Black Screen of death

[alortegac]

Hello forum.

I recently purchased a broken 7800. It came in with a 16v adapter with the wires spliced and taped to the original 7800 connector end. That is the only history.

 

It turns on to a black screen and silence, 2600 or 7800 game same. Screen is gray if I turn on without a game inserted, sometimes some machine noise.

 

I already replaced mj210, checked 7805 and replaced rf module. I think something is shorting somewhere or a bad chip..4013?

 

Any ideas?? Where to start? Please help, thanks in advance.

Edited February 20, 2016 by alortegac

[alortegac]

Is it time to start thinking about the recycle bin? Maybe the cartridge slot...I tried cleaning the pins but no luck.....

Edited February 20, 2016 by alortegac

[gorfcadet]

Have you tried a new adapter?

Are you sure your connection method works? Have you tried it with a different Atari or another system from that era? Not to be insulting, but I'm always surprised to see folks trying to connect to an incompatible flatpanel without the proper gear to adapt the signal.

Good luck.... it can be saved!

[gilsaluki]

Whoa! 16 Volt adapter. Too much. I believe it is 9 volts. Overdrive. Not saying that is what is wrong, just saying.

[alortegac]

I apologize I was not clear in my original posting. I mentioned the adapter because that is the only history I know about this console. I immeadiately threw ithat thing away to my junk bin and I am currently using an Atari 7800 original power adapter 9v 1A.

 

That is why I started by suspecting about issues with components that are part of the on-off - reset circuit such as MJ210 and 7805. I also replaced all swtches, check caps and zenner diodes. I have not replaced the 4013 IC.

 

I replaced the RF module. So it is not it that either.

 

The black and soundless screen is all I get. it does not react to different games or anything. Perhaps a I/O ic?

 

 

Thanks for your help, all ideas are welcome.

 

Alberto

[+Mitch]

Have you gone through the troubleshooting flow chart?

http://atariage.com/forums/topic/216763-7800-theory-of-ops-ts-guide/?p=2830927

 

Mitch

[alortegac]





 

Wow, thank you so much! Let me review it, I never seen it before. I will do my best to try to save this one from the recycler.....

 

Alberto

[alortegac]

I replaced the 4013 IC with no luck. The old one seemed to be working fine, but still I took the chance to see if there was any change. NO change. I read the information provided by Mitch, but I am not an expert in electronics, do not have an oscilloscope and do not have the test cartridge.

 

I checked all the pins mentioned in the diagram with my meter as much I could, they have voltage or toggle. Continuity does not seem to be the issue either, but again I do not know for sure.

 

It looks as if J1 is shorted, broken or does not read the carts. Or 6502C is failure. I noticed 6502C gets hotter in I leave the console "ON" for a couple minutes. It is the only IC that gets hotter. Not sure if normal or abnormal.





These are the screens I am getting randomly including nothing and completely black when press On/Off. The black with static colored snow and buzzing sound is without cart inserted,.

 

I can follow instructions......if someone wants to teach me to trouble shoot. I would appreciate it.

Any other ideas? please feel free.

Thanks!!



Edited February 22, 2016 by alortegac

[Stephen Moss]

The fact that the 6502 is getting hot would suggest that may be the problem however before jumping to conclusions I would check...

Check the output voltage of the 7805

Do a continuity check of J2

Re-solder all the joints of J1 (Cartridge Connector) in case of bad joints.

 

If everything looks ok there check the following...

 

Low = 0 - 0.4V, High = 2.7 - 5V

 

U1 (Maria): Pin 1 = Low, Pin 25 = High, Pin 7 = Clock signal (check with Oscilloscope)

 

U2 (6502): Pins 1 & 21 = Low, Pin 8 = High, Pin 40 = Low (Reset))

 

U8 (TIA): Pin 1 = Low, Pin 20 = High, Pin 11 = Clock signal (check with Oscilloscope)

 

U9: Pin 1 = Low, Pin 20 = High, Pin 34 = Low (Reset)

 

Finally it is my understanding that the 7800 using the MARIA chip for 7800 game graphics and the TIA chip for 2600 game graphics, if you have both 2600 and 7800 cartridges do you get the same result with both? If not that may indicate one or the other as a potential problem.

[alortegac]

Hello Stephen.

 

Thanks for your response.

 

I will do exactly what you are suggesting and report back with findings. Once again, thanks you.

 

Alberto

[alortegac]

Check the output voltage of the 7805 = 4.90 V

Do a continuity check of J2 = Only Pin 1, 9 and 18 continuity with ground.

Re-solder all the joints of J1 (Cartridge Connector) in case of bad joints = Removed, cleaned and re-soldered.

 

Low = 0 - 0.4V, High = 2.7 - 5V

 

U1 (Maria): Pin 1 = Low OK

Pin 25 = High = OK

Pin 7 = Clock signal (check with Oscilloscope) = DO NOT HAVE OSCILLOSCOPE...sorry

 

U2 (6502): Pins 1 & 21 = Low = OK both

Pin 8 = High = OK

Pin 40 = Low (Reset)) = 4.90 V HIGH

 

U8 (TIA): Pin 1 = Low = OK

Pin 20 = High = OK

Pin 11 = Clock signal (check with Oscilloscope) = DO NOT HAVE OSCILLOSCOPE...sorry

 

U9: Pin 1 = Low = OK

Pin 20 = High = OK

Pin 34 = Low (Reset) = OK

 

 

I also checked U12 pin 11 is high (same V as U2 PIN 40) , 12 is high, 13 is low and 7 is low. and U10 pin 13 is HIGH

 

And finally, yes, pretty much same behavior 2600 / 7800 game.

 

thank you so much!

Edited February 25, 2016 by alortegac

[Jinks]

So your reset button is on all the time?

Just a guess...

[Stephen Moss]

Sorry, brain not working, software conditions not withstanding the Reset values should have been high with the unit "On" so Pin 40 of U2 is correct, Pin 34 of U9 is wrong.

 

I am not entirely certain if Pin34 of U9 is an input/output or Both therefore with the unit in its on state check the following...

U10 (4013): Pin 13 = High

U12 (74LS32?): Pins 11, 12 & 14 = High, Pins 7 & 13 Low.

U9 (6532): Pin 24 = High

 

Is U9 socketed for easy removal?

[alortegac]

Hi Again Stephen,

 

U10 (4013): Pin 13 = High = OK

 

U12 (74LS32?): Pins 11, 12 & 14 = High = OK

 

Pins 7 & 13 Low = OK

 

U9 (6532): Pin 24 = High = OK

 

U9 is soldered, I can remove and socket it, but I rather not if I can avoid it.

 

U12 is KS74HCTLS32N

 

U13 is KS74HCTLS174N

 

 

Thanks for your help!

Edited February 26, 2016 by alortegac

[Stephen Moss]

Everything looks ok then in regards to any problem with Reset switch and in general with the system reset line.

The output at pin 11 of U12 should go to the Reset pin of U9 (Pin34) which you previously reported as being low. With the unit in the on state check Pin 11 of U12 and Pin 34 of U9 again.

 

If pin 11 of U12 is High pin 34 of U9 should also be High, however if it is still Low as previously reported that would keep U9 in reset which is probably the main cause of your problem. The most likely causes are a bad joint at pin 34 of U9 (re-solder it) or a break in the track linking pin 11 of U12 to pin 34 of U9 (do a continuity check to confirm).

[alortegac]

Hi again.,

 

 

With the unit in the on state check Pin 11 of U12 and Pin 34 of U9 again = BOTH ARE HIGH. ( I must have made a mistake, my apologies).

 

I rechecked all other readings again,....all are correct.

Edited February 26, 2016 by alortegac

[alortegac]

I carefully removed U9, socketed and swapped with a fresh one I had in my box. Still the same issue, no change. thanks

Edited February 27, 2016 by alortegac

[Stephen Moss]

Damn, I hoped that would be the problem, as it is not I am not certain how much more I can help as I don't know enough about how the 7800 works. If I had a copy of the service manual that may help but as the fault diagnosis section probably refers to tests requiring a test cart and Oscilloscope I doubt I could find comparable tests that could be done without them.

 

Presumably with the unit on U2 (6502) is still getting hot as you mentioned earlier.

I would not expect it to do so but if you have another 7800 you can check against to be sure that it should not be doing so.

 

Assuming that it should not be getting warm try connecting a wire to both pins 7 & 8 of U10 (4013) to keep the unit in reset and turn the power on, does the 6502 still get warm? Try both with and without a cartridge inserted.

[alortegac]

Thanks Stephen for your response.

 

I know., I am sorry for my mistake in the reading of that pin. It is not an excuse, but some pins are coated with some sort of clear resin that prevents good contact with the meter . I noticed it when I removed/replaced U9. I will keep this in mind.

 

In any case, yes, 6502 still gets HOT (really hot after few minutes of operation). I have a new 6502 sally coming in the mail in the next few days. I will carefully replace the original with this fresh one.

 

In the meantime, I will conduct the test you are suggesting and report back. As a note, one of the first things I tried was I replacing 4013 with a new one, so this IC should be ok. I will review the board again for any cold joints.

 

thanks!!

Edited March 2, 2016 by alortegac

[alortegac]

I did the test, this is what I found.

 

There is definitely something wrong with this board. If I get pins 7 - 8 bridged, there was only a slight difference in temperature gain in U2 (still warmer than the rest of the IC's). I could not tell exactly how much, but if feels just a bit less hot or getting hotter a lower rate. The screen was not longer black, it was totally blank - gone. An interesting thing happened while I was doing the test WITHOUT game; I noticed some tilting in the brightness of the led. I removed the bridge in U10 and tested again. I noticed same thing WITHOUT game, tilting and sometimes even turning light off completely. I measured voltage....I was only getting from 3.5V then sharply declining to 2.3 V in the LED. I then checked power supply with 10.3+V, so it is ok. I then checked the 7805, it was only getting 2.8 declining to lower voltage over time, again only without a cartridge. I let it cool off and I tried it with a cartridge and I was getting only 4.5V and declining over time. I thought I had fried the 7805 or something, so I replaced it with a new one. Voltage going from strong +4.90 V going down to 2.8V or lower when I power the console without GAME. Unless you think differently, I think U2 is shorting somewhere or internally.

 

thanks for your help!

Edited March 3, 2016 by alortegac

[Stephen Moss]

The purpose of forcing a reset and testing was to try and determine if the heating in U2 was caused by one of the IC's connected to it Address or Data bus.

Although it is not a conclusive test as I am relying on the assumption that while in Reset the in I/O pins of the 6502 are either input, output low or in a tristate condition as the data sheet I read were not entirely clear on the matter.

 

It is looking like it is probably an internal short on U2 but you will only know for certain when you replace it, if the new one has the same problem then you will have to look at the devices attached to it for which a current probe would be useful but unfortunately are neither cheap or readily available.

[alortegac]

Hello Stephen.

 

It took me a few days to receive the new 6502C IC in the mail. Bad news to report. After carefully replacing the 6502, the problem is still present, no major change. The only difference is I no longer see the voltage drops or hotter 6502, but depending on the game inserted I am still getting static, noise, black screen or blank screen same as before. (however I did not keep the unit ON for long time, I fear on damaging 6502 again). The board must have a short or a bad part somewhere else.

 

At this point, I would want to summarized the parts I have replaced to decide on what to do next:

1.- Initial unit operation test. Unit turns on, but getting black screen, etc. Clean board, examine for cold joints.

2.- Replace rusted RF module with AV Composite output. (no change, only getting exact same black screen/sound without snow)

3.- Replace all 4 momentary switches

4.- Replace U10

5.- Replace MJ210

6.- Replace 7805

7.- Remove, clean and re-soldered J1.

8.- Replace U9

9.- Replace U2

10.- Replace U3

 

 

 

I have spare parts for everything other than U1, U5,U6, U7. I think I can get them all in the mail but U1 which is hard to find. Should I remove U8 next? I can test it in a Atari 2600 socketed board....

 

By the way, I managed to get another working 7800 board for testing. I just do not know what to test.

 

As always, you assistance is greatly appreciated! thanks!!

 

Alberto

Edited March 8, 2016 by alortegac

[alortegac]

Update 9:50 pm.

11.- Replace U8 TIA.

 

 

Nope,. NO CHANGE....SAME BLACK SCREEN OF DEATH,

[+-^CrossBow^-]

Have you replaced the RIOT 6532? Though I have personally tested and without the chip 7800 games will still fire up.

[alortegac]

Thanks Cross Bow, Yes, I replaced U9 6532 with a new IC. (Action #8 on my listing).

 

I just noticed my other working board has the MARIA U1 socketed......(which is not common I think). My next action will be to remove U1 MARIA from the non WORKING board and test it in the working board. Then will socket it. I am waiting for the sockets to come in the mail.

 

In the meantime, I will start by checking CR6, CR4, CR3, CR6, CR7, CR13 diodes, R2 through R26 and C7 through C16. This is just kind of random....somewhat by looking the schematics and because when I bought this console they were using a 16v Adapter.... I will try to compare voltage values with the working board with the same game inserted in both boards.

 

I am afraid to keep the unit ON as the new custom IC's U8 and U2 may get damaged. So I will use the old ones for this testing.

 

My hypothesis is this board must have a short somewhere. I admit my approach probably does not make sense to people that really know what to do in this cases......I am not an expert in the field........ I am just pissed off at this board...........I appreciate any help I can get.

 

thanks!!