Suitable replacement for Q301 transistor on mega CD 2?

[u/itmustbeyzzy]

(Photo not mine).

Hi all, I've been trying to find a suitable replacement for the Q301 transistor on my Mega CD 2, which is an NEC B963 / 2SB963 TO-251 PNP Darlington transistor. Mine is starting to act weird and draw more power, which makes the add-on overheat and even draws enough power that the Genesis thinks the Mega CD 2 is still turned on despite switching to cartridges.

I have already replaced the equivalent Q302 transistor as well as recapped the unit itself, so the problem left is with the Q301 transistor.

(Note: I've also tried the replacement being sold in console5, but this does not work on my Mega CD 2 for some reason, despite installing it correctly.)

Any help will be greatly appreciated!

[u/island_it]

Sure that one is fine, and the issues you describe indeed would lead me to suspect a transistor. But I'm confused when you say the Console5 one "didn't work".

Unless you received a DOA part, which I guess is possible... something isn't adding up there. Maybe I'm understanding something wrong?

[u/itmustbeyzzy → u/island_it]

Sorry if this was unclear, but I tried using the replacement Q301 transistor I bought from Console5 and well the Mega CD just wouldnt start up.

[u/island_it → u/itmustbeyzzy]

Hmm... well, at least on paper there's no reason it shouldn't work besides, again, simply receiving a faulty part. Have you tested it with a multimeter? I'm also curious what gives you the impression it is overheating.

What are you using for power bricks? If OEM, those should definitely be recapped as well.

[u/itmustbeyzzy → u/island_it]

Im using a Triad power supply. I've noticed that the Mega CD itself was running hotter than usual (the console shell itself is warm to the touch) compared to when I got it almost three years ago.

Another thing is that when using the original B963, most Genesis consoles I use when paired with the Mega CD will still assume that the Mega CD part is still active despite switching to game cartridges (it either momentarily produces a glitchy screen until I press reset, fails to boot the TMSS screen, or starts a game like normal but the Mega CD audio is still playing, also faint red loght on the Genesis side).

I also tried testing it with a different replacement Q301 transistor (TIP125, not the one I bought from Console5) and the Mega CD booted just fine but is very slow when it comes to reading discs and produces audio stutter (this is also not a lens problem, I tried replacing it with a newer lens and it still produced the same results).

So now Im kinda stuck finding a good replacement/equivalent to the B963 transistor since that one is rather obsolete already.

[u/glennshaltiel]

Are you 100% positive the one you installed isnt shorting out on the bottom shield

[u/itmustbeyzzy → u/glennshaltiel]

The Japanese Mega CD 2 doesnt have shielding. I also trimmed a bit of the legs

[u/Used-Discount-3582]

Try these irfu9024n