vputz

Haha... but in this case, your ROM instinct was right. We got a whole working 800 (underpackaged, in "media mail", with most of the keys blasted off the keyboard, but they went back on just fine) swapped the personality board and it popped right up. Not sure which component on the personality board, but that was evidently the bugger. Always the last place you look. Thanks for the pointer to Sam's! We had compared the scope traces to the pics in the 800 field service manual and they seemed to hold up, but this seems like a good resource; I'll check it out. Although I'm probably going to be tapped for some 8-bit retro entertainment for the evening now that it's back up and running

Thanks, but alas, a new 68B21 didn't do it either. I think we may be going with the nuclear option and haunting ebay and other sales. On the plus side, the DIN cable came in, and that solid blue screen looks pretty swell under S-video...

Thanks a bunch! The LM3086 is what I picked up hoping it would work, so I could still try that; thanks for the verification. I'm using composite video out so I'm not suspecting anything from the RF mod (but I no longer suspect video since I'm not getting any chirps on the speaker either). PIA seems doable too; can grab a 68B21 for around $10 including shipping, so if that's a drop-in replacement it may be worth a try (but that'd be the last chip on the motherboard we'd replace...). Hmm. We'll also watch the sales and see what we can learn about working 800s

It's cursed. Tried replacing every 74LSXX chip on the motherboard, the CMOS hex buffer, and the small chips on the personality board, all to no avail (the one exception being the "Transistor Array" on the motherboard since I wasn't sure I got the right chip. Solid blue screen every time. Sigh.

Yeah, I'm puzzled myself to be honest. Part of it is my lack of understanding of how the thing works together (I'm happy with basic circuitry, microprocessors, discrete logic chips, etc... but how they really work together so that I can understand the system and its boot process is a stretch for me, which is good and educational but I haven't found a nice description anywhere). We actually have a pretty good "junk electronics" store in town that tends to have bins full of old ICs, so I may take my friend's son downtown and go diving just for fun; that's the direction I would prefer to take, but I think they're losing interest I'll see if I can convince them to try that, though.

Yep, all things are reseated on all boards We may just get another 800, part it over until we isolate the defect, repair that, have two 800s, then sell one... but I'll flail a bit longer first.

The power supply, yes--every pin on the power supply board connector seems to give a nice clean signal on the oscope with almost no ripple at the voltages described in the service manual. The two big capacitors have tops that don't look 100% flat but are not notably bulged and I can't fault the oscope measurements. Haven't tested any chips in the ram boards, but have tested the ram boards themselves by cycling them (we have three). Have not tested the personality board or discrete logic on the motherboard mostly because I'm not sure how; suggestions welcome! By now my friend is considering buying a whole new 800 just to have swappable parts, and I can't say he's wrong, but it's be nice to have a less clumsy plan...

Also--same blue screen with no ram, which is interesting (and we've tried several boards). And the colour is changeable with the potentiometer on the CPU board, should we wish to look at a depressing green screen instead.

Ok, I'm at wit's end. By now we've replaced the whole CPU board and POKEY, and still a solid blue screen, no speaker sounds. One cartridge, submarine commander, gives a light blue screen (and some buzzing from the speaker once and never again). The next step on the flowchart is "call Atari". But that's probably not a great option. Any ideas?

Curiouser and curiouser.... disassembled it again, still don't see any obvious caps, but connected it to a different monitor with composite video... no banding whatsoever on the blue screen on this monitor, or white screen with cartridge in left slot, but cartridge in right slot gives "no video" message on this monitor. That blue screen is nice and solid--and interestingly appears regardless of the ROM/RAM cards being in place. I reseated every chip on the motherboard and rom/ram cards to no avail: blue screen. What do you think... replace POKEY? Any known suppliers besides ebay vendors I should patronize?

Hmm... although all the voltages at the power supply-motherboard connector looked pretty clean when I probed them with the O-scope. There was one large cap that looked sliiiiightly domed, but I can't convince myself fully of that.

Hmm, progress of a sort. I've been using a jury-rigged composite cable (literally a jack with two wires jammed into the bottom (ground) port on the DIN connector and the composite (immediately to the right of bottom as looking into the port?) holes on the DIN plug, but it turned out the problem was on the TV side; jiggling that gave me more solid results, but they aren't that illuminating: - With no cartridge, solid blue screen with minor artifacts (thick bands slowly scrolling up) - With "Submarine Commander" cartridge in LEFT slot, more off-white screen that looks pale blue in pic. Interestingly, pulling the cartridge and rebooting gets this same white screen, but if I leave it powered off for a while and boot without cartridge, I get the blue screen again. - With cartridge in RIGHT slot, "broken video" as if sync was strange (both horizontal and vertical). Why would left/right make a difference? Anyway, see attached and let me know if it rings any bells. I will say that the field manual says under the "Solid Blue Screen" flowchart, "Are the words "MEMO PAD" on the screen? No? Swap out the POKEY chip" so that's the likely next step, but I wanted to check before ordering one; as you say, about $20, not going to break any banks, but hey.

Russg: It's "obvious", but I missed it at least once. We totally tried powering it up without the ROM/RAM before kicking ourselves. DrVenkman: Hmmm, the problem is we swapped out the entire CPU board (6502, ANTIC, GTIA, everything) and got exactly the same results. All power pins on the power supply board tested with good voltages, too. I sorta feel like it's a problem somewhere between the CPU board and the video out. I will say I don't trust our RF mod results, because the TV in question has a digital tuner and those old RF mods were never THAT precise, but the composite should have given us better results, and the lack of sound is still distressing. Hmm.

Wonder if you folks can help... I'm trying to restore a friend's 800, which is giving... well, just awful video. Using the RF mod, when powering on the 800, the screen definitely CHANGES, but the screen is close to static (you can almost see a distorted frame as the display cycles around). We attempted composite video from the 5-pin DIN, but didn't get much of a picture, although trying the O-scope on the composite port yielded the below picture; it's trying, but not giving a picture. We found the repair manual and followed the flowchart for grey/black screen, tracing all the clock pins (which all seemed to look OK). Pin 25 of the GTIA gives a nice clean (composite sync?) signal. Since the flowchart recommended replacing the GTIA, just in case, I bought a "known tested" CPU board from eBay, which gives the same results. So I don't think it's the GTIA, but maybe something in between it and the RF mod/DIN port. But I'm not sure what to check next. I found this schematic https://atariage.com/forums/uploads/monthly_06_2012/post-26063-0-46972400-1338873000.jpg, but it'll be mildly painful to trace the whole thing through and I'm not 100% sure what I'm looking for. Any suggestions for the next step? Thanks--it'd be quite a thrill to get this working again. Oh! One more clue (maybe?)--I haven't owned an 800, so I don't know; the speaker never seems to make any sound, either when powered on or when trying control-2 (which I hear buzzes). Is it supposed to? Not sure if that helps.