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Sega CD model 1 not booting games motherboard problem

Tokimemofan

Well-known member
Original poster
May 30, 2019
84
28
18
Trying to fix a Sega CD model 1. System plays audio CDs but doesn’t boot games. It is definitely the motherboard, I have tested the drive and mixer/power boards in another unit and they both work fine. I have recapped the board but no change. All the traces seem to be good and the solder joints on the main asic seem to be fine. The bios loads normally and there are saves on the system so most of the functionality works. Any ideas?
 

segasonicfan

Active member
Jun 8, 2019
33
15
8
hrmmm this is unusual, normally any difficulty playing games has to do with the CD PCB section.
However, the main board is known for having nasty capacitor failures, Ive changed out the silver SMD electrolytics and there was plenty of acid on the units I've worked on. I would start there.
 

Tokimemofan

Well-known member
Original poster
May 30, 2019
84
28
18
hrmmm this is unusual, normally any difficulty playing games has to do with the CD PCB section.
However, the main board is known for having nasty capacitor failures, Ive changed out the silver SMD electrolytics and there was plenty of acid on the units I've worked on. I would start there.
I gave up on it, I had already recapped it. It seems to have been the main asic had failed. The odd part is that it wouldn’t even read a game as an audio cd and would just keep spinning the disc. I’ve fixed many of these over the years but never seen a problem like this one
 

segasonicfan

Active member
Jun 8, 2019
33
15
8
I gave up on it, I had already recapped it. It seems to have been the main asic had failed. The odd part is that it wouldn’t even read a game as an audio cd and would just keep spinning the disc. I’ve fixed many of these over the years but never seen a problem like this one

Ah, I understand. Well, if you want to send it my way for parts I could take a stab at it. Ive had a lot of success repairing these, and came up with a new upgrade for the ejecting drive. I have a bunch of videos to compile on my site with a new guide, but just haven't had the time to do it yet. I also have some NOS ASICs and am good at replacing those.
 

Tokimemofan

Well-known member
Original poster
May 30, 2019
84
28
18
Ah, I understand. Well, if you want to send it my way for parts I could take a stab at it. Ive had a lot of success repairing these, and came up with a new upgrade for the ejecting drive. I have a bunch of videos to compile on my site with a new guide, but just haven't had the time to do it yet. I also have some NOS ASICs and am good at replacing those.
I might hit you up on that, I think I have a few boards with asic problems
 

BlackFX

New member
Feb 12, 2021
2
0
1
If your thinking about parting out some broken ones I am currently looking for the VRAM ICs off one...
 

segasonicfan

Active member
Jun 8, 2019
33
15
8
I might hit you up on that, I think I have a few boards with asic problems
cool :cool:

If your thinking about parting out some broken ones I am currently looking for the VRAM ICs off one...
are you sure its VRAM? That's such a rare failure. In my experience it's usually trace issues. Does SCD have diff VRAM from the genny btw? Might be easier to pull it from a Gen1 or Gen2..

Edit nvm its different IC. Heres the SCD1 VRAM but not that cheap:

 

BlackFX

New member
Feb 12, 2021
2
0
1
are you sure its VRAM? That's such a rare failure. In my experience it's usually trace issues. Does SCD have diff VRAM from the genny btw? Might be easier to pull it from a Gen1 or Gen2..

Edit nvm its different IC. Heres the SCD1 VRAM but not that cheap:


Yeah, I took an oscilloscope trace of all the data lines on the VRAM and D0 on VRAM1 is stuck low :)
 

segasonicfan

Active member
Jun 8, 2019
33
15
8
ah cool. and im assuming you lifted the pin (out of circuit) to confirm its not the ASIC or 68K?

EDIT found TC511664BZ-80 at a good price - are you in USA? Send me a PM after you check.