Sync Signals Off of the PlayStation1 Motherboard

[RARusk]

After finding the sync and RGB video signals off of the PlayStation2 motherboard, covered in another topic, I decided to sit down and do the same to my old PlayStation1 unit. As most of you know Sony did not put in a dedicated sync line into the A/V plug for the PS1 and PS2 for RGB and thus requires you to get the sync from the video, using a sync chip like the LM1881, so you can properly use the RGB. By finding the sync signals from the motherboard itself you can avoid the need to use a sync chip for the PS1/PS2 units.

The PS1 unit I have is:

Model: SCPH-7501 (NTSC)
Serial #: U2792160
Manufacture Date: October 1998 (it also has a Parallel I/O port)

I do not know the motherboard revision at this time.

Compared to the PlayStation2, dealing with the PlayStation1 was child's play. After quickly opening the unit all I had to do was desolder the small shielding unit to gain access to the chips. A big plus was that the PS1 had no problems being run with just the bare board with nothing else attached which made my task of finding the signals much easier. Since I did not need to deal with Component Video and MacroVision (like I had to do with the PS2) all I needed to do was find the sync signals. I can get the rest off of the A/V port.

The first picture shows a section of the motherboard that contains one of the main chips and the video chip. Note the red rectangle.

[RARusk]

This is a close-up of the red rectangle area. Notice that the sync signals are pretty close together and that there are two good places to get the Composite Sync line. However, getting the signals from the bottom is actually the best place to get them because......

[RARusk]

.....of these big fat solder pads. I wish Sony did this for the PS2. Would've made my job a lot easier.

I should note that not all motherboard revisions may have these pads or that the signals would be in the same place. But given the hackability of the PlayStation1, the sync signals should not be too hard to find regardless.

[phreak97]

find the CXA1645, afaik every psx has one. composite sync is on pin 10.

[RARusk]

I don't remember seeing a 1645 on the motherboard. I think that the A2106R chip on the left side of the picture at the top may be the video chip on this motherboard. I'll take another look.

[phreak97]

on some models it is on the underside of the motherboard. one of mine was, the other was on top. just look for the first chip the av port traces go to.

[NFG]

I'm reasonably certain the CXA chip isn't used on all PS1 systems.  If memory serves they included the encoder functionality inside another chip when they consolidated the chipset.

[phreak97]

ok, well.. of the two consoles i have checked, both were different revisions, and both had the CXA chip. one was an older one which has the rca plugs on the back, and one was a newer one, but i dont know how new. i have two other consoles, plus two psones if you'd like me to check (i might later anyway)

[Ocelot85]

I've got a question. Do those gold pads that contain the H & V sync have to be scrathed back first before soldering wires to them, or is it fine just soldering to the gold coating?

[l_oliveira]

http://www.4shared.com/file/55499740/c1881fda/SCPH-7500ServiceManual.html   
Hope this help you finding the signal you need.

Also, remember it's 3.3v level.

[Piratero]

Wow. I can't believe I'm going to bump this!


I have a 5501 ver. and I used the mod specifically for this version.

And I just applied the mod on the underside of the main board. It's 1:1 to what is in the picture RARusk posted.


I get no signal. Could it be that it's too weak? Any way I can check?

[juanmiglesias]

Hey just a quick question on PSOne mini with csync on SCPH-101.
every post I found says it won't output csync, only H and V. sync.
but after going to the schematics pin 156 on the gpu actually is csync.
just tried it on my NEC xm29plus, also the LM1881 stripper will pass through the csync son no need to mod the cable.