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Atari 2600 black screen issue

atari 2600

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#1 d_a_parker OFFLINE  

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Posted Wed May 15, 2019 10:55 AM

Hello,

 

I have a later-model Atari 2600 "Darth Vader" with a rev. 16 board.  It worked fine a few years ago.  But now when I power it on, with or without a cartridge, I just get a blank screen with a colored line down each side.  It's a similar problem to the one posted here, but on a different model 2600:

 

http://atariage.com/...h-black-screen/

 

I checked the voltage regulator and it has ~9V in and ~5V out, so that seems fine.  The power switch looked fine, but I cleaned it anyway.  I also cleaned the contacts in the cartridge slot as best I could.  I checked the three main chips (TIA, CPU, and RIOT) and none of them feel hot while the unit is powered on.

 

Unfortunately, the chips are soldered onto the board instead of in sockets, so it's not a simple task to swap them out.  With that in mind, is there anything else I can check and/or do to try and fix this system?  I've never worked on a 2600 before, so I'm not exactly sure where to go from here.

 

And if it's dead,  I'll just need to be ok with that.  :-)

 

Thanks!



#2 Stephen Moss OFFLINE  

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Posted Thu May 16, 2019 1:09 AM

Someone has just posted the service manual, you may find something in there that will help.

For me the first three things to check in a digital system in order are...

Power: If something in not getting the correct voltage it won't work so check power is getting to all the supply (Vcc & Vss) pins of the IC's, you can measure the Vcc voltage but for Vss you may be better switching off and measuring continuity to the ground pin of the regulator.

Reset: If a device is held in reset it will not function (Reset = 0V)

Clock Oscillator: If the clock is not getting to all the relevant IC's (I think relevant pins are labelled OSC, 00 & 02), no digital system will work without it, not easy with a multi-meter but anything other then a fixed 0V or 5V should be ok.  



#3 d_a_parker OFFLINE  

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Posted Thu May 16, 2019 8:19 AM

Thank you for the information.  I tested the chips and they seem fine, as far as I can tell:

  • Vcc is ~5V on each chip
  • Vss has continuity to ground on each chip
  • Reset is ~5V on the CPU and RIOT (I didn't see a reset pin in the diagrams I found for the TIA)
  • Clock is ~1.8V on the RIOT (I didn't see a clock pin in the diagrams I found for the TIA and CPU)

(EDIT: I missed the fact that the TIA does have an OSC pin, which is holding at ~1.5V)

 

Based on these simple tests, it looks like the correct voltages are getting to the ICs.  Is there something else I can check?

 

I looked for the service manual, but I only found the one for the six-switch VCS with an earlier board revision.  Does anyone know if there is one available for the later model 2600 with the rev. 16 board?

 

Thanks!


Edited by d_a_parker, Thu May 16, 2019 8:24 AM.


#4 d_a_parker OFFLINE  

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Posted Thu May 16, 2019 10:10 AM

I found the correct service manual, and followed through the "Black or Solid Colored Screen Troubleshooting" flow chart (J).  I got as far as this step:

 

Is 4-5v p-p osc. signal present on pin 11 A201?

 

That's the OSC pin on the TIA, and I only have 1.5V on that pin when measured with a multimeter.  So if the answer is "no" then the flow chart goes on to say:

 

Open between C203 and pin 11 A201.

 

Which leads to:

 

Repair

 

I'm afraid I don't know what an "open between C203 and pin 11 A201" means, nor do I know how to repair it.  Does anyone have any advice?

 

Thanks!



#5 alex_79 OFFLINE  

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Posted Thu May 16, 2019 10:49 AM

Is 4-5v p-p osc. signal present on pin 11 A201?
 
That's the OSC pin on the TIA, and I only have 1.5V on that pin when measured with a multimeter. 

[...]

You can't measure oscillating signals with a multimeter, you need an oscilloscope for that.
"p-p" means "peak to peak"

http://www.hobbyproj...asurements.html



#6 d_a_parker OFFLINE  

d_a_parker

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Posted Thu May 16, 2019 11:14 AM

Thanks!  I didn't know that, but now it makes a lot more sense.  Unfortunately, I don't have an oscilloscope to check this with.  Dang.



#7 ChildOfCv OFFLINE  

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Posted Thu May 16, 2019 11:45 AM

Still, an inbetween voltage is suggestive that the clock signal is working.  If the multimeter has a frequency mode, you can also get a readout of the frequency (who knew?).



#8 DrVenkman OFFLINE  

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Posted Thu May 16, 2019 12:32 PM

Still, an inbetween voltage is suggestive that the clock signal is working.  If the multimeter has a frequency mode, you can also get a readout of the frequency (who knew?).

 

Assuming the meter can read a clock signal that fast (not a guarantee - most are only intended to read AC wall current of 50 - 60 Hz).  ;)

 

The full Field Service Manual, covering all 6- and 4-switch models (excluding Juniors) is here:

 

http://www.atarimani...vice_Manual.pdf

 

The FSM has detailed symptom-based troubleshooting flowcharts. Some of the tests are intended to be run with a diagnostic cart and test plugs that connect to the joystick ports but you can usually work around that limitation with a meter and some common sense. :) 



#9 ChildOfCv OFFLINE  

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Posted Thu May 16, 2019 2:22 PM

 

Assuming the meter can read a clock signal that fast (not a guarantee - most are only intended to read AC wall current of 50 - 60 Hz).  ;)

 

Well, in frequency mode, many can count up to 19.9MHz, which is plenty good for an Atari.  The "poor-man's" method of measuring the voltage is done in DC mode, and you just get whatever the meter sees as the average voltage from its ups and downs.  In AC mode you won't see an accurate depiction of Vp-p, but it should still be greater than zero.  But in the end, a scope is still the best indicator since you can also tell if the signal is weak or deformed.



#10 d_a_parker OFFLINE  

d_a_parker

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Posted Fri May 17, 2019 8:52 PM

Unfortunately, I don't have access to an oscilloscope right now so I can't do the proper checks on this thing. I have a multimeter with a frequency setting, though. When testing these points for voltage I get a non-zero reading somewhere between 1v and 2v. When I test for frequency, I get a seemingly random value each time, which quickly falls to zero within a few seconds.

Any thoughts or ideas on where to go from here are much appreciated. I'm going to try to borrow a scope next week if possible, but I'm not sure I'll be able to.

Thanks!

#11 ChildOfCv OFFLINE  

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Posted Fri May 17, 2019 9:34 PM

That is strange.  You have the black probe on a ground point somewhere and the red probe on a clock pin, and you don't get a stable count?



#12 d_a_parker OFFLINE  

d_a_parker

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Posted Yesterday, 8:03 PM

I just realized that my multimeter only measures up to 20 KHz (not 20 MHz), so I think the problem here is that the clock frequency on the 2600 is out of range. I need to get a scope.

But the voltage on the various clock points seems fine (it's not a solid 0V or 5V). Assuming the clock is okay, what else could it be? The ICs all have good voltage going to them, the voltage regulator is working fine, and the switches are clean. Could one of the chips have gone bad?

Thanks!





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