C64 U21 memory failure
in [Commodore]
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From: Jack Tseng on 28 Feb 2010 22:02 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? JT
From: Clocky on 1 Mar 2010 00:16 "Jack Tseng" <tseng4(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.
From: Jack Tseng on 1 Mar 2010 21:01 "Clocky" <notgonn(a)happen.com> wrote in message news:4b8b4dbb$0$8789$c3e8da3(a)news.astraweb.com... > > "Jack Tseng" <tseng4(a)hotmail.com> wrote in message > news:s7Gin.9733$mn6.7678(a)newsfe07.iad... >> C-64 diagnostic checks the zeropage, stackpage, colour ram, etc... It >> found the bad memory U21 on 64K ram. I was checking the mainboard, there >> is no U21 printed on the board. I dont know if the board is different. >> The board was made in 1986 and Hong Kong. Other printed is W-18 94HB. >> Anyone help me where I find the memory chip? >> > > > http://www.c64-wiki.com/index.php/Image:C64Cmotherboard.jpg > > If that looks like your board, there are two DRAMs directly above where it > says PCB ASSY on the mainboard. > > DRAM failure is common for that board, especially if the power supply has > ripple so you best check that too. > I think I found C64 PSB ASSY #250466, it looks exactly one as mine. http://www.auctiva.com/hostedimages/showimage.aspx?gid=45129&ppid=1122&image=300723127&images=300723127&formats=0&format=0
From: Clocky on 1 Mar 2010 21:11 "Jack Tseng" <tseng4(a)hotmail.com> wrote in message news:Uj_in.215862$OX4.209979(a)newsfe25.iad... > > "Clocky" <notgonn(a)happen.com> wrote in message > news:4b8b4dbb$0$8789$c3e8da3(a)news.astraweb.com... >> >> "Jack Tseng" <tseng4(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=1122&image=300723127&images=300723127&formats=0&format=0 > > 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.
From: Sam on 2 Mar 2010 16:14
Hello Jack, This is the rare version motherboard and used in the C64C. The serial number ends with B3... And Clocky is right: the two 18 pins are the DRAM's ! Here you can find the different C64 motherboards: http://www.cbmhardware.de/c64/c64board.php?Lang=E SAM |