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PostPosted: Fri Aug 10, 2018 3:36 am 
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Thanks a lot for the recommendations. I'll start today after work :)

About USA SNES, PAL SNES and SF PSUs, I think there might be AC/DC differences for different regions actually. I bought this PAL SNES in Germany a few months ago, but all my life I've used USA consoles exclusively. My original consoles are back home and don't have them to check atm, but so far I have seen some pics of SNES PSU from different regions and seems that the NTSC (USA/Japan) output DC and the PAL ones output AC. Jeez.

I will try to upload a complete report of the debugging soon.


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PostPosted: Fri Aug 10, 2018 4:04 am 
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Great!
Keep us informed and good luck! :wink:


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PostPosted: Fri Aug 10, 2018 4:54 pm 
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Alright, I did some testing and noticed a few things:

When I tested the Famicom turned off, plugged to the PSU:

- The power sub-board seems to work correctly, I followed the power flow up until the on-off switch and it was all ~5v.
- Just in case I checked if there was any voltage in the mainboard, but there wasn't.
- I checked the connection between the power sub-board to the main board and found the VCC cable:

Image

There I saw the VCC marked cable, and in the back of the board I saw that the two cables to the (right in the photo) of the one marking VCC are connected.
None was delivering any current to the main board.

For now everything seemed to be okay. I turned on the switch and tested again, to see:

- The 7805 is now outputting what seems to be exactly 3V. Not sure if this is the normal behavior.
- Now the mother board is powered with the same charge of 3V, by the three cables mentioned before.

This may be okay, I left it turned on a few minutes and started touching the ICs. I touched them with the skin just above my nails which is a bit sensible. What I noticed is that some ICs heat a bit, some more than others, and some don't really heat:

Image

Here I marked the ICs with dots to find them easier.

- The blue dotted ones (TC40H368P) don't heat at all.
- Also both ones next to the purple dotted ones (SN74LS139N and HD74LS373P) doesn't seem to heat at all.
- The green dotted one (RP2A03E) and the one above it (RP2C02E-0) heat up a bit. Let's say they get warm.
- The purple dotted ones which are both TMM2115BP-15 start heating up. If I leave my finger on it, it burns a bit after some seconds.

My knowledge on these motherboards is pretty much null, so I don't really know what is each IC.
How much heat should they produce?

Then things got interesting:

After maybe 3-4-5 minutes I started smelling a bit of heated up plastic. And smelling around, I found out that it came from the power sub-board.
- Then, I realized that the whole metal cover had an intense heat, that would burn my fingers if I touched it.
- I turned it off and unplugged everything.
- I plugged the PSU and turned on the famicom again after everything cooled down (10~ mins).
- I noticed that the 7805 was heating up really fast, heating the small heat sink and the whole metal cover that's in the power board.

I don't have how to measure temperature, but it was really hot, much more than the ICs. Not sure if this is normal though.
I didn't want to leave it turned on much more.

Do you think that the ICs are fried? In that case, it's pretty much not worth it to find substitutes?


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PostPosted: Fri Aug 10, 2018 5:00 pm 
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@Addam: Does your FC have a fuse somewhere?


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PostPosted: Fri Aug 10, 2018 6:09 pm 
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The 2 ICs that heated a lot may be defective. Try the diode test on them.
Also, it's not normal the 7805 outputting 3v neither heating that much.

The burnt smell makes pretty sure there's a short circuit somewhere and possibly are these ICs.
They are the RAM of the console, the one that is connected to the 74LS373 being the CHR RAM, the other is the PRG RAM.

Try to find what's causing the sort circuit before powering up again, if you need to test, watch the 5v output to see if the short is gone or more damage can be made.

Good luck!


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PostPosted: Fri Aug 10, 2018 6:17 pm 
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The CMOS RAMs (e.g. the TMM2115) tend to be some of the most easily damaged parts in a NES/Famicom. I wouldn't be surprised if that's why it's broken now.

A 7805 will emit less than 5V if one of two things happens:
- Too much current is drawn (which is also consistent with the RAM being damaged)
- Too little voltage is supplied (which you've already verified is not true)


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PostPosted: Sun Aug 12, 2018 6:34 am 
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@FIsher: So I've done the diode test, using the thread you suggested to me.

I used the image in this post for the names of the pins:
https://forums.nesdev.com/viewtopic.php ... st#p201653
Even if some chips have slight different names and numbers I used the pin names found there.

In the lower 2k x 8 SRAM I found:
- A10 pin - infinity
- all other pins show different values

In the upper 2k x 8 SRAM I did'nt get infinity on any pin.

In the PPU
- On Pins 14, 15, 16 and 17 when I test, the values move a bit and drop to zero. Seeing the image one of these pins is GND.
- No pin has infinity.

In the CPU:
- /IRQ pin has infinity
- CLK has infinity

In the 74LS139 there's no pin with infinity.

The 74LS373P guy has no pin with infinity either.

The I measured the two toshiba TC40H368P at the bottom on my motherboard. For this i used the datasheet:
https://www.datasheets360.com/pdf/7486811487654332985

In the one on the left (on the last image i posted of the mother):
- 6A, 4A, 2A, 1A = inifity

In the one on the right (on the last image i posted of the mother):
- 6A, 5A, 4A, 3A, 2A = infinity

Well, I have done this test twice both on saturday and sunday, to confirm the measures.
I guess I have a few doomed chips and they are probably the cause of the short circuit.


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PostPosted: Sun Aug 12, 2018 10:25 am 
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You can try to remove the suspicious chips and see if the sort circuit persists by watching the tension at the +5v line.
Try to test it quickly or you can have the bad smell again and something more can be damaged.

To do these kind of tests I used to unsolder the +5v and/or gnd, but I was told that's not a good practice so I recommend you to remove the suspicious chip entirely.

Good luck and happy father's day!:-)
Please, keep us informed of your progress.


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PostPosted: Sun Aug 12, 2018 3:36 pm 
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Haha I see you are from Brasil! :) :beer: happy father's day to you too :)

I desoldered the CPU and quickly measured the 7805 output. The outputted voltage measured around 3,7 volts.

I was desoldering the ram and my unsoldering unit started working bad. I will try to fix it and go on tomorrow.
Will keep posting the results.
Thanks again :)


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PostPosted: Sun Aug 19, 2018 2:27 pm 
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nnov wrote:
@Addam: Does your FC have a fuse somewhere?

No fuse, I just replaced the 1000uf cap and found a suitable PSU.
I was lucky, the damaged component was easy to find.
You might need to do a little more diagnostics. Do you have a multimeter?


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PostPosted: Mon Aug 20, 2018 4:37 am 
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Yes, I borrowed a multimeter from a friend.
I followed what Fisher told me to test, so I made diode testing on all the IC's.
I found that removing the CPU made voltage increase a bit, but it seems there's still a short circuit. I started de-soldering the suspicious ram chip but the desoldering unit was heating the chip way too much.

All in all I ended up buying a famicom top-loader, but I still want to fix the original famicom. Right now I believe chances are that I blowed a few IC's. And I guess that fixing this would involve buying several junk famicoms and make some sort of frankenstein unit. I doubt it is a capacitor (or only a capacitor) at this point :(

I will go back at desoldering tonight.


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PostPosted: Mon Aug 20, 2018 12:46 pm 
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I would be tempted to cut my losses and just buy another cheap famicom like this:
https://www.ebay.co.uk/itm/Untested-As-is-For-Parts-or-repair-NES-Console-Famicom-NINTENDO-FC-AU-Oa8/192592628934?ssPageName=STRK%3AMEBIDX%3AIT&_trksid=p2057872.m2749.l2649


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