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July 18, 2019, 08:12:16 AM
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Author Topic: Blown famicom need help!  (Read 152 times)
Posts: 2

« on: July 12, 2019, 03:09:18 PM »

Hello! As a little introduction, I am great with a soldering iron but not very educated in how the components all work together. With that said, here are the details of what I have performed so far in the quest of powing on this famicom.  The power supply outputs about 15v when I tested it, so that's working. I tested with a working Genesis 1 adapter as well and that made no difference. When I first opened the famicom, I noticed a 1.5a fuse on the bottom of the board. I tested continuity, dead as can be. So I replaced it with 1.5a pico fuse. Tested console to find no picture on channel 95 or 96. So I opened it back up, and here is where I'm just as confused as can be. I then replaced the 7805 to see if that was the issue. But after replacing the 7805, it still didn't power on and that's when I noticed the fuse doesn't have continuity in circuit anymore. I assume the new fuse blew before I replaced the 7805 (which probably explains why I thought the 7805 was not functioning properly). Now here is where i'm really confused and need a schooling on how this works. I followed the traces from the power adapter's terminal all the way to the fuse and to the 7805, both the positive and negative paths. The fuse appears to be at the end of the entire circuit of the board. Is this correct or am I viewing this all wrong? If it is correct, how does a fuse at the end of a circuit protect the loads in the circuit? When I turn the power switch on and test the voltage regulator I'm seeing nothing from the terminals on my meter. When I test the "blown" fuse for voltage, I'm seeing about 15 volts on the meter with the famicom's power switch on. But why would there be a voltage reading on the fuse at the end of a circuit that appears to be farther down the circuit than the voltage regulator that has no reading? Any advice or material you can point me to online that would explain whats happening here? Even if I don't get it working, I'd really like to answer these questions because I've always had this lack of certainty when dealing with this kind of issue.

So I need some direction on where to go from here. I read on another forum where a guy couldn't get his super famicom working and had the same issue (kept blowing fuses) and all he said he had to do was replace all the caps on the board. What do you think? Is that all I need to do to get it to work, and everything I just described up above is misinformed hogwash?

Thanks in advance for your time!

Heres some pictures to just in case you all see something wrong that I'm not.
AV Famicom
Gender: Male
Germany Germany
Posts: 383

Not dead yet.

« Reply #1 on: July 12, 2019, 07:02:12 PM »

15V on a Famicom?? That's 3x the current the chips work with.
The 7805 regulates voltage down to 5V, otherwise the ICs and components get damaged. Hence the fuse in there to turn off the FC when it's blown.

Did you try adding another fuse after replacing the 7805 regulator with a new one? Does it still blow up? if so, then something else is faulty. Capacitors I doubt it since the few the FC uses are all ceramic and not electrolytic. I think there's like 3-4 of them only. If their top isn't bend then those are fine and nothing to worry about.

Since the PPU/CPU have probably recieved the 15V various times I wouldn't be surprised if they overheated or the whole board has been damaged.

If all fails, buy a new Famicom or socket everything and test the chips out. Tongue
Posts: 2

« Reply #2 on: July 12, 2019, 07:13:35 PM »

Thanks for the reply! 15 volts is what the original famicom's power adapter read when I tested it, and when i tested the voltage of my sega gen 1 adapter it had about 13v. Why if the ratings are 10v are these power supplies going higher than their rating? I agree with your logic, and i have no knowledge on the matter, but wouldn't supplying more voltage than the regulator needs (within reason) be a good thing, considering thats why there is a regulator? Would there be any point to a 5v voltage regulator if the power adapter supplied a perfect 5v?

I have not replaced the fuse a second time yet after replacing the voltage regulator. But that will be my next step in a couple hours. I have 9 fuses left so I don't want to keep blowing them all, but I'll try that first. I suspect there could be a faulty cap even though they all physically look good. I ordered a cap kit from console5 in the meantime.

Like i've stated, the voltage regulator isn't showing any reading, not even on it's pin 1 which should theoretically be the 15v from the power adapter or close to it. So maybe there's hope that the whole board isn't damaged.  I'm really looking for answers as to why the fuse isn't showing continuity anymore when I test it, but yet when the power is switched on the only component in the board i get a reading on is a 15v reading at the fuse..... That's where im confused as heck.
Twin Famicom
Gender: Male
United States United States
Posts: 656

Octoroc Hunter

« Reply #3 on: July 13, 2019, 08:28:56 AM »

Did you test for continuity starting from the power terminal,then working your way up to see if there's any break,think I might have the same board,will trace it out for you.

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