Graphics Glitch - DUO

[mamejay]

Hey Guys,

I finally decided to try and tackle a junk DUO I purchased some time back.
Basically the console works perfectly except for the graphics.
i get constant graphics glitches on any screen.  This happens even on first start up and the Super CD rom menu so I suspect it is something to do with the video ram.
Can anyone help me with this?  i am pretty good at soldering so i could replace most of the chips on the motherboard.  Its just trying to identify which one is the correct one to work on.
i would prefer to fix it than junk it as I hate to see retro console get trashed.
Here are some pics of the issue and the motherboard.  Any help will be greatly appreciated

[mamejay]

I think the chip that is causing the issues is a Sanyo lc3564pm-10L.
This is the VRAM for the PC Engine.
Now all I need to to try and source out is a working chip from somewhere to test this.  Can anyone on the forum help?

[ApolloBoy]

I'd get on replacing those caps ASAP while you're at it. Doing so might even fix the video issue you're having.

[thesteve]

thats not the Vram for the system
look at IC904 and IC905 both V-RAM

[mamejay]

Thanks for that Steve.  So do you suspect it could be IC904 and IC9045 VRAM causing the issues?

[Duo_R]

Does the TG16 have the same part?

[mamejay]

I have no idea.  I would suspect yes but really cannot answer that one

[Duo_R]

What is the markings on the chip where Steve mentioned. I can check my junk TG unit if it has it

[mamejay]

Will need to check when i get home.  i found this thread
http://www.pcenginefx.com/forums/index.php?topic=9946.0
On the schematic the IC904 and 905 are labeled with 20256 which I have found a few on the eBay.  Will confirm 100% but I want to make sure that this could possibly be the problem I have

[thesteve]

take  a logic probe across them and make sure all the data and addressing lines are active first.
a bad connection/trace to them will have the same results

[MottZilla]

I agree with thesteve. The RAM chips may not be bad. You might just have a bad/dry solder joint or maybe a damaged trace. You could try reflowing/resoldering the RAM chips and see if that fixes the issue. Judging by the partial graphics correct display, maybe one or more of the address lines on the RAM chip is dry/poor contact. I'd suggest locating the RAM chip (make sure it is the right chip) and get a pinout and figure out which pins are address lines. Resolder those. If you fix it I would certainly like to hear what you had to do to get it working.

[thesteve]

remember its 2 chips addressed the same (all pins except data D0-D7 tied to both chips the same)
each 8BIT wide (combined for 16Bit graphics)

[Keith Courage]

Has anyone ever come across a system where one of the two chips were actually bad?

[mamejay]

Looks like mine are stuffed. 
Found the culprits on the underside of the motherboard.  Here are some pic of them.  i do not have a logic probe but I traced every single pin on them and they all seem fine.
Touching the pins cause the image to change somewhat but is still not good so I suspect these are fried.  Anyone got a couple of these from a junk board i am can grab??

[Duo_R]

I can donate from a junked tg-16 unit shoot me a pm