AV/Power module sourface mount element

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Badmax90
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AV/Power module sourface mount element

Post by Badmax90 »

Lately I purchased a dead NES PAL-B version and trying to fix this.
The main issue is that there is no Video output for the composite signal.

I began with cleaning everything and doing a full recap on main and AV/Power PCB.
Next was installing an new replacement 72-pin connector and cutting the Lock Chip.

Non of this was helping, so looking on the forum I found this topic referencing that the PPU could be a problem.
viewtopic.php?t=13762

I bought a replacement UA6541 and switched it for the original, with no effect.
Finally I did what should be my first step and traced the video signal just to relies that I had a fried element on my av\power board.

Presuming this is some kind of transistor but I'm not sure. Seems there is no description of this element and I could not find it anywhere on the internet.
The revision of my board is for sure one of the ALPS, but again referring to the already mentioned topic which has a lot of pictures of different revision AV/Power boards, non of those fit to mine.

The only similar board I found was this guy's nes-raspberryPie project:
https://www.igorkromin.net/index.php/20 ... onnectors/

Could someone help me recognize this surface mount element? Is there any replacement for it?

Here are some pictures of my board:
1.jpg
2.jpg
3.jpg
4.jpg
lidnariq
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Re: AV/Power module sourface mount element

Post by lidnariq »

Do you have any diagnostic tools? (oscilloscope, voltmeter, &c)

I don't recognize a 6-pin SOT23 part, but I agree it looks like it's part of the video path. You may be able to get away with bypassing it, or replacing it with "just" a transistor. Unfortunately, all the RF modulators are underdocumented.
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Badmax90
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Re: AV/Power module sourface mount element

Post by Badmax90 »

Unfortunately I don't have a oscilloscope or logic analyzer, just a multimeter.

From what I measured on the element with power on and using a 9V DC adapter to power the system:
5.jpg
5.jpg (14.17 KiB) Viewed 1249 times
In my opinion it's definitely a short on pin 3 - 6 and at least one signal should be GND. I can also see a constant 5V signal on the video output.
Normally what values can I expect on the video output?
lidnariq
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Re: AV/Power module sourface mount element

Post by lidnariq »

Does your multimeter have a diode test? If so, can you see if there are any diode drops across the various pins?

In purple is my best guess as to the primary baseband video path:
1_video_marked_cropped.jpg
As such, you might be able to get away with just removing the 6-pin part altogether, depending on what exactly the white squiggly bits are.
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Badmax90
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Re: AV/Power module sourface mount element

Post by Badmax90 »

Unfortunately de-soldering the smd element didn't resulted in any positive result for the video output.
I got readings between 1,5 - 1,05V instead of the stable 5V previously.

For more transparency regarding this circuit I've de-soldered the av\power PCB and the big capacitor.
6.jpg
7.jpg
8.jpg
Yes I have a diode test in my multimeter, so I have checked a few of those.
The diodes from the bridge rectifier show a good result of 0,5V in forward direction and LO on backwards.

I've checked all the elements on the video path You marked.
11.jpg
We have a C1740 NPN transistor on the input and the 2 elements in the bottom are a 40 ohm resistor and a diode.
For the 2 diodes that are connected to the video output I got strange values of 0,54 V in forward direction and 0,93V backwards direction.

Are those any special kind of diodes or just damaged?
lidnariq
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Re: AV/Power module sourface mount element

Post by lidnariq »

Badmax90 wrote: Wed Aug 10, 2022 4:02 am Unfortunately de-soldering the smd element didn't resulted in any positive result for the video output.
Is the SMD element still structural enough to see if it has any diode drops across it? My only guess is that it's one or two BJTs inside.
The diodes from the bridge rectifier show a good result of 0,5V in forward direction and LO on backwards.
I assume the power LED works, and maybe audio does too? Just video doesn't?
Are those any special kind of diodes or just damaged?
They're fairly normal - although high β / hFE - BJTs.

Since you've already desoldered the RF board, what happens if you just provide the mainboard with 5V and plug the baseband video pin on the RF modulator into your TV's composite input?
darleiv
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Re: AV/Power module sourface mount element

Post by darleiv »

nes-001-schematic---power_-av_-rf-switch.png
lidnariq
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Re: AV/Power module sourface mount element

Post by lidnariq »

That's not helpful. There were at least 7 different "RF" boxes that showed up on the front-loader, and that's only one version... and Electronix Corp's reverse-engineered schematic has some errors on at least one other sheet so I wouldn't count on this one being correct either.
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Badmax90
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Re: AV/Power module sourface mount element

Post by Badmax90 »

lidnariq wrote: Wed Aug 10, 2022 10:52 am
Badmax90 wrote: Wed Aug 10, 2022 4:02 am Unfortunately de-soldering the smd element didn't resulted in any positive result for the video output.
Is the SMD element still structural enough to see if it has any diode drops across it? My only guess is that it's one or two BJTs inside.
Referring to the previous picture of the SMD element I got only a diode drop on pin 1 -> 4 of value about 0,68 V. The rest is either dead or LO.
The diodes from the bridge rectifier show a good result of 0,5V in forward direction and LO on backwards.
I assume the power LED works, and maybe audio does too? Just video doesn't?
Yes, the power LED definitely works, as for audio I'm not sure. Previously I got only a monitor with avToHdmi converter and it was not able to start without the video output waking the converter, but the signal readings for audio seemed to make sense, so I assume it works.
Are those any special kind of diodes or just damaged?
They're fairly normal - although high β / hFE - BJTs.

Since you've already desoldered the RF board, what happens if you just provide the mainboard with 5V and plug the baseband video pin on the RF modulator into your TV's composite input?
For the test I got a breadboard with a power unit and soldered a few wires here and there and also took an old LCD TV with composite input.
The main board was powered from the breadboard and the video output on the cables.

What I observed was that I had to plug the cable many times to got a certain timing to "catch" the signal for the TV.
As the screen got on most times it was either blue or black.

14.jpg
13.jpg

This was probably a bad connection to the cartridge, so I screwed the loading tray and the connector to the board and that is what I got:

12.jpg
lidnariq
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Re: AV/Power module sourface mount element

Post by lidnariq »

Sure looks like it's almost working, and probably only needs the output voltage adjusted.

Without any good evidence, I'm going to guess that part is a transistor or two, even though you only saw one pin pair with a diode drop.

The Pirates! screen there looks close to right, but a little dark. Maybe PNP-based emitter-follower is sufficient.

You could also rebuild the entire video path if you don't anticipate needing RF in the future: https://github.com/mspinksosu/NES-Power-Board could be used for reference
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Badmax90
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Re: AV/Power module sourface mount element

Post by Badmax90 »

After some time waiting to get all the parts, I have constructed the basic scheme following this:
16.PNG
As for the more advanced schematic including the cap, it was not working at all as I tested it on my breadboard.
17.PNG
It's for sure some kind of high pass filter for the video, but the resistor values are wrong for my NES or there are some errors in the scematics.
I also got this wavy lines on the screen:
17.jpg
Anyway, the sound and video are working now. I leave this as is for now, maybe in the future I will consider a NesRGB mod.
Many Thanks to You Iidnariq for all You support. Really appreciate that. It was fun and I learned a few things along the way. :D
lidnariq
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Re: AV/Power module sourface mount element

Post by lidnariq »

Those wavy lines are an inadequate power supply - something about the 7805 becomes an FM modulator when its input and/or output capacitance is too small. Since you said you already recapped everything, try checking for cold solder joints?
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