YSG2020 Posted February 6, 2020 Share Posted February 6, 2020 OK, Did the board mod on my Rev-D 800XL board to add Chroma signal (S-Video) to my Video 5 Din port. It worked great and I now have a very sharp crisp picture... However, I have vertical banding on the screen so it is not a totally clear picture. I lifted the right side of C54 and it makes no difference at all to the vertical banding on the screen whether it is lifted or not. I have seen a recommendation to add a 100ohm resistor to the new Chroma mod wire going to 5 din port. Will this help? Any ideas how to get rid of this vertical banding? I am using a powered video converter box with an adapter cable going from the Atari's Din video port to S-Video in on the converter box, and then out to VGA and then into an SVGA CRT monitor. The banding does not seem to be a problem with the converter, nor the monitor, and does seem to be in the S-Video signal coming from the Atari. Quote Link to comment Share on other sites More sharing options...
+mytek Posted February 6, 2020 Share Posted February 6, 2020 It's pretty certain that the banding is emanating from the Atari video output, and not your converter. I see this even on my 1200XL with a UAV installed, although the effect is much less pronounced then when it was a ClearPic modified output. I think sometimes it's chroma mixing with the luma that causes it, or DRAM switching noise. Since you lifted C54, I would imagine that pretty much rules out chroma bleeding into the luma. Also sometimes grounding comes into play. I saw this with the UAV situation, and got it to be a little better by playing with where the cable ground coming out of the DIN-5 jack was actually connected to, as well as where the UAV got its ground. Its all magic smoke. 1 Quote Link to comment Share on other sites More sharing options...
YSG2020 Posted February 6, 2020 Author Share Posted February 6, 2020 (edited) I've only tested it with a loose motherboard so grounding could be an issue. Also, why would there be no visible difference regardless of C54 lifted or not - Lifting that resistor does nothing at all apparently on my Rev-D board. ??? Edited February 6, 2020 by YSG2020 Quote Link to comment Share on other sites More sharing options...
+mytek Posted February 6, 2020 Share Posted February 6, 2020 44 minutes ago, YSG2020 said: I've only tested it with a loose motherboard so grounding could be an issue. Also, why would there be no visible difference regardless of C54 lifted or not - Lifting that resistor does nothing at all apparently on my Rev-D board. ??? C54 is shown as a .001uf capacitor bridged between the chroma and luma circuits in order to create composite video. By disconnecting it, you would normally only see B&W coming out of your composite video pin on the DIN jack. You said you did the S-Video mod, which I interpret as connecting the chroma output to the DIN jack, since luma should already be connected from the factory. If you are using the S-Video aspect (separate luma and chroma) to feed your converter, then disconnecting C54 should eliminate any cross-talk between the luma and chroma circuits, and thus give you a cleaner image without banding. However if it did not, and your connections for S-Video are correct, then you either have a grounding issue, or you might be seeing noise from the DRAM circuits bleeding over. 1 Quote Link to comment Share on other sites More sharing options...
YSG2020 Posted February 7, 2020 Author Share Posted February 7, 2020 The really weird thing is that C54 is also labelled C54 under it on the pc board, but this component part looks like a resistor to me, not a capacitor. ?! I didn’t know they made capacitors that look like resistors. Is there a possibility that everyone is lifting the wrong component on the board for this step of the mod? Why would Atari label this part that looks like a resistor with a C instead of an R? Quote Link to comment Share on other sites More sharing options...
YSG2020 Posted February 7, 2020 Author Share Posted February 7, 2020 Can somebody shoot me a photo of where C54 is located on the board? I’m pretty positive the part everyone is lifting that’s pictured in the mod is in fact a resistor and not the capacitor that actually needs lifting. ?? Thx. Quote Link to comment Share on other sites More sharing options...
+DrVenkman Posted February 7, 2020 Share Posted February 7, 2020 5 minutes ago, YSG2020 said: The really weird thing is that C54 is also labelled C54 under it on the pc board, but this component part looks like a resistor to me, not a capacitor. ?! I didn’t know they made capacitors that look like resistors. Is there a possibility that everyone is lifting the wrong component on the board for this step of the mod? Why would Atari label this part that looks like a resistor with a C instead of an R? It’s a capacitor. Atari used a lot of tiny axial ceramic caps like that back in the day. That form-factor has gone out of style for ceramic caps in the intervening decades. 1 Quote Link to comment Share on other sites More sharing options...
+Stephen Posted February 7, 2020 Share Posted February 7, 2020 6 minutes ago, YSG2020 said: The really weird thing is that C54 is also labelled C54 under it on the pc board, but this component part looks like a resistor to me, not a capacitor. ?! I didn’t know they made capacitors that look like resistors. Is there a possibility that everyone is lifting the wrong component on the board for this step of the mod? Why would Atari label this part that looks like a resistor with a C instead of an R? There are several capacitors that look like resistors in the Ataris. The SIO caps people mention are another example. There is a similar colour code to identify the values. Quote Link to comment Share on other sites More sharing options...
YSG2020 Posted February 7, 2020 Author Share Posted February 7, 2020 (edited) That is bizarre. I’ve been working with electronics for 35 years and I’ve never seen a .001uf capacitor that looks exactly like a color banded resistor. Ok I just found them on google. Evil little buggers do look like resistors. I think I do vaguely remember these from back in the day but forgot about them. Edited February 7, 2020 by YSG2020 Quote Link to comment Share on other sites More sharing options...
YSG2020 Posted February 7, 2020 Author Share Posted February 7, 2020 (edited) Interestingly enough I also get the exact same vertical banding using a composite output on two different unmodded 800xl boards I have here. One is a rev A. The other a rev D. Im going to try some different monitors to see if I can isolate this vertical screen banding issue. Edited February 7, 2020 by YSG2020 Quote Link to comment Share on other sites More sharing options...
+bob1200xl Posted February 7, 2020 Share Posted February 7, 2020 Axial caps have green bodies, axial resistors have tan/brown bodies. Color codes are the same except that the third color is pf. Brown/black/orange is .001ufd (1000 pf) - I think. Except when it's different... Vertical banding is from ground bounce on REFRESH cycles. Count the bands, should be 9 on a GR.0 screen. I don't know how to fix it. Seems like I have seen extra ground wiring added on stock machines. Maybe. Bob 1 Quote Link to comment Share on other sites More sharing options...
ChildOfCv Posted February 7, 2020 Share Posted February 7, 2020 36 minutes ago, bob1200xl said: Axial caps have green bodies, axial resistors have tan/brown bodies. And axial inductors have blue bodies. Quote Link to comment Share on other sites More sharing options...
YSG2020 Posted February 7, 2020 Author Share Posted February 7, 2020 Yes there are 9. You are a wizard Bob. And everyone else thanks for your answers and suggestions too. I’m going to play with the grounding to see if I can solve this unless anybody else has any other ideas? I wonder if it’s because the SVGA monitor has such a sharp picture capability compared to only SVid or Composite, that this banding could not have been seen 30 years ago when displays were not as high quality as the newer ones? Quote Link to comment Share on other sites More sharing options...
SoundGammon Posted February 7, 2020 Share Posted February 7, 2020 (edited) I read somewhere that the 800Xl video circuits get power from the same power rail as the clock, causing the banding. The solution is to raise one leg of L5, next to U20, that is "suppose" to filter it and run a wire to positive (+) end of C2, next to the power switch! Haven't tried it, but I would pull up the end of L5 toward the back of the computer and hook the wire there! Edited February 7, 2020 by SoundGammon 1 Quote Link to comment Share on other sites More sharing options...
+bob1200xl Posted February 7, 2020 Share Posted February 7, 2020 I can see banding on my 35 year-old monitor. Try soldering a wire to J2-2 (ground at the DIN connector). CAREFULLY touch the wire to the ground pin of the ICs on the m/b while watching the screen. See if the banding goes away. Try the ground side of R52. If you have a scope, look at the grounds with the scope probe ground connected at the J2-2. Bob 1 Quote Link to comment Share on other sites More sharing options...
YSG2020 Posted February 7, 2020 Author Share Posted February 7, 2020 Both great ideas. I will try both on my third 800xl board so as to spare the other two in case I fry something. Thx! Quote Link to comment Share on other sites More sharing options...
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