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Atari 2600 rev 16 intriguing issue


alortegac
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Looking for some ideas on where to start trouble shooting. This Atari works well except when pressing fire button. The fire is out of timing, goes in reverse direction, goes in parabole or dissapears and re-appears from the screen. Some games like Combat work fine, but others have this issue. For example, sea quest, river raid.... Very weird behavior.

 

Swapping chips is not easy as they are soldered, need to try to pin point more carefully to avoid excess disoldering or ic damage.

 

Any ideas? Thanks for your help!!!!

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Based on only a conceptual understanding of the hardware, I'm guessing that the various games having a problem use the same TIA programming object (Missile, Ball, player, etc.) to render the thing you describe as going in reverse, disappearing, etc. In some cases, the thing being fired could the ball object, sometimes the missile, could be a player object. Just depends on how it was programmed.

 

Again, I'm just guessing but if my guess above is correct there could be a problem with the TIA, one of the three bigger chips.

 

Are even the biggest chips soldered in without a socket? If they have sockets, I'd try to re-seat them (pry them up slightly then push back into their sockets) just because that's a cheap thing to do that can sometimes fix problems in electronic equipment. If feasible, I'd swap out the TIA chip with a known good one.

 

If experience is any indication, someone who really, really knows the hardware and programming inside and out will be along shortly to explain why I'm incorrect. :)

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Sounds like a bad 6532 RIOT to me, but I suggest you google up a copy of the Atari VCS Field Service Manual and dig through the symptom troubleshooting flowchart. But at first blush I'd think either TIA or the 6532 (RIOT) chips. I have a new to me Vader with a soldered Rev 16 board as well - serious pain in the ass compared to working on a Woody.

 

 

Sent from my iPhone using Tapatalk

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Thank you for your responses and assistance. I agree with both of you. I suspected TIA or RIOT too. Unfortunately, I do not have oscilloscope or the testing plugs/cartridge. I could not find reference to this problem in the manual.


I mentioned REV 16 because this one has an IC55 Clock that the others do not. Could this IC affecting this behavior? This is an 8 pin chip that I can more easily change...but I wanted to know if this could be even related before doing anything. Swapping chips here is a major pain w/ higher risk of damaging them. They seem to be well soldered both ends, very hard to de-soldering a 40 PIN.


I posted some pictures to show you....Seaquest game...logic of the game is ok, except for shooting which is a constant forward line that goes from side to side of the screen in a loop following the sub until I press the fire button...then fire shoots come out from behind the sub in a constant line too. The normal game shoots forward and intermittent lines.





IMG 0866


IMG 0856


IMG 0859


IMG 0857


Edited by alortegac
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Behavior changes when you hit the fire button, so it's recognizing it the button press, as opposed to it appearing to be stuck. I'm still leaning toward the TIA.

 

You're right, desoldering a 40 pin chip that you want to preserve from a board that you want to preserve can be a pain with just basic tools.

 

I have a cheap desoldering tool that I would attempt that with, but I'd realistically expect that I might damage the chip. I have, however, pulled such chips with this tool and a soldering iron to heat the pin from the other side of the two sided board. Pretty easy to burn something up this way, including one's fingers.

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Looking for some ideas on where to start trouble shooting. This Atari works well except when pressing fire button. The fire is out of timing, goes in reverse direction, goes in parabole or dissapears and re-appears from the screen. Some games like Combat work fine, but others have this issue. For example, sea quest, river raid.... Very weird behavior.

 

Swapping chips is not easy as they are soldered, need to try to pin point more carefully to avoid excess disoldering or ic damage.

 

Any ideas? Thanks for your help!!!!

It may not be the system itself causing the issue, it could be the cartridge or maybe the connector on both the console and the games could need a thorough cleaning, and if you clean the cartridge connector of the system itself, you had best clean the connectors of all the games as well or you will just put all the dirt you just cleaned out of the system right back again. This is what I do every time I get in a new batch of cartridges, I clean THEM and the system prior to testing. I also as a precaution clean my Atari and games after every 40 to 60 hours of playing time just to be sure.

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BigO, thanks for your input. I agree with you. It looks TIA is the best place to start. I have tried to de-solder 40 pin sockets and IC in the past.....to tell you the truth must of them got destroyed in the process trying to preserve the board. So I think this TIA is doomed:)...I will need to get a replacement one. I will get it socketed too.

 

RichG1972, thanks for your input too., I carefully checked the cartridge port with a magnifying glass to make sure all pins are present and clean. This console has seen very little use, it is like new. You are totally right about issues like this one can be caused by contamination of the game or the port. I had a situation once when inserting a particular game the screen would black out immediately. A piece of soldering somehow got attached to the game shorting 2 pins......I was about to throw the game away after multiple cleaning attempts with a qtip with alcohol when I thought about checking the pins with a magnifying glass, I just removed the debri with pliers and problem solved. But it could have caused serious damage.

 

Stay tuned please, all ideas are welcome. I will get try to get to the bottom of the issue and report back, maybe helpful to others. I was also thinking about posting pictures of other TIA failures. I have 3 defective TIA chips from other consoles I repaired, everyone is a totally different failure mode....weird stuff.....

Edited by alortegac
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I forgot to mention, I did test both LEFT and RIGHT controllers. Both act the exact same way...thus I do not believe is an issue with smaller components in the trigger circuit. It must be a system issue, IC (TIA or RIOT) or cartridge PORT related. The fact that only some games work well seems unusual too. I will review the Cartridge port circuit lines carefully tonight.

 

I am still unsure about this A205 CLOCK IC 55.....I do not even know what it does honestly. Hopefully someone helps me here. I think it has to do with the start up of the system.

Edited by alortegac
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The fact that only some games work well seems unusual too. I will review the Cartridge port circuit lines carefully tonight.

If I understand what little I know about the TIA, I can see why different games might show the problem and others wouldn't. If, for example, the Missile "object" was broken in the TIA, that problem would only show up in a game that used the missile object.

 

The "objects" are separate registers in the hardware so they aren't just concepts or software programming constructs.

 

If you were to somehow find a cross reference of which games used which TIA objects, I'd bet a nickel that you'd find some correlation between the use of a specific TIA object and which games misbehave and which don't.

Just one nickel, though. :)

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Hi, I have been wondering about IC55 A205. May you know what is its function?

 

I checked Stella and was able to almost replicate the issue I am seeing in my console. by using ALT+M. Disable HMOVE. Do not know exactly what this mean.....but I guess it is related to the TIA then.

 

 

See pic. note the horizontal line on the left side of the screen. It also changes when I press fire button.

 

thanks for your response.

 

Seaquest (1983) (Activision) 0033005b

Edited by alortegac
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Hi, I have been wondering about IC55 A205. May you know what is its function?

 

The IC is a 555 timer. It's been quite awhile since I've worked with those.

 

At a quick glance, the way it's configured with no connection to the Discharge pin, it looks like it's meant to run one time at power up rather than oscillating or debouncing/pulse stretching which require a periodic reset.

 

Given that the output is connected to the reset pin of the 6507, I'm assuming that its job is to assert the reset signal for some minimum amount of time after power on.

This would allow sufficient time for the circuitry in the system to stabilize before the CPU starts processing instructions. It could be that one particular part of the system initializes slower than the CPU so this assures that the slower components are ready when the CPU starts talking to them.

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The field service manual: (http://www.atariguide.com/pdfs/atari_2600_vcs_domestic_field_service_manual.pdf) confirms that Rev. 16 and up have this type of circuitry:


"Revisions 16 and up contain the model differences described above; they also include a timer chip (A205) added to the reset circuitry of the MPU chip. This chip eliminates the problem of power-on reset failures."



If there was a problem with the 555, I think your system would be totally flaky like not booting or resetting itself sporadically.

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Final UPDATE ! Problem Solved!! Thank you guys! It was the TIA as we suspected. I carefully removed the old TIA with de-soldering tool very hot, leaving it for few seconds on each pin to suck as much solder as possible from both sides, remove the Chiclet capacitor to be able to use a fat flat screw driver to wiggle the IC out very carefully .. (a pain.)...Then clean with alcohol, installed a 40 pin socket and finally installed a new TIA I bought in EBAY a few days ago.

 

My console works great!

 

Thank you very much to all. I really appreciate it!

 

 

IMG 4137[1]

Edited by alortegac
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Thanks for your help! I used this cheap tool and worked very well. I did it with much care to preserve the board. (the IC was defective to begin with, I am not sure if after all this heat it got totally fried :)). I liked it so much that I also removed the RF module and AV mod the unit as I was at it ... :).

 

Good luck!

Capture

Edited by alortegac
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