SX repair help ~ pic link included
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From: polishedball on 16 Feb 2010 13:44 Well my search for an SX-64 brought me to a broken one, I was thinking no problem plenty of repair guides and I was a bench tech for 10 years until board swaps became the norm. I haven't dug in far yet but was surprised that the suggested chip swaps did nothing. I am suspecting a logic chip and am curious if anyone has any guesses as this unit isn't friendly to work on in it design while hot. Gonna download the schematics now. 1) Have garbage screen with border (maybe the check-board i have read about) 2) Cartridge slot doesn't appear to work. 3) Swapped Vic Chip with known good Same problem 4) Swapped PLA with known Good Same problem 5) Swapped character rom Same problem Screen pics http://home.comcast.net/~polishedball/screen.jpg http://home.comcast.net/~polishedball/screen1.jpg Thanks for any thoughts John
From: polishedball on 16 Feb 2010 13:46 On Feb 16, 1:44 pm, polishedball <polishedb...(a)gmail.com> wrote: > Well my search for an SX-64 brought me to a broken one, I was > thinking no problem plenty of repair guides and I was a bench tech for > 10 years until board swaps became the norm. I haven't dug in far yet > but was surprised that the suggested chip swaps did nothing. I am > suspecting a logic chip and am curious if anyone has any guesses as > this unit isn't friendly to work on in it design while hot. Gonna > download the schematics now. > > 1) Have garbage screen with border (maybe the check-board i have read > about) > 2) Cartridge slot doesn't appear to work. > 3) Swapped Vic Chip with known good Same problem > 4) Swapped PLA with known Good Same problem > 5) Swapped character rom Same problem > > Screen pics > > http://home.comcast.net/~polishedball/screen.jpghttp://home.comcast.net/~polishedball/screen1.jpg > > Thanks for any thoughts > > John Also it presents the same screen using an external monitor.
From: Sam on 16 Feb 2010 14:46 Hello John, I've seen your screen pics and I think one of the 4164 RAM chips (UA4 thru UA7 & UB4 thru UB7) is bad. Ray Carlsen wrote: "See if any of the RAM chips (there are eight of them) get warm or hot... feel each one with the back of your finger after the computer has run for about 5 minutes. Shorted chips will get hotter than the others. Note: bad RAM doesn't always get hot." If you feel no difference you can try the "piggyback" trick. Good luck ! Regards, SAM
From: polishedball on 16 Feb 2010 14:54 On Feb 16, 2:46 pm, Sam <siemappel...(a)quicknet.nl> wrote: > Hello John, > > I've seen your screen pics and I think one of the 4164 RAM chips (UA4 > thru UA7 & UB4 thru UB7) is bad. > > Ray Carlsen wrote: > > "See if any of the RAM chips (there are eight of them) get warm or > hot... feel each one with the back of your finger after the computer > has run for about 5 minutes. Shorted chips will get hotter than the > others. Note: bad RAM doesn't always get hot." > > If you feel no difference you can try the "piggyback" trick. > > Good luck ! > > Regards, SAM Thanks will socket them and do some swapping from a working donor C64. John
From: polishedball on 16 Feb 2010 19:26
I just swapped all the Ram out all 8 from a known good machine and still have the same garbled screen. Ideas? Thanks On Feb 16, 2:54 pm, polishedball <polishedb...(a)gmail.com> wrote: > On Feb 16, 2:46 pm, Sam <siemappel...(a)quicknet.nl> wrote: > > > > > > > Hello John, > > > I've seen your screen pics and I think one of the 4164 RAM chips (UA4 > > thru UA7 & UB4 thru UB7) is bad. > > > Ray Carlsen wrote: > > > "See if any of the RAM chips (there are eight of them) get warm or > > hot... feel each one with the back of your finger after the computer > > has run for about 5 minutes. Shorted chips will get hotter than the > > others. Note: bad RAM doesn't always get hot." > > > If you feel no difference you can try the "piggyback" trick. > > > Good luck ! > > > Regards, SAM > > Thanks will socket them and do some swapping from a working donor C64. > > John |