Special PCB investigation (SCI-repair)

[kissedin]

I'm stuck with my SCI. And would appreciate some help.

There is no sound, graphical errors and lacking sprites ... But first things first...

By replacing one TMM2063 RAM and a PAL (c09-19) the game boots. I see the taito logo and a scrolling machine typed letter. Then when it's supposed to show a demo of some actual driving it resets.

I can access test menu and there it says "RAM OK". My first question: is this reliable information?

RAM at ic19 and 20 (tmm2063) for example is showing weak adress lines and some i/o:s are stuck low. these rams are getting their adresslines from the tc0170abt (ic16) (part of Motion Object Generator chipset) ... Please note the long time/div on picture of a5 on rams.

(Also adresslines a12 to a23 seem weak on main cpu(note the high intensity on scope). But only a13 goes to the custom.)

 

[kissedin]

So. I guess I can to answer my own question.

NO. That RAM check in test menu is not reliable at all.

Even though I've piggybacked all RAMs the game wouldn't start. But piggybacking doesn't work if there are pins stuck high. And there is always the risk of bad contact.

Therefore I changed all RAMs in the main cpu area. And ...

Still a long way to go. No sound and a lot of graphic corruption. But now the actual game runs! Oh, and the force feedback seem to work. Happy Days.

 

[kissedin]

This was easy! I just changed all the tmm2063, put in a new ROM (C09-01) and now the game runs almost perfect. All weird behaviour that I feared was one of the many customs were just cheap ram.

Sound is working. But some samples are corrupted. These are stored in 834100 mask roms and there is no direct eprom substitue.

But googling around it shows that a man called "Guru" just made a fix for this. https://gurudumps.otenko.com/ (look for a post made 1 st november 2023.) Thank you arcade gods.

Guru has made an adapter for 27c400 to be read as 834100 mask roms and is kind enough to share the gerber file (a donation will be on it's way). Oh, and on his page there are three (3) repair logs of SCI. So if you reading this because you are looking to fix your own board - check out his page.

I'll update when the pcbs arrive. Meanwhile it is time to lubricate the force feedback, recap the psu and other cozy arcade-duties.

 

[tiff_lee]

Good work your perseverance paid off, those Toshiba tmm2063 are notorious for failing.
Also good to see the Guru has another website to host all his work i was wondering if he was getting rehosted after iinet (Australian web provider) shut down the customer hosting service it was on before.

 

[kissedin]

Ahhh... when I stumbled upon his page I found it strange that I hadn't seen it before. So much good information!

 

[kissedin]

The Guru-pcbs have arrived. I soldered a socket on top and square pin headers below. (I've ordered machined headers).
Burned the rom on a 27c400.

Power it up and is greeted with a hissing and corrupt sound. Not good. Remove the adapter but problem persists.

Getting nervous but fix was easy. The 12V line only supplied 2 volts due to bad contact in the hanty us250 psu. Reflowed and cleaned connectors.

Power on. Sound is back and I notice a catchy bassline in the "press start" track that wasn't there before. Have played the game for a while now wo issues so I hereby declare the pcb completely restored.

Case closed.