7800 acting up! Help please?

[juggalot]

I bought a an Atari 7800 at the pawn shop the other day. They plugged it in for me and everything seemed to work fine. I finally got around to playing with it(or trying) yesterday and it works fine for a few minutes and then the screen scrambles and makes a bunch of noise like i didnt have the cart in right to begin with(only after a couple minutes of playing fine). I replaced the voltage regulator attatched to the heatsink and all three capacitors but none of that did anything. Also something that looked odd to me was a resistor soldered to the leg of one of the chips. This could be normal but Ive never seen it before. Any ideas would be greatly appreciated.

[+xucaen]

Just a quick comment on the resister. Looks like there may have been a few different revisions of that board. One of them has a resistor on that chip.

 

[juggalot]

Yeah I figured something different was up with that. Ive been inside almost all of my consoles and have never seen that before.

I dont have any 7800 games yet. I wonder if its only messing up with 2600 games? Just a thought. Ill have to try and pick one up tomorrow before or after work and give it a try.

[juggalot]

I was also considering reflowing the whole board just because Im out of things to try. I see theres a couple pots but I have no idea what theyre for, but I doubt they would have anything with my games crashing on me.

[Trebor]

I see theres a couple pots but I have no idea what theyre for, but I doubt they would have anything with my games crashing on me.

 

You are correct, it does not have anything to do with games crashing.

 

The pot closest to the cartridge port is for calibrating the colors of the 7800 mode.

The pot below it does the same for the 2600 mode.

[Everett1954]

You could get a can of Freeze Spray and and try and pinpoint the defective component.

[juggalot]

How would I do that with freeze spray?

[Keatah]

You determine how long it takes for the unit to crash. Then freeze one or two chips and see if it runs longer, or maybe doesn't crash anymore. Repeat till you narrow it down, if it's a thermal failure to start with.

[+-^CrossBow^-]

Well if he starts off by using a 2600 game to see if it freezes or not, then that will isolate the MARIA pretty quickly.

[juggalot]

It looks there's another regulator between the heatsink and where the power cord is plugged in. Anyone know what that one is for? I didnt change that one because I couldnt find anywhere online that said it might be the culprit. I havent reflowed the whole board yet because Im not the best at soldering so Im going to use that as a last resort. With that many small pins so close together odds are Id probably do more damage than good. Im off work in a couple days do Im going to get some freeze spray and try that then. Thanks for all your suggestions so far. I will figure this out eventually.

[juggalot]

Something else I discovered that may be helpful in figuring this out. I went to play gorf and if I turn on the game and don't push start right away it will crash within a few seconds but if I either push reset or press the fire button to start the game it starts and works fine. Until I lose my last guy and then it fizzles out instantly. Also when I get to the space warp stage sometimes the circle that the ships spin out from will be on the left side of the screen but the ships still appear from the correct spot. Just hoping these clues might be something that someone has encountered(and fixed) before. I still don't know if that other regulator I mentioned in my other post could be connected to this problem in any way. I honestly don't even know that's what it is but it looks like the one I replaced that is hooked to the heatsink.

[+xucaen]

Let me ask you this - how are you cleaning the cartridge slot and the cartridges?

[juggalot]

I use rubbing alcohol on both with q-tips on the games and a credit card wrapped in a cloth for the cart slot. Is there something else that would work better?

[juggalot]

Well what I thought was another regulator was actually a transister(MJE 210 9 737). The store I went to didnt have the same one so they gave me the closest thing to it. Ill attach a picture of it. Does anyone know if it will work. I dont know if it will fix my problem so I will use it as a last resort. I bought a 7800 game yesterday to try and it wouldnt work at all. Just lines rolling up the screen. I also bought a DK Jr. 2600 and it worked until I got to the electric level and then fizzled out. I tried it a couple times with the same result. Unless someone has a another suggestion Ill be reflowing the whole board today. Im going to call Best Electronics also to see if they have any suggestions for me.

[+-^CrossBow^-]

The MJE 210 is part of the power on power off cycle process and wouldn't really be related to the crashes you are getting I don't believe. It sounds like to me the issue is likely be one of the main logic chips. I say this because you can't get 7800 games to start at all, but you can at least get a 2600 to start. The 7800 always starts up in 7800 mode first and then when it doesn't find the info it needs for a 7800 game, the system switches over to 2600 mode. It is at least doing that much.

 

I think there is either some faulty ram on the 7800 or possibly a power issue. About how long does it take time wise when playing a 2600 game for it to fizzle as you say? And to be clear exactly what happens again when it fizzles out?

[juggalot]

when I put the game in and turn it on if I dont push reset/start within a few seconds itll do it but if I do start the game it will get to a certain part of the game(same part every time). On gorf it will go until I lose my last guy and then do it. On Donkey Kong Jr it does it when I get to the electric stage where the sparks circle around and you have to jump and avoid them. It usually just makes a low rumbling like noise that is descending for a second or two and then no sound. Ill try to make a video and see if I can post it.

[juggalot]

Ok I got two videos. the first is playing Gorf and its fine if I push start/reset right away until I lose my last guy and then it goes to crap. Then if I turn it off and back on I have to push start real quick and itll work again otherwise itll do it again right away. The second video is Donkey Kong Jr. and with that game I can wait as long as I want to push start and it works fine until I get to the electric screen.Then it does the same thing as before on Gorf. Hopefully seeing it will be better than me trying to explain it. I tried reflowing some of the solder points that looked bad but no difference. .....Ok nevermind it wouldnt let me upload the videos so Im trying to put them on youtube then Ill try to add a link.

There they are. Hopefully this will work. Ive never done it before.

[+Stephen Moss]

Some 7800's have a built in game, what happens when you turn the power on with no cartridge inserted?

If you have access to a multimeter what are the voltages at the input and output pins of the 7805 regulator and the system reset (pins, pin 13 of U10, 4013, pin 40 of U2, 6523, pin 34 of U9, 6532 and pin 1 of U11, 74LS174) with Gorf inserted and power brick connect when...

1) The console is off

2) The console is on and the game playing normally

3) When it goes wrong after loosing your last life

 

Also, in the video the reset button had no effect once things had gone wrong therefore I would like to know...

a) does the reset button function correctly while the game it is playing correct or does pressing it create the same problem as loosing your last life?

b) when Gorf fails after loosing you last life does is restart normally after a system reset? You will need to temporally connect a 100 - 200 Ohm between pins 13 and 7 of U10 to force a system reset while the unit is on, just hold the resistor there for a second then remove it to release the reset.

 

You have already stated you cleaned the carts and connect, have a look at the cart socket for any damaged contacts and try reflowing the solder the connections/looking for and pad-track breaks for the cart socket as either of those could be causing bad cartridge reads.

 

[juggalot]

• Ok it took me awhile to work thru that but here goes. When I turn the system on without a cartridge in I get a bunch of lines so maybe it does have a game on it but doesnt work? If I press the fire button during this I can see part of the lines shift to the right a little and then return when I release the button. These are the voltages you asked for. 7805 IN-with system off-0, running normally-9.95, messed up-10.05. 7805 OUT-with system off-0, running normally-5.14, messed up-5.14. RESET BUTTON-with system off-0, running normally-5.03, messed up-5.07. A. The reset button does work normally while the game is playing. It starts the game over. It doesnt work after its messed up. I have to turn the system off and on to play again. B. I wasnt exactly sure what you meant by "system reset". Is that pushing the reset button, turning the system off and back on, or something else altogether? I didnt have a 100-200 Ohm resister to try what you asked. Would that be kinda like jumping the reset button using a resistor? Once you got to the part in the parenthesis I was pretty much lost.I tried to find some schematics for my particular board with no success and the ones I did find were a little confusing trying to figure out what was what. I can get a resistor today if that will help narrow the problem down. Theres a couple more things I wanted to mention.In the other picture Youll see it looks like someone drilled a tiny hole to break a trace. I figured this was because they wanted to make that connection with the resistor thats soldered to the leg of the chip in the first set of pictures I posted but I wasnt positive. And finally I went to clean my 7800 Pole Position 2 cartridge to try it again and I figured out that the edges had been broke off by someone. Probably trying to get it to fit into a 2600. I didnt realize it before because thats the only 7800 cart I have so I thought it was supposed to be that way. Im going to try to find another one right now so I can see how the system works with a good 7800 cart. Ill grab one of them resistors while Im out as well. Thanks for your help. It is greatly appreciated. Hopefully I wont have to buy another Atari 7800 but I will if all else fails.

Edited January 18, 2017 by juggalot

[+xucaen]

I just wanted to comment that only consoles released in Europe had a game built in - Asteroids. If you have a North American console, it doesn't have a game built in.

[+-^CrossBow^-]

Looks to me that there is an issue with the TIA once things get warmed up. Will be more confirmed once he can get an actual 7800 cart in there to play since I believe the TIA or most of the TIA functions are shut off while in 7800 Maria mode.

[juggalot]

I actually got another 7800 cart today and it seemed to work ok except I dont think the cart slot is big enough. That may be part of my problem. When I got it in enough for the system to read it I could die and it wouldnt mess up like it was before. The game is Kareteka. I dont know if that cart is supposed to fit tight or what but I dont think I got it in far enough for the system to read it properly. Im getting ready to bust out the dremmel and loosen it up a bit and Ill let you know how it goes after that. If I do have a problem with the TIA can I get a replacement somewhere or do they only come with the 7800s?

[juggalot]

ok its not working too good after all. I still need to cut a little more into the slot. I just dont want to go too far and nick something on the board.

[juggalot]

Time to give up for the day. Im starting to get frustrated. Wasted most of the day trying to figure this thing out. Im thinking I might be better off looking for another one on ebay or somewhere. Maybe Ill be refreshed in the morning and ready to continue searching for an answer. After messing with the Karateka cart in the slot for awhile I was able to finally get a clean screen but the sound started skipping(for lack of a better word) and gameplay stuttering as well.

[+Stephen Moss]

 

• Ok it took me awhile to work thru that but here goes. When I turn the system on without a cartridge in I get a bunch of lines so maybe it does have a game on it but doesnt work? If I press the fire button during this I can see part of the lines shift to the right a little and then return when I release the button. These are the voltages you asked for. 7805 IN-with system off-0, running normally-9.95, messed up-10.05. 7805 OUT-with system off-0, running normally-5.14, messed up-5.14. RESET BUTTON-with system off-0, running normally-5.03, messed up-5.07. A. The reset button does work normally while the game is playing. It starts the game over. It doesnt work after its messed up. I have to turn the system off and on to play again. B. I wasnt exactly sure what you meant by "system reset". Is that pushing the reset button, turning the system off and back on, or something else altogether? I didnt have a 100-200 Ohm resister to try what you asked. Would that be kinda like jumping the reset button using a resistor? Once you got to the part in the parenthesis I was pretty much lost.I tried to find some schematics for my particular board with no success and the ones I did find were a little confusing trying to figure out what was what. I can get a resistor today if that will help narrow the problem down. Theres a couple more things I wanted to mention.In the other picture Youll see it looks like someone drilled a tiny hole to break a trace. I figured this was because they wanted to make that connection with the resistor thats soldered to the leg of the chip in the first set of pictures I posted but I wasnt positive. And finally I went to clean my 7800 Pole Position 2 cartridge to try it again and I figured out that the edges had been broke off by someone. Probably trying to get it to fit into a 2600. I didnt realize it before because thats the only 7800 cart I have so I thought it was supposed to be that way. Im going to try to find another one right now so I can see how the system works with a good 7800 cart. Ill grab one of them resistors while Im out as well. Thanks for your help. It is greatly appreciated. Hopefully I wont have to buy another Atari 7800 but I will if all else fails.

 

 

So from that I think we can say with reasonable certainty that nothing is consuming more power than it should and thus getting rather toasty as the output from the 7805 is as is should be when the problem occurs as opposed to having gone into thermal shutdown.

 

The reset button resets the game presumably by either clearing the program counter or jumping to a specific address, as the reset button did not function correctly once you had lost your lives I was curious to see what effect a system reset would have while retaining the data that was in the system which is why you have to try and pull the reset line down with a resistor to trigger a system reset without turning it off.

The system reset is connected to...

pin 13 of U10, a 4013

pin 40 of U2, a 6523

pin 34 of U9, a 6532 and

pin 1 of U11, a 74LS174

I wanted you to check these just in case there was a problem and some of them were being incorrectly reset.

 

Normally you would break a track but cutting it in two places and removing the section between the cuts rather than drilling a hole, if you want to know if that is related to the resistor just see if the resistor is connected to one or both ends of the broken track in the image.