
4. If possible could this be fixed with a modification to the VG8235’s output circuit?

Thanks in advance for your insights...

By shaiwa

Champion (392)

17-03-2020, 13:42

Battling some time with a similar problem with a NMS8280 and my scaler.
But instead of horizontal lines mine are wobbly vertical lines.
Tried sync cleaning via an Extron PA250 (On Composite on Green it passes the sync to Csync) but it does not help.
Hopefully a solution for your VG8235 can fix my problem too.

By Pentarou

Hero (517)

17-03-2020, 14:20

sdsnatcher73 wrote:

4. If possible could this be fixed with a modification to the VG8235’s output circuit?

What are the rev. # of your 8235?
If you have the DIN version you have to replace the sync part of the video circuit with FR version.

By sdsnatcher73

Prophet (3951)

17-03-2020, 19:38

Pentarou wrote:

sdsnatcher73 wrote:

4. If possible could this be fixed with a modification to the VG8235’s output circuit?

What are the rev. # of your 8235?
If you have the DIN version you have to replace the sync part of the video circuit with FR version.

Appreciate the help!

Not sure (not good with hardware fixes, but I know a guy who knows his stuff). I have the Dutch /20 version (which has a DIN output for A/V) if that is what you mean.If so, should I have the sync circuit modified according to the /19 model? And is the difference described anywhere?

If I look in the service manual of both the /00 (which is also for the /19) and the /20 the encoder unit seems the same. I do see both SYNC and C-SYNC on the output. Did they use C-SYNC (which is Composite SYNC IIRC) on the SCART output instead of SYNC and should I switch it to SYNC?

By Pentarou

Hero (517)

17-03-2020, 20:29

sdsnatcher73 wrote:

Did they use C-SYNC (which is Composite SYNC IIRC) on the SCART output instead of SYNC and should I switch it to SYNC?

Basically yes, C-SYNC instead of CVBS. There's also a further mod that helps with horizontal stability, but I don't know if you need it, as it should be required for 2+ upgrades.

It's a fix from Jipe and you can find it here: https://archive.org/stream/tablette3/Tablette%20MSX/tablette7#page/n1/mode/2up

But reading your first post it's strange that you haven't problems with the 8220, as is shares the same video circuit with the 8235 :o

By sdsnatcher73

Prophet (3951)

18-03-2020, 09:00

I rechecked the 8220 and it is rock solid. I’ll get the 8235 fixed (it needs a drive upgrade anyhow)... thanks again for your help!