Sega Cd mod1 video issue

my sega cd model 1 has some very odd video issues..ive replaced some caps but no change.for a split sec when the planet image shows on screen right before the "sega" graphic is displayed its 100% clear,but as soon as the dancing sega logo pops up the screen box goes just like the picture.

after you start a game,the sega logo with sonic is perfect..

 

sol??

 

Replace ram with similar components.

 

it seems if it was ram it would do it on the entire screen.and like i said a couple of the screens it doesn't do that on.

 

No, that does look like ram. Chips can also fail as they heat up.

It looks like the vram and if only a certain part of the ram has failed or one address line has failed it would only happen in certain places and work fine in others.

 

well crap.any clues and which chip it may be,and or a lead to find a supplier?

 

seems that your right.as sonic cd plays fine outside of the movie.so anytime fmv is displayed is wheb the problem happens.

it seems i have two vram chips with a zip pinout.
TC511664BZ-80 9221HBK .and a TC511664BZ-80 9212HBK

i found a seller on ebay with a picture of the TC511664BZ-80 9221HBK but lists it as a TC511664Z chip.will that one work? and also can i just get two of the 9221hbk chips for both or do i need to get a 9221hbk and a 9212hbk how it is now??

 

x

 

You could probably fault find that by hitting the chips with freeze spray. Sounds like it gets worse as they warm up. Being cold might make it work and also ID the correct chip

 

This is a good recommendation.
If cold is not available, you can also use heat the same way.
The glitches will change if you hit the right IC.
Just don't cook it

 

well that wasn't it.i replaced the vram at ic7 and ic8 and no change.

 

Check out the Sega CD Repair thread on Sega-16 forums. Amazingly useful.
Also, it sounds silly but...have you tried another Genesis console to rule out that issue?
Video RAM is what it sounds like to me as well, but it could be an ASIC pin corrosion issue too. If it boots fine and THEN gets corrupted it is very, very, very likely to be RAM though.
Save yourself some headache and buy a broken one with a bad laser but good video output. Will run you about $20 on ebay.

-Segasonicfan

 

That is broken traces between the ASIC and the WORD RAM chips. Leaky capacitors are the likely cause.

Word RAM are the large ZIP chips near the leds at the front.

 

l_oliveira would you be interested in fixing this mobo for me if i sent it to ya??

 

I could try but I wonder if that is worth the hassle... Photos? (of the board damage, not how it runs on the TV)

 

Welp nvm its working now and i am not sure what i did.

Things i tinkerd with tonight are

Resolderd c49 as it popped lose tonight when i moved it.

I popped ic4 out to look under it for broken traces.

I had dismissed some Old capacitor gunk on pins 1-15 of the sanyo lc8951 as dust,and it seemd pins 3-7ish were shorted,but after cleaning pins 3-6 are still shorted so idk if any were shorted to begin with.

Thats about it.idk wth i did tho.maybe c49 wasn't soldered very well to begin with idk.

 

Like I said more than a year ago, it's just broken traces (or maybe the ASIC has cold joints on the pins related to WORD RAM). WORD RAM is used specifically as a "swap area" for the CD side and MD side swap data around in a efficient manner.

It's a kludge with two banks of 64KB/16bit ram which can either be used as a single 128KB RAM or be split into two 64KB banks that can be swapped around with a write on the CD ASIC register. That RAM is used to move data from the sprite scaling unit on the CD ASIC to the MD VDP or for moving FMV video frames to the VDP and that's why you see the weird glitches only on these things.

 

No it wasn't.i went through and spent about 10hrs on the traces and reflowing the acis pins.but that did nothing.

It was either a bad solder joint on c49 or that left over Electrolyte on the sanyo chip.

 

The Sanyo chip has nothing to do with the stuff you had issues with. The Sanyo chip takes the I2S stream (audio signal from CD error correction DSP at the CD drive board) and process it to extract CD-ROM data sectors. If the Sanyo were faulty the unit would not be able to boot games, you would mostly have it playing audio tracks. And the Sanyo chip is not used at all during the processing of the scaling effects at the logo screen.