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Modded PSX (SCPH-7002) Will not boot Retail games.

AiNA_TE

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Hello, I was cleaning up and testing some old Playstation consoles. This one I tested would boot backups but would not boot retail games.


I decided to open it and have a look at the chip. When I saw it, the soldering looked bad and the board was very dirty.

01-old.jpg

I began cleaning the board with some Isopropanol Alcohol and an a toothbrush. As I was cleaning a couple of wires popped off the board so I imagine they were very old and cold joints. I fully de-soldered the chip and cleaned the board completely.

02-clean.jpg

While the board was in this state I reassembled and tested a retail game again and it booted straight away.


Then I re-soldered in the chip, with much shorter wire runs and overall tidier than before.

03-rewire.jpg

And again on re-assembly it will boot backup's but not retail games. This time I tested with a retail version of Final Fantasy IV NTSC, and it did not boot. I then put the disk in my PC and used Imgburn to make a bin/cue, Burning this the game boots fine as a backup.


Does anyone have any idea,
What this chip is?
Why it's not booting retail games?
Is it missing some connections?
and is there anything I can do with it to get it working properly other than buying some blank pic's and burning a mm3?

Thanks in adavance
 

Trimesh

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The chip is the old standard 4-wire non-stealth modchip, sometimes referred to as "Old Crow" after the guy who first released the design as open source.
It's booting copies but not originals because pin 5 is wired in the wrong place - the purpose of this signal is to shut off the wobble data read from the disc so what's happening is that when you boot an original disc the data stream decoded from the wobble is colliding with the one generated by the chip and the result is a corrupted mess that the mechacon MCU can't recognize.
Try moving the wire from pin 5 on the PIC to pin 10 of IC706 - although the pad it normally connects to seems to have been ripped off the board and you will have to solder directly to the pin.
It's also possible that the driver on pin 5 of the PIC is damaged since it seems to be connected to a power rail.
 

AiNA_TE

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The chip is the old standard 4-wire non-stealth modchip, sometimes referred to as "Old Crow" after the guy who first released the design as open source.
It's booting copies but not originals because pin 5 is wired in the wrong place - the purpose of this signal is to shut off the wobble data read from the disc so what's happening is that when you boot an original disc the data stream decoded from the wobble is colliding with the one generated by the chip and the result is a corrupted mess that the mechacon MCU can't recognize.
Try moving the wire from pin 5 on the PIC to pin 10 of IC706 - although the pad it normally connects to seems to have been ripped off the board and you will have to solder directly to the pin.
It's also possible that the driver on pin 5 of the PIC is damaged since it seems to be connected to a power rail.

Thank you very much for the response, I took a picture under the scope.

05-pad-lift.JPG

The original install did indeed lift the pad leg 5 was supposed to connect to. I removed the wire from the cap and soldered it to leg10 of the IC706. then ran a test.


As you can see it's now working great, finally I tidied up the soldering again.

06-done.JPG

Thank you very much again Trimesh for the detailed response and the fix :)

EDIT: Any idea why the original install decided to connect leg 5 of the 12C508 to that capacitor? what was he trying to do?
 

Trimesh

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Thank you very much for the response, I took a picture under the scope.

<snip>

EDIT: Any idea why the original install decided to connect leg 5 of the 12C508 to that capacitor? what was he trying to do?

Glad to help - it's always nice to see things fixed :)

My guess is that what happened was the original installer managed to rip off that pad and just soldered the wire somewhere close and then tested it with a CD-R - when it booted they assumed it was OK and didn't realize what the function of pin 5 was (which is not surprising - although there were plenty of install diagrams available they were all "wire this pin to this pad" without any description of what the connections actually did).

Incidentally, there are some games that will refuse to boot with that chip and give you a "your console has been modified" screen - this only applies to a few early titles though - in the later library release code was added that detected if the game was running on a PAL console and disabled the modchip check.
 

AiNA_TE

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Thanks again for the info Trimesh. I began working on another PSX this one again is PAL SCPH-5552 with a PU-18 board. It booted backups and original games correctly but when I looked at the modchip it appeared to be installed incorrectly.

IMG_0119.JPG

This one had leg 7 of the 12C508A going to the mainboard instead of Leg 8, but it seems the chip was working correctly. I desoldered it anyway and reinstalled it with shorter wire runs and used leg 8 of the 12C508A instead of Leg 7.

IMG_0129.JPG

It's working fine also with the shorter wire runs, Just curious if you know what the Leg 8 connection is? (ground?) and why it was working when Leg 7 was soldered instead.
 

Trimesh

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Yes, pin 8 on the PIC is the ground pin - I'm honestly surprised it worked with the ground in the wrong place...

I guess one possibility is that there is a normally reverse-biased diode to ground as part of the pin structure - so the ground terminal will end up about one diode drop (~0.6V) above ground - which should still provide enough voltage for the PIC to operate. Just shows how incredibly tolerant of bad operating conditions PICs are.
 
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