Help Troubleshooting Atari board REVB C010433

[Trellot]

Hi all,

 

ISSUE: I have an old Atari 2600 REVB board, for the six-switch console, which outputs nothing, when powered on, to my mid-1990s Panasoncic Omnivision TV/VHS unit.  If I move the main board + switch-board around, while powered on, every so often the screen turns from the channel 2 or 3 solid blue look to a black screen with some buzzing noise from the speakers.  

 

Below are the debug steps I have taken thus far:

• Thoroughly cleaned the main board really well to begin.  (there was some corrosion near the base of the 12-wire harness connections)
  
• Pulled all socketed IC chips from the non-working board and tested them in a known good working unit and found that they all work fine (8021E, R6507, R6532). 
  
• Electrically tested the UA78M05 voltage regulator on the switch board with power plugged in and the power switch turned On: (IN = 7.8volts; OUT = just over 5 volts). NOTE: This switch board works on my known good Atari board but with bad washed out colors; only Black and White seems clear on certain games. 
  
• Electrically tested the power adapter on the main board with power On: (both power points read around 8.10 volts). 
  
• Desoldered the 12-pin wire harness from the board and cleaned up the through-hole area really wetll, then ran continuity on all 12 wires which was good. 
  
• Soldered the harness back on and checked continuity again which was good. 
  
• Re-flowed solder on the on-board power adapter as well; got the same voltage readings of around 8.10 volts. 
  
• Ran continuity checks on a lot of the traces on the back of the board and everything I checked seemed good.  (NOTE: I'm a Noob so this mean nothing  )  
  
• Observation: when power is applied to the board I can feel the chips getting slightly warm so they appear to be getting power.
  
• I'm using the same 9volt AC Adapter on the non-working Atari as on the working Atari.
  

 

At this point I'm not sure what to check.  I've thought about replacing the voltage regulator and the 2200 UF-16V big cap on the switch board but this switch board basically works on my known good Atari board which makes me think the issue is with the main board.  Any suggestions from the community would be greatly appreciated.

 

Thanks in advance,

 

Trellot

[CrossBow]

That input voltage seems rather low to me. I know that back in the day when I used to have a few of the universal power supplies on hand and used to experiment with lowering the voltages in real time, that my 2600 basically would never boot on anything in the 7volt range, but if I turned it on with 9volts to it, and then lowered it to 7 while it was on, it would stay up and barely working, but the colors would be all over the place. So again, the input voltage reads a bit low to me. I realize the 7805 is still outputting +5, but yes, you always start with power first.

[RickR]

That input voltage seems rather low to me. I know that back in the day when I used to have a few of the universal power supplies on hand and used to experiment with lowering the voltages in real time, that my 2600 basically would never boot on anything in the 7volt range, but if I turned it on with 9volts to it, and then lowered it to 7 while it was on, it would stay up and barely working, but the colors would be all over the place. So again, the input voltage reads a bit low to me. I realize the 7805 is still outputting +5, but yes, you always start with power first.

I agree.  If possible, measure the voltage right at the power connector on the board.  If it reads 7.8V there, it is too low.  If it's 9V or above there, let us know...then we would know it's an issue between the power adapter and the 7805. 

[Trellot]

Thanks guys.  I'll get back to you after running the requested test.

 

~ Trellot

[Trellot]

I agree.  If possible, measure the voltage right at the power connector on the board.  If it reads 7.8V there, it is too low.  If it's 9V or above there, let us know...then we would know it's an issue between the power adapter and the 7805. 

So in measuring the power connector on the board with the 9V adapter plugged in I am getting 15.5volts.  With the power button turned on, via the switchboard, I am getting 8.10volts.

 

~ Trellot

[Atari 5200 Guy]

But is the 2600 working with a different power supply in use?  Pictures of the boards would help.

[Trellot]

But is the 2600 working with a different power supply in use?  Pictures of the boards would help.

Unfortunately, I only have the one 9V adapter.  I'll see about uploading pictures of the board.

[Atari 5200 Guy]

Unfortunately, I only have the one 9V adapter.  I'll see about uploading pictures of the board.

Just for clarification, the 8021E is TIA and the 6532 is RIOT. Are these two VCS systems all you have? If so I was going to suggest something but did not know if you were willing to take a gamble. Replace the regulator with the one in your working unit. It would mean taking your working unit apart and desoldering it but in effect you would be able to see if it is the problem or not. Just a thought.

[Trellot]

Hey guys,

 

Any idea on how to upload photos here?  I created a Flickr account but it won't let me post the link.  Sorry for my extreme noobness!

 

Trellot

[Trellot]

Hi All,

 

I'm back at troubleshooting this Atari issue.  I ordered a few replacement parts from Console5:

• 7805 +5v Voltage Regulator 3-Pin TO-220 MC7805ACTG 5v
• 2200uF 16v Axial Nichicon VX Electrolytic Capacitor
• Atari 2600 VCS DC Power Jack

NOTE: I was testing the Atari mainboard/switchboard with a game installed and power applied to simulate a full load to the system, then I remeasured the same points above.  Here's what I got:

• Voltage regulator IN = 7.58v
• Voltage regulator OUT = 4.72v
• Power jack = 7.82v
• I also measured reset Pin-1 on the Micro Processor chip (R6507) and got 4.71v

Once I get the parts I will start with the voltage regulator then go on from there.  But from the numbers above, would anyone know if this should be enough power to boot the board?  Crossbow above mentioned that his board wouldn't power on under anything in the 7v range unless he started high then lowered it.  Also, some material I've consulted suggests that the numbers are too low, below the 1/10th of a volt spread +/-, at least in the case of the VR IC.  I'll update again when I've swapped out the VR.  Should be a few days to a week before I get them due to the Easter break.

 

Thanks,

 

Trellot

Edited March 31, 2018 by Trellot

[RickR]

To upload pictures:  Click the "More Reply Options" below and then you should see attachment options.  This assumes you are using a laptop or desktop computer.

 

Those test voltages you mention are too low.  9V and 5V are what you want. 

[Trellot]

Thanks rickr for your help on the pics, that was easy!

Edited April 1, 2018 by Trellot

[Trellot]

Alright fellas now I'm getting somewhere.  I replaced the 7805 voltage regulator and I'm getting 10-11 volts IN and 5 volts out under a full load.  The power jack also reads 10+ volts under a full load.  What I get now is a completely solid black screen.  Should I check the graphics chip for this?

 

Thanks,

 

Trellot

[RickR]

TIA chip.

[Trellot]

TIA chip.

Ok, I got down to business today.  I broke down my working Atari and started running experiments.  First I tested both Atari switchboards on my working unit  and they both work great now that I replaced that 7805 earlier today.  Second, I went about replacing all three IC chips, one-by-one, from my working unit to my non-working unit.  After each replacement, sadly, I only get the solid black screen.  On a positive note, however, all 6 chips are working since I tested them in my known good Atari. 

 

The only chip I haven't tried swapping is the smaller A203 (4050B) due to it being soldered down.  I've been trying to follow this flowchart from Atari: http://www.atarimania.com/documents/Atari_2600_2600_A_VCS_Domestic_Field_Service_Manual.pdf .  But I'm not sure whether I'm taking some of the requested voltage readings correctly.  For example, it asks to check that Pin-8 of the A203 IC has +5 volts applied, but for me this pin reads 0v...I then did this test on my working board and get the same 0v.  So that confuses me a bit.     

 

So I'm contemplating now whether it's worth it to me to risk damaging my good board by desoldering the A203 and moving it over simply to check?  I'm noobish at soldering but definitely getting better.  Curious if anyone else would do this test?  If not, what would you guys do in this scenario?  Solder reflow on some of the chips, socket replacements?  

 

All suggestions welcome, thanks!

 

Trellot    

Edited April 8, 2018 by Trellot

[RickR]

Me personally, I would not take that risk.  If it were me, I'd stop at this point and leave that console as a donor machine.  If you do need another, they are cheap to buy in working condition.

[Trellot]

Me personally, I would not take that risk.  If it were me, I'd stop at this point and leave that console as a donor machine.  If you do need another, they are cheap to buy in working condition.

Sound advice.  Thanks RickR!  I might try a few more things, but yeah I'll probably leave that chip alone.

 

Trellot