Heavy Sixer - button always "pressed"

[Stingray]

I have a Sears Telegames heavy sixer that has developed a problem. Both players always seem to have the button pressed and held down. No it's not the controllers, happenes no matter what controllers are plugged in, or even if none are plugged in at all. I swapped the RIOT chip. No effect. I then swapped all of the chips, just for the hell of it. No effect. This system was working until recently. Nothing oin the board looks obiously burned or broken.

 

 

Help me Obi Wan Kenobi, you're my only hope.

 

-S

[Stingray]

And the huge number of typos is that post are a prime example of why you should always hit "preview" before you post.

 

-S

[A.J. Franzman]

Check for missing/burned/poorly soldered pullup resistors on the fire button circuits. I believe schematics are available on this site but you'll have to find the exact locations of the actual resistors by tracing the circuits on the boards.

[Stingray]

Well, as I said, nothing on the board looks damaged or burned. I looked the entire thing over pretty thoroughly. It seems strange to me that both fire buttons are displaying the same defect. They surely wouldn't both go through the same resistor would they?

 

-S

[hex65000]

This is an experiment I tried with one of my 2600s that had a bad CMOS inverter. I soldered a wire to ground and then measuring with a meter tried to pull down the inputs on the IC. If the output was inverted all is well. You may try something similar on your unit. Although, be smarter than I was about it. Toss a 330 ohm R between your test points and ground. That way if you short something it's not a dead short (bad thing).

 

You can also try the same technique with one end tied to +5V, but put a 1kohm in series with your test wire,

 

Some ideas that worked for me.

 

Hex.

[ Will I accomplish ANYTHING today? ]

[A.J. Franzman]

Ben Heckendorn had the same problem when chopping a 2600 Junior down to make a portable, and he discovered that a couple of resistors he left off caused the game to act the same as you describe. (Operation Successful!) If your resistors test OK, re-melt their solder connections and look for cracked copper tracks associated with them. In fact, you could probe the TIA pins (35 and 36): With power off, they should each read 10K ohms or less to the +5V bus (pin 20). With power on and a game running, they should read close to +5V to ground (pin 1 or 22).

[A.J. Franzman]

One other thing it could be - this is extremely unlikely, but you're running out of possibilities: shorted capacitors. This would have caused low voltage readings in the final test in my previous post, but open resistors would do the same thing. If the resistors, capacitors, circuit tracks, and solder joints are all tested good, and the power bus is between 4.75 and 5.25 volts, there's only one possibility left - a bad IC. It would probably be the TIA but could also be the 6507 processor.

[Stingray]

Ben Heckendorn had the same problem when chopping a 2600 Junior down to make a portable, and he discovered that a couple of resistors he left off caused the game to act the same as you describe. (Operation Successful!) If your resistors test OK, re-melt their solder connections and look for cracked copper tracks associated with them. In fact, you could probe the TIA pins (35 and 36): With power off, they should each read 10K ohms or less to the +5V bus (pin 20). With power on and a game running, they should read close to +5V to ground (pin 1 or 22).

 

This sounds like a good possibility. I'll give that a go.

 

-S