[SOLVED] Bad chip or what? Corrupt video on Duo-R

[wilykat]

From the thread: https://www.pcengine-fx.com/forums/index.php?topic=19470.0 since the issue is not with game disc but with Duo-R itself.

Here's a video of the issue running Might and Magic III and Ys III.

Suggested it may be related to the RAM chips, I am going to go over them with a strong magnifying glass to see if I can rule out bad solder joint or bad trace.  Hopefully it's not the chip itself as I don't have the tool to desolder those chip (pins curled under chip, needs hot air station to remove it)

[wilykat]

I got a good photo of the area with the 2 RAM CHIPS: https://i.imgur.com/RMGndOz.jpg

No obvious trace damage. I would have to check all the VIAs. Since no schematic exists of Duo-R I would have to guess the 2 RAM chips shares the same address, row, column, and enables and only have separate data (4 bits each).  I'd have to look closely and poke around to figure out which pins goes to which, mostly to the large chip on top of the picture.

Tiny pins sucks.  My trusty and loyal digital meter may be finally showing its age after serving me for 22 years, its probes are about 0.1 inch at the thinnest (about 2.54mm) and those pins are much smaller, easily in the range of 0.026 inch for the pins itself (about 0.7mm)  Time to steal a PLCC18 socket (if it exists, all I can find are 20) to mount on top of the RAM chips for easier probing.

[thesteve]

those ram chips are not on the same data bus
they are mapped here https://www.pcengine-fx.com/forums/index.php?topic=16503.msg338114#msg338114

[wilykat]

Thanks for the info, that should cut down the amount of time spent probing.

[thesteve]

the txt file first post

[wilykat]

Ok I went over all of the pins between the 2 RAM chips and the host chip. There is no continuity between pin 73 and either of the RAM's 14 (address A0) so I think I may be on something.  Looking at the closeup picture, there is a small solder blob on the trace from pin 73, right next to silkscreen number 75. There is continuity from solder blob to pin 73 but not to RAM chip.  The trace goes under IC509 so I can't tell why it's bad.

I did notice that data D0-D4 on both chips are connected together but /OE and /WR are separate so I guess the host chip reads/writes in half byte? Enable one chip for lo half, enable other chip for hi half.

Time to dig out kynar wires and hope that's it.

[wilykat]

it works!! No more glitched graphics with Ys III.

 


For reference, the wire I used is AWG-30 which is 0.25mm in diameter.

[bozo55]

Damn, good job there wilykat! I hate dealing with QFPs like that.  So easy to bridge and destroy the legs.

[OldMan]

Tiny pins sucks.

Get 2 T-handle stick pins, (They are used for sewing hems in clothes. You'll know them when you see them.) and 2 wires with clips on the ends.  Tape 1 wire to each pin, so they don't come loose, and small pins are no longer a worry:)

[thesteve]

and thats why i wrote the txt file