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Y030

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  1. Y030

    SE/30 video redraw problem

    My package of deadstock 74 series chips arrived today from Poland and sure enough, it was UB8. During the wait I got a new fan in there to replace the noisy squirrel cage which made a huge difference, and a SD to SCSI card - yet to be installed. https://imgur.com/JQnyCgr Just need to find a better tube without the burn in. Does anyone know if the tubes used in the Plus and or Classic/II were the same or compatible? Spares for these seem more abundant. Anyway, another Mac liberated! Thanks for your help guys!
  2. Y030

    SE/30 video redraw problem

    Thanks Bolle. I grabbed some more time on this and checked the VADR lines, all good, so setup a second good se/30 on the bench for comparison. This has what looks like a later revision board and different and socketed PALs. Otherwise, ICs are labelled the same (except the PALs curiously) and at a cursory glance circuit looks identical. Showing the same ‘waiting for boot’ startup screen i could identify that outputs (P 7&9) of UB8 had a very different reading - on the bad board I could clearly see a clock signal with 50% duty cycle, and on the good board this was a very narrow 0v spike and the remainder of the pulse cycle was high. Traces were good so I figured UB8 was at fault so pulled it, then found I didn’t have any spares.... replacement is now in the mail. Will update once I’ve got the UB8 back in.
  3. Y030

    SE/30 video redraw problem

    OK - tested lines A0-A15 from the mux inputs back to the PDS, all is well there too. Looking more and more likely its an IC at fault. Is there a good method to test the PALs? I was going to get a working SE/30 and compare the signals on each pin, unless there's a more obvious/simple procedure. Thanks again.
  4. Y030

    SE/30 video redraw problem

    Thanks guys very helpful. I traced D24-D31 back to the ROM and PDS slot, everything fine there. Also fine were RA0-8 and the other lines RAS/CAS, etc back to the PAL ICs. Were there any others I should check? Unless there is something else - then I guess either the 253 mux’s or a bad PAL. Are PAL ICs known to die? Long shot but there a reliable source for replacements? seems unlikely 30+ years later anyone Is burning fresh ones... Further info, my board is p/n 820-0260-10. It looks like an early revision as it has a factory cut trace to UI6. PALs are marked: UE6 341-0637-A 918NNDKB UE7 341-0688-A 918YZLAB UG6 341-0635-A 921ZIMOB UG7 341-0633-A 918NLTJB UI6 341-0665-A 917NJFCB
  5. Y030

    SE/30 video redraw problem

    Yes it’s an odd one... Hmm couldn’t upload images. (Am I doing something wrong?) So instead here are a couple of links: During POST Waiting for boot disk Board is plugged in using an atx extender but behaves the same plugged directly in.
  6. Hi folks, this is my first post here and I’m looking for some help diagnosing yet another video issue with a Mac SE/30 - hoping that someone could point me in the right direction. Usual story, dug the Mac out of storage to find it didn’t boot, display full of stripes and noise. Removed the caps, cleaned out the electrolyte, dirt and oxide, replaced caps. The board looks great, no visible broken traces and squeaky clean. Connected to power, the Mac chimes, POSTs and boots all the way to the Finder normally, the mouse and floppy work. The issue is only the left quarter of the screen is being drawn, as if divided into four columns, leaving horizontal strips across the rest. In the Finder I can make out the trash and menubar but being continually overwritten in the same quarter screen. It’s as if only 25% the VRAM is being written, but the whole memory is being read back out to the video circuit. With the RAM and ROM SIMMs out the Mac shows a stable full screen stripe pattern. Swapping out both RAM/ROM with a known good set yields the same results. I’d appreciate it if anyone could offer any advice on what could be happening. Before I buzz out the entire board or start replacing chips I’d like an idea of what’s going on.
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