Hong Kong Famicom with AV Mod - Dead :(

[populated]

I have a Hong-Kong Famicom with the Makko Toys RF board inside.  When it came to me it had a blown voltage regulator and a faulty capacitor on the RF board which I have replaced.

I have also made up the RF mod according to http://www.jpx72.detailne.sk/modd_files/fc/avmod.htm

I am getting no picture from the Famicom and I don't know if it is my AV mod thats the problem or the famicom itself.  I have re-wired the RF board with just the 5v and GND connections to the Famicom main board as I assume thats all it needs.

How can I tell if the Famicom itself is working?  I have checked at pin 40 on the PPU and I am seeing 5v.  Hope somebody can help!

[Pikkon]

Damn,what happened to that famicom,there's a section missing from the motherboard.

[populated]

Its a 'Hong-Kong' Famicom.  Back in the day when grey market Famicoms were imported to Hong-Kong, many of them were modified.

They replaced the RF board with an aftermarket one, usually manufactured by a company names Makko Toys.  Instead of the standard ribbon cable, jumper wires were installed to connect everything up.

[Pikkon]

I know about the system but the motherboard is still missing a section so that could be the problem unless you have the wires jumped correctly.

[populated]

I see what your saying, whoever did the mod back in the day could have been a bit 'chop-happy' when modding the board and sliced through some things.  These were probably jumpered originally to repair the issue.

Now I need to find a hi-res image of the same revision PCB so I can check and see whats missing or not connected.

Are there any test points on the Famicom PCB itself I can meter to confirm the Famicom is working or not?

[80sFREAK]

Be sure, that slot is clean and pins are tight. Blown 7805 does mean it was crosswired or used with AC/too high voltage adaptor. In this case it's a lotto.

[populated]

If the slot was not clean would I get anything at all on the screen?

[Pikkon]

Do you get any kind of flicker on the screen when you try to boot a game.

You can always uninstall your video amp and just solder a single video cable to pin 21 of the ppu, plus ground.If it works you would get a image,it wont look great but you would know that the famicom is working.

[populated]

Nothing at all, no flicker, nothing.

I am going to disconnect my AV mod and connect a lead straight to pin 21 and ground.  I didn't realise you could do that, then I can make sure the Famicom is alive before working on the AV mod.

[populated]

I have finally managed to find some time to take a look at the Famicom.  As suggested I have disconnected my AV mod and just soldered an RCA cable to pin 20 and 21 of the PPU.

Connected up to my TV and on the right AV channel but nothing, no flicker or anything.

I have checked the voltage at pin 40 on the PPU and it is getting 5v.

Can anyone suggest my next move?

[Pikkon]

Did you lift pin 21 then solder a wire to it.

[2A03]

I have finally managed to find some time to take a look at the Famicom.  As suggested I have disconnected my AV mod and just soldered an RCA cable to pin 20 and 21 of the PPU.

Connected up to my TV and on the right AV channel but nothing, no flicker or anything.

I have checked the voltage at pin 40 on the PPU and it is getting 5v.

Can anyone suggest my next move?

You're going to get weak video just tapping from pin 21, you need to connect it to an amp circuit first.

[populated]

I realise I am going to get a poor signal tapping pin 21 directly but I am trying to work out if my Famicom is dead or not before connecting the amp circuit.

I have not lifted pin 21, is that necessary?

[Pikkon]

Pretty sure as it will completely bypass the rf.

[populated]

Just realised that I have removed the transistor already so in effect the pin is already lifted.  I have +5v on the PPU, would this suggest that the famicom is working?  Is there somewhere I can probe maybe with a logic tester to see if things are working?