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7800 controller port (?) problem


shear_xear
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Hi everyone. I just received a 7800 that has a weird issue that I've never seen before. I can play single player games perfectly on the system, but when I try a two player game the second player just moves automatically to the left. Anyone know how I can possibly resolve this? Thanks!

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I replaced the RIOT first, but it still has the problem. I'll have to try the other one tonight...

 

If the RIOT is known to be good, and you've got a socketed board, verify that all the pins are making good contact with the socket wipes. If there's nothing wrong with the chip or the socket, you'll need to pull out a multimeter and verify continuity all the way from the controller jack pin all the way to the chip. Something is shorting the pin making the system think the controller is being held. There's probably a tiny piece of conductive debris (solder blob from prior mods or repair work?) shorting the pin, or you've got a shorted capacitor on the line.

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Only one of the ic has a socket, and it isn't the RIOT. I just desoldered the old one and took one off a parts board. I will check to see if there something wrong between the chip and the port. Maybe I will replace the capacitor first. Thanks!

 

Ah, too bad. :( I always recommend installing a socket if you remove an IC from a soldered board. That way on the off-chance your replacement chip is wonky or fails again, you can replace it more easily (bitter experience - having purchased two 2600's over the years with bad RIOT chips).

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  • 1 month later...

I replaced the RIOT first, but it still has the problem. I'll have to try the other one tonight...

 

What became of this? I've got one now I'm AV modding for someone and in my diags testing I found that player 2 can't move left at all and it registers both fire buttons being triggered constantly. 1 player games work fine though.

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What became of this? I've got one now I'm AV modding for someone and in my diags testing I found that player 2 can't move left at all and it registers both fire buttons being triggered constantly. 1 player games work fine though.

 

Boy the directional issue sounds like the RIOT , though I wonder about that fire button issue. On the 2600, FIRE read by the TIA as are the paddle lines. If there's not debris or something obviously wrong with the board like shorted traces, I guess it's possible both chips are going bad. I mean, I've got 2600's that have had problems with each of those independently though not at the same time.

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Yeah...I've actually had to replace the RIOT in my primary 7800 when I found out the AVox+ wouldn't work properly on it. Very odd with the RIOT was that normal game play was working fine but some 2600 homebrews like Stay Frosty for instance I had trouble jumping properly and some other stuff that I had no idea it was the RIOT until I got the AVox+. The one I'm AV modding, the client is now sending me a junker 2600jr he has on hand. So it will become the donor for one or both chips depending on my testing. I had planned to replace the RIOT first to see.

 

This 7800 has been an interesting animal. After I first put it together, it would turn itself on when inserting a game cart?! Later found out that something with the RF shielding is shorting against something. Once I got the shield in just the right place, it stopped doing it and was working normally. So strange...

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  • 2 years later...
On 7/17/2017 at 7:09 PM, DrVenkman said:

 

If the RIOT is known to be good, and you've got a socketed board, verify that all the pins are making good contact with the socket wipes. If there's nothing wrong with the chip or the socket, you'll need to pull out a multimeter and verify continuity all the way from the controller jack pin all the way to the chip. Something is shorting the pin making the system think the controller is being held. There's probably a tiny piece of conductive debris (solder blob from prior mods or repair work?) shorting the pin, or you've got a shorted capacitor on the line.

Hate to bring this one back up again, but I dragged this one back out to see what I can find.  What I found was that when checking continuity with pin three on the right player controller jack (the one that would pull left automatically) it showed continuity with pin one of the RIOT (ground).  As I can’t see how pin three runs out to the RIOT (there is no trace that I can find) any hints where I might look to fix this?  Thanks!

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15 hours ago, shear_xear said:

What I found was that when checking continuity with pin three on the right player controller jack (the one that would pull left automatically) it showed continuity with pin one of the RIOT (ground).  As I can’t see how pin three runs out to the RIOT (there is no trace that I can find) any hints where I might look to fix this?

Pin 3 of both controller ports definitely runs to the RIOT, because that's the chip that reads the directions. :) Per the schematic (and pardon for the large screenshot but the schematics are big but hard/blurry when too small):

 

\image.thumb.png.232a4d61f32809fce78c56647cb5c813.png

 

Pin 3 of the right controller port (J4) should run straight to pin 10 of the RIOT. So check continuity with between those two points.

 

However if you look at the schematic, there's a zener diode (CR8) and a filter capacitor (C38) that are on the same line and connect to ground. If one or both of those is damaged and shorted to ground, that would likely be the source of your problem. 

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24 minutes ago, DrVenkman said:

Pin 3 of both controller ports definitely runs to the RIOT, because that's the chip that reads the directions. :) Per the schematic (and pardon for the large screenshot but the schematics are big but hard/blurry when too small):

 

\image.thumb.png.232a4d61f32809fce78c56647cb5c813.png

 

Pin 3 of the right controller port (J4) should run straight to pin 10 of the RIOT. So check continuity with between those two points.

 

However if you look at the schematic, there's a zener diode (CR8) and a filter capacitor (C38) that are on the same line and connect to ground. If one or both of those is damaged and shorted to ground, that would likely be the source of your problem. 

Awesome.  I will check out the diode and capacitor.  Hopefully it’s one of those.  Thanks!

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3 minutes ago, shear_xear said:

I checked continuity to pin ten and that was good so I replaced the diode and voila!  Everything works perfectly.  Thanks for all the help!

Interesting. I've never seen those diodes go bad but I have seen those caps go bad and replaced one or two in the past. Glad you were able to get it sorted and working again!

 

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