Technical and Repair Assistance

[skere26]

Hi,

For those who are FDS savvy, in the photo posted in:

http://www.famicomworld.com/forum/index.php?topic=786.msg4995#msg4995

Is the head adjustment screw the Philips screw in the middle or the Allen wrench screw in the middle?

Thanks!

EDIT: Figured it out, and after raising the spindle a bit and tweeking the head screw, I've been able to get about half of my games to work, the other half I get a error 27, so we're almost there!

[zappi]

hi there, long time lurker first time poster.

i recently took the plunge and got a Famicom Disk System and unsurprisingly i can't get it to work.
i managed to replace the belt ok, but can't get anything but Error 22s and the very occasional Error 21.
i've adjusted the motors potentiometer carefully for hours with three different disks, all from reputable sellers who say that the disks were checked and worked perfectly.
so any suggestions on what to do next would be gratefully received, as i'm getting close to giving up on it as a lost cause e.g. earlier on in this thread there was some mentions about aligning the spindle correctly, but all links to photos/guides are now dead.

[Nightstar699]

My pirate 4in1 has the usa tmnt game on it, but when i select it, it goes to the title screen. When i push start, it goes to the map. When i try to go to a level, it freezez, infinitely playing the music. The other games snow bros, chip n dale, and frog adventure work fine. Please help!

[superpope]

I tried the Famicom Disk System error thread, but I guess this is the appropriate place to be asking this.

I bought a Sharp Famicom Twin for my son's 8th birthday.  I tested it last night and it worked great, as far as I could tell.  The disk game that came with it (Which as best as I can translate is called "Super Deformed Gundam World: Gatchapon Fighters Scramble Wars") loaded up fine and played fine.

Today, however, the NiB Famicom Disk System Metroid and Zelda games I ordered came in.  After reverently breaking the seals on the packaging, I loaded each of them up and created save files. Each one gave me an "Error 26" after I created the save, and then wouldn't let me play. I put back in SDGW:GFSW and loaded a game saved by the previous owner with no problem.  Then I tried saving.  Error 26 again.  Ironically, because I sprung for new FDS Zelda and Metroid games hoping to get copies that still worked after twenty-five years, I cannot play them at all because they have no saved games to load and my drive refuses to save.   

Anyway, if you know any resources you can point me to about how to maybe clean the drive head or get the thing repaired, I'd be very grateful.  I've scoured the web and turned up nothing useful.  His birthday's on the 19th, and I don't want to give him a box of joy followed by immediate soul-crushing disappointment.

[MS-DOS4]

You bought your son a sharp twin famicom?

Can you be my new dad, please?

[Padoca]

defective sector in rom...

[133MHz]

Unfortunately the only way I can think of for troubleshooting this is by using an oscilloscope to monitor the WRITE DATA and /WRITE GATE signals along their path. I'm by no means an FDS expert (some people here know way more about it than I do) but since it seems that the FDS-related questions are piling up, I'm gonna chime in with a brief explanation.

Error 26 just as you said it means that the system isn't being able to write to the Disk Card. There are two lines responsible for writing to the disk: WRITE DATA, which carries the actual data to be written, and /WRITE GATE, which tells the disk drive to accommodate its circuitry to start writing data to the disk instead of reading.

In a common FDS drive, these signals come out of the RAM Adapter, pass through the Power Board on the FDS drive, and in the case that the Power Board contains copy protection, they get monitored by some special circuitry which interrupts them in case it detects that you're trying to rewrite the whole disk, otherwise they just pass unaltered. Then they enter the disk drive mechanism itself, and arrive at the Drive Controller chip (which can be either the FD7201 or FD3206). When the chip sees the /WRITE GATE line going low and the WRITE DATA broadcasting, it prepares the drive for writing and sends electric pulses to the drive head in an alternating fashion, using two specific wires that go from the controller chip to the drive head.

So this is the path that the data has to travel in order to get written to the disk:

RAM Adapter ---> Power Board ---> Drive Chip ---> R/W Head

Any of those points could be bad and preventing the data from being written. Since the drive reads disks and loads save files fine you can isolate the fault to the write path alone, and this being a Twin Famicom only makes things harder, because everything is so tightly integrated, there's not much room for simple faults like loose connectors.

The write signals carry high-speed digital data so there's not much you can do with a simple multimeter, maybe just check continuity across the signal's path. To "see" the write signals you need an oscilloscope or a logic analyzer (very expensive).

The other option is to swap the FDS drive mechanism with a known good one and see if the problem goes away, basically isolating the problem to a particular section (FDS drive mech vs. the rest of the Twin Fami).

As far as I see it there's no easy fix . But again, I'm no FDS expert so more input on the subject from our resident FDS guys would be greatly appreciated .

[Nightstar699]

Is there anything i could do to fix it?

[133MHz]

Don't underestimate dirty contacts. Give the cart edge connector a good cleaning. Also try it on another console if possible.

[cubelmariomadness]

Probably just a bad put together pirate tho, if it's not dirty, it's broken probably.

[superpope]

Thanks for all that info!  It sounds complicated all right, but I do have access to an oscilloscope and may give some of that a shot.

You mentioned swapping the drive mechanism for a known good one.  Is the drive itself the same as in an original FDS system?

[133MHz]

Well if you've got access and the skills to use an oscilloscope I can provide you with the relevant pins that carry the write signals so that you can have a look at them .

You mentioned swapping the drive mechanism for a known good one.  Is the drive itself the same as in an original FDS system?

Correct, it's the same drive mech that it's used in the original FDS. If it works with another drive mechanism then your problem lies on the connector, drive controller chip or R/W head.
If it stays the same you'll have to delve into the Twin's innards, deep down to the 2C33 chip.

[superpope]

Well if you've got access and the skills to use an oscilloscope I can provide you with the relevant pins that carry the write signals so that you can have a look at them .

That would be great! I also have access to a university electronics professor with a PhD in physics (my father), so hopefully I can learn a thing or two through this process.  I myself got a degree in art...it's served me well, but not when it comes to repairing electronics.

[phatphunk]

Hi guys. I just acquired a Famicom light gun and there seem to be a problem with it. Seems it's not able to detect any light, even when I point the gun up close to the TV. However, it's able to detect when I pull back the trigger. I've tried it on 2 CRT TVs, and both yield the same results   I then tried a FamiClone light gun and it work like a charm.. I'm suspecting that the phototransistor has worn out, but strangely there is current going through it. I've not gone deeper investigating if there are any changes when light goes into it. I look up the internet and found that it's using this phototransistor made by Panasonic

http://it.digikey.com/1/1/22617-npn-photo-transistor-pnz154.html

Sadly I can't find this particular phototransistor here in my local electronics shop. Any ideas on how I can troubleshoot this?

[133MHz]

The light gun circuitry is simple enough that you can replace components one by one until you find the culprit. I'd start by checking up the cable, then the resistors & capacitors and finally the phototransistor.

Fortunately phototransistor specs are not too critical for this purpose so you can replace it with a similar looking one.