at5200forever Posted February 2, 2020 Share Posted February 2, 2020 Been working on my A/V mod, and general maintenance/upgrade work on my Atari 7800 system. Almost done -- but unwritten some solder bridges in place and plugged it in with RF shield. Some part of it stated to burn. I think it was the part next to the power cord. I fixed the short circuiting situation. Now when I plug the unit in, it immediately powers up (without my pressing power button), and no matter what I do, I can't turn off power without going to wall power pack and unplugging it. Something's out of line... What's the part next to the power supply input called, and how can I get another component to replace it? Thank you. Quote Link to comment Share on other sites More sharing options...
+DrVenkman Posted February 2, 2020 Share Posted February 2, 2020 Some photos of your 7800 board would help people here help you with your 7800. That said, the “part next to the power supply input” is probably a capacitor (tall, cylindrical blue component). Those can certainly produce smoke if they get blown. If your system isn’t responding to the power button, it’s probably the 4013 flip-flop chip. Unfortunately, those are generally soldered to the board and replacing it will require desoldering the old chip, installing a socket and then a new chip. 1 Quote Link to comment Share on other sites More sharing options...
at5200forever Posted February 2, 2020 Author Share Posted February 2, 2020 Ah, the flip-flop. That does make perfect sense. The little puff of smoke came from under the RF ?hield, in the upper right corner right in that area. I’ll see what I can do to replace that and let you know how it turns out. Thank you sir! Quote Link to comment Share on other sites More sharing options...
+DrVenkman Posted February 2, 2020 Share Posted February 2, 2020 12 minutes ago, at5200forever said: The little puff of smoke came from under the RF ?hield, in the upper right corner right in that area. I’ll see what I can do to replace that and let you know how it turns out. Thank you sir! There’s a second, smaller electrolytic capacitor under the RF shield so that’s likely blown and shorted in addition to the 4013 being dead. Per the schematics, that should be C61, 220 uF radial, but confirm that once you remove the RF shield. Good luck with the repairs! Quote Link to comment Share on other sites More sharing options...
at5200forever Posted February 2, 2020 Author Share Posted February 2, 2020 Here’s a set of photos of my Rev C board, w/ UAV Rev. D. I’d be interested to know if anything else catches your attention. 1 Quote Link to comment Share on other sites More sharing options...
at5200forever Posted February 2, 2020 Author Share Posted February 2, 2020 This is an eBay unit I’m fixing up, because I have wanted one for myself since the first preview of the 7800 in a 1984 AtariAge magazine. Bought two from eBay, first arrived with a smashed case, and other issues. This is the second, better one. The other is a Rev B where this is Rev C. The caps are all new (Console5 7800 cap kit). Replaced pause switch that looked like someone spilled drink on it. Then replaced power switch after the incident last night. Blue LED mod just because we can. New volt regulator. Considered Longhorn A/V for this unit but no skill, prior experience, nor luck with the surface mount work required. That is the reason for the socketed chip below the resistor pack. Dremel cuts to the cartridge slot guide for Imagic carts and the RF ?hield for wiring A/V jacks. AtariGuide power supply brick. Beyond that it’s a stock 7800 from circa 1988. Quote Link to comment Share on other sites More sharing options...
+DrVenkman Posted February 2, 2020 Share Posted February 2, 2020 At first glance, I don't see and damage to the top of the caps, though it's also possible for them to split down by the bottom out of view, so make sure to give them a good look-over. I do see you have the UAV sitting on top of the system BIOS chip - what are you using to insulate the bottom of the UAV to prevent any contact with the stuff underneath? 1 Quote Link to comment Share on other sites More sharing options...
at5200forever Posted February 2, 2020 Author Share Posted February 2, 2020 The UAV is held to BIOS (and insulated therefrom) by some industrial strength fasteners (Velcro). I followed Cros$bow’s lead on that from his video, seemed solid advice. This box is as old as this effort. Easily 12 years. Quote Link to comment Share on other sites More sharing options...
at5200forever Posted February 2, 2020 Author Share Posted February 2, 2020 The flip-flop is on order. A socket awaits it... Quote Link to comment Share on other sites More sharing options...
+Stephen Moss Posted February 4, 2020 Share Posted February 4, 2020 If you can remember where the solder shorts were (what was shorted to what) it would help to try and identify any component that may have failed, however if you are not certain it might just be the image but to me the 4th item from the left in that group of components immediately below the 4013 looks like something might have happened to it. If C55 is open circuit the 4013 will not get its reset pulse as the external power is applied, it is possible that a race condition could result in the output of the 1st stage (pin 1) going high (5V) when it should be low (0V), however I would not expect that to affect subsequent power on/off cycles resulting form pressing the power switch. An Emitter to Collector short on either Q9 or Q10 would result in immediate power on and no power off. Quote Link to comment Share on other sites More sharing options...
at5200forever Posted February 4, 2020 Author Share Posted February 4, 2020 Hi and thanks for your note. No damage to 4th from left in the row under 4013 socket — it’s just a diode, not a resistor. ? My mistakes were replacing the voltage regulator, without (a) noticing the solder had bridged, and then (b) installing the RF shield not noticing it was making contact with the legs of the voltage regulator which I had not trimmed. Not my finest hour... I think the rest of the system besides the 4013 chip may be intact. I rescued it very very quickly at first sign of issues, fixed the short, then observed that it wouldn’t turn off the next time I tested. Output seemed unaffected. Won’t know until late in the week. Quote Link to comment Share on other sites More sharing options...
+-^CrossBow^- Posted February 4, 2020 Share Posted February 4, 2020 Yeap most like the flip flop. I had a 7800 with the same issue a number of years ago. Soon as you plugged it in, it would turn on and never turn off. Replacing that IC took care of it. Had another one before that wouldn't power on at all and it actually had that small ceramic/tantalum cap just above pin 14 on the flip flop burned to a crisp on the board. Ended up having to replace it and the MJE201 tranny before that one worked again. Quote Link to comment Share on other sites More sharing options...
Dustin22mason Posted September 9, 2023 Share Posted September 9, 2023 Needing some help I’ve just did a full tune up with composter's on my 7800 and replaced the voltage regulator and did a av mod on it everything work but I’m getting smoke coming from the voltage regulator any ideas Quote Link to comment Share on other sites More sharing options...
+x=usr(1536) Posted September 9, 2023 Share Posted September 9, 2023 Already being covered in the following thread: Please don't post the same question in multiple threads. I get it, you need help with this, but keeping everything in one place is about the only sane way to provide help. Thanks. 1 Quote Link to comment Share on other sites More sharing options...
Dustin22mason Posted September 9, 2023 Share Posted September 9, 2023 Quote Link to comment Share on other sites More sharing options...
Dustin22mason Posted September 9, 2023 Share Posted September 9, 2023 Quote Link to comment Share on other sites More sharing options...
Dustin22mason Posted September 9, 2023 Share Posted September 9, 2023 Quote Link to comment Share on other sites More sharing options...
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