Famicom Disk System issue

[LaughingElfMan]

Hi all!
I recently replaced the belt in my FDS, which went suspiciously smoothly. I was right to be suspicious.
Now, the drive always thinks there's a disk inserted. Tries to read constantly as soon as it gets power.
Did I break something? Can you think of anything I might have done that would cause that?

The thing hasn't been used in about 12 years, but it worked when the previous belt was installed (around 2012). It only works with batteries, so I assume it needs a voltage regulator. I thought it best to identify the other problem before buying one, but I'm happy to go ahead and get one if you think that could somehow be the issue.

I'm not *completely* incompetent with respect to electronic repair, but I know enough that I can confidently say that I'm *mostly* incompetent. Even coming away from here with a better understanding of the device would be a small victory.

Thanks for any help you can offer!

[Skawo]

Check whether you haven't jammed any of the sensor switches in the drive; particularly the on the side:



If they're fine (i.e not always shorted), then measure the 2SB1009 transistor on the power board:

[LaughingElfMan]

Check whether you haven't jammed any of the sensor switches in the drive; particularly the on the side:



If they're fine (i.e not always shorted), then measure the 2SB1009 transistor on the power board:

The switch LOOKS fine - I'll check it with my multimeter when I get home. What should I see from the 2SB1009? Would you consider that to be a "novice-replaceable" part?

[Skawo]

It's no different than replacing a voltage regulator. Very similar sort of package.
Unscrew the transistor, blob solder on all three pins to heat them up all at the same time, pull the transistor out. Clean up excess solder with soldering braid, put new transistor in.

Just check what each pin reads and report here.
Middle pin is ground. Both pins on the sides should read ~1.5V when the drive is meant to be running and ~7.5V when it isn't.

[LaughingElfMan]

It's no different than replacing a voltage regulator. Very similar sort of package.
Unscrew the transistor, blob solder on all three pins to heat them up all at the same time, pull the transistor out. Clean up excess solder with soldering braid, put new transistor in.

Just check what each pin reads and report here.
Middle pin is ground. Both pins on the sides should read ~1.5V when the drive is meant to be running and ~7.5V when it isn't.

Will do, and thanks! It looks like I'll have to wait for my new multimeter to arrive. My old one gave up on me (it's not the fuse) and all I need to diagnose its issue is... another multimeter. Never a dull moment!

[LaughingElfMan]

It's no different than replacing a voltage regulator. Very similar sort of package.
Unscrew the transistor, blob solder on all three pins to heat them up all at the same time, pull the transistor out. Clean up excess solder with soldering braid, put new transistor in.

Just check what each pin reads and report here.
Middle pin is ground. Both pins on the sides should read ~1.5V when the drive is meant to be running and ~7.5V when it isn't.

Finally got myself a new multimeter! Looks like the 2SB1009 transistor may need to be replaced. Both sides read 8.7V when in use, which I would guess is well outside of the acceptable range.
Now that RadioShack is gone, where can I find one of these?

[Skawo]

Well, online is your best bet.

There's this aliexpress listing, but the seller doesn't have the best feedback.

You can definitely substitute this transistor with a 2SA1217, 2SB1217 and BD376.
2SA1359 should also work.

[LaughingElfMan]

I

Well, online is your best bet.

There's this aliexpress listing, but the seller doesn't have the best feedback.

You can definitely substitute this transistor with a 2SA1217, 2SB1217 and BD376.
2SA1359 should also work.

I found one through a (somewhat) local seller. I try to buy things like that locally, since my motivation to repair the machine is on the same level as my motivation to clean the oven. I have to strike while the (soldering) iron is hot!

Thanks so much for your help, and I'll update you once I get the new part in place.

[Skawo]

Nice.

There's a slight chance it's one of two other components, but hopefully it'll work.

[LaughingElfMan]

Nice.

There's a slight chance it's one of two other components, but hopefully it'll work.

Got the replacement transistor installed! On the bright side, the FDS now runs via the AC adapter. Unfortunately, it's still experiencing the same issue...
You mentioned two other possibilities?

*edit* Possibly related:  The FDS only displays on my TV when running via batteries. When on the adapter, my screen stays black.

[Skawo]

Welp, yep, so the transistor WAS bad, but there are multiple faults.

Hm, just to check - you're using a negative center AC adapter, right?



The other two possibilities are:
More likely: the dual operational amp chip


Very common, cheap part; can be replaced with any other dual operational amp, for example an LM358N

Less likely: Q2 and Q3 transistors (both C2021).

[LaughingElfMan]

Welp, yep, so the transistor WAS bad, but there are multiple faults.

Hm, just to check - you're using a negative center AC adapter, right?



The other two possibilities are:
More likely: the dual operational amp chip


Very common part; can be replaced with any other dual operational amp, for example an LM358N

Less likely: Q3 transistor (C2021).

Yes, the AC adapter is center negative. It's a daisy chain situation, powering both the main console and the FDS.
It looks like you replied before I could edit my previous post, so I'm pasting it here: Possibly related:  The FDS only displays on my TV when running via batteries. When on the adapter, my screen stays black.

[Skawo]

Well, that sounds like there's a short to ground.

Incidentally, could you take a picture of your work having replaced the transistor?


If you make the FDS run for a minute or so, do any of the components get very hot when touched?

[LaughingElfMan]

Here's a picture: https://postimg.cc/9R5JQzFQ

I know, there's plenty of room for improvement. It's just so rare for me to get a chance to practice...

I'll check for hot components shortly.

[LaughingElfMan]

I don't feel anything getting hot, but my old, calloused fingertips probably aren't the best for that purpose.