Sega Saturn PSU high

Hi guys,
I've just picked up a faulty Saturn (black screen of death) that I'm trying to repair. I just metered the PSU and it's pushing out 12v 5v and 5v to the mainboard, so I'm guessing this is the culprit.

Any ideas about which component to test/swap out on the PSU?

 

Ignore previous post... Have found the spec for the type c PSU and I see this is the correct voltages. Used to working on earlier units with 9/5/3.3 rails.

Really not sure what is up with this unit though. Left it alone for a bit switched on and came back to find it sitting at the language select screen with the red flashing highlight cycling very very slowly....

 

Those PAL units have a tendency for locking up until they have been "warmed up". I don't know the cause unfortunately, beyond that they are extremely susceptible to voltage ripples.

Recapping can help a lot with that, but it won't fix them instantly, you'll still need to let them run a little bit.

This is assuming that there's no other problem on the board either, like broken traces etc.

 

Board is clean as a whistle. No signs of any damage. I wonder if it's something as silly as a dry solder joint on one of the ICs like the memory or something....

Think I'll recap it for the hell of it and reflow some of those ICs while I'm at it.

Haven't made it back to the language menu again since that one time.

 

i have seen on Youtube a video where someone had the same symptom as you and changed some Caps on the motherboard and video was restored. You may want to find the video on the Tube and try it yourself.

 

If you have or can borrow a scope, have a look at the signals coming out of the clock PLL - I've seen a number of Saturns with unstable clock signals and thinking about it, they were mostly PAL units.

 

Did they happen to be mostly single board model 2s (VA7/9/13)?

Actually, I'm sure they were, since unstable clocks also explain why the screen is "shaking" (unstable video sync) and why there is interference from the CD drive in the video signal.

 

So, if I leave the console on long enough the date/time screen does appear eventually but it's totally unresponsive.

No movement at all from the drive unit.

I don't have a scope unfortunately. If the clock signals were unstable out the PLL what would be the treatment? Is it still likely to be a bad capacitor symptom or would the IC need replacing?

Still trying to decide if it's even worth pursuing this repair or if it's better to salvage the drive and psu and move on...

 

The drive should center the laser on every boot if the CD Block itself functions. If that happens, then the drive itself works, as well as the CD Block subsystem. Those parts are standalone and have their own bootup process, which involves centering the optical pickup, and it runs even if the rest of the system is broken. I don't think they proceed any further than that without input from the SH2s, so if that part crashes, then the system won't do anything else but centering the laser.

I'd replace the caps on the motherboard as a start. It helped for me in the past on units with such problems.

 

That sounds about right - it was a while ago and I can't remember if I made any notes (I can't find them in any case) - but it was common enough that it was something I checked early on in troubleshooting. It's very obvious on a scope - a good machine has a nice clean clock and a bad one has jitter and missing pulses.

In my experience, it was the PLL chip that was the problem. I guess bad caps could have a similar effect, but that wasn't the problem in the units I looked at - you could change the caps and the fault remained, but swapping the chip from another board fixed it.

Also note that if your CD unit is one of the later "no oscillator" versions (the ones with a white band around the edge of the board) then they rely on a clock signal coming from the main board and will be pretty much dead if the main clock is bad.

 

I couldn't work out from the title whether your Saturn had been smoking drugs, or this thread was an academic institution for teaching about Saturn PSUs

 

Perfect 5/7 would smoke that again.