X68000 Expert HD odd video issue, but only on certain games

[cr4zymanz0r]

With the help of BlueBMW I finally got a working X68000 pieced together. However, on Fantasy Zone and Cotton I'm getting a weird video issue. Here's what the video issue looks like: Sharp X68000 video issue on Fantasy Zone
It's not present on the loading screen and only starts showing up from the title screen and on. The distortion on the game screen doesn't show up the best in the video, but as you can see the edge distortion is very noticeable even in this video. The issue is exactly the same in Cotton, the initial loading/logo screens are fine but then it all goes to crap at the title screen and in-game.

I've played Castlevania, Ghouls 'n Ghosts, Final Fight, Gradius, Gradius 2, Nemesis '90 Kai, and probably some others I'm forgetting and none of them had any video issues. I've tried two different VGA adapters and the issue is the same on both. I also tried hooking the X68000 to my XRGB3 and outputting to a HDTV. The issue was still there even with the XRGB3, but it was more a wavy edge distortion on it rather than the fine lines shown in this video with the CRT. I don't know if it's related or not, but when I played through Castlevania every so often  (maybe once every 5 or 10 minutes) I might've gotten a single split second line of video distortion on the upper half of the screen. At the time I just assumed it was either due to some random split second video interference, or the fact this is just some random CRT monitor I got that was going to be thrown away after being replaced with an LCD.

Has anyone seen this issue before? I probably would've just blamed the monitor, but the fact that it acts up on the XRGB3 too makes me think the monitor isn't at the hardware at fault.

[eidis]

 I have very distorted picture if I connect my ACE HD to a LCD monitor. The picture is fine though if connected to a CRT monitor. It could be linked to capacitors.

Update: Try to replace capacitors in the PSU and see if it helps.

Keep the scene alive !
Eidis

[SuperDeadite]

Fantasy Zone should be played in 24khz (push Help) anyway.

[cr4zymanz0r]

Well, today I got home and tried a different disk dump of Cotton and while it wasn't perfect it was much improved. I played for a few minutes then I reset it and loaded the previous disk dumps I used. Once the game was loaded it was back to being fairly bad. I reset again and loaded the dumps I didn't try until today and now they were acting the same too.

The X68000 had been completely off (standby power off too) the whole day, so it seems once it's been running/powered for a few minutes then the video in Cotton and Fantasy Zone got worse. I'm no expert, but that's making it sound more like a capacitor issue to me too. Should I just recap the entire video output board?

[BlueBMW]

Well, today I got home and tried a different disk dump of Cotton and while it wasn't perfect it was much improved. I played for a few minutes then I reset it and loaded the previous disk dumps I used. Once the game was loaded it was back to being fairly bad. I reset again and loaded the dumps I didn't try until today and now they were acting the same too.

The X68000 had been completely off (standby power off too) the whole day, so it seems once it's been running/powered for a few minutes then the video in Cotton and Fantasy Zone got worse. I'm no expert, but that's making it sound more like a capacitor issue to me too. Should I just recap the entire video output board?

Considering the age of these systems, that wouldnt be a bad place to start.  I think they're all radial caps on that board so it should be quick and easy.

[eidis]

The problem here seems to be unstable power. This is an early sign that something will break in the near future if nothing is done. Usually, if ignored, the PSU dies, but other components survive.

I can tell from my personal experience that all faulty caps which have 100uf or greater capacity can be culprits for various strange symptoms.

Start off by recapping PSU, then motherboard and floppy drives. Don't omit the PSU, otherwise there will be an unpleasant surprise pretty soon. I would advise to refrain from using the X68k until a full recap is done.

Keep the scene alive !
Eidis

[cr4zymanz0r]

The problem here seems to be unstable power. This is an early sign that something will break in the near future if nothing is done. Usually, if ignored, the PSU dies, but other components survive.

I can tell from my personal experience that all faulty caps which have 100uf or greater capacity can be culprits for various strange symptoms.

Start off by recapping PSU, then motherboard and floppy drives. Don't omit the PSU, otherwise there will be an unpleasant surprise pretty soon. I would advise to refrain from using the X68k until a full recap is done.

Keep the scene alive !
Eidis

The PSU was already completely replaced by a new small ATX PSU before I received it, and it looks like a pretty nice replacement job too. As far as everything else, I'm not entirely sure what all capacitors I would need to replace. Do I only need to worry about the cylinder shaped electrolytic capacitors? I'm under the impression those are the only kind that generally tend to fail since the chemicals in them end up drying up or expanding and causing capacitors to swell.

The floppy drive seems to be working fine, so i don't particularly want to do anything to it unless it starts getting finicky. Where else are there capacitors though? I know there are a good few on the detachable video board (which I'm guessing is the most likely culprit for my issue), I'm pretty sure I remember seeing a decent few on the bottom board where the sound hardware is too. There's also the very large board (I don't know what its called) that the video board attaches to, but I don't recall if I saw many/any electrolytic capacitors on it.

Also, are there any modern replacement non-electrolytic capacitors for these 'larger' electrolytic ones or am I just doomed to recapping it every 20 years?

[eidis]

 Try recapping the main motherboard. The one in my ACE HD looks like this:
http://content5-foto.inbox.lv/albums/e/eidis/X68000/Top.jpg

There are only three capacitors in the middle left corner which need to be replaced. Please make sure that the new ones are the same height, otherwise you might run into problems when assembling the system.

There are ceramic capacitors which are shaped like a disc. They don't have polarity and usually last for a much longer time than electrolytic ones. Unfortunately they have small capacity values.

Here's a good article about capacitors, in general:
http://www.electronics-tutorials.ws/capacitor/cap_1.html

Keep the scene alive !
Eidis

[BlueBMW]

I've got in the original problem system described in this thread.  I'll let you guys know what I find

[cr4zymanz0r]

I've got in the original problem system described in this thread.  I'll let you guys know what I find

Actually, the one you got was the one described in the "X68000 VGA adapter frying stuff and blowing fuses" thread .

[BlueBMW]

Haha thats right.  I forgot the original post changed. 

[BlueBMW]

I am now experiencing this same issue but on a compact system.  Mainboard and PSU have both been fully recapped.  The issue only comes up in certain games like Cotton.  Its like some of the lines dont display quite right and are shifted for a cycle.

Any of you guys have a good idea where to start?

[lydux]

Hi BlueBMW,

I've forgotten this unresolved thread. Not sure but...

The last week, with the help of Caius, I've managed to do a bit of analysis of HYSTERIA/OSCIAN which are responsible of the video clock generation. As far as I can tell now, the pixel clock is based on the 69.55199Mhz oscillator (I don't know about the 38Mhz one yet). I'm pretty sure this one can get lazy with time and tend to not be as accurate as it should (but it has to).

Got a frequency counter ?

You can also try with a known good 69.55199Mhz oscillator, just to confirm.

[BlueBMW]

I'll see if I can find a good one to test with and go from there!  Thanks for the info!

[cr4zymanz0r]

I'm curious to see if you get this fixed so I'd have a better idea how to fix the issue with my X68000 Expert.

[BlueBMW]

Ok I've got some more info here....  I just got in an XPC-4 and I noticed an unusual issue with my regular XVI system.  In regular 31k games there is a slight jitter to the image.  It does not show up on a CRT monitor, but it does when I run the video through the XPC-4.  I tested an Expert system with the same game also through the XPC-4 and it did not exhibit the same issue.  Then I tested this compact that has the wierd streaking issue.  It did the jitters and the streaking was MUCH more pronounced through the XPC-4.  If I switch a game to a 15k mode or even some of the odd 31k modes the problem stops.  So its related to certain 31k video modes.

Here's a pic up close of the streaking issue.

[lydux]

Nice shot BlueBMW !

Ok, we can clearly see an horizontal delay on certain scanlines meaning a sync issue after an HBLANK period. Then, on next HBLANK, the pixel clock get sync again.
It also seems the jitter delay always beeing the same... (about 8 pixels)

I can't see any relation with the video configuration for these 2 games. Except that they use an uncommon resolution (but different) for a 31khz horizontal clock.

The HSYNC interrupt is not used at all, so this is not MFP or CPU clocks related.

Looking to the XVI/compact schematics, there is no so much components involved.
Again, to me, it could be around the 69.55199 Mhz oscillator which is the base clock for the horizontal pixel clock generation. The 38.8636Mhz one might be involved with the vertical counter.
Both are wired to and only to OSCIAN, which does some sync and division with these two to generate the whole video parts clocks.

You will not be able to find these oscillators anywhere on the net, so you should test with one from a working x68000.

I myself have a CZ600 with a totally dead 69.55199Mhz oscillator... Thanks to battery leaks ! I plan to replace it with a DDS.

[BlueBMW]

I'll try swapping the oscillator and see what happens.  I've got a few compacts that seem to have ok video output (just not audio hehe)  I'll swap out out of one of them.

Update: I swapped an oscillator from another compact but still got the same results.

Turns out the jitter issue on my XVI-HD was in the video board (probably caps) because that problem went away when I swapped a different video board in.

[cr4zymanz0r]

I'll try swapping the oscillator and see what happens.  I've got a few compacts that seem to have ok video output (just not audio hehe)  I'll swap out out of one of them.

Update: I swapped an oscillator from another compact but still got the same results.

Turns out the jitter issue on my XVI-HD was in the video board (probably caps) because that problem went away when I swapped a different video board in.

I wonder if the issue with my Expert is on its video board too. Is the XVI video board similar to an Expert video board? All the caps on mine look fine (though I know that doesn't necessarily mean they are fine), but I'd hate to recap the whole board and it still not fix the issue.

[BlueBMW]

The video board seems to be exactly the same on the expert and xvi systems.  Caps may look fine, but they can still be weak / dried out.

[cr4zymanz0r]

Let me know if you end up recapping the video board on yours to see if it fixes the issue. I might end up trying it on mine at some point, but it'd be nice to have confirmation that it's the caps for sure rather than some other faulty component on the board.

[lydux]

I'll personnaly not bet on capacitors... To me, we are facing a a sync issue, which is digital related, not analog. Bad capacitors on video part would cause bad colors outputs.

Such video issue can be very hard to identify, and I can only rely on BlueBMW picture. But it could be faked because of the XPC-4 ! I don't know its internal structure, but it's strongly possible that it does color pixels buffering, and outputs them on each horizontal sync pulse triggered by the x68000 sync + an internal one. A missing one could cause delays.

Also, I've forgotten about the video output board which is non existant on Compact models. It has been replaced by an all in one solution (the CXA1260).

So, by elimination I can't see only one common remaining section, which is a buffering/invertion  on HSYNC/VSYNC signals.

I don't have a good Compact board picture on hand. But it should be a 74ALS05 (IC32) probably near VICON. (Btw, it reminds me this thread : http://nfggames.com/forum2/index.php?topic=4901.0 )

Please BlueBMW, can you check for this ? Depending on the result, we will see for the Expert.

[lydux]

Update :

Caius just told me that the SYNC inverter for Compact models is located on the back of the motherboard, marked IC118 and is a 74ALS04.

IC32/74ALS05 is for twin-tower XVI models.

Thanks to him !

[BlueBMW]

Ahh!  I didnt think to look on the back.  Ill probe the chip and see what I get.  If I cant find anything definitive Ill try replacing it.

Also, I did get word back from the manufacturer of the original 69mhz oscillator...

>>
>>Dear Sirs
>>
>>We regret to say that 69.551MHz oscillator is very old item and it was
>>discontinued product. Then we are not able to supply anymore.
>>
>>Best regards.

[BlueBMW]

I swapped that IC but got the same results.  Lydux, have you got a compact system to test with?  Maybe I could send you this mainboard (or a whole system if you need it)

[lydux]

Also, I did get word back from the manufacturer of the original 69mhz oscillator...

>>
>>Dear Sirs
>>
>>We regret to say that 69.551MHz oscillator is very old item and it was
>>discontinued product. Then we are not able to supply anymore.
>>
>>Best regards.

Yeah, I know of it. That's why I'm thinking about using a DDS instead.

I swapped that IC but got the same results.  Lydux, have you got a compact system to test with?  Maybe I could send you this mainboard (or a whole system if you need it)

Yes, I do have one, but well... Actually, I'm wondering how to spot for the faulty part with tools I have here. I might need to build a specific one.
Understand that I don't want your board to travel half of the world and finally I will be unable to find the issue !

Please be patients guys... Thinking, thinking...


I also would like to make a call to x68000 owners to try playing for Cotton or Fantasy Zone. To see if this issue is more common than expected !

[BlueBMW]

If I send it, I dont want it back   I'd just like to see it fixed and used by someone.

I also have a 68030C that powers up but doesn't seem to want to boot from anything (floppies, hard drive etc).  That will be the next tricky project

[lydux]

Back on this topic !

I were studying the video part and figured out that pixels outputs are sequentially fetched from the VRAM using its serial port.

Basically, VRAMs are splitted into 2 blocks : one that is a simple framebuffer most of the time for displaying text that we called TVRAM, and the second is for more advanced graphics operations : GVRAM.

As for example, Human68K only use TVRAM and games will made extensive use of GVRAM.

Unlike TVRAM, it seems that the serial clock for fetching pixels from the GVRAM is provided by a NOR gate IC : 74AS02 (IC36 on XVI).
For more identification of this IC, one of its input comes from VICON pin 138 and the second from OSCIAN pin 18.
If at any time, this IC become lazy or don't output correctly, it will create clock delay on VRAM serial port, and so will start displaying pixels too late.
Also, serial data is resynched by VICON on each beginning of line, which could explain why the next one is displayed correctly.

I don't know for Expert models yet, but I'm pretty sure there is such similar IC wired with VICON pin 138.


Please let me know !

[BlueBMW]

I will definitely look into this!  Ive actually got several systems that exhibit this issue to one degree or another.

[cr4zymanz0r]

Did anyone ever find a definitive solution for this (particularly on non-compact models)?

[cr4zymanz0r]

I have an XVI (full tower) now that does not have this issue so I decided to do some experimenting. I took the video board out of my XVI and put it into my Expert that does have the issue. Other than the image being darker it still had the same exact issue. When the Expert hasn't had any power connected to it for a little while you can boot up Fantasy Zone and the video issue is barely there. However, after it's been running 5 or 10 minutes it gets to where it's showing the issue very frequently.

I'd say this rules out the video board as the culprit. I'll have to get the mainboard out and see if I can locate the 74ALS05 and 74AS02. At this point those 2 ICs and what few capacitors there are on the mainboard are my only leads that I know of.

[BlueBMW]

On your XVI I replaced that one suspect logic chip.  Should be easy to find as I installed a socket for it.  If you can remove that same IC from your expert without damage you could try swapping it into the XVI pretty easily to see if that makes a difference.

[cr4zymanz0r]

I've actually got that chip (74ALS05), some sockets, mainboard capacitors, and the 74AS02 chip that lydux mentioned all ordered. I've already located them on the Expert mainboard. I want to replace them one at a time to find out which is the exact culprit (if any of them are). Now I just have to wait on the parts and hope desoldering those chips isn't too much of a pain.

[BlueBMW]

Desoldering the one I did was a little tricky but not too bad.  Ive since ordered a proper desoldering iron to do it properly next time.

[cr4zymanz0r]

Well, I replaced the caps on the mainboard and I replaced the 74ALS05 chip and there's no change in the video issue.

The only thing left to try that is the 74AS02 chip (unless anyone has some more suggestions). I'm going to delay desoldering that for a day or two until my Hakko desolderer arrives. Desoldering the 74ALS05 with my radioshack desolderer was a pain and took forever.

EDIT: Here's some pictures of the Expert mainboard if it helps http://imgur.com/a/xCJBb

[cr4zymanz0r]

The 74AS02 chip has been replaced......and no change  . The video issue is still present with little to no change since the beginning. I'm at a dead end unless anyone else has some suggestions.

[kamiboy]

Maybe this so called flaw is inherent to the platform and thus not a flaw at all.