Technical and Repair Assistance

[133MHz]

Must be this one, right?



Read the inscription of that three-legged device which is screwed against that aluminum heatsink, must say 7805 somewhere on it.

[ericj]

Also, the LED on the Twin doesn't stay on when you turn on the unit. It will light up when it reads disk information. It does, however, flicker when you first power on the unit. If the LED flickers when you turn it on, then you may want to first check the voltage readings on the 7805 with a DMM before removing it, since the problem may be elsewhere.

[jpx72]

I have a question that should be in this thread so (sorry for interupting the Twin FC question):
Maybe someone have seen something simillar - My newly purchased faulty famicom is bothering me - after switching ON, the image on TV begins to slowly fading away untill (about 10s) it switch to pitch black. (This is important - I have it connected directly from PPU pin21, through my custom AV mod PCB, that is working on my other famicom). It looks like the frequency on the crystal is fading or something, but the sound is working OK, and by using the oscilloscope, I found out that on the input and output of the oscillator (pin 29 on CPU and pin 18 on PPU) remains the same (sinunsoidal) through all the fading process, and after it also. So far I have tried to change 74-368 (2x), 74-139 and 74-373 with no luck. I got the RFbox/7805 smaller board disconnected and tried to put the rest directly on +5V with NO behavior change (only more fuzzy picture, because of missing capacitor- 1000u that is connected at 7805 for "cleaning out" the power input). Also I tried to change both CPU and PPU (and crystal) with simillar famiclone CPU PPU and crystal (only PAL) and the situation is the same (fading away till black, only the sound is slower due to different crystal frequency). I know, there's not much to do, maybe I should replace all the resistors and capacitors, and it will be ok, but I was thinking if the S-RAM chips cannot be the reason. I have no other SRAMs to change them with (the famiclones usually have the other - wider chips - the same 28pin but about 0,5 cm wider). So I only changed them between each other but with no behavior change at all.

I know there's not much to do anyway, but so far I have changed some capacitors, and some resistors, but I am afraid it wont help. I think somewhere is something really stupidly mistaken, so I am only asking if someone has witnessed the same "fading away" behavior, and what did you do about it. Thanks!

EDIT: I DID IT! It was the bloody transistor after all, I thought it behaved strangely...the Q3 on the Ntd_8bit schematics. So thanks for reading, and in case of fading, look for the faulty transistor!

[133MHz]

Try some freeze spray / hair dryer on the components, it might be a thermal failure.

[knux123]

Hi guys,
I've just got a Famicom Disk System, but I keep getting the error 02, using both batteries and the Ac adaptor.
Why is that? the LED doesn't turn on, but it seems that the console works okay, since it boots up and finds the disk when I put a disk in.

[ericj]

Could you disassemble it and post a few pics of the power board (the board underneath the battery tray)?

[knux123]

Okay, later i'll do it and post some pics.
Post Merge: September 13, 2010, 09:25:07 am
Here are some photos:






By the way, sorry for the shitty quality

[JBOGames]

What's wrong with my Famicom?

The sound works fine aside from a buzzing noise. The problem I am having is with the graphics. Every game I try comes up with the sprites all glitched. I thoroughly cleaned my games and the pin connector on the Famicom, and still get the same thing. I'm pretty sure it's not the pin connector, because the games always boot up without fail. Also the graphical glitch is exactly the same on every boot. The graphics are not randomly glitched on each new boot, they stay in the same exact spot. The games works fine aside from the graphics. I can play them if I wanted to, I just won't be able to see what I'm doing.

[ericj]

Could be a cold solder joint where the cart connector connects to the board. One of my game doctors just had that problem. I re-flowed and touched up the joints and it works fine again. Just an idea.

[knux123]

Any suggestions? I really have no idea on what should I do.

[ericj]

Does the drive spin the disk when you put it in?

[knux123]

Does the drive spin the disk when you put it in?

Well, the LED doesn't turn on and i can't hear any noise coming from the FDS, so I guess the answer is no.

[ericj]

Check the 7805 voltage regulator (the thing screwed into the heatsink) and also check the drive belt.

If the 7805 looks okay physically, check it with a DMM. IIRC, looking at the front of it, the first leg on the left is input (should show around whatever voltage your AC adapter outputs), center leg is ground, and right leg is output (should be at 5V).

[knux123]

umm... I don't have a DMM 

[ericj]

You could buy one. They're handy for lots of stuff.   

Even a cheap $10 multimeter is better than no multimeter at all. It's hard to diagnose circuit problems without one, unless something is physically awry.