video ram error

ttooddddyy

ttooddddyy

PNG FTW,
Joined
Nov 29, 2001
Posts
8,335
MV-1T

Address 00008000
write 5555
read 55DE

which 256 smd ram is this likely to be.
It had a blank with some squares, did a blanket change of the ram, now works with blocky gfx with the unibios and the error message with original bios.
Suspect I have put a faulty salvaged ram IC in.
 
channelmaniac

channelmaniac

Mr Neo Fix-it
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$8000 is the 2kx8 DIP SRAM on most systems.

You should check the OE/CE/RW lines on the chips first to make sure one isn't buggered.
 
MKL

MKL

Basara's Blade Keeper
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It's the SONY CXK5814 DIPs.

Connections for your board are:

1 LSPC (146)
2 LSPC (145)
3 LSPC (144)
4 LSPC (143)
5 LSPC (142)
6 LSPC (141)
7 LSPC (140)
8 LSPC (139)
9 LSPC (60)
10 LSPC (61)
11 LSPC (62)
12 GND
13 LSPC (63)
14 LSPC (64)
15 LSPC (65)
16 LSPC (66)
17 LSPC (67)
18 GND
19 LSPC (149)
20 GND
21 LSPC (76)
22 LSPC (148)
23 LSPC (147)
24 VCC

1 LSPC (146)
2 LSPC (145)
3 LSPC (144)
4 LSPC (143)
5 LSPC (142)
6 LSPC (141)
7 LSPC (140)
8 LSPC (139)
9 LSPC (68)
10 LSPC (69)
11 LSPC (70)
12 GND
13 LSPC (71)
14 LSPC (72)
15 LSPC (73)
16 LSPC (74)
17 LSPC (75)
18 GND
19 LSPC (149)
20 GND
21 LSPC (76)
22 LSPC (148)
23 LSPC (147)
24 VCC

The problem is with the one whose I/O lines are connected to LSPC 60-67.
 
ttooddddyy

ttooddddyy

PNG FTW,
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OK thanks guys

Replaced the 2 x CXK5814 now have a 8018 address error.

Will try another as Im not sure how good the salvaged ram i am using is.
 
ttooddddyy

ttooddddyy

PNG FTW,
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Posts
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Fixed, it was the ram that MKL alluded to, must have replaced with a faulty IC first time round :oh_no:

Just need to fix the Z 80 error now :spock:

Thanks again guys
 
channelmaniac

channelmaniac

Mr Neo Fix-it
15 Year Member
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Posts
4,316
Replace the Z80 CPU with a Z80A CPU.

For some reason SNK got REALLY cheap and put Z80 CPUs on instead of the Z80A. The board is even silk screened for the Z80A!

RJ
 
ttooddddyy

ttooddddyy

PNG FTW,
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Posts
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This is a board that Briggs of HardMVS kindly gave me some years ago, it had a Z80 error, traced it to some broken traces around Z80/SM1 rom and 6116 ram. The board then worked well untill I tested it the other day and found the ram issue.

I think because it has been in a stack of boards for some time something may have been disturbed around that stage.

Have you actually had a cases where Z80A will work where a Z80 will not ?
 
channelmaniac

channelmaniac

Mr Neo Fix-it
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No. The difference is clock speed ratings. The Z80A is rated faster. The Z80 will work in place of a Z80A or a Z80B but it's life expectancy is shorter as it will run hotter than normal.

I've seen Z80 chips in place of Z80A that run for years - every CPS1 game and Neo-Geo system has that. They will eventually fail though.

RJ
 
ttooddddyy

ttooddddyy

PNG FTW,
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Posts
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channelmaniac said:
No. The difference is clock speed ratings. The Z80A is rated faster. The Z80 will work in place of a Z80A or a Z80B but it's life expectancy is shorter as it will run hotter than normal.

I've seen Z80 chips in place of Z80A that run for years - every CPS1 game and Neo-Geo system has that. They will eventually fail though.

RJ
Click to expand...

What about Z08400s (Zilog branded) generic Z80 ucoms, I have seen these as original on MVS boards.
 
channelmaniac

channelmaniac

Mr Neo Fix-it
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You have to check the spec sheet and see what the clock speed ratings are for that particular IC.
 
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