master system 1: button 1 issue

I've got this master system 1 and a problem is drivin me crazy, when power on seem that button 1 (start) is permanently pushed (even with controller plugged off), it bypass rapidly the title screen and game begins, I put sonic in it goes to stage 1, sonic do a jump and then nothing

If I plug a controller everything works but button 1 is not working, it seem that console read it as permanently pushed, I checked with multimeter all connections and everything seem fine, they bring from pin 9 of controller port to pin 20 of 315-5237

someone could help?

 

http://www.smspower.org/uploads/Development/sms_schematic.gif?sid=6f46d070d6259f3078bf02872238a0e6

Shows pin 9 of port 1 goes to 315-5216, pin 30 but you mentioned different chip number so maybe you are using the SMS2. the smaller system without card slot?

If you have logic probe, use it and check the pins. When the controllers are not plugged in, all controller input should be reading high. If pin 9 is low, there's a short somewhere. Is there a filter between controller port and the chip like the one in SMS 1 schematic above? If there is no filter or if you removed it and the chip still reads low on the controller pin, and you can't see any short like solder blob or a loose change, the chip could be damaged.

 

thanks for tips
is a pal va3 sms1 and got 315-5237
I think button 1 is related to pin 6 (not 9) and checking voltage with multmeter it's 1.2v and it should 5....on contoller 2 port same pin gave me 5v

there is a "filter" I don't know how to call them these transistor like 3 pin things with '222' on them trying with another one for an old sms but nothing changed

could be the chip damaged?

 

Ah so it is PAL, explains the difference in chip # and pinout. The transistor-like things are likely emi suppression. Picture of common filter schematics:



Those used in Sega consoles are"Tee" style, 2 inductors in series plus a cap to ground, that dumps unwanted AC spikes while protecting digital pins. If you can desolder, see if by removing it helps. If the pin on the IC goes back to 5v with the filter removed, the filter is bad. You can jumper pin 1 and 3 to reconnect controller pin to the chip, take care it doesn't short to ground on pin 2.

 

thanks for explanations

yeah I already desoldered that filter and put another one from a broken sms1, same result. now tried to bypass goin to pin 1 to pin 3 like you said but no success....

 

The chip's probably bad then

 

I see....damn!

 

I don't remember exactly, but i've seen this on another page and someone fixed it. It used a pull-up or a pull-down resistor.