Video Problem / RIOT?

[Grover Torbel]

I bought a fairly inexpensive "working/tested" Atari 2600 light sixer that was shipped to me.  When it arrived, the box was crushed, but the 2600 was visually unharmed.  When I hooked it up, the picture was badly distorted and in B/W, but it appeared that the games were functioning and sound worked.  After trying several different aged TVs, I inspected the board visually, reseated chips, reflowed power connection, etc., but nothing changed.  I guessed that the RF circuitry could be the culprit and thought it could be a good candidate for a composite mod.  Composite mod was relatively simple, but once completed, the 2600 still had the same exact same display problem even though it was now via a composite connection.  Do you think this could be an issue with the RIOT chip?  I've heard they are most prone to failure, but am not certain if the RIOT (6532) chip would cause this problem.  For reference, I've attached a photo and brief video of the distorted screen with a combat cartridge in the system.  Any thoughts?

Edited June 28, 2019 by Grover Torbel
Correct typos

[+DrVenkman]

I doubt that's the RIOT. TIA produces a video signal. Since all Sixers are socketed, try swapping it out. 

[ChildOfCv]

Looks like it's not getting the sync pulse.  Does the heavy sixer have the output buffer chip?  If so, that's also a suspect.  No sync, no color either (it doesn't know when to look for the color burst).

[+DrVenkman]

52 minutes ago, ChildOfCv said:

Looks like it's not getting the sync pulse.  Does the heavy sixer have the output buffer chip?  If so, that's also a suspect.  No sync, no color either (it doesn't know when to look for the color burst).

Yes, a Light Sixer has a 4050 but that IC is not socketed. 

[Grover Torbel]

Since I do not have any spare TIA chips, I tore open a working Vader that I hoped was socketed.  No socketed chips.  ☹️

 

Anyone have a spare TIA you like to sell?  Looks like I can get one from Best Electronics, but I'd hate to spend $25 plus shipping just to test.

 

Just for grins, I reflowed the 4050, but there was no change to output.  I'm certainly willing to desolder the 4050 and replace with a socket and new chip if you think that's the root cause.  I'd like to get the light sixer running, but don't want to spend more in repairs than I would for a working light sixer on eBay.

 

Canyon Bomber and Combat both seem to work, but exhibit the display corruption.  Centipede does not seem to work at all (no display and no sound).  All carts are known good working in the Vader.  

 

 

Edited June 29, 2019 by Grover Torbel
Additional Information Added

[+DrVenkman]

Yeah, I gather most Vaders are fully soldered (mine is too - I had to remove a dead RIOT and install a socket and a new chip one a few years back). 

 

As for the 4050, at least these are commodity chips still made today - you can buy then for a few dimes each at any electronics site or the EvilBay. Worth a try at least.

 

New TIA's have gotten stupid-expensive lately from BEST. I guess Brad is running low. Good thing is you can probably pick up a used junky 4-switch for next to nothing if you look around and aren't too picky. Most of the chips inside will likely be fine. Woody's are all socketed, as are other Sixers, and the three main chips are all interchangeable (Woody's don't have 4050 buffer chips however).

[ChildOfCv]

Well, the 4050 is cheaper than a TIA if you don't already have a known good one to test with, so it wouldn't hurt to replace it now and look for a new TIA if it doesn't fix the issue.

 

[Grover Torbel]

4050 desoldered and waiting on sockets and new 4050 chips.  ?

[Grover Torbel]

Well, the 4050 chip is now replaced with a brand new TI chip that is resting happily in its new socket.  Sadly, there is literally no change in the video.  There is a "working" 4-switch woody on its way that should provide a TIA to swap for testing.  Hopefully I'll know more next week when the 4-switch 2600 arrives.  

 

PS: I can't believe the price of TIAs. It was actually less expensive to buy a whole working 4-switch woody than to buy an individual TIA chip.  

[Grover Torbel]

Received the donor light sixer and did a quick test swap of the TIA.  Perfect video!  Now I just need to find a working TIA and I'll have two working light sixers, one composite modded and one original. ?

[+DrVenkman]

10 hours ago, Grover Torbel said:

Received the donor light sixer and did a quick test swap of the TIA.  Perfect video!  Now I just need to find a working TIA and I'll have two working light sixers, one composite modded and one original. ?

Glad I was right.  

 

I don’t know where you live, but it’s a good idea to pick up a cheap 2600 locally and use it as a donor board. If you are comfortable desoldering chips, you can generally get Vaders and Juniors pretty cheaply. 

[Grover Torbel]

I'm very comfortable with desoldering, but hate to destroy any working Atari console. I'll probably just bite the bullet and buy a new chip from Brad at Best Electronics. ?

[Osgeld]

I might have a TIA kicking around

[Osgeld]

looks like I got 2 TIA's sitting in the parts drawer if your interested I am sure we can work something out less than 25 bucks

[Grover Torbel]

looks like I got 2 TIA's sitting in the parts drawer if your interested I am sure we can work something out less than 25 bucks

Just realized that I may have never told you, but the TIA fixed the problem. Working 2600 now. [emoji106]

[Osgeld]

Super

[+-^CrossBow^-]

Good to see a replacement TIA fix his issue...bad that yet another TIA has died with age...

[ZaxxonZaxxoff]

I'm having the exact same issue with mine (distorted video, sometimes sound, sometimes not) and while testing I noticed my RIOT chip was SUPER hot. Like Soldering-iron, can't-even-touch-it hot. The other chips stay room temperature.

[Osgeld]

riot chips are exposed directly to the real world though the cart slot and joystick ports and thus make them prone

 

in my limited sampling of only 100ish dead atari's I actually find dead

 

1. No Problem Found / user error / dirty contacts 
2. CPU
3. RIOT
4. TIA

 

and I do not think I have ever found a machine with 2 chips dead at once from the wild unopened, but its 1970's tech luck will vary 

Edited March 12, 2020 by Osgeld

[+DrVenkman]

On 3/11/2020 at 11:15 PM, Osgeld said:

riot chips are exposed directly to the real world...

The RIOT also reads the Select, Reset, Color/BW and difficulty switches. In you touch one of those in dry conditions, static discharge can be conducted straight into the chip and damaging it. In fact, there’s even a recommended mod in the Atari Field Service Manual to add a Zener diode to prevent static shocks. I’ve run into at least 2 different 4-switch machines with RIOT chips that would not properly read one of the two difficulty switches. Swapping the chip fixed the issue.

 

One of those same machines had a dead TIA too - colors were all messed up and wrong for every game I played. Probably zapped by whatever damaged the RIOT chip.