juansolo Posted October 12, 2020 Share Posted October 12, 2020 (edited) Centre negative tends to be used on things that have battery and DC power as they can use sockets that switch the battery out when the DC jack is plugged in. The vast majority of guitar effects pedals are a good example. That said, manufacturers like to throw polarity curveballs out there for no reason also, like the Sinclair Spectrum for example that's also centre negative. But as you say, it's unusual and always, always double check. EDIT: Cleggy just beat me to it, as he says, you might have got away with it and at most it'll be a small handful of borked components. Edited October 12, 2020 by juansolo 1 Quote Link to comment Share on other sites More sharing options...
+mksmith Posted October 12, 2020 Share Posted October 12, 2020 21 minutes ago, juansolo said: If you've blown the cap you got the polarity backwards of the PSU. Hmm - was thinking that after it blew. Was positive ? it was ok. 18 minutes ago, Andrew Davie said: Center-negative is not that common in my experience. It was a bit of a surprise to read that. But in any case, you should be measuring the polarity on the good PS and making sure you have the same on the one you're making. Also, I was planning to whack in a diode on my effort so it would be absolutely save to plug the thing in the wrong way or use an opposite-polarity PS. Oh well... such is life. Sorry mate - obviously my confidence outwayed my ability or lack there of. Watching too many repair videos clearly. 16 minutes ago, marauder666 said: Maybe Q10, Q11 and the regulator are dead too, try cap first though. Centre negative, very common for guitar pedals. Thanks will check those as well. Quote Link to comment Share on other sites More sharing options...
marauder666 Posted October 12, 2020 Share Posted October 12, 2020 If my pluscart didnt have strange behaviour on my PAL 7800, you wouldn't have plugged it in. Sorry! 1 Quote Link to comment Share on other sites More sharing options...
+Andrew Davie Posted October 12, 2020 Author Share Posted October 12, 2020 Just now, marauder666 said: If my pluscart didnt have strange behaviour on my PAL 7800, you wouldn't have plugged it in. Sorry! You think you have problems. I'm still dealing with the the overwhelming guilt I feel. He wouldn't have tried to fix it if I hadn't have asked for a loaner. 1 Quote Link to comment Share on other sites More sharing options...
marauder666 Posted October 12, 2020 Share Posted October 12, 2020 Looking at the schematic the 9V is isolated by a few components from the 5V. Probably got away without damage to the major ICs. 1 Quote Link to comment Share on other sites More sharing options...
+batari Posted October 12, 2020 Share Posted October 12, 2020 I've plugged in a 7800 backward a few times when connecting to a digital PSU for measurement. No damage. As for the issue, one difference with the PAL 7800 is how it detects a 2600 cart. It doesn't run the signature check but instead reads a range of addresses from the cart to check whether a 7800 cart or a 2600 cart is installed, and whether to run the built-in game Asteroids or not. It also runs through a few addresses that we typically use as hotspots. I am wondering if the cart is responding to these hotspots? If so then a possible fix is to ignore hotspots until we are sure the 2600 code is actually running. 2 Quote Link to comment Share on other sites More sharing options...
RevEng Posted October 12, 2020 Share Posted October 12, 2020 Obviously too late to help here, but maybe adding a diode in to these barrel-connector conversions would be in order... not sure if the 9v being dropped a tiny bit will affect things or not, but I suspect not. This is the reason I've put off any such conversion - not that I'll personally blow it, per se - but that someday someone else will plug in the wrong adapter while playing adapter roulette. 1 Quote Link to comment Share on other sites More sharing options...
+batari Posted October 12, 2020 Share Posted October 12, 2020 If anyone is really concerned about connecting a power input with reverse polarity, a full-wave bridge rectifier, if installed right, will allow you to use any AC adapter with the correct voltage, regardless of output polarity (or you could use one that puts out raw AC as well.) 2 Quote Link to comment Share on other sites More sharing options...
+-^CrossBow^- Posted October 12, 2020 Share Posted October 12, 2020 24 minutes ago, RevEng said: Obviously too late to help here, but maybe adding a diode in to these barrel-connector conversions would be in order... not sure if the 9v being dropped a tiny bit will affect things or not, but I suspect not. This is the reason I've put off any such conversion - not that I'll personally blow it, per se - but that someday someone else will plug in the wrong adapter while playing adapter roulette. On the NTSC machine this could be done pretty easily by replacing out the ferrite bead (FB2) that is on the unregulated input voltage side to the large filter CAP with a diode? Wonder had needed that FB2 is actually? 1 Quote Link to comment Share on other sites More sharing options...
+mksmith Posted October 12, 2020 Share Posted October 12, 2020 10 hours ago, marauder666 said: If my pluscart didnt have strange behaviour on my PAL 7800, you wouldn't have plugged it in. Sorry! All good! 10 hours ago, Andrew Davie said: You think you have problems. I'm still dealing with the the overwhelming guilt I feel. He wouldn't have tried to fix it if I hadn't have asked for a loaner. Just disappointed I got it wrong Andrew - I wanted to make that change anyway as the power supplies are bloody hard to find. Unfortunately the worst part is I can't help you out with the issue just at the moment. So please don't feel any guilt over this. 9 hours ago, marauder666 said: Looking at the schematic the 9V is isolated by a few components from the 5V. Probably got away without damage to the major ICs. Well maybe some good news hey! I'll look over the board the next couple of days and check those items you suggested. None of the chips were warm afterwards so you never know... Quote Link to comment Share on other sites More sharing options...
+mksmith Posted October 17, 2020 Share Posted October 17, 2020 Great news @Andrew Davie were back in business mate. Replaced the blown cap, the regulator and Q10 and we are fully operational - everything checks out and is working. You still interested in me sending it up to you? Quote Link to comment Share on other sites More sharing options...
+Andrew Davie Posted October 17, 2020 Author Share Posted October 17, 2020 Just now, mksmith said: Great news @Andrew Davie were back in business mate. Replaced the blown cap, the regulator and Q10 and we are fully operational - everything checks out and is working. You still interested in me sending it up to you? That is good news! Can you hold off on it for a little bit, as @Al_Nafuur has purchased on on eBay and he has a better chance of understanding/fixing the issue. 1 Quote Link to comment Share on other sites More sharing options...
+mksmith Posted October 17, 2020 Share Posted October 17, 2020 39 minutes ago, Andrew Davie said: That is good news! Can you hold off on it for a little bit, as @Al_Nafuur has purchased on on eBay and he has a better chance of understanding/fixing the issue. Sure mate no problem. Let me know if you still need it ? Quote Link to comment Share on other sites More sharing options...
+mksmith Posted October 17, 2020 Share Posted October 17, 2020 Also thanks @marauder666, @juansolo, @-^CrossBow^-, @batari and @RevEng for your suggestions and encouragement ? 2 Quote Link to comment Share on other sites More sharing options...
+Al_Nafuur Posted October 17, 2020 Share Posted October 17, 2020 11 hours ago, Andrew Davie said: That is good news! Can you hold off on it for a little bit, as @Al_Nafuur has purchased on on eBay and he has a better chance of understanding/fixing the issue. the 7800 has arrived this morning, and I found a power supply with a connector that's fits in the 7800. But: the power supply has 9V AC and 800mA intensity the connector has notches like the 7800, so it fits in both directions. Can someone provide a link with the correct voltage and pinout? and of course the correct intensity (I want to minimize the amount of spectacle if something fails ? ) Quote Link to comment Share on other sites More sharing options...
+Al_Nafuur Posted October 17, 2020 Share Posted October 17, 2020 3 hours ago, Al_Nafuur said: Can someone provide a link with the correct voltage and pinout? and of course the correct intensity (I want to minimize the amount of spectacle if something fails ? ) Found the spec. here: I searched the whole house for hours now, but I can't find a Power Supply that has the 9V DC voltage and supports 1A (intensity) Quote Link to comment Share on other sites More sharing options...
juansolo Posted October 17, 2020 Share Posted October 17, 2020 Don't put AC into it, that would be bad... 1 Quote Link to comment Share on other sites More sharing options...
+Mitch Posted October 17, 2020 Share Posted October 17, 2020 They don't use the same connector but the Atari Lynx and Atari Jaguar power supplies have the correct power specs. As well as the Sega Master System and Sega Genesis. Console5.com used to sell adapters but I think they sold out. Mitch Quote Link to comment Share on other sites More sharing options...
marauder666 Posted October 17, 2020 Share Posted October 17, 2020 (edited) More amps is fine. It'll only use what it needs. 1A might not be enough for the 7800, the ST dev board, and wifi module. I'm using a Mean Well 9V 1.66A PSU into a 2.1mm DC barrel jack installed in the 7800. Edited October 17, 2020 by marauder666 1 Quote Link to comment Share on other sites More sharing options...
+batari Posted October 17, 2020 Share Posted October 17, 2020 4 hours ago, Al_Nafuur said: the 7800 has arrived this morning, and I found a power supply with a connector that's fits in the 7800. But: the power supply has 9V AC and 800mA intensity the connector has notches like the 7800, so it fits in both directions. Can someone provide a link with the correct voltage and pinout? and of course the correct intensity (I want to minimize the amount of spectacle if something fails ? ) 800ma is probably enough for testing purposes, if you can convert that AC to DC. I have run 7800s with a digital power supply, and with a normal cart they run around 630 ma. With a Concerto I've seen 700 ma. If you want something going today, you could crack open another AC adapter that puts out DC and scavenge the rectifier(s) out of it, and use them on the 9v AC one and get DC output at a current sort of close to what you need. This generally only applies to older AC adapters as a lot of the newer ones don't use the old-school transformer plus rectifier method. Quote Link to comment Share on other sites More sharing options...
+Andrew Davie Posted October 17, 2020 Author Share Posted October 17, 2020 2 hours ago, Al_Nafuur said: I searched the whole house for hours now, but I can't find a Power Supply that has the 9V DC voltage and supports 1A (intensity) Just reminding you when you do find somethng... to get that polarity right. Some DC adaptors with barrel plugs have center positive, some negative! 1 1 Quote Link to comment Share on other sites More sharing options...
+Al_Nafuur Posted October 19, 2020 Share Posted October 19, 2020 I did a short test with a 560mA 9VDC Power supply. The 7800 boots with a normal 2600 cartridge and with the PlusCart too. Despite that the image on my CRT is much better than with my PAL 2600Jr, I had some wrong pixels in the menu text. I am not sure if it is because of the power supply or if the TIA in the 7800 has some issues? On page changes a ROM starts at folders with more than 3 pages, folders with 3 (or less) pages showed an empty directory on page changes (I have no offline ROMs at the PlusCart tested).. ? 1 Quote Link to comment Share on other sites More sharing options...
+Andrew Davie Posted October 19, 2020 Author Share Posted October 19, 2020 8 minutes ago, Al_Nafuur said: I did a short test with a 560mA 9VDC Power supply. The 7800 boots with a normal 2600 cartridge and with the PlusCart too. Despite that the image on my CRT is much better than with my PAL 2600Jr, I had some wrong pixels in the menu text. I am not sure if it is because of the power supply or if the TIA in the 7800 has some issues? Current DEV has a character error in the header bar on the left edge of the WiFi symbol, which is my fault. I am correcting it. So, if that's the wrong pixel you refer to, ignore that one. Quote Link to comment Share on other sites More sharing options...
+Al_Nafuur Posted October 19, 2020 Share Posted October 19, 2020 20 minutes ago, Andrew Davie said: Current DEV has a character error in the header bar on the left edge of the WiFi symbol, which is my fault. I am correcting it. So, if that's the wrong pixel you refer to, ignore that one. No, the errors where in the menu text. I will do some retesting tonight and send a picture.. Quote Link to comment Share on other sites More sharing options...
+Al_Nafuur Posted October 19, 2020 Share Posted October 19, 2020 The font spacing on this 7800 is wrong, same issue like on the 2600 of @ZeroPage Homebrew . I have ordered a new power supply with 2A to replace the 560mA one: https://www.amazon.de/gp/product/B07NSMYZXS it should arrive tomorrow. Quote Link to comment Share on other sites More sharing options...
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