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d_a_parker

Atari 2600 black screen issue

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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/forums/topic/207387-broken-atari-2600-with-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!

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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.

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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

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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!

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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.hobbyprojects.com/oscilloscope_tutorial/voltage_measurements.html

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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.

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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?).

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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.atarimania.com/documents/Atari_2600_2600_A_VCS_Domestic_Field_Service_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. :)

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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.

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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!

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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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Well, it could *always* be one of the chips :P

 

The other thread you linked, everybody seemed to think it might be the RIOT chip. That does make some sense.

 

Also, do you see any sign of water damage or bug damage on the board?

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The RIOT chip was the prime suspect in the other thread, but the OP said that it turned out to be the CPU. They did not say how they traced it to the CPU, but in their case the chips were in sockets, so it's possible they just swapped them out until it worked. It's an awful lot of de-soldering/re-soldering for me to go that route, so I was hoping to track down the problematic component before starting any physical work on the board.

 

The board does not seem to have any water damage, bug damage, or corrosion. But the traces are bubbled up. I have found a few posts online (such as this one) which indicate that bubbled traces are not uncommon in systems of that era, and generally do not cause functional problems unless there is also corrosion. That doesn't mean they're not the problem here, but this thing worked a few years ago and I doubt the bubbling is new since then.

 

Thanks!

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Well, I suppose you measure the voltage of one of the address or data lines. If it's somewhere between 0 and 5V and seems unstable, that's a sign that it's "doing stuff". The 2600 is a simple system. I'm pretty sure the CPU is the only chip that drives the address lines at all, and the data lines will be storming in response.

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Sorry for the long delay, I just got the chance to do these tests. I assume the voltages on the address and data pins are measured against the unit's ground (if not, then please ignore these results and correct me).

 

After the unit is powered on, the address and data pins on the CPU have a variety of different voltages, but each pin remains at a certain voltage, with only the occasional 0.01V variation up or down. After the unit has been on for a few minutes, the voltages suddenly change: all of the address pins are at 3.2V, and all of the data pins are at 0.02V. I did these tests with a cartridge in the slot, although I doubt it will be different without one.

 

Any thoughts or ideas are much appreciated!

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I have tested 5 cartridges at random, with the same results every time (black screen). I did not change cartridges during my tests when I measured the address and data lines, though.

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For that matter what are the chances it could be the cartridge slot connector itself? I had an Atari that was giving me a black screen no matter WHAT cartridge I put into it, soon as I turned it on, black screen turned out a good bit of dirt and dust got into the unit by going under the black plastic covering the cartridge connector. Luckily a good few applications of a light spritzing of contact cleaner cured things

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Another thing is, when you LAST used the Atari when it still worked, what kind of TV did you use it with? Was it a traditional CRT type?

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That's a good point about the cartridge slot. I sprayed it with a can of air and cleaned it as best I could with 91% isopropyl and cotton swabs, but it's a very narrow opening and I don't think I really did much. I'll try to get some contact cleaner that I can spray right in there.

 

It was plugged into a CRT each time I used it, and that's what I'm testing with now.

 

Thanks!

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Also if it's not one with rotary tuning dials, sometimes turning it on, and then running the channel scan locks in on the Atari's signal, I'd much rather you not use alcohol on the cartridge slot because it doesn't evaporate as fast as a can of Johnsen's Electronic Cleaner, it works very well for me, MUCH better than the CRC cleaner I used to use. Here is a direct link to it, but you MAY be able to get it locally as well.:

https://www.walmart.com/ip/JOHNSENS-4600-Electronic-Clnr-10-Oz/579422342?wmlspartner=wlpa&selectedSellerId=1148&adid=22222222227000000000&wl0=&wl1=g&wl2=c&wl3=42423897272&wl4=pla-51320962143&wl5=9002215&wl6=&wl7=&wl8=&wl9=pla&wl10=112562587&wl11=online&wl12=579422342&wl13=&veh=sem&gclid=EAIaIQobChMI0_3-17PC4gIVTFqGCh0esABDEAYYASABEgIN5fD_BwE

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Someone recently posted a copy of the field service manual, there is a test procedure flow chart for Black or solid colour screen troubleshooting on page 4-9 (page 53 of the PDF I have) which may help. It does mention p-p voltages for which you need an Oscilloscope but with a multi-meter if you are getting around the 1.8V you measured for the clock or higher presume it is OK.

Unfortunately, I does also mention swapping out parts a lot which is difficult of your don't have them to hand and particularly where the IC's are soldered but following it may at least help narrow down the problem to a specific area thereby limiting the number of parts you would need to swap out.

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Thanks, but I already tried following that flow chart and found that without an oscilloscope, it's not easy. Everything seemed to be ok when measuring voltages with the multimeter, though.

 

I'm going to try cleaning the cartridge slot again. Does anyone have experience with the WD-40 Specialist Contact Cleaner available at Home Depot?

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I usually start cleaning with some 90% or higher isopropyl before moving on to harsher chemicals. I take old credit/debit/gift cards and cut them up to fit the slot width. Wrap around some thick paper (card stock works very well) and soak it with the isopropyl. Then work it in and out of the slot. The card stock is perfect as it's thick enough not to tear when wet, and the surface of it has a little texture to it.

 

If you go the contact cleaner route, just make sure it's safe on plastics and quick drying. That should be noted on the can.

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