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IIsi Boots with Vertical Black Lines (and has a PSU That Refuses to Cooperate)

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I've got a IIsi (not the same as the other thread of mine) that boots just fine, but has a series of this vertical lines across the screen. The board has been recapped and some traces from UE5 to UF7 that were eaten by corrosion from the nearby caps have been repaired (the lines were there prior to working on the board, however). Once booted into the OS, I get nearly identical graphical artifacting to what is shown in this thread:

I know the IIsi uses the 1MB of onboard RAM as VRAM, so I'm assuming the issue lies there. Could this be an address or data line that's shorted (or a bad RAM IC altogether), or should I be looking elsewhere? Most of my experience with testing RAM is on (much older) arcade boards that have very simple interfaces between CPU and RAM and no truly discrete video circuitry, so I'd at least like to confirm I'm not too off base in where to start looking.


Additionally, this thing has a PSU that just refuses to live. I have thoroughly cleaned it, recapped it, and serviced the 10-pin daughtercard (recapped, cleaned, removed/cleaned under/replaced the IC, reflowed darn near everything), but it just won't run. If I short pins 9 and 10, The relay will click a few times, getting gradually weaker/quieter each time fires until it just stops. Again, PSU experience is somewhat limited to old linear units from arcade cabinets, so I'm just banging my head against a wall at the moment.


Any help anybody can offer is greatly appreciated.


Edited by warmech
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  • warmech changed the title to IIsi Boots with Vertical Black Lines (and has a PSU That Refuses to Cooperate)
  • 68kMLA Supporter

I didn't pursue my issue any further yet as the Centris I had the issue with isn't a priority machine - Coincidently I was thinking about this problem recently again within the past few weeks taking into account some of the additional experience I have gained in troubleshooting various problems since then.  My plan was to go back and test all of the lines that deal with video (video chip / VRAM etc.) to see if I had an issue there before condemning the VRAM. 

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19 hours ago, warmech said:

And now I've got chimes of death out of nowhere. That's two dead IIsi's on my desk now. I quit.


The IIsi is a harsh mistress for sure. Even if you get the logic board working, the PSU is usually borked -- especially that riser board with SMDs in the PSU. :(

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