Graphics corruption

[rvo_nl]

For almost a year now I have barely touched my Amiga, because it suffers from a major graphics corruption issue, as can be seen below.
 

 

 
It doesnt look good.. The strange thing here is that my Workbench (OS3.9) screen itself shows up fine, as does early bootmenu / boot without startup-sequence. Its when I start diropus and perform some tasks that glitches start appearing. Usually just a pixel or two, then a line here and there, until it gets really bad and text on buttons and in menus becomes unreadable. When watching a serie of pictures, its even stranger: most pictures show up fine, but a few come out really bad, as can be seen in the second screenshot.
 
Now, I might sound like a complete moron, but believe me when I say its not a software issue. Years ago I did a very clean, well-documented installation of my machine, and havent touched anything since. And dont forget it ran fine for years before this issue came up. Also, I've tried many times commenting stuff out in my startup-sequence, all without effect.
 
I suspected the Bvision, too. So I replaced it, twice. I've tried 3 Bvisions now, and they all have this issue. Ofcourse I swapped the Bvision cable / PCB, too and tried reseating the card aswell as the ppc board many times.
 
It could be memory corruption, which Ive tried ruling out by running Memtest for a day, with 100% good result.
 
It could be the PPC or 68K CPU. (Surely hope not). Its very hard to test this, since I cannot display PAL and I need the PPC to use the Bvision.
 
It could be a power issue. I power the motherboard using a refurbished PSU that feeds power to the a1200 power connector, AND the floppy connector. I have new cables and new switches. But I read somewhere about a certain issue with sound output, when you only power the motherboard via the floppy connector? Well.. its hard to know for sure since my cabling is so messy/broken, but I think my sound output isnt working. Could this be an indication? I mean, are other components on the motherboard affected when power is only coming in over the floppy connector?
 
Last, it could be the motherboard. Ive replaced it 3 years ago, but perhaps I need to do it again.. ?
 
Any other ideas? Please help me out, I want my machine back!
 
Thanks for reading.

[Karlos]

What software versions are you using? Specifically RTG and so forth?

But I read somewhere about a certain issue with sound output, when you only power the motherboard via the floppy connector?

Never run your system from the floppy power supply only, especially if you have a BlizzardPPC + BVision.

My 1200T has the same hardware and is very stable. Power is supplied from a single 150W PSU via the original power connector (0, 5, 12 and -12V) with supplemental power for the 0, 5 and 12V rails via the floppy port. This ensures that you aren't pushing all the current drawn by the motherboard/accelerator/graphics card through one location.

You need to supply power for the -12V line for proper operation of audio and serial, unless you like your audio half wave rectified and your RS232 incapable of a full voltage swing for signal low

[Zac67]

Insufficient power/voltage may well be a problem. Just like with probably most 'hard-core' users my C64 developed somewhat similar (horizontal) stripes after a few years. Later, I discovered that the PSU design was a problem and learned how to repair this fault.

Much later on, I repaired an unstable PET that wouldn't work reliably after a RAM expansion. Raising the PSU voltage a bit plus using thicker leads did the trick.

Check the exact voltages on the RAM chips and on the PSU output. If there's a larger discrepancy you need to enforce the power traces on the board for better distribution. If the level is too low (<<4,95V) you need to beef up the PSU or replace it.

PS: Listen to Karlos: that feeble floppy connector can't seriously power all that hardware...

[rvo_nl]

Thanks for your replies so far. Perhaps I wasnt clear, Im not intentionally powering my system only over the floppy connector. Im just saying that perhaps the normal power supply is malfunctioning or 'jumps' a little bit. Im not sure this is even possible..

Im running the latest CGX4 with the very latest patches. I believe version number is then 4.3 rc5. Im using a tweaked bvisionppc 'monitor', that goes up to 76khz -is that a problem? I remember tweaking that monitor a little while before the trouble started.

[Karlos]

Im running the latest CGX4 with the very latest patches. I believe version number is then 4.3 rc5. Im using a tweaked bvisionppc 'monitor', that goes up to 76khz -is that a problem? I remember tweaking that monitor a little while before the trouble started.

Anything is possible. Revert it and see what happens.

I'd start by stripping down the system to just the absolute minimum you need for RTG: your accelerator card, graphics card and work your way back up.

[paul1981]

Is your audio working do you know?

[Zac67]

Im using a tweaked bvisionppc 'monitor', that goes up to 76khz -is that a problem? I remember tweaking that monitor a little while before the trouble started.

Overclocking the video memory bus or the video chip can also cause problems like these. Can't you just try with a lower res?

[Karlos]

Overclocking the video memory bus or the video chip can also cause problems like these. Can't you just try with a lower res?

I am inclined to agree that it's a configuration (or power or both) issue simply because the chance that 3 successive bvision cards all suffer the same specific defect seems remote.

Make sure any overclocking tooltypes are disabled in the monitor driver (hint: 2AIDEMREPYMNONAFADELLATSNII, MELTDOWN)

[rvo_nl]

Hmm the more you people suggest, the more Im starting to think it IS a software issue after all.. Some nice things to try out, thanks again. Will report back soon

[rvo_nl]

Make sure any overclocking tooltypes are disabled in the monitor driver (hint: 2AIDEMREPYMNONAFADELLATSNII, MELTDOWN)

good one! they were enabled indeed, but disabling them didnt help at all.

[Karlos]

good one! they were enabled indeed, but disabling them didnt help at all.

Try a completely clean reinstall of cybergraphics, removing any monitor spec files that were created. I'm not entirely convinced your problem is with a 76kHz monitor preset (IIRC, I have a 96kHz one, but it's all in the pixel clock), but there are many parts to a typical CGX install and any one of them could be duff.

Once reinstalled, try a completely bog standard VGA 640x480 mode, and see if you get any corruption. Then work your way back up, but ensure that when defining your monitor spec your pixel clock does not go outside the acceptable range for your RAMDAC*. For 8/15/16 bit depths, this is something like 230MHz, down to 145MHz for 24 bit (packed pixels - not 32-bit with ignored alpha) and around 100MHz for 32-bit.

It has been a long time since I used it, but I recall the CGX the tool that configures your display modes won't allow you to define modes that will stray outside the pixel clock limits, but IIRC, you tell it what those limits are.

*cue Delshay and his fastest RAMDAC in the west. Whatever you do, don't listen to him, he's modified his hardware. Stay inside the limits.

[rvo_nl]

sigh.. I guess I will try. I really hope it helps, I've spent so much time installing my machine, the thought alone of reinstalling makes me feel down

Indeed, CGXMode is a pretty safe tool. The only thing you tell it before you can start tweaking the Monitor is the maximum khz your physical monitor supports.

[freqmax]

What is this floppy power connector? picture?

Anyway I suspect memory transmission error. It's very perculiar that only every n:th bit gets corrupted. Perhaps some PCB trace is dirty such that a capacitance has developed?

[TCMSLP]

I had similar issues (without bvision, standard chipset) and it was traced to an overheating chipset made worse by running high resolutions.  My solution was to add a fan to exhaust hot air from the case.  No problems since.

I have an example video on youtube of the corruption I experienced:-

http://www.youtube.com/watch?v=am73Zsn6ntA


Steve

[nscaleworld]

Just think, for the amount of money you paid for that setup, you could have gotten yourself an AmigaOne with OS 4.1 and had hundreds of dollars left over. You people with your Amiga 1200 computers really crack me up, lol.
 
My advice:  Part that piece of crap out and sell the items on eBay.  Then take about $1000 of the money you will get and buy yourself an AmigaOne with OS 4.1, and an ATI Radeon graphics board.  You will have a much nicer Amiga computer, for less money.