Saturn power supply popped, tripped a circuit and smells burny

I finally got around to grabbing a replacement component for a faulty TOP202YAI component on my Saturn's PSU (thread here), and made the mistake of adding in a 2200uF 10v cap with the positive wired to the AC line (should have printed out a larger picture of this!!!!!). Without switching it on, when I plugged in the AC cable it sparked and made a popping noise and tripped the power circuit. It smells a little plasticy burny as well.

So, two questions that perhaps someone can help with:

1: Since the Saturn was not powered on (mechanical switch was in the off position), does this mean I've only damaged the PSU?
2: If so, how likely is it that removing the cap will be all I need to get it back up and running again, or is the PSU likely to be fried?

I don't have time tonight to get cracking on it (already late getting dinner started!), but wanted to field some thoughts in the interim!

 

It depends on exactly how the cap was miswired. Presumably the +ve end was wired to the end of R54 that goes to the line plug? If the -ve end was wired to the same place as it's shown on the drawing (I.E. the other end of R54) then I would expect the cap to be the only damaged component.

If it was wired to the pins on the optoisolator, then there is a very good chance that it has damaged at least the PSU and possibly the Saturn too - at 60Hz, that cap is going to have a very low impedance (about an ohm), so it all comes down to the other resistances in the circuit.

 

Yes, you're spot on - I was going from the marking on the PCB and connected the +ve point to R54. I'm definitely feeling a bit daft, so here's a picture to illustrate what not to do



I'll remove and replace the cap and see how my Saturn goes afterwards. I'll also check the fuse in case that took the brunt of the AC and replace if necessary.

Feeling a bit hopeful that the damage may not be as bad as I first thought though!!

 

I decided I wanted to check it out before going to bed - I think I murdered it



I clipped off the cap and tested the fuse (came up okay) and tried power it on, and nothing (though it didn't trip the circuit, so that was nice.

Is it worth trying to salvage? Otherwise I might try to find a replacement power supply, though I recall I've had trouble with that in the past too, so it might mean I'm on the hunt for a new console

 

x

 

Yeah, I'm feeling pretty bloody stupid at the moment.

How likely is it that it made it to the console? Tossing up whether I should bother sourcing a power supply/board or just bite the bullet and grab another PAL Saturn...

Edit: Ouch, Looks like I'll be paying $70+ for a new Saturn, might post something in the wanted forum!!

 

That has to have been a low-impedance connection between line and ground - if you look at the copper splashes on the insulator sheet you can see that it blew out in 4 places at the same time, which requires huge amounts of current.

Since the Saturn only has a 2-wire power cable and the power switch was off, the only place I can think of for the ground connection to have come from was through the earth on the A/V cable. The tracks that are obviously blown out shuoldn't matter - they are just used for a bleed resistor between the DC ground and the neutral side of the line that I'm pretty sure is only installed on the US units with a polarized power cord. But at those sore of current levels it's possible that it managed to induce significant voltages in the ground lines on the rest of the board.

 

Ouch, that certainly sounds nasty. I might try the PSU if I can get one cheaply, but I think realistically I'm going to find a new Saturn. Such a shame they're so expensive locally!

 

Can you clean up the board and take a photo of the trace damage?

 

Sure can - I had a look today and I think the transformer was the final point in the damage run, as all the caps on the other side of the PCB are pristine with no signs on the PCB of damage.

 

Update - cleaned up, here's the result (click for high-res):



I've run my meter and can confirm the traces are dead where I've indicated and I snipped out the cap last night and put it in the bin.

If I'm feeling adventurous I might wire in some wires to complete the copper traces and see what happens; any other advice though would be welcome!

 

Since R54 presumably isn't installed on that board, those damaged traces don't do anything. All they do is connect one end of R54 to one side of the AC line and the other side to the system ground. So if it's not working then something less obvious is blown up too.

Try plugging it in without the Saturn connected and see if you get any volts out of it. It might also be worth pulling the main board out and checking for damage on the traces running from the two ground pins at the end of the PSU (the two pins furthest from the power connector) - since that appears to have been the place the current was flowing to.

 

Alright, I did both of those things - I can confirm that the PSU, disconnected from the Saturn but switched on (i.e. using the mechanical switch), is outputting absolutely no DC voltage across any of the output pins. So I'm confident it's probably dead - I was only using my small digital multimeter that isn't rated for 240v AC, and my other one was out of battery (needs a 9v one, have one spare), so I haven't checked if the AC is flowing through and where it terminates before the transformer.

Second, I checked the Saturn - no visible damage on the PCB, it looks clean.

So, I'm tentatively hopeful that the Saturn may have survived, but the PSU is knackered.