C64 U21 memory failure
in [Commodore]
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From: JPPBM on 8 Mar 2010 02:07 On Mar 4, 12:23 am, "Clocky" <notg...(a)happen.com> wrote: > Jack Tseng wrote: > > "Clocky" <notg...(a)happen.com> wrote in message > >news:4b8ee8bc$0$8757$c3e8da3(a)news.astraweb.com... > >> Jack Tseng wrote: > >>> "Clocky" <notg...(a)happen.com> wrote in message > >>>news:4b8c73bd$0$8841$c3e8da3(a)news.astraweb.com... > > >>>> "Jack Tseng" <tse...(a)hotmail.com> wrote in message > >>>>news:Uj_in.215862$OX4.209979(a)newsfe25.iad... > > >>>>> "Clocky" <notg...(a)happen.com> wrote in message > >>>>>news:4b8b4dbb$0$8789$c3e8da3(a)news.astraweb.com... > > >>>>>> "Jack Tseng" <tse...(a)hotmail.com> wrote in message > >>>>>>news:s7Gin.9733$mn6.7678(a)newsfe07.iad... > >>>>>>> C-64 diagnostic checks the zeropage, stackpage, colour ram, > >>>>>>> etc... It found the bad memory U21 on 64K ram. I was checking > >>>>>>> the mainboard, there is no U21 printed on the board. I dont > >>>>>>> know if the board is different. The board was made in 1986 and > >>>>>>> Hong Kong. Other printed is W-18 94HB. Anyone help me where I > >>>>>>> find the memory chip? > > >>>>>>http://www.c64-wiki.com/index.php/Image:C64Cmotherboard.jpg > > >>>>>> If that looks like your board, there are two DRAMs directly above > >>>>>> where it says PCB ASSY on the mainboard. > > >>>>>> DRAM failure is common for that board, especially if the power > >>>>>> supply has ripple so you best check that too. > > >>>>> I think I found C64 PSB ASSY #250466, it looks exactly one as > >>>>> mine. > >>>>>http://www.auctiva.com/hostedimages/showimage.aspx?gid=45129&ppid=112... > > >>>> What are the numbers on the two chips in the left corner of the > >>>> board above the bare section to the left of the empty solderpads? > >>>> Those two 18 pin chips look like the DRAM's. > > >>> it is MN41464-15 Japan 64432 on the U9 and U10 sockets. > > >> That's them. You can replace them with virtually any xx464 memory > >> chip, I would recommend removing both DRAMs and replacing them with > >> sockets. > > >http://www.jameco.com/webapp/wcs/stores/servlet/ProductDisplay?langId... > > > how s about it? > > Perfect! U21 in the test equals U10 on your 2 DRAM board... It helps when you have the manual that goes with it and the DEAD-TEST Manual the updates for later PCB revisions.... replace that one. And check the output of your power supply.. anytime ram is found to be bad.... |