Hit Bit w/broken graphics

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By sd_snatcher

Prophet (3551)

sd_snatcher's picture

14-12-2015, 01:38

This one is easier. The DRAM corresponding to the data bit 0 is stuck to 0. Either it's a bad soldering on that socket, or the DRAM chip is bad.

By pseen

Resident (60)

pseen's picture

14-12-2015, 17:28

Alright, success! This 12+ year old thread finally reaches a happy conclusion. I am very grateful for all the invaluable input you guys have given, my very first computer now comes back to life after a quarter of a century in oblivion. Thanks!!

The problem turned out to be:
1. The broken fuse in the PSU.
2. A broken trace in the VRAM network. Specifically, IC12 didn't have a connection between pin 2 (DATA IN) and the ADDRESS7 pins on the VRAMs/VDP. Soldering in a jumper from pin 2 on IC12 to pin 13 on another VRAM solved this. The broken trace probably stems from the process of desoldering the old VRAMs and soldering in the new sockets, some force had to be used here and there...

Checking the service manual was crucial:

Quick and dirty fix:

It works, cheers everybody!

By l_oliveira

Hero (534)

l_oliveira's picture

14-12-2015, 18:47

You have no idea how pleased I am for seeing you were able to revive your own computer. I know how it is when you fix your own stuff and when it's the very first one you ever owned it's even more special.

Grats

By pseen

Resident (60)

pseen's picture

15-12-2015, 13:16

Running Naked in a Field of Flowers

By SuchAGoonie

Expert (108)

SuchAGoonie's picture

15-12-2015, 14:00

This thread is an awesome read. Good to hear you managed to resurrect your MSX! Smile

By Wild_Penguin

Hero (644)

Wild_Penguin's picture

15-12-2015, 20:44

Gongratulations!

By fubukimaru

Resident (45)

fubukimaru's picture

25-02-2017, 12:03

Sorry for reviving such an old thread but I made a post in my blog for detecting visually which vram bank is failing (if only 1 is failing at time):
http://www.gamerachan.org/fubu/dijkstra/?p=93

Thanks for this thread as this was the main source of information used to debug my machine :).

By Grauw

Ascended (10619)

Grauw's picture

25-02-2017, 12:32

Nice post!

By pseen

Resident (60)

pseen's picture

26-02-2017, 09:18

Cool!

By user888

Expert (66)

user888's picture

03-03-2017, 21:55

Wow, what I nice thread to read. Next time check back more often, could have save you replacing the VRAM Smile

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