Is there a way to replace the PLL chip in the Sega Saturn?

[ivirtualzero]

I think i may have killed the PLL (Hitachi HD49422) chips in 3 of my VA0 Sega Saturns. One was after doing the 50/60hz mod and lifting/soldering pin 1 to 5v and the second one was recapping it, but i used my rework station to desolder some of the caps, which may have heated up the PLL chip and killing it as a result. The other one was using a rework station to replace the dip bios since my desoldering station stopped working and that heat may have also transferred to the PLL chip, killing it as a result.

But i now have a Hakko Desoldering gun which should make replacing the dip bios’s in the VA0 much easier. All 3 of these give the typical black screen issue and i always check the traces of the bios before soldering in the socket. I only recently realised a dead PLL chip was the cause of black screen errors. I thought it was always the bios or a mod being installed wrong, wish i knew about this problem earlier. And since there is a DFO mod for the Sega Saturn, does that bypass the PLL chip or is there a replacement PLL chip? Or are these Saturn’s essentially bricked?

[zyrobs]

Try removing the battery, waiting a little while, and testing it again. I've had quite a few dead consoles resurrected just that way. Of course you'll lose your saves and the clock settings, but you might get the console back.

I don't know of any way to replace the PLL, it does a lot more than just generate 1 clock. It's also incredibly fragile and usually the first thing to die in the console after the laser. When I mod the console, I usually try to avoid going anywhere near the thing and always cut traces or ground lines much further up the board, away from that chip. I couldn't even replace the PLL with one from another console, because it just dies during desoldering.

The DFO would not help help since the HD49422 generates 4 different clocks from 2 inputs and has 2 custom divider selector pins.
The schematics are available in the leaked service manual, so I guess someone could come up with a replacement.

For what it is worth, here are the PLL clocks I measured on a Japanese VA0 Saturn:
PLL pin 5 SCPCLK TP22 11.28 MHz (output, computed from EXTCLK)
PLL pin 6 EXTCLK TP92 8.464 MHz (input, computed from 33.8688 MHz CD drive clock / 4, sent through the CD ribbon cable)
PLL pin 17 SNDCLK TP21 22.57 MHz (output, computed from EXTCLK)
PLL pin 18 DOTCLK TP85 26.86 MHz (output, computed from main clock input)
PLL pin 28 FSC TP23 3.578 MHz (output, main clock input / 4, NTSC colorburst frequency)
PLL pin 9 OSOUT2 - none
PLL pin 26 OSOUT1 - 14.318 MHz (output, this is just the other leg of the master clock input)

These were in the BIOS, so the console was in 320px mode. In 352px mode, the Dot Clock would be 28.6 MHz instead (NTSC clock * 8). This is decided by a 1708/1820 divider controlled by the PLL pin 2.
There's also a 910/1135 divider hooked up to PLL pin 1, so the PLL can output approximately the same dot clock on a PAL console which uses a 17.734 MHz master clock.
So in total you have 2 inputs, 4 outputs, and 2 external divider pins.
VA10+ and later boards only had 1 master clock input and 5 outputs instead, the 33.8688 MHz CD drive clock was generated by the PLL and sent to the CD drive instead of the other way around.

Later NTSC boards and the final PAL board used a different programmable PLL which is much more reliable, so replacing the Hitachi HD49422 is possible, but you would still need to find a way to program a new PLL to the same spec.
The good news is that the outputs are all hooked up to IC23 and IC24 which is much easier than if you'd need to cut traces or so to potentially install a new PLL.

[buckoa51]

Later NTSC boards and the final PAL board used a different programmable PLL which is much more reliable, so replacing the Hitachi HD49422 is possible, but you would still need to find a way to program a new PLL to the same spec.

Zyrobs do you happen to have a motherboard with this PLL, could you tell me the serial number to look for to find a system with this PLL in it? I want to investigate this further with Bas @ BetaGamma's help.

[zyrobs]

Jul 2, 2023 11:07:29 GMT buckoa51 said:

Later NTSC boards and the final PAL board used a different programmable PLL which is much more reliable, so replacing the Hitachi HD49422 is possible, but you would still need to find a way to program a new PLL to the same spec.

Zyrobs do you happen to have a motherboard with this PLL, could you tell me the serial number to look for to find a system with this PLL in it? I want to investigate this further with Bas @ BetaGamma's help.

Every NTSC model 2 except VA8 and VA9 uses those. For PAL only the VA13 boards use them and those are fairly rare, being the last PAL models ever produced.

Note that there are three types, for three different configurations. The number suffix is for whatever internal program is set from factory.
- CY2292SC-04 used in VA6 and VA7
- CY2292SC-32 used in VA10+
- CY2292SC-45 used in VA13 PAL
The Tectoy VA13 service manual has a wiring diagram for the CY2292SC-32. It calls the chips as the Sega 315-6021, but all chips are marked as CY2292SC-xx in the consoles.

I haven't tested these further so I don't know what the difference is between VA6/7 to VA10+.
VA13 PAL should only differ in an extra 910/1135 divider for the main frequency input.

Note that unlike the old Hitachi PLL, none of these have a PAL/NTSC selector pin, they are all hardcoded to NTSC, except the CY2292SC-45 which is hardcoded for PAL.

I'd be very interested in hearing about whatever you find. Where will post your investigations, a discord channel?

[buckoa51]

Well right now I don't know if we'll be able to find anything lol, but yeah I'll report back here. I'm also on Classic gaming and my life in gaming Discords (PM me if you want screen names etc). Leaving Twitter soon because f that hot mess.