Strange Sega Saturn problem

[Taffer]

Hey.

Well this problem has been persistent for quite some time now and I would like to find a solution. For the record my system is one of the early model 2 types with the oval buttons, 21-pin ribbon cable and 64-pin IC and it hasn't been modded at all. The problem seems to occur only when the system has been powered on for some time and then switched off and then immediately back on again. So for example I could be playing a game for say 15 minutes, turn the Saturn off and then on, at which point it will fail to boot any disc, taking me to the control panel with the message "Drive Empty". At the same time there are vertical scrolling bands present on the screen and a strange whining noise coming from both the unit and the speakers on the TV set. My first thoughts were that this was some kind of overheating issue, but so far it has never occured during a game, only when powering off and on again.

Anyway I decided to open the console and have a look inside to see if I could isolate the source of the internal noise. At first I thought that this noise could be coming from the motor that moves the laser along the rail because as I moved the gears I could feel the motor resisting and forcing the laser to the inner part of the rail (i.e. as if it's jamming it towards the center). It's hard to judge, but I also thought that the noise could be coming from the power supply section, as this could potentially cause some interference/modulation with the RF output and hence result in the same sound I was hearing from the TV set. Being the inquisitive type I measured the d.c power rail voltages during play for about 20 minutes: 3.31V, 5.07V, 8.95V - these values seem consistent with what they're supposed to be (3.3, 5.0 and 9.0V). I then switched the unit off and then back on and measured the voltages whilst it was making the noises and failing to boot and the 9.0V rail varies from 8.9V to about 9.4V, the other voltages remain stable.

My only guess is that one or more of the power supply components have developed an increased sensitivity to heat, resulting in some voltage fluctuations on startup that prevent it from stabilising and causing other components like the laser motor to malfunction.

Has anyone else had a problem similar to this? Is there any way to fix this problem? (Replacement parts, self repair). What would perhaps be useful is a schematic of the Sega Saturn power supply =P

I'd like to hear some thoughts/opinions on this.

Thanks

 

[Kuta]

Chack all the capacitors to see if any are bulging out the top.

 

[Taffer]

Thanks for the reply. I have just checked all of the capacitors and none of them appear to be bulging from the top. I also tried something else. I disconnected the CD drive assembly from the power supply via the connector coming from the mainboard after playing for about 15 minutes (enough time for it to fail on the next immediate hard boot) and switched the unit back on. This eliminated the CD drive as a possible source of the noise and I'm now pretty convinced the whining/humming noise is coming from the power supply section. Is there anything else that could be causing this noise? If a faulty power supply is the problem I'm doubting it will be easy to repair so perhaps my only alternative is a replacement power supply. As I mentioned before I think this is an overheating issue. If I play with the cover off from the start I can usually play for about 10 minutes and then immediately hard boot again without problems, any longer and it would start to malfunction on the next hard boot. However, with the cover on this initial playing time is reduced to about 5 minutes. During play there are no problems with the console at all and I can change discs and use the reset button, it's just hard booting that it doesn't like once warmed up.

 

[Taffer]

UPDATE:

Ok, I have just acquired another Sega Saturn (Model 1) which I knew was faulty and it has the same problem as I have described above. The only difference is that there is no noise coming from the unit, but the banding/wavy lines are still present on the screen and it refuses to boot after being switched on already for some time. It simply crashes to the control menu unable to read the disc. It seems that this problem is not to do with the power supply after all but some fault on the mainboard. This appears to be a 'common' fault with the early models, I just want to know what's causing this so that I might be able to fix it. Please, does anyone have any idea what's going on here?

​

 

[cgfm2]

If you have an oscilloscope, try examining the various voltages and see what kind of ripple you get. It sounds like the +9V rail may have quite a bit of it from your first post unless that's just when the CD drive's spindle motor is active.

You may want to replace all the capacitors on the power supply board, even though they look fine - not all capacitors will necessarily leak when they stop working properly (or when their performance degrades). Usually in a power supply having excessive ripple indicates a problem with the capacitors connected to the voltage regulators. Just be sure to get identical replacements.

I don't know which voltage regulator the Saturn power supply uses, but these can go bad. The 7805 is a 3-pin chip with a metal tab connected to a heatsink which gives +5V output, I'm sure there is a similar part for the +3.3V rail and perhaps the +9V rail too. These are cheap and also easy to replace. However they usually fail completely rather than perform worse as time goes on.

 

[Taffer]

Thanks for the advice. Unfortunately I don't have access to an oscilloscope; all I have is a multimeter. Now I think about it, I think you're right in that the voltage fluctuations on the 9V rail I had previously observed are only caused by the CD drive spindle motor activity. The erratic movement of the motors on the CD board when the saturn fails to boot and the audible whining noise (now also present on the other power supply I recently acquired and after putting my ear close to it seems to be coming from the secondary side of the circuit board) leads me to believe that there is some high frequency signal getting onto the D.C output part of the circuit i.e the capacitors aren't doing their job properly. This could perhaps cause video problems (wavy lines) and the motors to malfunction. Do you think this sounds like a plausible explanation? It's a real pity I don't have an oscilloscope to check for an A.C. component at the output. I will try to source some replacements for the large filter capacitors and re-solder the board with the new components and see what happens.

One other thing I noticed was a potentiometer next to the d.c output part of the circuit.

This allows for fine tuning of all three voltage outputs. I adjusted it slightly to see what would happen. To my surprise when I turned it anti-clockwise to decrease the output by a few hundred millivolts the video output switched to what I can only describe was a sort of widescreen mode (what the hell?!) with black borders top and bottom. Increasing it back to where it was before restored the video output. Tweaking this pot didn't seem to affect the current problem of it not booting properly though.

 

[cgfm2]

The erratic movement of the motors on the CD board when the saturn fails to boot and the audible whining noise (now also present on the other power supply I recently acquired and after putting my ear close to it seems to be coming from the secondary side of the circuit board)

I had a Sega CD power supply that died (catastrophically, smoke everywhere) which had a audible hum or whine to it too. I guess that's a sign something isn't right.

leads me to believe that there is some high frequency signal getting onto the D.C output part of the circuit i.e the capacitors aren't doing their job properly. This could perhaps cause video problems (wavy lines) and the motors to malfunction. Do you think this sounds like a plausible explanation?

It seems like a perfectly reasonable explanation. If you do get around to replacing the caps it would be great to hear if that fixed the problem or not.

 

[Taffer]

Well I replaced all of the electrolytic capacitors on the power supply with new ones. I wasn't able to find exact component values (some of the capacitors have a slightly higher working voltage, but stated capacitance doesn't differ by more than 14uF at most). Anyway, I reinstalled the power supply and turned on the saturn (it didn't explode, yay!). Unfortunately though replacing these larger caps has not fixed the problem and after 15 minutes of play I hard booted again and it crashed to the control panel with wavy lines, whining noises and all. I didn't replace the capacitors located near the transformer (they are disc shaped, probably resin dipped) or any other components, but I remain convinced that the problem still lies with the power supply. It's unlikely it is one of the ICs as they usually either work or they don't... perhaps it's the transformer? At the moment I don't have the time, funds or equipment to carry out a complete fault diagnosis and repair, so I guess it'll have to wait. Either that or I find a store that will be able to repair the unit for me, but goodness knows what they'll charge. Any other suggestions?

 

[vnvx]

You know... it'd probably be cheaper and easier to buy a 'broken' or even working Saturn from eBay and swap the power supplies. Anywhere that'll still repair Saturns will charge you through the roof.

As far as the (possibly) broken caps though, google the part numbers on each one and you'll find most of the exact same parts are still being produced and sold online. It'd be difficult to diagnose exactly which ones are causing the issue though without replacing them all (or at least I'm not that experienced yet .) Good luck!

 

[Taffer]

Sorry to bump an old topic. I was wondering if anyone else since has experienced a similar issue and succeeded in fixing it? The other thing I did try was swapping the power supply out after 30 minutes of use for the cold one from the other unit with the same fault. In this case the Saturn booted up without any problems, so I'm now more convinced it's an issue with heat sensitivity with some component(s) on the PSU. Anyway, if anyone knows where I can source a working replacement 240V input power supply or is able to sell, please do let me know.