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talk of off colors, and noise and other issues , common culprits


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#1 _The Doctor__ OFFLINE  

_The Doctor__

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Posted Wed Apr 10, 2019 10:13 AM

I have seen quite an uptick in folks who either bring for diagnosis or talk about issue on the forums about the color shifting towards green, random glitches all manor of weird behavior.

some continue using the machine to failure. others go down a big rabbit hole to make a fix... many times it after the long drawn out thread you see it was a bad connection or damage from a 'bad power supply' or the same within a power supply...

 

if you see random glitches, off color issues, like... it looks good until it warms up etc... then it shifts noticeably... etc... looks for cold or cracked joints in the power supply and main pcb power rails... I bring this because today yet another person brings me an Atari that has all these issues and lo and behold they tell me of the help received on the forums and no joy....

 

Within minutes I have a known good supply on it ,  not just some spare laying around or ebay purchase... the machine was fine... I had the fellow bring his 'parts' Atari and other 'good' power supply....  and both machine were flakey, the one was dead... but I changed a single chip to bring it to life.... (more on that)

 

In both cases the power was checked via meters, well the meters are too slow to see noise and fluctuations from the power supply, the caps in the Atari do their job and try to clean it up but a variance occurs bringing the voltage seemingly negligibly lower.. but it's a warning folks

 

so he did the swap the chips turn the color pot fix....

 

this solves the problem but not really, it just looks solved and gets you by, but the machine isn't 100% reliable, and the starved current situation affects the machine... it all meters out close enough but no cigar...

 

unless you monitor the machine and keep a power graph over hours you might not see the brown outs, or use a scope you might not see the static, instead you see the color shift or jail bars, maybe a slight banding issue... (remember notes about starved video and choke/cap fixes?)

 

BOTH of his power supplies had hairline cracks and one had an out right cold joint with mechanical contact.. Voltage reads just fine on even my fluke meters... but on a scope... you see static and other issues... I get the whole voltage is voltage argument, and looked at him. I said bear with me, heat up an iron... touched up the power supply joints.... plugged both of his machine in ran the tests... put in the problem software...

and.... rock solid... but the color pots had to be put back to what they were before the monkey business.

 

once done... the colors behaved as they should on any Atari...with clean power and shields on the banding and bars, glitches all gone.

 

He played some games with me... and left happy.... I explained once again the speed at which the DMM samples input, and the smoothing by capacitors lead to slight power and current starvation. The Atari video circuit is very sensitive and shows this as noise and color shift.

 

Don't toss the power supply, just touch it up.. it's easy to fix! it's cheap to fix! Please don't apply the frying glitch you've seen on the 2600 unknowingly to your' 800 series computers...

 

 



#2 _The Doctor__ OFFLINE  

_The Doctor__

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Posted Wed Apr 10, 2019 10:29 AM

A further note, the rebuild-able brick used rivets at the power cord connections, these rivets often need to be soldered to the pcb, they often have cracked or cold or have loosened over time....



#3 _The Doctor__ OFFLINE  

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Posted Wed Apr 10, 2019 11:58 AM

Just went through another power supply, this one sitting in the get to me bin...   weak wire leading into the power supply... moving yielded slight noise and color shift....

cut the wire back and soldered it.. all looks good again...

 

interestingly on the single PAL unit I had access to... the color shift didn't appear as pronounced... not sure why or if it had to do with the display used or what. This might mask the issues for folks in PAL countries a little... but a scope and some wiggling over time should still show up test the power supply under load right after the jack into a computer feeding itself and a power hungry peripheral.

 

I had to replace the regulator in another  brick, it just barely showed as in tolerance on the low side.... I nice strong replacement brought the supply up to snuff. The sio2sd is much happier as well.  I'm done with today's marathon.

 

I will get the back log out of the way for a more important project.. A member has provided me with a nice pcb a little while ago, I have some parts on the way. It should be interesting.



#4 ChildOfCv OFFLINE  

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Posted Wed Apr 10, 2019 9:27 PM

It may be in the technology.  PAL stands for Phase Alternating Lines, which describes its color modulation philosophy:  Every alternating line begins with either 45 degrees or -45 degrees for the color burst reference, switching every line.  This apparently helps keep the color oscillator in phase.



#5 gs80065xe OFFLINE  

gs80065xe

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Posted Thu Apr 11, 2019 9:41 PM

Some of the color on the restored NTSC 800 I received yesterday looked soft. Some of PAC Mans board lines were dots instead of solid lines. Theyre solid on my 65 XE. Guess I should try another power supply.

Edited by gs80065xe, Thu Apr 11, 2019 9:43 PM.


#6 _The Doctor__ OFFLINE  

_The Doctor__

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Posted Thu Apr 11, 2019 9:48 PM

the 800's power supply is internal, the brick on the outside is just a transformer. solid lines appearing as dots.... I think this one needs pictures.. something seems amiss...



#7 gs80065xe OFFLINE  

gs80065xe

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Posted Sun Apr 14, 2019 5:23 PM

Sorry for the delay. Between work and storms, I haven't had a chance to setup the 800 again. The other thing I noticed is the 800's screen is dimmer. And the Text from the Select/Option screen wasn't as crisp as the 65XE. Both connected to the same TV with the same Composite video cable. Changes cables didn't help.

 

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