Saturn won't turn on

Hey guys!

I had a problem with my Saturn - some of the graphics were messed up when I turned it on, for example the text was scrambled, but everything else was fine. When I pushed down on the motherboard everything would go back to normal, so I assumed that there was a loose connection inside. I decided to re-solder all the legs on the chips to see if it would help. I would solder a few of them and then hook up the Saturn to see if it helped. Unfortunately, I did a massively stupid thing one time and forgot to unplug it. Now when I try to turn it on, the PSU makes a high squeaking noise and nothing happens. I tried it with another tested PSU and it did the same thing. Is there anything that can be done or did I screw myself over?

Thank you deeply in advance for help
Tom

 

With "motherboard", do you mean the power supply pcb?

 

No, I mean the main pcb with all the stuff on it.

 

what was the last chip you soldered when the psu started making noise

 

Well, the sound you hear is your PSU screaming because it's getting a unbearable load, most likely due to a short on either the mainboard or the PSU. First thing, take out the PSU, connect something driven by DC voltage with at least .2A (easiest would be an old 12V case fan) to the 9V output of your PSU, switch it on an watch what happens. If the fan is starting to turn an no noises are coming from your PSU, take a Multimeter, set it to DC 20 and start measuring the outputs against the markings on the output connector. If it runs smoothly and all voltages are there, the PSU should be good.

Next thing to check is your mainboard, first thing, look over every joint you've touched on there, watch out for solder bridges across pins. If everything looks good, take a highres picture of your mainboard, top and bottom, as sharp as it gets. Post it here. It's impossible to give any further advice at this point, since the Saturn has gone through shitloads of revisions, so we'll need to see what board it is.

What exactly did you do at this point? Did you solder on there while it was switched on or just plugged into mains?

 

Thanks, I'll get to that right away. At that point it was just plugged in, not switched on.

 

That's good, don't think it's the PSU. My guess it's a short on the board. If it was just plugged into mains while soldering, there shouldn't be any current coming from the PSU at this point, especially since the low voltage lines are all isolated from the AC and the AC was cut with the switch.

 

I sadly haven't found any bridges between legs. I didn't touch anything on the bottom aside from the AV socket. On the top I touched a few chips and I did close-up pictures of them. I should mention that the region switch mod was there when I got the Saturn, but as I said earlier it worked fine before I dug in. I uploaded the pictures to imgur since I was having issues with posting them here directly. Here they are (I'll upload some more later if needed - I took these during the night so the lighting is iffy):

http://imgur.com/a/Rd90k

 

I'll take a deeper look at it when I get home, but I haven't seen anything obvious from the pics. Here's what you can do, connect the PSU again and let it run. Take your Multimeter and measure the rails, see if one of them is dragged down and take a note which one it is (3.3, 5 or 9V). While plugged in, touch anything what looks like an IC or transistor on the board, if there's a short, one of the little buggers will turn very, very hot in a matter of seconds, depending on the size of the IC. Try to stay away from the yellow wire, whatever muppet did the 60Hz mod, didn't even bother too secure the lifted pin on there with hot glue, if you've got a hot glue gun, I would secure that pin asap, if it goes, so goes the board.

Ideally, you could use some freeze spray for this step, but it's not something most people have laying around.

 

Nothing on the board got hot, but I did notice that all rails are lower than they should be - the 9V was 2,27V, the 5V and 3,3V were both 0,27V. I then took the PSU from my other working Saturn and the readouts were 1,17V for 9V, 0,29V for 5V and 0,32 for 3V. I also secured the pin.

 

There has to be, did you check the underside? It doesn't have to be an IC, theoretically every component across ground and positive can be shorted out. I saw some regulators on there, small SMD packages with on pin on top and 2-3 pins on the bottom, check those too. If there's absolutely nothing you can find, we'll need to check with the Multimeter manually, but this will take some time since we can't circle in on a specific area. I would start with going through the caps first, if there was a voltage spike for some reason (could be from residual voltage inside the PSU while it was connected) usually the first one's in line after the power connector are most likely to go, but this doesn't have to be the case. There are also filter caps on the IC's. Just start checking the big electrolytic caps first, just to be sure, then go through the SMD types next. Also check every transistor/regulator against ground. It's tedious work, but eventually, you'll find it.

The missing voltage on all rails is for the same reason your PSU is screaming, due to the short on the board, something on there sucks so much current through the main output to the board, it overloads all the other rails. This current is usually converted to heat on the faulty component, this is why something on there should be getting really hot.

 

I'm sorry but I'm not quite sure what to do when checking capacitors, could you explain?

 

Put your Multimeter in continuity mode and just start checking the positive and negative leads on every cap, if your meter shows continuity across the leads of one cap, that one would be shorted. If it shows OL or 1, the cap is ok.

 

All standard caps are fine, but a lot of the SMD ones are busted, I'll get to replacing them soon.

EDIT:

It turns out to be harder than I thought - how can I be sure about the capacitance of specific capacitors? I tried to look for service manuals but I only found one from June 1995 for the model 1 Saturn. I've read that all revisions were relatively similar, but I don't want to risk it. Any ideas?

EDIT 2:

My Saturn differs from the one in the manual, for example the capacitor marked c34 is in mine but the manual lists it as not used.