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No picture composite mod.

Composite mod no picture

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#1 SignGuy81 OFFLINE  

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Posted Mon Apr 17, 2017 8:55 PM

I just got done doing a composite mod on an atari 2600 and thought I would go over some issues incase anyone else experiences the same problem I had.

 

 

Instead of getting the parts and doing it myself I figured I'd just buy the kit because it came with everything plus has a nice looking PCB and also it was about as cheap as me getting all the parts separately but here is the mod kit I got http://www.ebay.com/...V0AAOSwnbZYHzc7

 

I bought two of them and will be modding another 2600 to compare and post back the results.

 

Well to start off with I bought a GPX KCLD8886DT under cabinet TV to put at my work bench thinking it would make a good TV to test consoles.  Well I hooked up my atari flashback in thru AV and everything was fine, it looked perfect.  Then I hooked a Vader 2600 to it thru RF and looked normal for RF.

 

I did the mod upgrade with the kit and then I hooked it up to that same TV but this time thru AV since mod was done and sound was perfect but had no picture.  I kept checking around the board looking for loose solder joints then wiggled the wires right near the ground, +5V and video signal where the RF board used to plug into.  The picture came on and looked fine.  I'd turn off the console and start it back and same issue again so then I'm thinking I must have a bad solder joint.  I look at it real close both sides of board solder looks fine.  I reflow it anyway.  Still same problem.  So then I check the +5V with my oscilloscope, and video signal and used the ground right there first pin for my ground incase the ground was broke somewhere one the board.  Everything looked fine I had a video signal there and +5V.  Then I look at the video signal on the output and I had a video signal there but still no picture. 

 

After scratching my head for awhile I decided to try the Atari 2600 on another TV.  Picture perfect(other than some fine vertical jailbars but looks like all the composite modded consoles I've seen pictures of online have that).   Took it back to that GPX TV and still had same issue.  I figured by that point the problem is that the signal wasn't amplified enough for the GPX to recognize it as a signal so therefore blue screen, and what was happening was I guess when I was wiggling wires and probably touched the video signal and it caused a signal to go up high enough to trick the TV to display the picture. 

 

So I decided to show the comparison of the two video signals incase anyone runs into the same problem.

I'm including pictures of two separate video out signals with space invaders plugged in.  The stronger of the two is the flashback which plays fine on the GPX.  Very disappointing because the sole purpose of me getting this TV was to have something small at my workbench and be able to test consoles on.  I guess I'll have to get or build a separate amplifier now to plug consoles in that don't have a strong enough video signal.  My appologies for the poor picture quality, I took some too with an Iphone but couldn't find the cord and have no service here so couldn't email them to myself so I had to take them with my junk phone.  I might try to upload the higher quality images of the scope tomorrow once I can email the pics to myself.

 

My biggest concern with doing this mod if doing for other people is not knowing who's TVs this will work on and who's it will not so I think I will change some values and try to get it to more closely resemble the amplitude of the flashback unit.  I'm going to wait first until I do another mod and make sure the other 2600 also has a weak signal like this one to make sure it isn't anything I overlooked with this console but I don't believe there is.

 

 

If anyone has any questions or comments about this let me know.

 

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#2 Bantha421 OFFLINE  

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Posted Tue Apr 18, 2017 3:34 PM

https://www.google.c...ALZHuqy8BGa6c-Q

#3 Bantha421 OFFLINE  

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Posted Tue Apr 18, 2017 3:35 PM

Is this the way you did the mod? Just curious cause I was planning on following these instructions when the kit arrives.

Edited by Bantha421, Tue Apr 18, 2017 3:36 PM.


#4 SignGuy81 OFFLINE  

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Posted Tue Apr 18, 2017 3:46 PM

Is this the way you did the mod? Just curious cause I was planning on following these instructions when the kit arrives.

Yes it is the exact instructions I followed other than the addition of a 75 ohm resistor between the video output and ground which was supplied with my kit. 



#5 SignGuy81 OFFLINE  

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Posted Tue Apr 18, 2017 3:57 PM

Here are the clearer pictures.

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#6 Neuronic OFFLINE  

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Posted Tue Apr 18, 2017 5:59 PM

My picture was too dark until I removed the 75ohm resistor between the ground and video out. Got much brighter but not as bright as before the mod.

#7 SignGuy81 OFFLINE  

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Posted Tue Apr 18, 2017 7:39 PM

My picture was too dark until I removed the 75ohm resistor between the ground and video out. Got much brighter but not as bright as before the mod.

For me the brightness is great and picture was perfect other than fine jailbars and slight ghosting.  Sounds like it may be something up with your luma signals, I would trace it back to the TIA.  The buffer chip could be bad.   But if it was working fine before the mod not really sure.  When i get time, probably this weekend, I'm going to work on fixing the output so it is around 1V Pk to Pk like it should be on my console and get back with the results.



#8 SignGuy81 OFFLINE  

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Posted Tue Apr 18, 2017 9:16 PM

Okay so I decided to go ahead and tinker with it a little tonight.  I removed the 2.2k ohm resistor on the mod board and soldered in a 10k ohm pot.  The signal looked strongest when I had it right around 5k ohms and higher than that the signal started going back down.  I looked for a 4.7k in my stash  and couldn't fine one so put two 10k ohms in parallel and soldered them in.  Although still not near 1V Pk to Pk as it should be it is much closer.  It was slightly over 200mV Pk to Pk last time and as you can see above from my pictures but now it is around 600mV Pk to Pk after changing removing the 2.2k ohm and swapping it for 5k ohms.  Now my GPX TV is accepting the picture just fine :)  It looks just like the flashback console on that TV because it only has an 8 inch screen the jailbars aren't visible on it.  However my 55 inch TV still shows them after rechecking.  I don't think increasing the video signal anymore is going to do anything for those so I don't believe I will bother with that anymore. 

 

The main thing I wanted to point out and show how to fix is if you have done the mod and get no picture but sound that it is probably too weak of signal.  Hope this helps.

 

Also if anyone else that has done this same mod on their 2600 and also happen to have an oscilloscope handy could you please do the same(not swapping out resistors or anything just checking the output) and post your results here and show pictures of your scope as well so we can be certain if this mod problem may apply to all 2600s.  To take the measurement the easiest way(in order to be able to hold a camera and take a picture) if your console isn't apart is to plug in your RCA cables and use a spare RCA jack if you have any left from doing mods and plug it into the other end of the cable and then hook your scope ground and probe to it.


Edited by SignGuy81, Tue Apr 18, 2017 9:25 PM.


#9 SignGuy81 OFFLINE  

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Posted Sat Apr 22, 2017 11:38 AM

I wound up putting a 4.7k in place of 2.2k and I put a 6.8k in place of the 3.3k.  You can increase the resistances more and get closer to 1V P-P on the video output but the problem is that you introduce more color bleed(ghosting) when this happens.  I have slight color bleeding now but not much.  I'm probably going to try another circuit later on with 2 transistors.

 

The symptoms I was experiencing prior to changing from the 2.2k and 3.3k ohm resistors were that I rarely ever got a game to display on one of my TVs because the video signal was too low with this mod.  Sometimes a game would load after trying about 10 times in a row and the picture would be shifted and once in a while a game would load okay but when switching to different screen the picture would go back out and I'd be left with sound and a blue screen again.

 

With the two resistors changed out the video output signal is around 600mV P-P and now all my TVs play the Atari fine.  



#10 SignGuy81 OFFLINE  

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Posted Sun Apr 23, 2017 9:28 AM

I forgot to add that the board I used was Rev 14.  They all differ on the video output section on boards from 2600/2600A, for example the removal of the buffer chips, different resistor values, addition of 2 diodes on Rev 14 to prevent feedback on the sync and one of the luminescence lines on the TIA.  A transistor has been removed from oscillator circuit.

 

I'm going to try to check every different board I can get my hands on so I will know if the others also have too low of an output with the composite mod with included resistor values to be recognized by some televisions.  Once I am done I will post results here.

 

EDIT:

I believe I mentioned earlier about not being able to see the waveform good and also include the whole waveform on my scope due to the settings.  I thought I only had an option of 1V per division or 0.1V per division not thinking about my x1, x2 ans x5 selector switch(I hardly ever use that scope for anything), so I was able to put it on x2 which gives me 200mV per division which allows me to clearly see the waveform and see the whole thing and the flashback is about exactly 1Vp-p as it should be.


Edited by SignGuy81, Sun Apr 23, 2017 9:44 AM.


#11 SignGuy81 OFFLINE  

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Posted Sun Apr 23, 2017 11:34 AM

I just opened and cleaned out my other Atari so I can begin working on it shortly.  Man was this board nasty.  Whenever I get used electronics in, and I would suggest this to anyone, would be to have it sealed up well in something until you are able to take it apart and look in it(and to never buy used electronics that you don't intend on taking apart), and have a can of roach spray ready when you attempt to take it apart.  You never know and could get something that is full of roaches(I got a PS3 once that I didn't even attempt to open up because it was so bad you could see all the roaches in the vents, I wouldn't even give it away to someone for free if I find something like that).  This Atari unit wasn't bad but it did have one dead roach and one dead ladybug and was also full of rust.  When I get a unit like this instead of just washing the case I wash everything completely, board and all.  Before washing since I didn't see any live critters I went ahead and hooked it up to see if it worked and got it to play ms pac man.  Haven't tried it yet with controllers just wanted to see if it would load a game.  I got it heating in an oven now to get rid of moisture and when it is ready I will test this one to see if it has any problems.  I'm thinking the only problem with this unit(other than it was a complete mess) was bad connections in the card edge connector because I had to work the game back and forth a few times before it loaded, and also that the RF cord was cut so I had to use another. 

 

This unit is Rev 13 and I'm going to do the composite mod on this one to see if I have similar results as I've posted above.


Edited by SignGuy81, Sun Apr 23, 2017 11:38 AM.


#12 SignGuy81 OFFLINE  

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Posted Sun Apr 23, 2017 7:38 PM

Just want to update that it will be awhile before I mod the rev 13 board because I want to get it working properly first.  I got a unit with a bad 6532.  So far everything looks good and sounds good other than Joystick problems with the first controller port no input for right direction.  Checked solder joints then continuity between 4th pin of port and pin 15 of the 6532 and it was good, also checked and made sure joystick was shorting pins 8 and 4 on the port and it was, then tried joystick in other port and was good.  I just ordered a set of 5 on ebay http://www.ebay.com/...A4AAMXQeKNTOBes

 

How the heck do they refurbish the chips?  Anyways as long as they are good I guess that it all that counts.  While I was writing this I found 2 more from a us seller a little more but seemed cheap enough so figured I'd get those and not have to wait as long so maybe I'll have an update this weekend on how the composite mod does on the rev 13 board. 


Edited by SignGuy81, Sun Apr 23, 2017 7:39 PM.


#13 SignGuy81 OFFLINE  

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Posted Sun Apr 30, 2017 8:23 PM

I haven't got around to modding the Rev 13 board yet as I was planning this weekend as I had a lot of work around the house to do.  Instead I did do some documentation on jailbars before doing any modding so I would know if there were a difference pre and post mod.  I'll try to get back to working on this unit either this week after work or next weekend and I will measure the video output to see if it is any different than the Rev 14 was(I doubt it will be with this board and think it will also have a weak signal but I think it could perhaps be better on the prior revisions with the buffer chips but not sure till I get some more units to mod and test with A/V mod). 


Edited by SignGuy81, Sun Apr 30, 2017 8:25 PM.


#14 Keatah ONLINE  

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Posted Sun Apr 30, 2017 8:42 PM

How the heck do they refurbish the chips? 

 

It could mean they did a cleaning and a re-printing of the markings and numbers. Perhaps even replating or buffing and straightening the pins to a shine. They may also test to factory specification.

 

More likely they just selected that option on ebay's "item condition box".. Be aware that "factory" can mean an outhouse shop in china, and not a high-tech fab.

 

Real expensive chips can get pins replaced, or even repackaged in extreme situations. 40 year old shitbox console chips are just gonna get a cleaning. There's nothing a hobbyist can do on the inside of the chip.


Edited by Keatah, Sun Apr 30, 2017 8:55 PM.


#15 SignGuy81 OFFLINE  

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Posted Sun Apr 30, 2017 8:57 PM

 

There's nothing a hobbyist can do on the inside of the chip.

I wasn't being serious when I asked how they refurbish the chips I just thought it was funny that they had it in that category.



#16 Keatah ONLINE  

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Posted Sun Apr 30, 2017 8:59 PM

It's big business.



#17 SignGuy81 OFFLINE  

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Posted Sun Apr 30, 2017 9:04 PM

It's big business.

Now if I could just find a lot of refurbished TIA chips for around same price that would be great too to have lying around :).


Edited by SignGuy81, Sun Apr 30, 2017 9:04 PM.


#18 SignGuy81 OFFLINE  

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Posted Sat May 6, 2017 2:52 PM

Update:

 

I just got around to composite modding the Rev 13 board.  I did have a slightly higher output with this one to start off with using the 2.2k ohm and 3.3k ohm resistors.  It was close to 400mVpp.  Still my GPX TV would not recognize the signal.  I swapped the 2.2k ohm as before to 4.7k ohm, then the 3.3k ohm to 6.8k ohm, and just as before my signal increased, this time to around 600mVpp and the GPX played this one fine as well just like it did the Rev 14 Atari after increasing the resistor values.

 

I've seen several posts in the past blaming it on TV brand claiming cheap TVs are the problem.  This is not the case, it isn't the TVs fault you aren't sending it a proper NTSC signal which is supposed to be around 1Vpp.  The problem is the composite mod with the 2.2k ohm, 3.3k ohm, and 3904 transistor, not the TVs that have problems with it.  The TVs are perfectly fine.

 

I would later like to check the output of one of the other revision boards that have buffers on the outputs to see if there is a difference in those units with the mod as it comes but I do not have any at the moment but may get to it eventually.


Edited by SignGuy81, Sat May 6, 2017 2:53 PM.






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