Famicom/NES Repair Log

[Skawo]

I happened to stumble upon several "broken" Famicom boards for cheap. Decided to log my fixing quest here, as well as some repairs I've done in the past, since it might help people resolve similar issues later.



Here we go~

Board #1 - HVC-CPU-GPM-02
No picture

* Checked for voltage on the board (touch one probe of the multimeter to the RF shield, and the second to pin 40 on the PPU). Voltage present.

* Checked for composite output. Using a standard RCA->RCA cable plugged into the audio and video sockets, I plugged the audio jack into the RF out (to get ground) and then touched the video jack to pin 21 on the PPU (yes, without any supporting circuitry - the picture will look bad, but you WILL get a picture!).

This was when I noticed PPU pin 21 was cut. Seems like someone was attempting an AV mod.
Anyway, got gray screen.

* Restored connection to PPU pin 21 with a bodge wire for easier testing. Still no RF?!

* Moved the channel and game switch a bunch of times after soaking them with contact cleaner. RF finally came back.

* Cleaned contacts by soaking a piece of paper in isopropyl alcohol and putting it over a credit card. Inserted this into the console several times, making sure to get all the pins. Game booted after this.

* Adjusted the coil on the RF board until sound could play on my PAL TV. Added a capacitor to reduce jailbars.

Console fixed!
=========================

Board #2 - HVC-CPU-GPM-02
Working, but black and white image

* Cleaned contacts using method from Board #1. Game booted, but got no colour.

* Attempted to fiddle with the variable capacitor. No dice. Noticed that someone tried to replace this trimmer already, and the install looked a bit questionable, so I grabbed one from a spare broken board and replaced it. This made no difference.

* Replaced the timing crystal with a new one.

* Adjusted the coil on the RF board until sound could play on my PAL TV. Added a capacitor to reduce jailbars.

Console fixed!
=========================

Board #3 - HVC-CPU-05
No picture

* Checked for voltage on the board and composite out, both of which checked out and I got a gray screen.

* Moved the channel and game switch a bunch of times after soaking them with contact cleaner. No dice.

* Cleaned contacts using method from Board #1. Initially I just got a gray screen again, until I mashed reset a bunch of times - sometimes the title screen to Lode Runner started to appear, slightly corrupted. More advanced games, such as Super Mario Bros. would produce a blue screen in this scenario.

* Inspected the board more closely, and noticed more evidence of someone attempting an AV mod - the Q1 transistor had been clearly removed, and soldered back on in the wrong orientation. Resoldered it properly, and the RF signal came back.

* Inspected the board some more, and the pins around the CPU and PPU - where you'd typically install the decoupling capacitors - had a bunch of crud around them (dried flux?). Reflowed the pins.

* Adjusted the coil on the RF board until sound could play on my PAL TV. Added a capacitor to reduce jailbars.

Console fixed!
=========================

Board #4 - HVC-CPU-05
Occasionally boots Lode Runner, slightly corrupted. Super Mario Bros. boots to blue screen.



* Inspected the board, and found some solder bridges on the CPU. Removed solder bridges, to no effect?

* There's a lot of trace damage around the extension port...

* Noticed the CPU was getting hot. After some probing around, console just shows gray screen now. CPU seems to have died.

* But wait! I desoldered the CPU and found tons and tons of trace damage underneath. Mold was starting to grow on the CPU itself. Didn't have much hope, but I put it into a test board with sockets, and the CPU actually works! It now lives in one of my NESes along with an NTSC PPU and xtal, converting it from stinky PAL to chad NTSC.

Still, the original board is a fail.

=========================

Board #5 - HVC-CPU-07
Works, but graphics are extremely corrupted. Improved somewhat by cleaning the cartridge slot.

* Cleaned contacts using method from Board #1. Improved somewhat, but not fixed:


* Probed around following the schematic, checking every cartridge pin. Discovered Pin 51 is not connected to PPU Pin 30. Found trace damage from corrosion:


* Added bodge wire


* Adjusted the coil on the RF board until sound could play on my PAL TV. Added a capacitor to reduce jailbars.

Console fixed!


=========================

Board #6 - HVC-CPU-05
Works, but graphics are extremely corrupted. Missing RF port.



* Cleaned contacts using method from Board #1. No dice.

* Checked continuity from cartridge pins to respective chips on the board. Everything was fine.

* This leads to two possibilities: dead PPU, dead U2 (LS373) or dead RAM. Dead PPU and dead RAM probably wouldn't look this corrupted, so I'm betting on the LS373.

* Replaced LS373



* Replaced the RF/Power board with one that still had an RF port. Adjusted the coil on the RF board until sound could play on my PAL TV. Added a capacitor to reduce jailbars.

Console fixed!


=========================

Board #7 - HVC-CPU-05
Gray screen.

* Cleaned contacts using method from Board #1. No dice.

* Probed around, found nothing wrong.

* This usually indicates that either the U3 LS139, U1 SRAM or CPU is bad.

* Replaced LS139 and SRAM. No dice. CPU is dead.

* Checked later on a test board with sockets. Yep, CPU dead. PPU was good, though!

Fail.

=========================

Board #8 - HVC-CPU-03
Gray screen.

* Cleaned contacts using method from Board #1. No dice.

* Checked the continuity of each cartridge pin using the Famicom board schematic. Found no continuity on some of them, and, following them on the board, noticed corrosion around Q1 which ate away at the tracks. Restored continuity with bodge wires.

* Adjusted the coil on the RF board until sound could play on my PAL TV. Added a capacitor to reduce jailbars.

Console fixed!
=========================

Board #9 - HVC-CPU-07
Gray screen.

* Noticed the CPU seems to get pretty hot.

* Cleaned contacts using method from Board #1. No dice.

* Checked the continuity of each cartridge pin using the Famicom board schematic. Found no continuity violations.

* Replaced CPU with a socket and tested a Famiclone CPU. It worked. Original CPU is dead.

Fail.

=========================

Board #10 - HVC-CPU-05
No picture.

* Checked for voltage on the board. Found none. Checked the output of the 7805 voltage regulator and found proper 5 volts there.

* Checked the power switch. No continuity between the pins in the "on" position.

* Using a flat head screwdriver, carefully pried open the power switch, careful not to lose any of the parts. Cleaned the metal contacts inside with isopropyl and scratched them up a bit with a blade to make sure they make contact. Reassembled the switch after.

Console fixed!

=========================

Board #11 - HVC-CPU-07
No picture.

* Checked for voltage on the board. Found none. Checked the output of the 7805 voltage regulator and found proper 5 volts there.

* Checked the power switch. Working.

* The power board was pretty crusty, with the solder mask peeling off in a few places. After some probing, I noticed that a trace leading to one of the capacitors lifted. Replaced with bodge wire.

Console fixed... but I replaced the RF/Power board with an AV replacement from krzy

=========================

Board #12 - HVCN-CPU-02 (Famicom AV)
Console works, but there's an extremely loud buzzing noise.

* Replaced voltage regulator.

Console fixed!
Note that on old Famicom boards, the buzzing noise is more likely to be coming from the Player 2 microphone, though - clean the volume slider in the controller and it will go away.

=========================

Board #13  - HVC-CPU-05
Rust city! Both SRAMs removed.


* Attempted to clear the rust off the board as best I could with vinegar.
* Replaced all the resistors and capacitors with new ones
* Cleaned cartridge connector
* Installed sockets and put in new SRAM
* Checked for voltages. Shockingly - the power board, rusted as it was, seemed to work!
* Attempted power on. No picture on either RF nor composite.
* Noticed that the xtal trimmer was replaced with a random resitor...? Installed a spare trimmer. Now we're getting a gray screen.
* Did a bunch of probing of traces here, there was some damage around the controller ports, but nothing that should stop the console from working.
* Was suspecting CPU was bad at this point, but CPU nor PPU were not getting hot...
* U2 and U3 had clear corrosion on their legs. Replaced U3 first. Game booted, corrupted. Replaced U2.

Console fixed!
Was that worth the effort?
Uhhhhhhhhhhhhhhhhhhhhhhhhhhhhh...

=========================

Board #14 - NES-CPU-10
Gray screen, power jack falls out very easily and has to be held for the console to be powered. AV/RF module incredibly rusty. Cartridge caddy doesn't click down. 10NES seems disabled?

* Inspected the board - two bodge wires used to disable the 10NES as per schematic here.

* Desoldered the AV/RF module. This is a bit difficult, and requires a high temperature iron, a solder sucker and patience. Removed the rusty covers and soaked them in Phosphoric Acid for about an hour, then brushed with sandpaper. This removed the rust.

* Using a needle, bent the metal contact on the bottom of the power jack slightly upwards. This stopped the power jack from outright falling out, and power now stays on without having to hold it. Resoldered the AV/RF module.

* Removed the 72 pin cartridge connector. A ton of pins on the board side seemed really misaligned, as if someone tried to bend them and failed...? Cleaned the card edge on the board that connects to the 72 pin and straightened the pins out as best I could with a pin. Using the method from board #1, cleaned both connectors. Super Mario Bros. 3 booted, with corrupted graphics.

* Boiled the 72 pin connector as per internet advice. Did nothing.

* Kept fiddling with the pins until I got Super Mario Bros. 3 to load without corrupted graphics. It's still kinda intermittent, though. Might need a 72 pin connector swap, this one may be too far gone.

* On the cartridge caddy, pulled out this metal tab:


Bent the clip inside a little bit out. Reinserted into the plastic holder. Cartridge tray now clicks closed.

Console fixed...ish.

[Salduchi]

Interesting! Thanks for posting this.

[Skawo]

Got another one.

Board #15 - HVC-CPU-07

Produces an interesting rainbow-coloured screen when turned on without a game. With a game in, it gives a blue screen.

* Cleaned cart slot - no improvement.
* Opened it up, and noticed the CPU gets REALLY hot. Dead CPU.

Sad.

Console fixed by giving it a set of PAL CPU/PPU. Not ideal, but, well, it works. I tried to use JUST the PAL CPU, hoping it would work at the NTSC frequencies... and, well, it DOES, but it's very glitchy: https://www.youtube.com/watch?v=5TCmWDe_ek4.

[Skawo]

Lot #2
This one had less interesting faults, sadly.
In general, step 1 for all of these was cleaning the cartridge slot.

Board #16 and 17 - both HVC-CPU-GPM-02


No reaction when powered on.

* Checked input pin on voltage regulator - 0 Volts
* Checked fuse. Fuse dead. Replaced fuse.



Consoles fixed~

Board #19 - HVC-CPU-07

Works, but the controller doesn't work.



* This can unfortunately mean a few things: faulty CPU, faulty U7 or U8, or connection problems. Thankfully, in this case, it was the latter, and I immediately found a bad trace:



Bodged the connection with a wire:



Console fixed~

Board #20 - HVC-CPU-07

Works, but the controller doesn't work... kind of. You can press A and it acts as START, but only in some games.

* Well, in this case, all the traces seemed just fine, so I decided to try replacing U7... which, admittedly, was just a guess.



It worked~



Board #21 - HVC-CPU-GPM-02

Works, but there is no sound.

* Started checking continuity along the schematic until I got to the C2 (Which is C7 on the GPM) capacitor and noticed it looked like this:



* Replaced it and sound came back. Wonder how this happened.



Boards #22, 23 - HVC-CPU-07, HVC-CPU-GPM-02

These just worked after a clean. 

Board #24 - HVC-CPU-07

No reaction when powered on.

* Checked Voltage Regulator input and got ~6 Volts. It was also getting SCALDINGLY hot in an instant.
That's not good.

* Replaced Voltage Regulator.

Console fixed~

Board #25 - HVC-CPU-07

Gray screen. CPU heats up a lot.

* Desoldered CPU and replaced with Famiclone CPU. Console started right up. Dead CPU. Sad.

Board #26 - HVC-CPU-07

Gray screen. The CPU stays cool.

* Checked all the traces with a multimeter, and concluded they were OK
* Desoldered the CPU, put in a socket with a Famiclone CPU. Console started up. Dead CPU. Sad.