Single board (no daughter boards) version I picked up over a year ago ...
Overall in nice condition I don't think it's seen much use, these boards are known not to sync well. When I got it and fired it up my 1084 monitor couldn't handle it at all the sync was so bad, and despite hearing it was running the game, I remember smelling something burning in the audio section so quickly turned it off and it got shelved in the " I'll come back to that at some point " pile ...
Fast forward a year and now I've got this little HD Video Converter unit which takes in SCART and outputs HDMI which I can use it on my test bench with a LCD because it has the benefit of cleaning up bad sync signals really quite well ! So I've dug out a few boards recently which have ropey sync to work on ... including this one ...
Thing is, even this setup had trouble with the sync ..... it was close ... but just not stable enough ...
You can't really see it very well on the above pics but the screen was not holding Horizontally, constantly twitching or dragging left to right. Quite annoying but at least I could see the game was running fine and displaying correctly in the top half of the screen. Not much good the lower half though ....
H Sync was measuring around 14.25KHz which is too low and obviously a problem, I had some joy recently with a Toki bootleg which had a low sync signal which improved when the correct crystal was put in the board (It had a 18MHz crystal in instead of a 20MHz) so I had a look at this board and look at this .....
A 12MHz where the silkscreen says 14.7MHz !!! This looks factory installed too. The other crystal on this board is a 12MHz and I think the bootleggers just had a load of 12MHz and no 14.7's so just threw a 12 in here thinking it'll be alright , the arcade monitor will handle it !
I didn't have a 14.7 myself so threw in a 14 but that's done the trick Stable sync !!
OK so onto the obvious display/graphics issue .. and a fairly straight forward one ... anytime the screen or a portion of the screen is blanketed like above I always firstly suspect the highest priority graphics layer, which is usually the character/text layer ... so I went about identifying this part of the circuitry by bridging address pins of various RAM's on the board looking for changes on screen. Didn't take long to find what I was looking for ... 2x 6116 RAM's in the lower corner of the board by the Jamma edge ... messing with one of them gave corruption to the text layer in the good upper half of the screen, messing with the other one did absolutely nothing ... grabbed a new RAM and piggy backed this now prime suspect ...
You can see the improvement below left ... (pic below right is what the signals on this RAMs data pins looked like before piggy backing, obviously not great!!)
So got rid of that and put in a new RAM chip ...
Which fixed the graphics
I've added some de-coupling caps because this board had NONE ... And will do a re-cap in the audio section because despite all Music and FX/Speech being present, there is a bit of a high pitched squeal present and the Legion of Doom guys sound a bit like chipmunks (Something in this section definitely burned out last year when I first booted it) ...
Anyway ... I'm off for a Royal Rumble .....
Overall in nice condition I don't think it's seen much use, these boards are known not to sync well. When I got it and fired it up my 1084 monitor couldn't handle it at all the sync was so bad, and despite hearing it was running the game, I remember smelling something burning in the audio section so quickly turned it off and it got shelved in the " I'll come back to that at some point " pile ...
Fast forward a year and now I've got this little HD Video Converter unit which takes in SCART and outputs HDMI which I can use it on my test bench with a LCD because it has the benefit of cleaning up bad sync signals really quite well ! So I've dug out a few boards recently which have ropey sync to work on ... including this one ...
Thing is, even this setup had trouble with the sync ..... it was close ... but just not stable enough ...
You can't really see it very well on the above pics but the screen was not holding Horizontally, constantly twitching or dragging left to right. Quite annoying but at least I could see the game was running fine and displaying correctly in the top half of the screen. Not much good the lower half though ....
H Sync was measuring around 14.25KHz which is too low and obviously a problem, I had some joy recently with a Toki bootleg which had a low sync signal which improved when the correct crystal was put in the board (It had a 18MHz crystal in instead of a 20MHz) so I had a look at this board and look at this .....
A 12MHz where the silkscreen says 14.7MHz !!! This looks factory installed too. The other crystal on this board is a 12MHz and I think the bootleggers just had a load of 12MHz and no 14.7's so just threw a 12 in here thinking it'll be alright , the arcade monitor will handle it !
I didn't have a 14.7 myself so threw in a 14 but that's done the trick Stable sync !!OK so onto the obvious display/graphics issue .. and a fairly straight forward one ... anytime the screen or a portion of the screen is blanketed like above I always firstly suspect the highest priority graphics layer, which is usually the character/text layer ... so I went about identifying this part of the circuitry by bridging address pins of various RAM's on the board looking for changes on screen. Didn't take long to find what I was looking for ... 2x 6116 RAM's in the lower corner of the board by the Jamma edge ... messing with one of them gave corruption to the text layer in the good upper half of the screen, messing with the other one did absolutely nothing ... grabbed a new RAM and piggy backed this now prime suspect ...
You can see the improvement below left ... (pic below right is what the signals on this RAMs data pins looked like before piggy backing, obviously not great!!)
So got rid of that and put in a new RAM chip ...
Which fixed the graphics
I've added some de-coupling caps because this board had NONE ... And will do a re-cap in the audio section because despite all Music and FX/Speech being present, there is a bit of a high pitched squeal present and the Legion of Doom guys sound a bit like chipmunks
(Something in this section definitely burned out last year when I first booted it) ...Anyway ... I'm off for a Royal Rumble .....