Sega CD, random resets, modchip, and dead battery

[Vorde]

Hello,
I'm a lurker at GamesX, and I've been a member of the forum for about 7 years.
Anyways, I happened to score a used Sega CD system for 25 bucks
It came with Sonic CD (USA without manual for 3 bucks) and SpiderMan (with manual for 4 bucks).
Anyways, it was perfect, ...except for the factor that the old Sanyo battery inside for the internal save RAM was dead. So that's an easy fix...however...when I opened it, I found a modchip of some sort inside of it.
No it's not a unibios, as I just tried a japanese game on it, and it's got 2 chips on the board labeled HD74HC74P and some weird brown thingy with 2 leads.
They're soldered with 5 wires to specific places on the motherboard, and I seriously have no clue as to what it does. I'm thinking about disconnecting it, but since I don't know what it does, I'm just gonna leave it in it's semi-working condition.
Also, another thing is everytime I play Sonic CD, it either freezes or resets back to the BIOS during the first or second level, and on a burned copy of the Japanese version (I converted this to USA by the way) it will reset itself. I have no clue as to why, and yes I'm using a 1602 AC supply for it aswell so that shouldn't be the problem.
Does anyone have a clue?

[NFG]

A lot of Sega hardware had fixes in 'em.  Going by memory, that little board you have is an official Sega last-minute addon, so I wouldn't remove it if I were you.

I wonder if it's overheating?  You might try running it with the cover off and see if you get any better progress...  You also might try cleaning the connectors between console and CD.  It MIGHT be power, but since it's reliably (?) dying at one point, my guess is the problem lies elsewhere.

[Vorde]

Well the laser on the drive is clean, because I cleaned it when I first got it with a cotton swab and rubbing alcohol.
I'll leave the weird chips in because it's semi-working that way...
I'll see about the overheating thing, but I don't think it's that because I would have noticed if the casing was warm (which after 2 hours it didn't get warm at all).

[kendrick]

When troubleshooting a Sega CD unit, I would not start with any internal components. It's my experience that the connection between the Sega CD and the Megadrive/Genesis is the normal point of failure, as the bus connections are fiddly and frequently uncooperative. Are the slot or card connectors down there corroded or otherwise weak? I would take a pencil eraser to the Sega CD card edge before cleaning off the connector, and then I would take a slot cleaner to the Genesis side (really, a cotton cloth wrapped around a credit card edge should be fine.) Try that and see if you still see the random game failures.

[Vorde]

That sounds like a good idea, although the red piece of plastic was covering the slot. I guess it could still oxidize over time, etc.
I'll try that in a few minutes...after I find out wtf is wrong with my Dreamcast now.
I just tried playing Evil Twin on it, and it froze, and now no games are working on it. The disc refuses to spin, while the laser still works (I can hear it turning on and trying to read the disc). The little spindle thing (I don't know what it's called) is making clicking noises now everytime I manually spin it. Maybe something's stuck in there? 

[Vorde]

Ok, so the whole eraser to the pins on the side trick didn't work.
Although it's a lot cleaner now so that shouldn't hurt 
So my Lunar Silver Star Story burned copy didn't get passed the title screen (which is probably my fault since my CD-Burner doesn't burn lower than 16x and the CD-R i burned it to was fucking scratched), which pissed me off, so I decided to play Sonic CD. Everything was working fine right before I touched a ring, and then it reset itself. WTF?

[Drakon]

rules of the wise

1: test a system before you buy it

2: cd based technology dies....it's a fact of life

3: "So my Lunar Silver Star Story burned copy didn't get passed the title screen"

didn't get PAST

really wish I could help you but maybe NOW you'll understand why I praise cartridge based technology....My only suggestion is just try a different genesis and if you still have the same problem..then it's safe to assume the trouble is somewhere on the sega cd unit itself.

maybe you're now discovering why the system was 25$

[Vorde]

yeah no kidding. i'm thinking something might be wrong with the genesis (eventhough it operates fine by itself). i'm going to try to test it out on another one, and if it's still messing up I'm going to have to somehow try to run a hardware diagnostic on it, and probe around inside.

[l_oliveira]

If I were you, I would attempt:

1- Removing the Sanyo (Rechargeable) battery and checking for leaks and corrosion on the mother board
2- Check all eletrolythic capacitors on the main board (OLD front load units have SMD capacitors on the digital board and they more than often leak causing all sort of random problems (read erros on the CD drive due to increased digital noise on the power rails being the most common issue)
3- Check the power supplies on both CD and Mega Drive/Genesis for correct voltage/current.

Just mentioning, the battery on the SEGA/MEGA CD is of the rechargeable type. My Asian MEGA-CD was made in 1991 and it's internal battery still works. So I doubt yours are really damaged, unless if it leaked due to being discharged for too long.

If you see that the battery isn't leaked, just leave the unit on for two days without a disc inserted and see if it starts to hold the SRAM data again.

[Tiido Priimägi]

Those chips on a board are part of the system, don't remove them...

[Computolio]

    Have you tried another Genesis? If the results are the same, it sounds more like a RAM or CPU problem in the SCD than anything else.

    You may have to find a Sega CD with a dead drive and swap in it's motherboard.

[Vorde]

If I were you, I would attempt:

1- Removing the Sanyo (Rechargeable) battery and checking for leaks and corrosion on the mother board
2- Check all eletrolythic capacitors on the main board (OLD front load units have SMD capacitors on the digital board and they more than often leak causing all sort of random problems (read erros on the CD drive due to increased digital noise on the power rails being the most common issue)
3- Check the power supplies on both CD and Mega Drive/Genesis for correct voltage/current.

Just mentioning, the battery on the SEGA/MEGA CD is of the rechargeable type. My Asian MEGA-CD was made in 1991 and it's internal battery still works. So I doubt yours are really damaged, unless if it leaked due to being discharged for too long.

If you see that the battery isn't leaked, just leave the unit on for two days without a disc inserted and see if it starts to hold the SRAM data again.

Well I'll remove the battery tonight and see what happens, but if it isn't leaking, I'll definately see if I can get it charged up 
I don't really know how to check the capacitors on the board so...a little help? 
Also the adapters I'm using are SEGA brand and they both a the exact type listed on the bottom of the consoles.

However it was working for a long while, but has gone back to resetting itself for no apparent reason

[Drakon]

If I were you, I would attempt:

1- Removing the Sanyo (Rechargeable) battery and checking for leaks and corrosion on the mother board
2- Check all eletrolythic capacitors on the main board (OLD front load units have SMD capacitors on the digital board and they more than often leak causing all sort of random problems (read erros on the CD drive due to increased digital noise on the power rails being the most common issue)
3- Check the power supplies on both CD and Mega Drive/Genesis for correct voltage/current.

Just mentioning, the battery on the SEGA/MEGA CD is of the rechargeable type. My Asian MEGA-CD was made in 1991 and it's internal battery still works. So I doubt yours are really damaged, unless if it leaked due to being discharged for too long.

If you see that the battery isn't leaked, just leave the unit on for two days without a disc inserted and see if it starts to hold the SRAM data again.

Well I'll remove the battery tonight and see what happens, but if it isn't leaking, I'll definately see if I can get it charged up 
I don't really know how to check the capacitors on the board so...a little help? 
Also the adapters I'm using are SEGA brand and they both a the exact type listed on the bottom of the consoles.

However it was working for a long while, but has gone back to resetting itself for no apparent reason

well now we know why it was 20$.  Strange problem you're encountering.  Usually cd based units it's the cd drive that fails first.  But yeah if the power supply is cutting in and out then that would explain the resetting.

[Vorde]

ok, well i figured out what was freezing. i was playing music off of the JAP Sonic CD game disc, and the BIOS froze, but the music kept on playing, and it skipped to the tracks and such properly, so I'm guessing it might be those extra chips that SEGA put into the console. I'm going to check the connection with a multimeter.
If that doesn't work, I'm back to step 1 

[l_oliveira]

I'd say check the connectors, they could be rusty.  Is the ROM on the SEGA-CD board socketed ? Some early units were equipped with sockets for it's ROM and if it is bad it could cause freezing.

[Vorde]

lol, i'm sure it's one of the later units since it had those weird chips added to it from SEGA later on. They're software fixes for the BIOS or whatever.
I'll check the connectors, but if the connectors were rusty then how would it still be able to function for a few hours without freezing? 
This system is all too confusing...

[l_oliveira]

I own a very early asian MEGA-CD unit. It has the bios on an EPROM chip (labeled as EPR-XXXX not MPR as mask roms) extra chips in a daughter board on the clock oscilator and an chip with a wire that connect to that daughter board on the connector board wich connects the main MEGA-CD board to the Mega Drive.

I believe that in later units the daughter board and the chip on the communication bus were moved to the large 208 pin VLSI chip on the center of the mega cd board.  I saw US SEGA CD units that had no such "glue logic" on the board but upon comparing the board I noticed the SEGA CD had a different 208 pin VLSI chip. Hence this theory of moving the "glue" into the big chip at later revisions. 

Also I know that MEGA-CD 2 units (and SEGA-CD 2 units too) had a little board with two 74LSxx chips in it. Is that your case ?

[Vorde]

no, it has two chips, (they're labeled above), and they're both wired to the board, plus mine is american (SegaCD, not MegaCD), but w/e
I'm thinking of checking the wiring out soon too, but not having a multimeter fucking sucks

[l_oliveira]

Regarding region, the only thing that changes on them is the ROM and the outer shell with the printed name...