Fixing RGB output from a X68000 XVI

[thorias]

Hi all!

I'm the proud owner of a X68000 XVI, which is working perfectly fine. But being tired to be limited to 31Khz games, I got an chinese converter board called GBS 8220 which have kind of VGA input with two vga output, was expecting it to convert directly 15Khz to 31Khz Vsync as per its manual/specs, I plug everything together: X68000->vga cable->GBS 8220 input-> vga cable-> my lcd vga monitor....Switch on everything, got the converter menu on my vga lcd screen, but nothing from the X68000 (lcd screen says no input) played with the converter menus and check everything again same. Well connect back the X68000 direct to the lcd screen, no picture!! monitor was switching on/off/on/off damn, this thing killed something!!  
dismantle the X68000 mobo and rgb out and after troubleshooting I figured out that pin 2 on the SN74ALS05AN have a bad output (both Hsync and Vsync signals go directly to the SN74ALS05AN from RGB output pin 14 and 15), it is a HEX INVERTERS WITH OPEN-COLLECTOR OUTPUTS, it is located next to the white onboard RGB connector and there is only one type of this component out of the entire mobo so you can't miss it!!!.

Bought 5 of them and at the same time a 14 pins DIP round pin socket, removed old component from mobo solder the 14 pin DIP socket (in case if something happen again easier to change out!! hope no!!  ), put brand new SN74ALS05AN, put back everything together and tadaaa picture was back on my lcd screen!! I was so happy!!

This is just to share my experience with you guys as I saw other people had a similar issue with connecting some LCD TV and having lost their RGB output.

Sorry didn't took any pictures but these below will help you.

[eidis]

 Hi Thorias !

This is a very good tutorial and thank you for sharing it with us. The repair division is growing

Eidis

[Nelsinho]

Very nice!
Thank you for share !

[NFG]

Front page!

Good work, thorias.  =)

[thorias]

Humm! Nice thank you!! Later on will give some nice interesting stuff about X68000...stay tuned!  

[doubleflash]

Thanks for the manual, i have the same error on a x68000 expert, v-sync never reached the monitor, after a change it shows me a picture again

greetz Doubleflash

[thorias]

Thanks for the manual, i have the same error on a x68000 expert, v-sync never reached the monitor, after a change it shows me a picture again

greetz Doubleflash

Cool I'm happy that you fixed it!! one more X68000 alive!!  

[stt1]

Sidenote:

If you have X68030 and it's missing the picture on screen. Try first changing the caps on video board. I encountered once a twin-tower which did not have other problems than worn caps (debugged with another video board, which worked just fine - after changing caps all was fine again with the other as well)...

- Saku

[DustyBits]

Hi all!

I'm the proud owner of a X68000 XVI, which is working perfectly fine. But being tired to be limited to 31Khz games, I got an chinese converter board called GBS 8220 which have kind of VGA input with two vga output, was expecting it to convert directly 15Khz to 31Khz Vsync as per its manual/specs, I plug everything together: X68000->vga cable->GBS 8220 input-> vga cable-> my lcd vga monitor....Switch on everything, got the converter menu on my vga lcd screen, but nothing from the X68000 (lcd screen says no input) played with the converter menus and check everything again same. Well connect back the X68000 direct to the lcd screen, no picture!! monitor was switching on/off/on/off damn, this thing killed something!! 
dismantle the X68000 mobo and rgb out and after troubleshooting I figured out that pin 2 on the SN74ALS05AN have a bad output (both Hsync and Vsync signals go directly to the SN74ALS05AN from RGB output pin 14 and 15), it is a HEX INVERTERS WITH OPEN-COLLECTOR OUTPUTS, it is located next to the white onboard RGB connector and there is only one type of this component out of the entire mobo so you can't miss it!!!.

Bought 5 of them and at the same time a 14 pins DIP round pin socket, removed old component from mobo solder the 14 pin DIP socket (in case if something happen again easier to change out!! hope no!!  ), put brand new SN74ALS05AN, put back everything together and tadaaa picture was back on my lcd screen!! I was so happy!!

This is just to share my experience with you guys as I saw other people had a similar issue with connecting some LCD TV and having lost their RGB output.

Sorry didn't took any pictures but these below will help you.

Hi there ...

I have a X68k compact :-)

But the same error - black screen :-(

But my problem - no sn74als05 on the whole mainboard :-) I need a little help :-)

[lydux]

Hi DustyBits,

On Compact XVI models, the sync inverter is IC118 (a 74ALS04), located on the back of the motherboard.

Let us know if that fix your problem !

[DustyBits]

Hi DustyBits,

On Compact XVI models, the sync inverter is IC118 (a 74ALS04), located on the back of the motherboard.

Let us know if that fix your problem !

Thanks !!! :-) I will try to replace this IC :-) Thanks for your support !!! :-)

[DustyBits]

Hi DustyBits,

On Compact XVI models, the sync inverter is IC118 (a 74ALS04), located on the back of the motherboard.

Let us know if that fix your problem !

THX ... video out is now in function again...


BIG THX

[BlueBMW]

Do you guys thing this hex inverter should be replaced as a preventive measure or just wait til it fails?

[lydux]

THX ... video out is now in function again...

BIG THX

Thank for the report !

Do you guys thing this hex inverter should be replaced as a preventive measure or just wait til it fails?

It seems to me to be a possible common failure for every x68000 models ! Not really surprising as it's an highly solicited IC...
I think while you are at replacing capacitors or doing any kind of maintenance involving the main board, it will not hurt changing it for prevention.

[spud]

Debugging some screen issues with my RGB. When the SN74ALS05AN is faulty is that an all or nothing thing or will you still have  an image on some monitors and not on others?

My X68000 has no picture on a 15kHz capable BenQ BL912, but it has on a tiny monitor like this: https://www.dx.com/nl/p/7-hd-hdmi-lcd-display-screen-monitor-vga-hdmi-av-audio-412923#.W7vNhGgzY2w

[hyrulebr]

My guess is that your monitor don´t support the freaky timing from X68000. If I understood correctly (using google translate) this guy also have problem with the same monitor with X68000 (15khz):

http://fanblogs.jp/retrogamerz/archive/406/0

But I wrote to you because I´m interest in this tiny monitor. 

Do you have the same model as this one from dx.com? Can you tell me the model number?  I was already looking for a tiny monitor with hdmi to use with RAscsi and FDX68 but one with 15khz would be much better...

[spud]

Thanks! Yes I came across that link as well.

Weird that I other people do get the BenQ BL912 working. Would tweaking its clock and phase settings make any difference?

Guess I'll have to go the OSSC way then (via DSUB, not Scart as I read elsewhere?). Or is there a safe SCART converter available?

About the small screens. I just went looking for a productnumber on the box and screen, but there was nothing there.... Typically cheap Chinese stuff I guess. I have the exact one from the link, works fine with the X68k and my Amigas. Be aware it comes with a US/JP powerplug. If you're living in Europe like me you can easily get a different 240V adapter for it that works. (I believe it requires 12V 1,5A)

[hyrulebr]

Hi Spud

Even at 31khz your Benq didn´t work?

Which game you are testing at 15khz?

Do your X68000 have a virtual drive to test more games?

[spud]

I'm very new to this system. So far I have booted into an SD card (SCSI2SD), with an image loaded with games. (I bought it with that thing included) Nothing on screen, hence I couldn't select a game. the loader (not LHES) is something simple, which I can operate with just a joystick.

I also have a system floppy, that also didn't give any image on the BenQ.

With the smaller screen, the SD card loader was shown as was one game I tested.

Is there a way I can change the screenmode to 31kHz? Or do I "simply" have to know a game that runs in that mode? Which I obviously don't know

I could try my only original game I have, Overtake. But I'm a bit reluctant doing that without having tested both drives with something not original. But I need some floppies first

[hyrulebr]

Since you have a SCSI2SD I recommend you to write the v4 image with Lhes. I don't know other loader than lhes, but I can confirm that Lhes output is 31khz and should work with your Benq.

How to write (and also link to v4 image): https://gamesx.com/wiki/doku.php?id=x68000:creating_and_restoring_hard_disk_images_to_and_from_physical_media

Also you can use the same tutorial make a copy of your existing SD card image (who knows what's inside?  )

Some games with 15khz (even 24khz):

https://vintagecpu.wordpress.com/2010/12/31/switching-resolution-for-x68000-vga/

Have fun!

[spud]

Aha, that is interesting info! Thanks a lot! I can very much work with that. Although it seems weird then the loader on my SD would be 15 kHz.
Is there a default screen when turning on the machine without HDD and without floppies? And at what frequency is that?

I noticed that on the screen that works before the loader is visible I also see the typical Boot/DOS Japanese text. Which I also not see on the BenQ. Not sure what frequency that should be running or whether I can change the frequency of that?

I have an original copy of Overtake, which seems to run in 31 kHz. So I guess I'll take the risk running it, hoping the drives are both fine and not going to wrack the floppies If that works I may work on a different HDD image!

So you guys are saying that it will not be a faulty SN74ALS05AN? I assume if that's faulty I would have no image what so ever?

[hyrulebr]

The default screen is the one asking to insert a floppy (japanese text with a image). In 31khz. Same as DOS like screens.

It's very strange you cannot see these screens in your Benq. 

Sorry but I don't know enough about hardware to say that your X68000 is faulty. I would say that your monitor is the problem, since your x68000 works fine with a tiny monitor.

[spud]

OK some progress here. It's a bit of a hit or miss. But I can get it to work now on my BenQ. But from the moment I add the (passive) VGA switch I have no image whatsoever. I'll detail more in the monitor thread.