Odd Saturn Problems (advanced repair possibly)

Hey folks,
I've been repairing a batch of broken Saturns recently and have had some really great results. However, there are some units left that really have me scratching my head. Specifically a US model 1 that I have. This unit is I think a launch unit since it looks like the most primitive Saturn I've seen. The power supply is in the lid itself as is the CD tray detect switch.

The system boots fine but it never shows the graphics effect of the "shard of glass" that move to compose the Saturn logo. This is always shown when the laser reads the TOC or whatever, at the edge of the disc. Instead it just shows the static Saturn logo with no animation. This is usually what will happen if the laser is bad or the lid detect switch is open.

Well, the lid detect switch works fine and the entire laser assembly was tested on another unit and is working perfectly. It lights up, moves with the red laser, and spins the disc. It just doesn't move out to the edge.
Any ideas what would cause this?

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The other two I have don't output video or sound which is a bummer (one of them is a Hitachi). It has a good power supply and the 3.3v/5v/9v rails are all present. I could replace all the caps but I'm not sure that's the issue (maybe RAM problems?) The screen isn't even black - there's no RGB voltagepresent at all, and for some reason the CXA1645 was outputting composite at 2.5v which blew the output cap from 75ohm termination. Though the chip itself is getting proper rail voltages....so strange.

Anyway any help would be much appreciated! I've been putting in way more time than these repairs are worth simply because I don't want to see saturns junked. I love sega too much

 

I've seen you around the internet for a while SSS, and I would say that you're in that 'select group' of people that know more about electronics (but specifically Game Systems) than anyone else anywhere. If you can't figure it out... it'd say it's safe to say that no one can :/

With that being said, I was going to suggest checking the lid sensor (which you did). I was going to say try the drive assembly in another system (which you did), etc.

Based on your readings with the CXA1645 - I'd say that the system it toast. Likely more than one IC is the issue here. The fact it still boots is beyond amazing. I guess I would say... try swapping a different drive assembly into the system (even though you confirmed the one you have works) and see if that produces different results.

I'd also check to see if any of the IC's have been shorted to ground.
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Other than that, I hope you fix it :/ But on a side note - since you're as big a fan of Sega as I am. I'm sure you'll appreciate this - Model 2 Saturn Access LED (if you don't already know about it)

 

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Thanks SwampFox, that's really nice of you to say. I do believe you are giving me too much credit though I've learned a lot over the years but there are still many wizards around with powers far beyond mine. Like TMEE, Olivera, Xavier, Helder, etc etc. and this is the wizard watering hole, as far as I can tell right now ^_^

Thanks for the reply! That is precisely what is so odd...the entire drive and laser assembly was swapped with another system and the issue continued. The lid switch detected and the text never says "CD tray open." It just says it is trying to read the media, when in fact, the laser has stopped. The laser assembly from this unit worked great in the other system.... There must be some I/O issue with the ribbon cable plug or some "detect" trace...though not the switch itself, but perhaps the logic signal that activates it? So strange...

and Thank You for your feedback on the black screen issue. A recap makes sense to me and I think too many people are left in the dark (no pun intended) on this common problem. When you say "around the PLL" - which IC is that? Most of the caps are around the SH2s and the power rails and the video out. A picture would help a lot

-Segasonicfan

 

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Thanks. I see what you mean, the PLL for the mail xtal oscillator near the lower middle of the board. There's that big 100uf which would explain black screen for sure if it knocked out the clock signal.
The black screen Saturn (VA2) actually had the chip "TR5" blown- right next to the power bypass caps. From what I can tell this is the 5v>3.3v LDO regulator for the SDRAM. I wonder if the RAM chips are dead..

Thanks for the tip. I just tried another ribbon cable and no luck. I mean, it just can't be the motor assembly PCB or anything like that, I have 2 of them and they both work on my other Saturn but have the same problem on this one (attached pic).
There must be something wrong with the mainboard. If I knew more about the signals through the ribbon that would help. I tried an Action Repkay 4-in-1 in case it was some kind of region checking issue. No dice. Maybe someone had a modchip in here at one point that screwed things up?

-Segasonicfan

 

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Thanks so much, I had no idea there was a different board set with the VA0! I unscrewed everything and reseated the SH1 sub board and now it works perfect!!

Now onto the BSOD repairs. replaced caps and added 3.3v for missing SDRAM power supply rail. No dice yet so I'm gonna logic probe the clock signal, perhaps using a working one as reference if I'm adventurous. Ah, the efforts I will go to to save a Sega system

-Segasonicfan