NES controller electrical issue

[Hobie-wan]

Ok, just running this by people in case someone knows.

So I got a cheesy Advantage knockoff. I've cleaned it and everything looks ok inside, but it goes right unless you're pressing some other direction.

http://www.gamesx.com/controldata/nessnes.htm Ignore the bottom chip since this is a NES controller.

Nothing looks wrong, but while the system is running, if I test from the directional ground to the line on the other side of the directional switch, I get 5 volts as expected. I get 5 volts if I test on the other side of the resistor too, so I know that is good. However if I test from the directional ground to pin 7 of the IC, I get about 1.7 volts. If I test to 4, 5 or 6, I get 5 volts like I should. So that sounds like the chip is bad to me, but I'm no expert.

I might be able to scavenge a chip to swap in from another controller with a cracked PCB, but just thought to get opinions before doing that.

[Ziggy]

Hobie, did you ever get a desoldering iron? It makes swapping small ICs like this a ~5 minute job. Even if you wont use it often, it's worth the $10-15 investment.

[Hobie-wan]

Nah, I just got a desoldering pump. Worked well enough for the ICs I removed before.

[sonic2041]

Desoldering braid with flux will change your life forever.

[ApolloBoy]

Desoldering braid with flux will change your life forever.

Desoldering braid is OK for quick little jobs but you have to be extremely careful with it, or else you'll start pulling pads and traces off.

[Hobie-wan]

Desoldering braid is also not reusable. Suckers are. Anyway, desoldering is not my issue.

[CRTGAMER]

So I got a cheesy Advantage knockoff. I've cleaned it and everything looks ok inside, but it goes right unless you're pressing some other direction.

If I test from the directional ground to pin 7 of the IC, I get about 1.7 volts. If I test to 4, 5 or 6, I get 5 volts like I should. So that sounds like the chip is bad to me, but I'm no expert.

With that voltage drop, it does seem to lead to a bad chip. Hard to tell exactly what each pin should drop since the chip might "pull" that voltage down, maybe the readings are normal?

With the PCB exposed and no button pad or Dpad installed does it still make the character onscreen go to the right?

[Hobie-wan]

Yeah, with the system on, all of the other pins where directions go have 5. It is definitely on the board. With the stick portion disconnected it still does it. I pulled out the NES controller I have with a broken PCB and the chip is a different brand, but it is still a 4021B. So I'll just swap it and I imagine it will work.

[Omerta]

I'm with you on the bad chip. If we're reaching for straws, (and I'm no expert here) the only other possible explanation I could come up with would be that somewhere it's tracing (dirty with conductive debris, melted, or even inside the chip) slightly to that ground reference that's not enough for the full voltage, but enough to break the threshold that makes the processor see a directional input.

[Hobie-wan]

Still not sure why player 2 isn't working, but swapping the chip fixed the 'stuck right' issue so that's good enough for me since that's all it will be used for anyway.