MV-1FT repair log (and RGBS points)

HeavyMachineGoob

My poontang misses Lenn Yang's wang
10 Year Member
Joined
Apr 3, 2011
Posts
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Model: MV-1FT
Symptom: Backup RAM error

Picked up a parts/not working MV-1FT board. It entered my hands with a missing (lower) backup RAM chip. I checked over the solder pad, looked good, soldered in a new SRAM. Board booted to a backup RAM error.

Address $D000 Write 5555 Read 0055

Tried replacing the upper Backup RAM, no change. Checked the enable lines for it, /WE was missing. Patched trace from upper Backup RAM pin 27 to 74HC32 pin 8.

Board now booted, vertical lines in the sprite graphics. Cleaned slot, no change. Checked over the interconnector for bent pins, none were found. Looked over the board underside with a magnifying glass for gouged traces, found three in the graphics-related area. Patched them, all sprite graphics were fixed. Installed a new battery and played a few games.

Block diagram of MV-1FT RAMs

Code:
________   ________
|43256L|   |43256L|
|Lower |   |Upper |
|Backup|   |Backup|
-------    --------

________   ________
|43256 |   |43256 |
|Lower |   |Upper |
|Work  |   |Work  |
--------   --------
Video RAMs are near the 
Hard DIPs on MV-1FT

acnpSqo.jpg

0yKzRUV.jpg


For anyone who wants to consolize this board, the RGBS signals can be grabbed from here. (wires are color coded, white is sync).

5C56vG6.jpg
 
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