Neo Geo TV issues (AES/supergun)
Does the picture bounce/roll on your TV during gameplay as a result of screen transitions?
Is your picture wavy at the top of the screen?
I just fixed an early AES and I experience both issues on a 1992 32" Sony which led me to believe there's still something up with the video. Neither are apparent on a 1998 20" Toshiba though but in the case of the wavy picture the overscan is greater on the Toshiba and it might be covered up.
I believe the picture bounce to be from the brightness DAC bit toggling along with white to black transitions (screen flashes) making low frequency pulses on luminance. The pulses must be low enough to be wrongly interpreted as sync.
The wavy picture could be the result of a very poor sync signal without serration pulses (XNOR) but that seems a little unlikely for a commercial product. It could also be filtering from being AC coupled I guess. I know the Neo has a reputation for poor stock video so that's a possibility.
I still need to test my other known good (late model) AES on the TV, but if anyone else is having these problems it'd be helpful for me to know what's normal for an early model. I might try to come up with some solutions.
Last edited by Calpis; 07-02-2009 at 11:07 PM.
The larger my TV is the worse the picture is.
On my old 17" widescreen LCD it was crystal clear perfect and stable.
19" Slightly wavy but bareable.
Anything over than that...chaotic mess.
I tested my late revision AES with the Sony TV and it's perfectly fine... I'm going to look into correcting the issue, I suspect reworking the DAC/RGB encoder circuit will do the trick.
Best of luck. I just want it to be stable on my 19" as I can't fit a CRT in my cupboard.
Originally Posted by Calpis
Do you know which PCB revision you have?
No but I will find out for you and let you know tomorrow. I've had it open already and I know it doesn't have a daughter board and the serial number is 53,000 japanese.
Originally Posted by Calpis
My early AES has an 11K serial, but has the daughterboard. I'm not sure if the PCB actually goes with the case or not but I presume it does. I removed the daughterboard because it was getting in my way and with or without it the problems persist. Ironic that the board aims to enhance video without bothering to fix general incompatibility.
Well that was easy... Replaced the 100uF coupling cap on the composite line with a 470uF, both issues solved. 220uF solved the waviness (poor horizontal lock?) but still had some screen bounce (filter cutoff too high) so I suggest 470uF though it's a tight fit.
Last edited by Calpis; 07-04-2009 at 01:52 PM.
Interesting, I've never changed caps before, not sure I want to take the risk as if it goes wrong I can't afford to replace it at the minute.
Thanks for doing the research though, I might trouble you for more specifics at the end of the month when I get paid.