Hello all, first post here. And it might be a bit long. Sorry for that.
If you don't want to read everything, I highlighted my question.
I'm Dioxaz, live in France and successfully AV-modded a Famicom before, with help of that guide (probably a bit outdated now, as it doesn't prevent the "vertical bars" problem).
I'm posting here because someone recently sent me a nonworking Famicom, having no knowledge about how to check voltages from the LM7805 and wanting to AV-mod it (no choice when you live in Europe). And also, because I didn't see someone yet having the same problem as the one I'm writing here or something similar on various forums or places. I may continue my research indeed.
As soon as I got the system in hands, I quickly spotted a blown fuse (it's a HCV-CPU-GPM-02 motherboard), as no 12V or 5V could be got from the LM7805. I shunted the fuse and, good news, the LM7805 wasn't blown itself as it did its job properly.
Unfortunately, things got complicated when trying to boot a game.
The first time I tested the system, I used a cheap center-negative power supply outputting 6V at 1A. Switching the Famicom on gave me a wavy picture* (but no hints of a game screen) and tuning to other close frequencies to get sound gave me a 50Hz hum so I quickly switched the system off.
Then, I tried with an ATX one with no better results (only a black screen). Finally, I got a proper one in hands, from a Mega Drive MK1.
But it didn't got any better. With three games, including a previously tested one, I only get a black screen when powering on, instead of snow. As if no cartridge was in. I tried every possible solution I knew, cleaning the cartridge contacts with alcohol, cleaning the cartridge connector with a toothbrush, etc.
Is it possible that I damaged the motherboard by using that cheap power supply in the first place and trying an ATX one? Even If I never did a reverse polarity?
Is it possible to determine what could have been wrong on the motherboard and if it is fixable?
Indeed there's the possibility that it was broken before (as I found the fuse to be already blown) but I'm not really sure if Famicoms are really that fragile.
I also tried to pick up the audio directly from the board (in case it was the RF part that were faulty), but this only resulted in a drop out when switching on and off the system (no sound of a game).
Regards
* French TV sets can't take NTSC though their tuner (only through SCART and AV inputs), but I knew I could get an out-of-sync picture by tuning my TV to 96 or 97 MHz and using the original RF modulator (for CH2, 91MHz for CH1). This is quick test to see if the Famicom works correctly before AV-modding it
If you don't want to read everything, I highlighted my question.
I'm Dioxaz, live in France and successfully AV-modded a Famicom before, with help of that guide (probably a bit outdated now, as it doesn't prevent the "vertical bars" problem).
I'm posting here because someone recently sent me a nonworking Famicom, having no knowledge about how to check voltages from the LM7805 and wanting to AV-mod it (no choice when you live in Europe). And also, because I didn't see someone yet having the same problem as the one I'm writing here or something similar on various forums or places. I may continue my research indeed.
As soon as I got the system in hands, I quickly spotted a blown fuse (it's a HCV-CPU-GPM-02 motherboard), as no 12V or 5V could be got from the LM7805. I shunted the fuse and, good news, the LM7805 wasn't blown itself as it did its job properly.
Unfortunately, things got complicated when trying to boot a game.
The first time I tested the system, I used a cheap center-negative power supply outputting 6V at 1A. Switching the Famicom on gave me a wavy picture* (but no hints of a game screen) and tuning to other close frequencies to get sound gave me a 50Hz hum so I quickly switched the system off.
Then, I tried with an ATX one with no better results (only a black screen). Finally, I got a proper one in hands, from a Mega Drive MK1.
But it didn't got any better. With three games, including a previously tested one, I only get a black screen when powering on, instead of snow. As if no cartridge was in. I tried every possible solution I knew, cleaning the cartridge contacts with alcohol, cleaning the cartridge connector with a toothbrush, etc.
Is it possible that I damaged the motherboard by using that cheap power supply in the first place and trying an ATX one? Even If I never did a reverse polarity?
Is it possible to determine what could have been wrong on the motherboard and if it is fixable?
Indeed there's the possibility that it was broken before (as I found the fuse to be already blown) but I'm not really sure if Famicoms are really that fragile.
I also tried to pick up the audio directly from the board (in case it was the RF part that were faulty), but this only resulted in a drop out when switching on and off the system (no sound of a game).
Regards
* French TV sets can't take NTSC though their tuner (only through SCART and AV inputs), but I knew I could get an out-of-sync picture by tuning my TV to 96 or 97 MHz and using the original RF modulator (for CH2, 91MHz for CH1). This is quick test to see if the Famicom works correctly before AV-modding it