Sega saturn PSU Noise on 5v rail making the console freeze

Hi everyone, I have a problem on one of my saturn model 2 psus, when the console starts up and you close the lid switch with a disk in it will instantly freese the system.

I tracked it down to the psu after swapping it with several of my other systems and in each system it does the same.

Initually I suspected the caps and replaced all of the caps on the secondary side of the psu, this unfortunatly made no difference

I then as a test added a nice big cap to the 5v line and the problem suddenly disapeared... Or at least got a whole lot better.

The voltages all appear a bit high 5.24 volts stays at exactly that, and 12.16 - 12.45volts when the disk loads...

Problem is I dont have a scope to track down where the noise is coming from.

Has anyone had this problem before?

Edit: here is a picture of the powersupply in question, https://www.dropbox.com/s/p3firs1wd1k8e9b/20141121_152509.jpg?dl=0

Also checked the back of the psu no dry joints or damage, atarting to think it could be the large filter cap giving problems...

 

Edit: oh you said you replaced them.

Another suspect to check is the TOP IC (Power Transistor + PWM contro circuit integrated on the same part).

And the small 3 pin IC near the optical coupler (I don't remember it's name but it's part of the circuit which does control the feedback for the primary side and is likely do cause problems with the output voltage if it's faulty).

 

Is there a difinitive way to test those, and IIRC the TOP IC is a custom part?

 

Not a definitive way of testing custom ICs besides replacing them with known working parts or have a proper testing rig for them. :\

 

x

 

That's capacitor problem for sure.

But then when you replace one, you should replace ALL of them.

 

So just an update, I replaced all the caps now including the big primary side cap, still the same.

Tested all the resistors, and diodes all tested fine.

And my 3rd saturn is doing the same thing now, opened it up anly to discover its the same problem with the exact same psu, its not as bad but once every 10 boots it does it.

 

Could it be the problem discussed here:
http://www.assemblergames.com/forums/showthread.php?50186-Saturn-Heat-issue

Basically swapping out that TOP part since you've done just about everything else.

 

Make sure you test the DRIVE assembly on another Saturn of the same type to rule out optical pickup issues.

 

x

 

@Helder like Druid said, sadly my psu doesnt have that part

Tested that allready , and the same drive works 100% when I swap the psu.

 

http://www.righto.com/2014/05/reverse-engineering-tl431-most-common.html

That's a good read on the small IC I was talking about before. And it apply to all power supplies in general. The PS1 power supply for example, also use it.