Col7800 Posted October 17, 2016 Share Posted October 17, 2016 (edited) Hi All, this is my first post in these forums, so hello to everyone First off all, the below relates to a PAL console and all are PAL games. I am aware of the wrong colours between PAL/NTSC, this is a different issue. I have just bought a Atari 2600 jr as it was cheap, thought it would be nice to have a separate console just for 2600 goodness... Anyway after playing my Harmony cart on the 2600 I realised that I had a problem with my 7800 in 2600 mode. Specifically some of the colours are showing incorrectly (until I played the 2600 jr I thought this was normal), and some games that don't load on my 7800 work fine on the jr console. An example of incorrect colours, Pac Man 8K (pal or pal60 version) shows the score as light blue (instead of white) and the number one and half of the number 7 are yellow. On the title screen the high score shows in pink with the number one in orange. Many other games exhibit this scoreboard problem (with different colour combinations, but affecting the same digits). There maybe other colour differences but I haven't spent time comparing them as yet. Very strange issue and I can't find anything similar after many Google searches. I swapped out the TIA but this did not resolve the problem. Any ideas whats happening here?? The 7800 is composite modded and the 2600 jr is factory (RF output). The 7800 games show fine with a nice clear picture (albeit a little flickery on CRT TV's), and games in 2600 mode are nice and clear (with no flickering). The second issue is that some games don't load on the 7800 via Harmony (Kool Aid Man, all Supercharger games, not found others as yet) but all work fine on the jr. I read that this may be down to a timing circuit, but everything I found relates to NTSC consoles. Nothing found for PAL machines and if this can be fixed. Can it even be fixed on a PAL console (if the timing is in fact the problem)? Anyway, the colour problem may sound trivial but now that I know it's there, it's driving me nuts. I don't really want to have to change consoles every time I want to play a 2600 game, I bought the 2600 jr for another room. Hope someone can help me with either problem, it will be very much appreciated!!... Cheers! Edited October 17, 2016 by Col7800 Quote Link to comment Share on other sites More sharing options...
Col7800 Posted October 17, 2016 Author Share Posted October 17, 2016 Since I'm inundated with replies, I continued researching (with little success). As it is confirmed that the TIA isn't the problem, could it be one of the other chips (i.e. the RIOT chip)? If necessary I can post PIC's or a video of the problem if it helps... Quote Link to comment Share on other sites More sharing options...
+Mitch Posted October 18, 2016 Share Posted October 18, 2016 Have you tried adjusting the 2600 mode color pot inside the 7800? Mitch Quote Link to comment Share on other sites More sharing options...
Col7800 Posted October 18, 2016 Author Share Posted October 18, 2016 (edited) Have you tried adjusting the 2600 mode color pot inside the 7800? Mitch Hi Mitch, thanks for the reply. yeh I adjusted the pot but it just changed the tint of all the colours on screen, not just the parts that have a problem. I have just changed the RIOT chip and that didn't fix it either. Why is it just affecting certain numbers, always the same part of 7 and all of 1. Other games have this problem, with the same numbers, others are unaffected. Very strange. Stumped.... Is there any timing fix for the PAL system? Col Update, some other games show a yellow tint to certain parts that should be white. I played Thrust on my jr and the whites are brilliant, on my 7800 they are very yellow (no amount of pot adjustment will correct it). All whites are absolutely fine in 7800 mode... Edited October 18, 2016 by Col7800 Quote Link to comment Share on other sites More sharing options...
+Stephen Moss Posted October 18, 2016 Share Posted October 18, 2016 The fact that both the video outputs from the TIA and MARIA chips use U3 and the RF modulator and it only affects 2600 games would suggest that is a TIA related issue as virtually all other parts are use in both 7800 and 2600 mode. As you have tried changing the TIA without success try looking for bad joints on the TIA socket (if socketed) and the pull up resistors relating to the TIAs, Luma, Col and sync pins (R18-R22?). Also try measuring the resistance of those resistors which according to the circuit on AA look like they should be 1K (1000 Ohms), as it may be possible you are either missing a RGB colour completely (are you getting a good Red, Green and Blue colour where you should be?) or not getting the correct current/voltage on a bad resistor to give the correct amount of a particular colour. If there is a Test cart ROM you could put on your harmony Cart that may help pin point the problem or at least show if a specific RGB colour has a problem if it displays a standard set of colour bars? Quote Link to comment Share on other sites More sharing options...
Col7800 Posted October 18, 2016 Author Share Posted October 18, 2016 Hi Dragonstomper, thanks for the suggestions, I'll have a look today. I've tried the diagnostic Test Cartridge V2.6P and here is the result https://drive.google.com/open?id=0B_06EMEh6jeyMWY2ZGU0S1pxbDA Quote Link to comment Share on other sites More sharing options...
Col7800 Posted October 18, 2016 Author Share Posted October 18, 2016 (edited) Right, I've checked all pull up resistors: Lum0 R38 Lum1 R36 Lum3 R39 These show as 1K Colour R37 shows as 875ohm in the circuit (when removed it reads 1K) They are all showing continuity to the right pins of TIA (7,5,6 & 9) Both Maria & TIA are receiving 4.88V Here is Pac Man 8k https://drive.google.com/open?id=0B_06EMEh6jeyX2lZRkFOTHYyak0 I couldn't get a clear picture of the issue unfortunately but the number 1 of the high score shows in yellow the 0's are all pink. In the game the number 1 and part of 4 show in yellow others are whiteish (albeit a little blue tint). Any other suggestions? Could it be to do with csyn (I don't know what this signal does) I measured the volatge to the Pot (R43) connected to csyn signal and it measued 6V (schematic says it should be 7V). Would this be causing my issue? Oh, and by the way, is it normal to have a constant shimmering effect in 7800 mode? (it can be annoying) Edited October 18, 2016 by Col7800 Quote Link to comment Share on other sites More sharing options...
Col7800 Posted October 18, 2016 Author Share Posted October 18, 2016 Hi Stephen, apologies for calling you Dragonstomper, looked at the wrong name! Didn't realise this referred to the number of forum posts... I am new here... Quote Link to comment Share on other sites More sharing options...
Col7800 Posted October 18, 2016 Author Share Posted October 18, 2016 (edited) I have just tried the TIA from the 7800 in the 2600 and all is fine. So I categorically say that it's not the TIA. The yellow tint in Thrust shows the same on a friends Woody atari so I'm not concerned about that. My jr might actually need adjusting to show better yellow. The main issue is the number one showing in wrong colour (yellow) and part of seven (not 4 quoted in error earlier). When the score shows any other digit it is correct. Yes the TIA is socketed, would a bad connection cause this problem, or a shorted PIN? How would I go about checking for this on the board? (All the pins connect fine with the actual socket itself) I am still wanting verification about the flickering/shimmering on screen via composite. Is this normal for a PAL console? Hope someone can help as I'm ready to throw the bloody thing through the window! Update: adjusted the pot on the 2600 jr and the bits that were white are now yellow, apart from the ship which remains white. So it's just a matter of finding out what is causing the score board issue on the 7800 (2600 mode).... Edited October 18, 2016 by Col7800 Quote Link to comment Share on other sites More sharing options...
Col7800 Posted October 18, 2016 Author Share Posted October 18, 2016 I have just checked the Luma resistor values on the board and they are different than the ones in the schematic. Presumably changed by the previous owner who fitted the composite mod. R64 = 4.7K Lum 3 (10K on schematic) R67= 10K Lum 1 (20K on schematic) R65 = 20K Lum 0 (39K on schematic) R35 (Chroma) = 4.7K (same as schematic) Are these suspects? Are they good values for a Luma Ladder? Quote Link to comment Share on other sites More sharing options...
+Stephen Moss Posted October 19, 2016 Share Posted October 19, 2016 The colour bar image you provided does not appear to match either if those shown in the 2600 service manual so it is unclear to me if that is an error or not, however all three main colours appear to be present so the 7800 should be able to produce any require colour. I do not know if the changed resistors are an issue, the change may have been required for correct operation of the composite mode but without seeing the mod instructions you would will not know. I must be going blind in my old age as I cannot find R64, R65, R67 or pot R43 on the schematic I am looking at. I do not know if the flickering/shimmering is normal on such a mod but it could be that the display is only just coping with either the amplitude or frequency of the sync signal, if you can switch the display between using sync on Green and V or H sync try that to see if there is any improvement on that front. If you have access to an oscilloscope you could try checking the systems clock frequencies to ensure they are in spec. It is strange that the number 1 is not the same colour as the rest, I assume you have tried Pac-Man in a 2600 and all the digits are the same colour thereby eliminating any issues with a possibly corrupted ROM image? Check that Maria's video lines Pins 42 - 48 are constantly inactive (low, 0V) then playing a 2600 game, if they are not try changing the 74LS174/32. Unfortunately I think this is the limit of the help I can give as I cannot think of anything else to try. Quote Link to comment Share on other sites More sharing options...
Col7800 Posted October 19, 2016 Author Share Posted October 19, 2016 (edited) Thanks for the tips Stephen, very much appreciated. Yeh, all the games exhibiting this issue all work fine on the jr. Strange issue indeed, has me baffled. The schematic I use is this one http://www.atarimax.com/jindroush.atari.org/data/a7800/7800schm.gif If I can't sort it, I will buy a different console. Col Update: checked pins of Maria while playing 2600 and only 42 (lum 0) have voltage (1.5v) - disconnecting this pin makes no difference to 2600 display. I hate to admit defeat, but I think I'm done with this Atari This is the mod BTW https://drive.google.com/open?id=0B_06EMEh6jeyZVp4TzhmY19BQ0k The bare wire is just the audio which is not connected as yet.. Edited October 19, 2016 by Col7800 Quote Link to comment Share on other sites More sharing options...
Col7800 Posted October 19, 2016 Author Share Posted October 19, 2016 Just browsing this forum for any others who are experiencing the same shimmer/ripple on PAL consoles and found this: http://atariage.com/forums/topic/26719-help-with-7800-pal-composite-mod/ I tried the fix suggested but the picture remains B/W. Anyone else tried this 'fix' with success?? (see below) Posted Mon Jun 2, 2003 4:12 PM, by Vigo Here is the trick:Remove R74. The output should be black and white now. Solder a 74LS08 on top of a 14 pin chip. connect only pin 14 and 7 to the chip beyond. Now connect a cable from the right side of R44 (under Q9) to pin 1 and 2 of the 74LS08. Now connect pin 3 via a 1k resistor to MAria pin 3. You have got an excellent quality now! Quote Link to comment Share on other sites More sharing options...
Col7800 Posted October 20, 2016 Author Share Posted October 20, 2016 Do you ever get the feeling you're talking to yourself.... Anyway, SORTED!!!! Changed resistor R25 from Maria's chroma pin from 4.3K to 2.2K, changed L7 (directly after chroma resistor in circuit) to 1uf capacitor, changed R66 8.2K resistor on Maria's csyn to 1N4148 switching diode, changed R74 1K resistor on PAL colour clock line (before XN input of Maria) to 1N4148 switching diode. Adjusted both R42 & R43 pots and I get a great picture on both 7800 and 2600 modes!! 99% of the flickering/shimmering/ripple in 7800 mode has gone, all colours are correct in 2600 mode!! Glad I stuck at it, persistence has paid off! 2 Quote Link to comment Share on other sites More sharing options...
+Mitch Posted October 20, 2016 Share Posted October 20, 2016 Awesome work! Mitch Quote Link to comment Share on other sites More sharing options...
Col7800 Posted November 17, 2016 Author Share Posted November 17, 2016 (edited) Update on this: Although the above mentioned system still seems ok, I bought 2 more 7800's since then and they both exhibit the exact same problem. I'm wondering if this is a problem common to PAL consoles.... I haven't been able to resolve the issue on the other consoles Note: My 2 Atari Jr's and my Woody (light sixer) are all fine, showing all colours perfectly. Edited November 17, 2016 by Col7800 Quote Link to comment Share on other sites More sharing options...
Col7800 Posted November 24, 2016 Author Share Posted November 24, 2016 Right, the end of the saga... I ended up changing the resistors in the Luma chain to the following: 4.7k Lum3 (lum3 2600) 9.1k Lum2 (lum1 2600) 18k Lum1 (lum0 2600) 36k Lum0 The picture is now bright and vibrant, and I am able to adjust the colours on 2600 to show correctly If anyone wants a full summary of all then I will post, but I guess people are already bored of this tedious thread... 1 Quote Link to comment Share on other sites More sharing options...
alex_79 Posted November 24, 2016 Share Posted November 24, 2016 If anyone wants a full summary of all then I will post I do! Quote Link to comment Share on other sites More sharing options...
R.Cade Posted November 25, 2016 Share Posted November 25, 2016 The NTSC 7800 has color problems also in 2600 mode. I think they (Atari) just butchered the circuit or just weren't careful with the assembly and didn't care... Usually I have to tune them. Quote Link to comment Share on other sites More sharing options...
Col7800 Posted December 1, 2016 Author Share Posted December 1, 2016 I do! Hi, after trying this on my other 'Made in China' machine, it didn't solve the colour problem. I also noticed that there is colour ghosting on all machines, which is quite noticeable on some games. It seems there is no 'One size fits all' solution for composite out, and they all seem to have colour ghosting to different degrees depending on the machine. I would suggest you wait until someone comes up with a definitive solution where all 2600 colours show correctly, there is no flicker on PAL machines and there is no colour ghosting. I'm done with it for now, no idea what's causing the ghosting. But it's still a decent picture and I'll live with it... 1 Quote Link to comment Share on other sites More sharing options...
athousanddetails Posted August 21, 2020 Share Posted August 21, 2020 On 11/24/2016 at 1:29 PM, Col7800 said: Right, the end of the saga... I ended up changing the resistors in the Luma chain to the following: 4.7k Lum3 (lum3 2600) 9.1k Lum2 (lum1 2600) 18k Lum1 (lum0 2600) 36k Lum0 The picture is now bright and vibrant, and I am able to adjust the colours on 2600 to show correctly If anyone wants a full summary of all then I will post, but I guess people are already bored of this tedious thread... Hey man, I would love to acknowledge that Summary !! I'm having similiar issues on a 2600jr PAL still RF, waiting for my Composite mod! Your help is welcome! Thanks! Quote Link to comment Share on other sites More sharing options...
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