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  1. 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. 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 sp
  3. 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. 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
  5. 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 o
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