On the bench today is a Commodore 64 picked up from @Recta_Pete<\/a> at Atari Party East 2018. This revision is the cost reduced long board because of the sparse components around the VIC-II. I already spot several problems.<\/p>\n\n\n\n 1. The SID and PLA locations are swapped. SID should be U18 and PLA should be U17.<\/p>\n\n\n\n 2. There\u2019s a character ROM (901225) where the missing kernal (901227) should be (middle, U4)<\/p>\n\n\n\n 3. The VIC-II has some bent pins. These didn\u2019t bend back nicely. I may try to solder some legs to the remaining stubs if it\u2019s still good.<\/p>\n\n\n\n 4. This board features the prone-to-failure MOS 7709 which is a 74LS258.<\/p>\n\n\n\n September 24, 2018<\/em><\/p>\n\n\n\n I have some 74LS258s on the way. Meanwhile I scoped around the board and found the \/RES signal to the CPU never goes high so the #c64<\/a> will never start. It should go high after 0.5 seconds.<\/p>\n\n\n\n The 556 timer IC is the basis for the long board #c64<\/a> reset circuit (along with a capacitor that checked out ok). I removed the old 556 and swapped in a new one.<\/p>\n\n\n\n Progress! The #c64 diagnostic cart is able to start now and shows some bad RAM (or possibly RAM mux ICs).<\/p>\n\n\n\n September 26, 2018<\/em><\/p>\n\n\n\n I replaced the three MOS logic chips (2×7708 and a 7709) but that didn\u2019t fix the problem. They\u2019ll probably still fail at some point but are now socketed.<\/p>\n\n\n\n Also replaced RAM at U11 with no change. So far that\u2019s 1 for 5.<\/p>\n\n\n\n Decided to try the piggyback RAM trick at U24 and look at that\u2014 it\u2019s booting now. 2 for 6. Ignore BAD as there\u2019s no harness connected yet.<\/p>\n\n\n\n With the C64 diagnostic harness attached, it\u2019s working 100%! Final score: PLA\/SID swapped, bad PLA, missing kernal, bad 556 timer, bad U24 RAM. VIC-II ok with new legs, SID ok.<\/p>\n\n\n\n That was a fun repair! Thanks for joining me!<\/p>\n\n\n\n <\/p>\n","protected":false},"excerpt":{"rendered":" (This was originally a Twitter thread on September 23, 2018) September 23, 2018 On the bench today is a Commodore 64 picked up from @Recta_Pete at Atari Party East 2018. This revision is the cost reduced long board because of the sparse components around the VIC-II. I already spot several problems.<\/p>\n","protected":false},"author":1,"featured_media":0,"comment_status":"open","ping_status":"open","sticky":false,"template":"","format":"standard","meta":[],"categories":[6,15],"tags":[42,43,52,44,51,50],"_links":{"self":[{"href":"https:\/\/biosrhythm.com\/index.php?rest_route=\/wp\/v2\/posts\/2095"}],"collection":[{"href":"https:\/\/biosrhythm.com\/index.php?rest_route=\/wp\/v2\/posts"}],"about":[{"href":"https:\/\/biosrhythm.com\/index.php?rest_route=\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"https:\/\/biosrhythm.com\/index.php?rest_route=\/wp\/v2\/users\/1"}],"replies":[{"embeddable":true,"href":"https:\/\/biosrhythm.com\/index.php?rest_route=%2Fwp%2Fv2%2Fcomments&post=2095"}],"version-history":[{"count":3,"href":"https:\/\/biosrhythm.com\/index.php?rest_route=\/wp\/v2\/posts\/2095\/revisions"}],"predecessor-version":[{"id":2117,"href":"https:\/\/biosrhythm.com\/index.php?rest_route=\/wp\/v2\/posts\/2095\/revisions\/2117"}],"wp:attachment":[{"href":"https:\/\/biosrhythm.com\/index.php?rest_route=%2Fwp%2Fv2%2Fmedia&parent=2095"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/biosrhythm.com\/index.php?rest_route=%2Fwp%2Fv2%2Fcategories&post=2095"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/biosrhythm.com\/index.php?rest_route=%2Fwp%2Fv2%2Ftags&post=2095"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}![\"\"](\"https:\/\/biosrhythm.com\/wp-content\/uploads\/2022\/11\/1043906990832013312-Dnyz35FXgAArqU8-840x434.jpg\")
<\/a><\/figure><\/li>![\"\"](\"https:\/\/biosrhythm.com\/wp-content\/uploads\/2022\/11\/1045120853871128581-DoED3ulWsAYf3YY-800x800.jpg\")
<\/a><\/figure><\/li><\/ul><\/figure>\n\n\n\n\n\n\n\n![\"\"](\"https:\/\/biosrhythm.com\/wp-content\/uploads\/2022\/11\/1043929264528207872-DnzIIVzXcAEU5sG-600x800.jpg\")
<\/a><\/figure><\/li><\/ul><\/figure>\n\n\n\n![\"\"](\"https:\/\/biosrhythm.com\/wp-content\/uploads\/2022\/11\/1043929907854749696-DnzItxbXUAAqGiG-840x630.jpg\")
<\/a><\/figure><\/li><\/ul><\/figure>\n\n\n\n![\"\"](\"https:\/\/biosrhythm.com\/wp-content\/uploads\/2022\/11\/1043930312844152838-DnzJFZZWsAA7Yjo-600x800.jpg\")
<\/a><\/figure><\/li>![\"\"](\"https:\/\/biosrhythm.com\/wp-content\/uploads\/2022\/11\/1043930312844152838-DnzJFZRXkAAIYz3-840x630.jpg\")
<\/a><\/figure><\/li><\/ul><\/figure>\n\n\n\n![\"\"](\"https:\/\/biosrhythm.com\/wp-content\/uploads\/2022\/11\/1043930826562506755-DnzJjU_WsAA_L15-495x800.jpg\")
<\/a><\/figure><\/li><\/ul><\/figure>\n\n\n\n![\"\"](\"https:\/\/biosrhythm.com\/wp-content\/uploads\/2022\/11\/1044334054945038337-Dn44RGJXoAAiozH-840x630.jpg\")
<\/a><\/figure><\/li><\/ul><\/figure>\n\n\n\n![\"\"](\"https:\/\/biosrhythm.com\/wp-content\/uploads\/2022\/11\/1044334819860262912-Dn44-tZXkAANI2k-800x800.jpg\")
<\/a><\/figure><\/li><\/ul><\/figure>\n\n\n\n![\"\"](\"https:\/\/biosrhythm.com\/wp-content\/uploads\/2022\/11\/1045119410661445632-DoECjoEWkAAkTbB-600x800.jpg\")
<\/a><\/figure><\/li><\/ul><\/figure>\n\n\n\n![\"\"](\"https:\/\/biosrhythm.com\/wp-content\/uploads\/2022\/11\/1045120853871128581-DoED3ulWsAYf3YY-1-800x800.jpg\")
<\/a><\/figure><\/li><\/ul><\/figure>\n\n\n\n![\"\"](\"https:\/\/biosrhythm.com\/wp-content\/uploads\/2022\/11\/1045121536322162688-DoEEfiVXkAEr6YN-840x630.jpg\")
<\/a><\/figure><\/li>![\"\"](\"https:\/\/biosrhythm.com\/wp-content\/uploads\/2022\/11\/1045121536322162688-DoEEfiVXUAMMJw2-800x800.jpg\")
<\/a><\/figure><\/li><\/ul><\/figure>\n\n\n\n![\"\"](\"https:\/\/biosrhythm.com\/wp-content\/uploads\/2022\/11\/1045122835902078976-DoEFq-oXcAAwk5X-800x800.jpg\")
<\/a><\/figure><\/li>![\"\"](\"https:\/\/biosrhythm.com\/wp-content\/uploads\/2022\/11\/1045122835902078976-DoEFq-qXgAAxUfS-840x630.jpg\")
<\/a><\/figure><\/li>![\"\"](\"https:\/\/biosrhythm.com\/wp-content\/uploads\/2022\/11\/1045122835902078976-DoEFq-4XgAA568F-840x630.jpg\")
<\/a><\/figure><\/li><\/ul><\/figure>\n\n\n\n