ChmA2678
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Everything posted by ChmA2678
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I checked a 7800 game earlier and it works fine. The pic is the same as the 2600 game with the bypass. Much improved with the bypass instead of going through the RF. So you're saying that a transistor might be why the picture isn't super clean? I'll check them a bit later. If Best was offering to do the work I can see their point but I'm just trying to order it with a few other parts to do myself. I'll try to order again and see how it goes. Thanks again for all the help.
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Putting a mod in is the direction I was heading. I wanted to keep dealing with Best Electronics but they were basically insisting that I find the problem and get the video working before doing the mod. I've tried to order it twice now and get a reply back at how nobody would do the mod without the system working and the order wasn't filled. So I decided to figure out where the problem lies and learn a bit along the way. I've had a really good experience with them in the past so I'm not sure where this is all coming from. I'll try once more before checking other sources. I do thank you though for offering to send me a replacement RF.
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I got the circuit completed and bypassed the RF Modulator. The picture isn't perfect but it's 100 times better than it was. Is it suppose to be a cleaner picture or is this just a quick test? There obviously isn't any sound since it wasn't connected. So is it safe to assume that the RF Modulator is to blame? I also got it to load 7800 games.
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Fantastic, thank you. I've got the parts on order and am looking forward to bypassing the rf module to see if that's the culprit. Nice job with the diagram, very easy to follow. There was something I had a question about with the bypass. Don't you have to remove a couple resistors next to the rf modulator when doing a mod? What do those two resistors do and will it impact this test in any way?
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Yes it would be easier to let the Atari guys fix my system but where would the fun be in that. Learning new things is always a blast especially when you get everything figured out and it works! So yes I'll take you up on your offer and pickup the parts needed. Thanks!
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While I can solder, follow directions and test simple components with a multimeter; my knowledge of electronic components are extremely limited. With this foray into trying to diagnose my 7800 video issues I have to admit becoming more interested in the technical aspects on how everything works and why with all the circuits. I can swap out parts as needed but it's interesting to think beyond that. Back to the point, I do not have or ever used a breadboard but I know what it is. I'm sorry to say that even if I did have a breadboard that I don't know what a voltage follower is or how to make one to connect to the tv. I really appreciate your ideas and you've been of great help troubleshooting the issues. I just which I were more technically capable to follow through with some of the suggestions.
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I appreciate all the info and I'll check into those other mods. I've ordered from Bradley before and haven't had any issues whatsoever and he's always very helpful, quick to respond and deliver. In this instance he seems to be pretty set on me getting the video fixed first. I don't believe they do repairs or mods anymore since he recommended I look for someone to repair it from the atariage site. I sent an order in this morning and haven't heard anything from him even after I said that I would be getting a working board and mod that one. I'm sure he's just busy but this is a new experience from this company apart from what I've originally experienced.
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I'm trying to order the mod from Best Electronics but he says the video and system needs to be working before the mod is installed so he hasn't filled the order. Apparently any one of the chips could be bad and since they're on the same buss would have to be removed to be tested which could lead to trace damage further complicating the problem. So I'm probably going to just find a parts board and see which one is easier to fix and use the other for parts and then mod it.
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With the 7800 cartridge it's not complete static snow, I suppose it is static with varying degrees of lines running in multiple directions without any sound or identifiable images. I can adjust the RF Modulator to make it complete snow if that helps at all. I believe it may be light corrosion on the pins since they feel a little rough. The 20-29 pins also look like they were bent closer to the chip than the rest of them. As far as I can tell they all make contact with their traces. I was picking up .4 on a diode reading on one of the questionable pins.
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While I'm waiting for the mod to arrive I did manage to pickup a few 7800 games. Cleaned each one and get absolutely nothing, just snow on the screen with no static sounds. I even let it warm up for 15 minutes. Initially I got one faded snowy Atari 7800 logo and that was it and now not even that shows up. The 2600 game still loads with the problems previously listed. I did take a closer look at the MARIA IC and pins 21-24 look a bit odd, the pins 25-28 on the other side look similar as well.
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I got the alignment tools and it didn't help clear up the picture or sound. The picture instantly lost color when adjusted and I had to power off and back on to get the color back. The adjustment did make a change but it was just for the worse. Looks like it's on to replacing the RF Modulator with a mod. It'll probably be later in the week until I'm able to get that done. Meanwhile thanks again to both of you and I'll update when I have some different results.
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Thanks for all the great info. I did measure Maria wrong, had them backwards. So I'm getting 4.96v from Maria, 4.97v from the 7805, the two smaller IC chips on the bottom right are reading 4.96v but the small chip on the top right (tc40138p) is reading 4.5v
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I'm getting 4.16 volts from the MARIA chip and yes the game is BattleZone.
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Thank You both for the links, I should have more information tomorrow on whether or not the adjustments did anything. Bradley at Best Electronics doesn't believe an AV mod would make any difference and believes it's a motherboard issue. That being said I believe the mod would be a reasonable step if the adjustments fail to do anything. Are there video components that can be tested with a multimeter that feed into the RF Modulator?
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Thanks for the troubleshooting ideas. I am using a direct connection with an adapter so there is no switch in the mix. I tried wiggling and turning the cable but that didn't do anything for the picture. One thing I did notice is that simply touching the cable near the rf out caused me to lose color and just be in black and white. All it took was a light touch to change and I know it's not the connection since I held it further down the cable to move it without losing the color. I tried adjusting the rf modulator but I lack the correct tool. I did try to use a plastic qtip minus the ends and also a toothpick but I don't believe either one of those were able to turn the adjuster. I don't want to use anything metal since that will likely break it and cause interference. Any ideas on where to get the plastic hex wrench? I've attached a picture as to what the screen looks like. Another minor detail is that I only get color on channel 2 and not channel 3. Thanks again for the help.
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Hello everyone. I am having some difficulty with an Atari 7800 that I picked up that I hope, with the help of this community, we can figure out. The unit didn't have a power supply so I picked up a new switcher from best and it checks out fine and powers up the unit. The problem that I am having is the picture has a lot of static, you can barely make out the image but it has color and responds to control input. The second problem is the sound which is nothing but static, no game sounds what so ever. I did clean out the cartridge receiver on the board with 91% alcohol and a cloth over a credit card. I'm connected through an rf coax adapter using an rf cable. I've tried different cables and adapters, tried different cleaned 2600 games since I don't have any 7800 games yet, switching through channels on both the console and the tv, re-scanning channels on the tv with a game running on the console, running through a vcr to tv using the composite and then the coaxial output of the vcr, and lastly using an old tube tv. The ohm resistance on the rf output is 1 with a the meter set at 200 while my 2600 has an ohm reading of 100 with the same setting. I use to get a reading at .18 with it set above 2k but now it's just reading 1. Best electronics says it sounds like a motherboard issue and the av mod likely wouldn't make a difference. I'll try to upload an image of both sides of the board.
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