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Atari 7800 Controller Problems


thenickman100

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I posted this to the general Atari 7800 forum, but maybe this is a better spot for it.

 

My Atari 7800, out of nowhere, stopped working with controllers.  When playing any game, the game acts like both buttons are being held down.  I took off the casing and shield to inspect the circuit board, but nothing seems out of the ordinary.

 

Does anyone have any advice on how to troubleshoot/repair?  I'm not really wanting to buy a replacement console.

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Are they still "held down" even without the controller plugged in?

 

Also check that the wire that connects between both switches has +5V on it.  If not, then it's probable that pin 6 is no longer connected.  Reflowing the plug connections to the motherboard will probably fix it.

Edited by ChildOfCv
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2 hours ago, ChildOfCv said:

Are they still "held down" even without the controller plugged in?

 

Also check that the wire that connects between both switches has +5V on it.  If not, then it's probable that pin 6 is no longer connected.  Reflowing the plug connections to the motherboard will probably fix it.

Only when the controller is plugged in. Which wire are you talking about? When you say reflow, does that mean touching the solder with the soldering iron?

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8 hours ago, thenickman100 said:

Only when the controller is plugged in. Which wire are you talking about? When you say reflow, does that mean touching the solder with the soldering iron?

With the controller apart, there should be an orange wire connecting the two button boards.  From one of those connection points to the black wire in the middle of the bottom board should be 5V.

 

And yes, reflow just means melt the solder on each connector for a second or two, then remove heat.

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Just ran into this last night on one I have to receive a UAV in it. I always do a burn in test using the diagnostic rom's Cart integrity test and just leave it going for hours to make sure nothing goes south. Did this on one console last night and it was fine and clicking right along. I come back to it about an hour later and notice that it is toggling between the integrity scan and then the menu...integrity scan...menu. I was able to interrupt it enough to get to the joystick test and sure enough both player 1 and player 2 controllers were showing both fire buttons as bring pressed down. Soon as I plugged a controller into each port, they reset themselves automatically. Unplug the controller from the ports and let it run the integrity scan again and it will come back about 30min later. Tonight I will leave a controller plugged into each port and rerun the test to see if it comes back. I know that I discovered this similar issue with my personal 7800 sometime back while playing Xenophobe. After playing it a long while, player two suddenly startup on its own. And there was mention of something similar happening to others in the game Rikki and Vikki. So I don't know if this is perhaps just a quirk of the 7800 when there aren't controllers plugged into it, or an indication of failing TIAs that work fine until they get hot.

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The 7800 has an interesting controller modification circuit built in.  In TIA mode, the fire button (pin 6) is only a 10K pull-up, and shorting it to ground signals a button press.  On the Pro-line joysticks, the short to ground goes through a 680-ohm voltage divider, though.  That drops the voltage to around 0.3V, which is probably good enough for a "fire button" press.

 

In MARIA mode, it turns on a transistor (Q8) that provides full +5V to pin 6.  But each one is also individually controllable through separate transistors (Q5 for player 1 and Q6 for player 2) using a couple of ports from the RIOT.

 

So, if the RIOT is malfunctioning, you could be missing the hard pull-up on pin 6.  Well, the same is possible if any of the 3 mentioned transistors fail.  Anyway, without that hard pull-up, the Proline controller will only give you the main fire button, and should fail to activate either of the paddle input/2-button fire inputs (I0-I3).

 

If the stick is not plugged in, it is possible for static charge to build up on the paddle inputs which could be interpreted as a fire input.  If the plug is bad or any of the solder connections broken, the 680-ohm resistors could also fail to ground those inputs.  Same result.  I suppose a multi-player paddle game would be a good test of that scenario though.  So if paddle input has 680-ohm resistance to ground with the stick plugged in, and you still see random triggers, then it's likely that the TIA is bad.

 

In MARIA mode, pin 6 which will probably be set to full power, provides the +5V to each of the fire buttons (orange wire).  If pressing a fire button causes that voltage to drop, you probably have a bad transistor in the 7800.

Edited by ChildOfCv
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5 hours ago, -^CrossBow^- said:

I know that I discovered this similar issue with my personal 7800 sometime back while playing Xenophobe. After playing it a long while, player two suddenly startup on its own. And there was mention of something similar happening to others in the game Rikki and Vikki. So I don't know if this is perhaps just a quirk of the 7800 when there aren't controllers plugged into it, or an indication of failing TIAs that work fine until they get hot.

It's a design quirk that doesn't consistently affect all units, but appears to get worse with age. Essentially the four paddle inputs (I0 - I3) have an indeterminate state without a controller attached. Usually it'll stay low but as ChildOfCv correctly pointed out it can drift high after some time - which can appear as spurious presses to the game software. This is what caused the issue you observed in Xenophobe and Rikki & Vikki.

 

In the case of this unit : if you're seeing spurious presses in Xevious with a two button controller attached into Player 1's port, I'd recommend replacing the TIA. The fact that you didn't see the issue in Galaga makes sense, as this game doesn't use the paddle inputs (it's running in single button mode).

Edited by TailChao
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So in my case I need to test the cart integrity test again but with controllers plugged in to see if the same issue crops back up. On my personal 7800 the Xenophobe issues doesn't occur as long as I've got a controller plugged into both ports. So if the issues doesn't manifest with controllers plugged in, I'm going to call it good since I would think if the transistors were bad, the issue would crop up regardless of a controller plugged in or not in this case.

 

As for static build up, I hope not as I haven't removed the mainboard from the console shell yet and it is all sitting on my anti-static mat I use for electronics work.

 

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24 minutes ago, -^CrossBow^- said:

So in my case I need to test the cart integrity test again but with controllers plugged in to see if the same issue crops back up. On my personal 7800 the Xenophobe issues doesn't occur as long as I've got a controller plugged into both ports. So if the issues doesn't manifest with controllers plugged in, I'm going to call it good since I would think if the transistors were bad, the issue would crop up regardless of a controller plugged in or not in this case.

Yep, always keep in mind that the ProLine has two pulldown resistors inside it which hold the paddle inputs low when nothing is pressed. So whenever you see weird behavior like this just plug ProLines into both ports and leave them there. Nothing wrong with doing so - some units exhibit the quirk but most don't. Just as long as you're aware of it.

 

A problem with the transistors usually manifests as a game running in two-button mode seeing one-button (I4, I5) presses when using a ProLine. They're always suspect since you can short them out by using a one-button controller in a two-button game. Essentially holding down the trigger on a one-button controller in Xenophobe can break your hardware and the game feels no need to tell you otherwise. If you're using Rikki & Vikki with a ProLine and unexpectedly see the "please attach a two-button controller" message, that's a good tip off.

Edited by TailChao
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53 minutes ago, -^CrossBow^- said:

As for static build up, I hope not as I haven't removed the mainboard from the console shell yet and it is all sitting on my anti-static mat I use for electronics work. 

Static buildup can happen on any conductor that's near radiated energy but has no way to dissipate it.  For example, unconnected inputs.  It's not usually enough to damage anything (ie static shock), and it typically drains itself to a safe value even when such buildup slowly occurs, especially when the chip designs in ESD protection.  But it can fool electronics into sensing a high on input when nothing is present.

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Ran through the burn in testing again last night on this current 7800 I'm servicing only this time I had a 7800 controller plugged into each port. The testing ran for about 3 hours and the button issue didn't crop up. So it appears this one is just quirky and requires the controllers to be plugged in at all times. Then again, this is a pretty strange 7800. It was made sometime in May 1987 (Latest date stamp I found was on the RIOT at 8719 on it with all others about 10 weeks earlier than that). It has the extra components installed for the extra timing circuit found on many later made 7800s for newer 2600 games to be compatible (2600 Dark chambers). And actually has both 3904s installed near the audio adjustment coil whereas most of the earlier ones just had a vertically mounted resistor there. None of the chips are in sockets...but get this... It has the expansion port installed? It also has an Atari Corp sticker on the bottom so it is a mid timeframe made 7800 that still has the expansion port. I didn't realize Atari was still adding that in that late in the game as I've only seen them on original '84 and '86 made 7800s.

 

Anyway, I apologize for taking over this thread from the OP but just wanted to give a quick update on mine that keeping 7800 controllers plugged in results in a 100% functioning 7800. 

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It could be a refurb. My personal 7800 certainly was a factory refurb sold as new back in late 87 early 88 timeframe. I haven't an official diag plug for the controller ports (I do have the loopback for the 5200s). So I usually run these tests with controllers plugged in initially to verify everything is good and then run the cart integrity test for awhile in the background to verify over time. I wasn't aware there were loop back plugs for the 7800 testing? I do know that you only need a 4-port 5200 loopback board to use with both 4 and 2 port units since with the cover removed the 4 port loopback will fit and show up as port 1 and 2 on the test on a 2 port unit.

 

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