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RF Interference on Composite modded 2600? Homebrews only


Atarileaf

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I posted this on Atariage but I thought I'd try here too.

 

I purchased a modded Vader from a user who I've bought other things from before and he seemed to know his stuff and in fact this system does work very well and gives a nice picture on normal carts - except for one odd issue - some of my homebrew carts seem to give off what I can only describe as RF interference which seems impossible since the RF modulator has been removed. It only happens with some homebrews and not others and I'm assuming has something to do with the extra tech or lack of shielding in either those carts or on the board itself. Draconian, Lady Bug and Fall Down are the worst offenders but Space Rocks, Juno First and Colony 7 are fine.

 

Is there anything I can do to fix this situation? Pics below

 

post-92-0-01914200-1525685940_thumb.jpg

 

post-92-0-43784800-1525685948_thumb.jpg

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Since you said it only happens on some homebrews, I'm inclined to agree with your guess about the lack of shielding inside the homebrew carts. Could be they are picking up something in the RF range that is causing the video interference. 

 

have you tried to move the console around or perhaps other crazy stuff like tilt it on its side with a game in it and such to see if you can make those lines more around and change? If you can, that confirms it is outside RF causing an issue.

 

Also was the RF shield removed from the 2600 when it was modded? I always..ALWAYS tried to keep the RF shield in place as the RF modulator isn't the only thing to get affected by unwanted RF noise. Even the newer mod boards can be affected by outside RF radiation.

 

Although we don't use analog over the air signals anymore or RF modulators, we actually use more RF in the world today and all around us than we ever have before. Bluetooth, your Wi-Fi in your house..etc..all exist in the RF ranges. Even your cell phone, that is why we had to get rid of the old analog signals, because we needed them for other stuff. It is also why many of the older consoles tend to look even more on modern displays. Newer displays do NOT have the filters and such in them that our old TVs did to help filter that crap out of the video signal.

See what I'm up to over at the Ivory Tower Collections: http://www.youtube.com/ivorytowercollections

 

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Thanks guys, different cables didn't make any difference and the rf modulator was removed by the AA user from whom I bought this unit and the RF pattern does move so it's not static lines but moving the console around doesn't seem to have any effect but since the lines are always in motion I'm not absolutely certain that's true.

 

Another user on AA said a couple of resistors should have been removed to improve the video but he never said which ones and I'm not sure if that in itself would solve an RF bleed issue

 

Is there a way to shield the mod somehow or would that not have any effect. 

Edited by Atarileaf
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Well..when I mod consoles, I try and put the mod boards within the original confines of the logic. Thereby they are able to be covered in the original RF shield that the system came in. Now having said that, I've also heard some people state that an AV mod looked better when they put the RF shielding on the system but put the AV mod board outside of the shielding. Again, if you can move the system around and the interference pattern changes in the process, that is definitely interference causing it. Only other way to try and shield the mod board if you haven't the original RF in place, would be to add wire and move it so that it sits under the main pcb. At least that way, you are shielding it by using the main pcb as the shield itself. 

 

Also take some foil and lightly wrap it around the cart to see if that helps. If so, that indicates the issue is the lack of shielding on the homebrew carts. 

See what I'm up to over at the Ivory Tower Collections: http://www.youtube.com/ivorytowercollections

 

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The tin foil trick didn't work but when I was touching two of the wires and held them in my fingers just so the picture cleared up. The one wire is what I'm assuming is the ground as it's just soldered to that metal strip on the board and the second wire is the video wire that goes to the yellow composite out. It's attached to the top middle portion of the little mod breadboard. Those two wires moved just so clears up the picture. This would explain why when I first got the console Draconian looked fine. It was only because I had to open the console to do a slight adjustment on the color pot (fast foods purple pickles were blue) and then put it back together that I noticed some homebrews were showing this interference. I must have moved the very tenuous wire configuration to cause the problem 

 

All three gray wires are very thin and fragile looking and are tied together with what looks like a small green zip tie. Should these wires not be tied together like this? Are the wires themselves incorrect for this type of mod?

Edited by Atarileaf
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My first guess is that the ground itself isn't making a good connection. you said if you press on them just right, the picture clears up? As for them being zip tied together, that isn't an issue and is good that they were trying to keep them nice and tidy. 

 

I'm thinking the video out wire on the top center of the perfboard might not be making a good connection and this is why when you held it just so, the picture cleared up. Try just moving that one around a bit and see if it helps? If it does, then that wire needs to be hit with some more solder and heat most likely to secure it in place on the perf board better.

See what I'm up to over at the Ivory Tower Collections: http://www.youtube.com/ivorytowercollections

 

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I agree with CrossBow.  No offense meant to whoever did the mod. (I really dislike when people get super nitpicky about these mods). 

 

I think the most critical part of the mod is the ground wire that goes from the mod board to all three video/audo jacks.  I like to use as thick a wire as possible for that....and solid core. 

 

See if this helps:  unplug one or both audio jacks from the console and see if that fixes the interference. If yes, then that ground wire is probably loose at one of the solder points on the jacks. 

Edited by RickR
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I did one of these mods for StormSurge last year, but the mod was a bit different and used thick wiring. if I remember correctly, I had to remove a resistor along with the transistor. I know mods vary but if I can find that manual you might try removing a resistor.

 

I agree with others...the RF shield should have stayed. It doesn't take much to interfere with a VCS signal. Try a different power outlet as well that is not shared with any high power devices like a TV or A/C unit. Lamps can mess with them as well.

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Thanks I will try that. Hopefully tomorrow night. I was supposed to work on it a couple nights ago but I've been swamped with work and other family responsibilities that's kept me from working on the mod. I still want to post a video of what it's doing when I fiddle with the wires and show the solder points better

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Again the fact that the image changes at all when you touch or move the wires, is sure proof there is a loose connection. Or..worse...there could be a break in the wiring within the insulation itself. But i'm inclined to think that one of the connections and most likely the video connection on the perfboard is the one to be looking at first.

 

I do use solid core wire...sometimes. But if you plan to service the system much in the future, then it is best to use a larger gauge stranded copper wire instead to give yourself more flexibility. Or...like I do, I actually use header pins and connectors so that I can quickly unplug stuff to work on it. Because of that, I do use thin solid core kynar wire for connections that won't need to be moved around, and always make sure that my power and ground wire is thick gauge for best connections. Also important to run the video and power separate if at all possible in that I keep their wiring away from each other to prevent any noise that way. Although it isn't such an issue with DC voltages like it would be with AC voltage. That is the other reason I try and attach my video ground off the same gound as the TIA. If you just use the ground around the edge of the PCB, you do stand a risk of some non filtered noise running along that plane. Also not a bad idea to keep the ground separate from the audio and video since the audio actually uses AC voltage signals. 

 

The other more expensive option (and the one I would actually choose...) would be to rip that out and install a UAV in it instead.

Edited by CrossBow

See what I'm up to over at the Ivory Tower Collections: http://www.youtube.com/ivorytowercollections

 

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Well I removed the little ties holding all 3 wires together and moved the ground and video wire as far away from each other as possible but it made no difference. I guess i should try replacing the video wire and finding a thicker wire somewhere. I assume I'll have to pry the perf board off so i can get underneath it. I'm stumped with this as I've never dealt with mods before and the reason I bought a modded system was because I'm not comfortable with that level of solder work yet. 

 

If there's a manual for this mod out there I'd appreciate being directed to it.

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I found these instructions online - http://www.coolretroprojects.com/Atari_2600_AV_Mod_Installation_Guide.pdf

 

So first I'm going to remove the two resistors it mentions to remove to see if that does anthing - R209 and Q202

 

If that doesn't work I'm going to replace that wire that runs from the perf board to the yellow composite and hope that does the trick.

 

Problem is, what kind of wire? I don't think I just have wire laying around the house. If I buy some, Console5 sells it but it doesn't look any thicker or more insulated than what's already in there. In fact the person who installed this mod might have bought his wire from them - https://console5.com/store/30ga-kynar-hookup-wire-8-color-assortment-12-30cm-length.html

Edited by Atarileaf
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Might all be a moot point. The perf board is hot glued to the motherboard and I was able to cut it off the atari board fine but to get the glue off the underside of the perf board is impossible without destroying it. I may just live with it as is and chalk it up to a learning experience. The mod is fine with normal games but these unshielded homebrews are giving it a fit. Which is a shame since homebrews are what I play the most.

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If the glue is in fact hot glue...then you only need to use Alcohol and it will soften the hot glue and allow you essentially just peel it off he boad. But you really have to saturate it in there and make sure it seeps in under the glue.

 

As for the kind of wire, I also use basically the same kind of wire. I don't think the wire is to blame so much as a loose solder connection or possibly a break in the wiring that can't be seen within the insulation.

See what I'm up to over at the Ivory Tower Collections: http://www.youtube.com/ivorytowercollections

 

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I also wonder if it may be the power adapter or the 7805 regulator/transformer.  Do you have a different power adapter to try? 

I think there has to be a simple fix for this...instead of having to tear it apart and replace wires.  I just feel like it can't be the wires -- if it was, it would pretty much have the issue with all games.  It's gotta be a shielding or power issue. 

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Thanks again for the replies. I did try different power adapters with no change and the 7805 was replaced by the AA modder. I was wondering if it could even be the big 2200UF cap or the green chicklet cap being the issue. Strong enough for regular carts but some more demanding homebrews causing a strain? He said he only replaced the 7805 and cleaned the power and a couple other switches. I do wish I had the rf shield to at least try putting that back to see if it makes a difference. I don't have an extra one for a vader but I do have a heavy sixer rf shield. I know it won't fit but I wonder if just to test, I place the top part of the shield over the IC chips to see if it makes a difference, or is that crazy?

 

I'll try removing the glue tomorrow and take a look at of the underneath of the perf board, see if there's any bad solder joints and report back.

Edited by Atarileaf
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Well..now see the original 7805 is only a .5amp rated regulator because that was all that was needed. If you add components to a console, it will draw and require more current to provide it all the juice it needs. This is why I advise that any modded 2600 and 7800 have their 7805s replaced with higher current versions of at least 1amp. It might be I've not seen of these issues because I use my 7800 for all my 2600 and 7800 game playing, but it could also be because I've replaced out the 7805 with a 1amp dc-dc converter to provide better regulated power.

See what I'm up to over at the Ivory Tower Collections: http://www.youtube.com/ivorytowercollections

 

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 Is it common knowledge to swap out a stock 7805 with a more robust version when modding? If so I didn't know and haven't read anything about it in the modding guides I've been reading. I'll ask the modder if it was 1amp or not, if not I'll swap it out. I know the refresh kits console5 sells include 1amp versions and I have one or two of those kits here.

 

On a different note, going though the forums here I saw Osgelds sale post about his modded systems for sale (I was originally going to buy his but he doesn't ship to Canada) Anyway this line in his sale post caught my eye:

 

Removed RF modulator and installed composite video mod featuring a FMS636x video buffer/driver/filter

 

 

It got me wondering if this filter is something I should look at as a possibility to solve my issue because I'm sure my mod doesn't have one.

Edited by Atarileaf
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Very possible. Osgeld is basically installing a board that has a completely different encoder on it for the video. So it takes the signals from the TIA and then puts them through his buffer instead and then you get nice video. So I'm sure his mod board setup doesn't have this interference. 

 

I'm not sure the costs of Osgeld's modded 2600s, but a UAV only costs about $25 shipped and I know it produces excellent results as well. Additionally, you have the output jacks already in place on that 2600, So with the UAV you would only have to solder maybe a few more wires off the 2600 to the UAV and then solder the current wires off your RCA jacks to the UAV as well.

 

It is too bad you are in Canada because I'd be happy to look at it for you and see if I can clean it up or even offer a UAV install replacement on it for you. But as you said, you are in Canada and the shipping would likely be pretty scary to say the least. 

 

I'm located in the middle of the US and shipping a 7800 in a good sized box to ensure it is well protected costs me from $23 - $28 USD as it is...

See what I'm up to over at the Ivory Tower Collections: http://www.youtube.com/ivorytowercollections

 

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Thanks Crossbow I really appreciate the offer and you're right shipping would be crazy. I also agree a UAV is the way I'll probably go if I can't get this sorted. Is the UAV the one where you solder wires directly to the pins on the TIA? This Vader is one of the ones that has a resistor between two pins of the TIA to bump up the color, something I only discovered yesterday evening.

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