Investigating the Black Screen Faults in the Sega Saturn
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Hi I’ve been modding and repairing a bunch of Sega Saturns, many have been successfully restored and modded and sold to happy customers. But with others, I have been unable to repair them, and it’s because of a specific fault that plagues Sega Saturns. And it’s the infamous Black Screen fault and I’ve repaired some black screen faults by reflowing the IC Chips where the solder looked cold as well as cleaning up the corrosion, and others by replacing the Capacitors. The blown SMD Inductors that are on the motherboard L1 through L10, L7 and L8 are the high powered inductors. And the faulty PSU’s that some of these consoles have. But there are still those few that continue to give me a black screen despite me reflowing it even to the point of reflowing every single chip.
And testing it with a known working PSU, checking the SMD Fuses, Recapping it and none of it helps the console escape the Black Screen fault. Now a bad PLL IC is known to cause such an issue sometimes displaying a messed up HZ signal, Black Screen or nothing. Sometimes a light reflow of that chip can get it working again. But there is no replacement for that chip currently available. Other times that isn’t always known to cause such a fault. In my case with one of the consoles. A reflow of that chip didn’t fix it and I’m not sure if i made that console worse off due to the PLL chip being heat sensitive. So I decided to tear down the other 2 Black Screen consoles, down to the motherboard still in it’s shell with the controller board on these specific revisions connected.
I installed a Pico PSU board on to it and powered the console on. I decided to touch the top of each IC Chip making sure not to touch anything else such as the leg to prevent a short circuit and I discovered that on the two consoles. I tested this on, one IC Chip gets hot to the touch on my 2 Model 2’s with a Black Screen and it’s IC 6 (315 5963) on both my VA SD and VA SG Revisions which is an early Model 2 essentially a Model 1 in a Model 2 shell. So it still has the same PLL chip as a Model 1. Now IC6 sits right underneath the Bios and the SRams chips on these revisions. And I’m not sure what’s causing this issue. Perhaps the excess heat from replacing the SMD Bios which usually has glue underneath caused this chip to fail.
On the VA SG’s and beyond the PLL chip sits further away from the bios, so I’m not sure how the heat sensitive PLL chip can fail. More investigation of this fault is needed, will likely need to get somebody else that works with Oscilloscopes to have look into my 7 other Sega Saturns with Black Screen faults. But at least I know why these two aren’t working. I think i will be harvesting that chip from another Saturn that has a black screen with a working IC6 chip. The 315 5963 along with the PLL IC is another chip I would like see get cloned this could save many Sega Saturn with stubborn black screen faults. Does anybody have any info on this chip? I would like to know what this IC6 (315 5963) chip is responsible for.
Here is my previous post on the PLL chip fault: https://videogameperfection.com/forums/topic/the-sega-saturn-and-the-dreaded-pll-chip/
It’s definitely not always, as I have repaired a bunch of Black Screen faults which indicates general hardware failure. Usually excess heat getting to the PLL damages it, but that’s not always the case. Sometimes a reflow, 1 person fixed there’s by reflowing the PLL chip though recommend to be quick with the reflow using flux and lead free solder, and or a recap, or replacing the Clock battery, PSU, bad inductors labelled L1 and beyond, or replacing the VHC04 IC fixes it or there could be a bad trace somewhere. It’s always worth diagnosing it to determine what’s really going on. I wish I had and knew how to use an Oscilloscope, since this will need a Schematic level investigation. But I do wish somebody with the skills can manage to reverse engineer the heat sensitive PLL IC’s code since there are likely substitute IC’s out there to replace it, perhaps integrate the DFO mod into it with the ability to switch from 50 to 60hz.
so I have been working on a Model 1 Saturn with the black screen issue. You can see some data here. I did not want to go off topic too much so I’ll just put the rest here.
Long story short:
1-I’ve built a PLL replacement (I’ve named it “Goldilocks”) with a CDCE937 that works. Not perfect, but “just right” (hence the name).
2-Output clock(s) weren’t satisfactory so I worked them a little both on Goldilocks and by handling on-board impedance mismatching (with 18 to 47 ohms resistors and by placing carefully 20pF caps as close as the target chips as possible) and oh boy, there’s plenty of them on older electronics. It’s nuts how much hardware changes at molecular level with time.
3-It had been a bit disheartening at times since the Saturn would STILL be unstable and freeze randomly, even though clock inputs were as close as ideal as I could make them. Then I started to go sideways and scope probed all over the place, because it’s just what I do when I’m out of ideas.
3.5-as a side quest I have found out that not all ground joints are the same.
4-I found nothing significant. Everything worked just fine… until it wouldn’t, and I had ABSOLUTELY NO IDEA why. I would just make wild assuptions like internal ringings, overshoots or undershoots (that reflect on many outputs).
5-In the meantime I started replacing caps here and there and see what would happen. I tried to use the highest quality I could find in house (Nichicon for PSU, Panasonic ECE series for main power caps on board, bought specifically for Saturns) and some Kemet to put in the place of a few 10uF to decouple some stuff. The Saturn would get worse. I began to give up.
6-I used some Taiyo Yuden 100uF MLCCs to feed the two SH-2s and two central caps near the damaged 315-5746. It would make no difference.
7-In a stroke of luck I found some Kemet 1411 tantalum polymeric 100uF 6.3V laying around and I used them in place of the MLCCs I just installed. I thanked the past me for that gift. I had a good feeling about that.
Final point: it’s been standing strong in the boot menu the first test for 1 hour, then it’s been going for at least 10 minutes again after a power cycle.
Model 1 Saturns are EXTREMELY fussy and tricky to work on. There’s a wealth of information to be known JUST to be able to work on them. I’ll operate on it slowly to see what happens next. One of the next moves are to completely remove the 315-5746.
thank you for your words of praise. But Goldilocks should still be considered in “pre-alpha state” since I believe it has somewhat destabilized the SMPC through DOTSEL, and hence should not be used (yet). It does output the correct frequencies though, but it needs a better interface with the Saturn. Maybe it just has to be driven by a transistor but I have no idea what kind of output the SMPC gives – but I’m fairly convinced it stays on a microcontroller GPIO port, which has a specific output impedance that must be followed (at least in a safe zone) to be considered stable. I just ripped Goldilocks out of the system as soon as I realized the PLL was working again.
As far as I could understand, “black screen” can mean a lot of different things. One should first investigate if it is really a “black screen” or a “no display” issue. “Black screen” means the encoder (CXA1645M) outputs a signal that the TV can understand, but there’s no image in it. “No display” however means the encoder does nothing, either because of no/out of spec power (broken/rotten traces, dead caps, faulty PSU) or because the encoder is cack (rare but it can happen). In modern TVs this means no audio either, so the Saturn might appear dead even if it has no ways to communicate its state to the outside world.
“Black screen” instead can imply a communication failure between any of the 8+ chips on the motherboard. Since there are A LOT of connections between chips, A LOT of things can go wrong, and the joint refreshing work on all chips can help tons to fix the issue, since it restores communication. It can also mean that the VDPs or the audio circuitry fail to handle signals for some reason – dead chips could be a cause (very unlikely but not impossible), but a chip cannot work properly if its clock is messed up – it might mishandle a very low rising edge (coming back from an undershoot) for a falling edge or vice versa (getting down from an overshoot). Hence, PLL or impedance matching might be crucial for proper signal transfer. This can happen on data or address bus(es) as well; a falling edge instead of a rising edge at the wrong time can push the wrong instruction in a chip, causing illegal or unknown instruction errors, freezing the machine without warning. The Saturn was not designed to communicate these errors to the user (at least not with standard software) so addressing and diagnosing these kind of issues can be very challenging.
This experience boosted my motivation to deepen my understanding of Saturns though. I would be delighted to explore more systems.
Although I’m not 100% sure of the “PLL gets damaged because of too much heat” thing. Based on what I’ve seen, the Saturn feels so delicate and sensitive that I believe the PLL is just a tiny part of its problems, if anything. I might be incredibly wrong though. Only working on more Saturns will allow me to gather more useful information.
I just need to state that the best way to diagnose this is to first check the clock signals with a scope before doing anything else, if the signals look clean, i.e, in simple terms; no messy waveforms, it’s not the PLL. Another simple diagnostic test if you lack a scope but have an OSSC is to just check if the refresh rate frequency is stable and sync is locked in. You have to replace the caps before declaring the PLL dead, as Sega underspecced the voltage rating on the caps and by this point they measure an ESR of 20+ohms when they should be below 1ohm.
I’ve noticed that the VA0 boards are also plauged with IML and corrosion on the pads to the point where I can just poke at the caps to pull them off.
This of course also affects other pads like on the RAM chips, meaning a good chunk of the ICs might be missing connections to the mainboard.
If you try to reflow a chip and notice the solder wont really stick, you have to take off the IC, dewick the solder and scrape the oxidation off then solder it back on.
Seems to be more of a manufacturing defect as older consoles don’t seem to have this issue.
extended rusting was found on the metal parts of the ODD. I suspect it was kept in a very damp place or water poured in at some point, was picked up and dried somewhat and left there. Many joints were completely detached from their copper pads although they still had factory solder on them. Copper was oxidized. I have no idea if factory solder job was good at all.
Whatever happened, humidity crawled under weak points in the solder joints and ate healthy copper away. Luckily a very thin layer of oxide formed and protected the metal underneath – no copper pad was destroyed, they just had to be scraped to expose the healty metal. I was proficient enough to only rip 1 NC pad from a SH-2 footprint, cut another on IC3 (IC3 has extremely long pads so it wasn’t a big deal) and partially rip one while reattaching the VDP2. I still have to reattach the OCU, SH-1, SMPC and IC6 (DRAM controller?).
The laser lens is very dirty (no amount of IPA polishing cleaned it, most likely dirt, grime or humidity gathered inside the pickup body) and I think it will never work again. I have to see IF I can even make the motherboard do anything at all, THEN focus on the ODD daughterboard, THEN see if I can do anything to salvage the ODD frame, THEN see if I can find a replacement laser pickup. Thankfully everything is healthy enough to see what model it was.
I have ordered a Pico PSU and a 12V-5A power supply since its original PSU might be too dangerous to use – I have inspected it and there are no evidence of failure, but I cannot be too sure, it could burst into flames or pump 9V or more on the 5V rail, I don’t want to take the risk after all the work I have already done.
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