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BRIK
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3DO FZ-1 No Power - suspected PSU

by BRIK Mon Nov 16, 2020 7:15 am

PHOTO'S HERE

Hi all, apologies for the lengthy post but there’s a bit to explain.

I recently received a broken FZ-1 that won’t turn on. From what I can tell, at least two others have been inside before me, which is never good. The power cable had been previously cut, with the copper simply twisted together and held with electrical tape.

Capacitors 1, 35 and 36 had been replaced but with substandard soldering. While the pads were connecting to where they needed to go, the solder was dull and bumpy. Additionally, D2 was missing completely with R2 extremely corroded.

So, I got to work properly repairing the power cable, soldering the copper together and covering the breaks with heat-shrink. I redid the caps even though there was continuity, replaced R2 and also D2 using a modern replacement suggested on this Russian forum (eighth post from the bottom).

As you can see in the photos, the positive pad for C36 is a bit destroyed. There’s still continuity, however. At this point, the console still wasn’t turning on, so I started reading the service manual and technical guide. Following the flowchart on page 5-2 of the technical guide, I determined that the power switch was shorting as it’s supposed to when on/off and that the fuse was good.

The next section of the flowchart asks if AC 10-18V is being outputted to both CN1 terminals – and it turns out that’s not the case. I measured only AC ~0.23V on both. Is this the smoking gun? I’ve never worked on a 3DO before. In fact, I’ve never checked AC on anything. I simply switched my multimeter to AC mode and checked the pins on CN1 while holding the negative probe to ground. Is that the correct procedure?

On further chat with the guy who gave me the console, he thinks 240v may have been put through the system before he got it since we’re in Australia (the console is American). What does everyone think? Could it be that the PSU is rooted having had 240 put through it? Is there another way to check it besides from CN1? And if it is, does anyone have experience replacing these? I read this thread that talked about replacing the 110v one with a modern 240v equivalent. I should add that I’m of course testing with a step-down transformer.

Alternatively, could the problem be something I’ve missed completely? Any input would be appreciated. Cheers.
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pierrot
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Re: 3DO FZ-1 No Power - suspected PSU

by pierrot Tue Nov 17, 2020 3:25 pm

BRIK wrote:The power cable had been previously cut, with the copper simply twisted together and held with electrical tape.

Capacitors 1, 35 and 36 had been replaced but with substandard soldering. While the pads were connecting to where they needed to go, the solder was dull and bumpy. Additionally, D2 was missing completely with R2 extremely corroded.

Oh my god. So, basically what this sounds like is that someone potentially "modded" this console to work with 240V by pulling out the thyristor in the overvoltage protection circuit. I don't really feel like going through a Russian board. Do you have a data sheet for the thyristor you replaced D2 with? I'd check to make sure the gate_on voltage is 0.5V. Did you have to replace the fuse at all?

0.23V AC would indicate a dead short, but it matters where you're probing, and it's not clear to me where CN1 is relative to the rectifier. Also you would almost certainly be blowing that fuse every time you tried to power it on, if CN1 is before the rectifier. If it's past the rectifier, then you won't see an AC voltage. It's DC at that point. If that's where you're measuring, then the meter is likely reporting DC ripple as AC.


BRIK wrote:On further chat with the guy who gave me the console, he thinks 240v may have been put through the system before he got it since we’re in Australia (the console is American). What does everyone think? Could it be that the PSU is rooted having had 240 put through it? Is there another way to check it besides from CN1? And if it is, does anyone have experience replacing these? I read this thread that talked about replacing the 110v one with a modern 240v equivalent. I should add that I’m of course testing with a step-down transformer.

Alternatively, could the problem be something I’ve missed completely? Any input would be appreciated. Cheers.

If anything, I'd think the 5V and/or 9V regulators could have been damaged, but that seems like the worst case. You could measure the input resistance of those two packages to see if input voltage pins are shorted or not.
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Re: 3DO FZ-1 No Power - suspected PSU

by marurun Tue Nov 17, 2020 4:27 pm

Holy crap, pierrot lives!
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BRIK
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Re: 3DO FZ-1 No Power - suspected PSU

by BRIK Tue Nov 17, 2020 6:24 pm

I used this one: https://au.element14.com/stmicroelectro ... st=2341673

I've also since probed the transformer unplugged from the main board and only measured 6v (probed the blue connector).
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