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IIGS Super High-Res Graphics Corrupted

D

danc24

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Jan 14, 2024
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I have a Rom 01 IIGS that was recently brought out of storage. 40/80 column text and 8-bit high and double high graphics modes all display fine, but any program that displays the IIGS' native super high-resolution graphics appear corrupted. It does this in both composite and RGB mode. See image below. I've run the diagnostics disk and it doesn't report any memory errors. Has this happened to anyone else?

20240114_111850-2.jpg
 
Could be a bad RAM chip in the "slow RAM" bank. The VGC stores its frame buffer in bank $E1. Should be four chips labelled "STANDARD RAM" on the logic board.
 
njroadfan said:
Could be a bad RAM chip in the "slow RAM" bank. The VGC stores its frame buffer in bank $E1. Should be four chips labelled "STANDARD RAM" on the logic board.
Click to expand...
Thanks. I've got new ram on the way. I'll report back once it's installed.
 
Did that. It passed both the internal diagnostics and the IIGS diagnostics disk tests.
 
Is it a ROM 01 or ROM 3 board? The ROM 01 has a socketed VGC, although I've never heard of one coming loose.
 
I replaced all 4 standard ram chips with new sockets+ram, but no change to the super hi res graphics. Would finding a replacement VGC be the next step?
 
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What would be interesting to see as a differential diagnosis is whether a VidHD card gives you a clean rendered output. That would make it very clear if the problem is in the video circuitry, as the VidHD operates strictly by sniffing the bus for video writes and rendering them out to HDMI. The VidHD has been out of production for quite a while though. I am working on a similar project which sniffs and sends the entire bus out over Ethernet to an external host to do the rendering (as well as being useful for debugging and many other kinds of other things). I have working prototypes, but I'm quite a ways away from a sellable product yet.
 
Yes, I thought of that as well. VidHD or the ∀2 Analog card look like they would bypass the VGC for video. Unfortunately both are out of stock. I'm still patiently looking for another motherboard to source a good VGC from.
 
Well, maybe I'll have a working product to sell by the time VCFMW rolls around. The project is moving pretty fast.
 
I was able to find another working motherboard and swapped the VGC chips. Unfortunately it made no difference. The original VGC worked just fine in the new motherboard, but SHR graphics are still corrupted with either VGC in the old motherboard.
 
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