stargazerf3a Posted February 1, 2018 Share Posted February 1, 2018 (edited) Hello to all members ,Yesterday i had a lucky find outside the trash, a XEGS always wanted an 8 bit computer and voila but,When i power it up it goes to memory test which shows me two red squares for rom. Every ram square (40 of them) are passing the test ok.Already i tried to reseat the only socketed chips Rom and GTIA also used contact cleaner but the same happens.Also i've removed every capacitor and measure it with a capacitometer and every single one is ok.I am asking you is there a way to bypass the self test maybe put 5Volts to pin 6 of mmu?Is there anythink else i can do ? I have a full electronic lab except a logic probe.Thank you for your time... Edited February 1, 2018 by stargazerf3a Quote Link to comment Share on other sites More sharing options...
stargazerf3a Posted February 1, 2018 Author Share Posted February 1, 2018 And Rom shows as 2OM maybe this is a clue? Quote Link to comment Share on other sites More sharing options...
Paul Westphal Posted February 1, 2018 Share Posted February 1, 2018 (edited) Just replace the two chip ram, available from best electronics. I can almost guarantee you they are MT ( Micron Technology ) ram. The ram won't reset; it acts like statics ram, or just bits of it won't work at all.. The motherboards are cheap so take care in desoldering them because it's easy to pull up a trace and pad. I use a Hakko. Can you post a pic of your power supply please? Edited February 1, 2018 by Paul Westphal Quote Link to comment Share on other sites More sharing options...
1050 Posted February 1, 2018 Share Posted February 1, 2018 And Rom shows as 2OM maybe this is a clue? It is in my book, sure enough. Borderline timing issue that is effecting how both rom is read and ram is written/read back. I would attempt to piggyback a 74HCT08 logic chip onto the 74LS08 chip you already have to see if that makes a very noticeable difference. Be sure to squeeze the legs of the addon chip so that each leg makes good contact and you might want to be squeezing it and moving it ever so slightly to see if this might induce better contact and make the display straighten up. Chances that your ram and rom are both bad at the same time are slight. Your display is based entirely in ram and it's wrong with a single replacement 2om. Rom isn't reading correctly at all and yet most of the code is good? Rom usually makes a real mess of the bed when it goes bad. All of that running code is 99.999% good and it all comes from rom. Can't be both ways, but it sure can have a weak clock causing bad timing issues which the HCT08 will straighten out. We can hope. Quote Link to comment Share on other sites More sharing options...
EzdineG Posted February 1, 2018 Share Posted February 1, 2018 Had the same issue recently. Burned a new ROM and all was good. Quote Link to comment Share on other sites More sharing options...
stargazerf3a Posted February 2, 2018 Author Share Posted February 2, 2018 Thank you guys for your answers , My iron is of weller brand My power adapter is a sony ericsson mobile phone 5Volt adapter So first i will replace 74ls08 chip and then memmory chips Also question how do i burn the rom to the existing chip? Quote Link to comment Share on other sites More sharing options...
+DrVenkman Posted February 2, 2018 Share Posted February 2, 2018 You can’t burn a rom to the existing mask rom chip. The best option for you is probably to order a new rom. Alternately, if you have an EPROM burner and blank EPROM chip of the correct type, then you’d be able to burn a new one. Quote Link to comment Share on other sites More sharing options...
stargazerf3a Posted February 2, 2018 Author Share Posted February 2, 2018 You can’t burn a rom to the existing mask rom chip. The best option for you is probably to order a new rom. Alternately, if you have an EPROM burner and blank EPROM chip of the correct type, then you’d be able to burn a new one. I suppose a compatible eeprom is out of the question? Quote Link to comment Share on other sites More sharing options...
stargazerf3a Posted February 3, 2018 Author Share Posted February 3, 2018 Just changed the 74ls08 with a 74htc08 but problem is not solved so next i'll try changing ram chips Quote Link to comment Share on other sites More sharing options...
1050 Posted February 3, 2018 Share Posted February 3, 2018 I suppose a compatible eeprom is out of the question? Not normally done is all, I don't have a recommendation either. But you'll need a 27256 equivalent, eprom speed should be rather slow 200ns, don't know about eeprom speed though. http://atariage.com/forums/topic/259483-xegs-game-rom/?do=findComment&comment=3639787 It's likely to be the ROM but ram is lower pin count. Will need a programmer for eeprom too but there are some good cheap USB universal programmers out there on eBay for example. $40, I'd get one myself but I already have such a version in parallel printer port style made a bit before USB took over like it has. Quote Link to comment Share on other sites More sharing options...
stargazerf3a Posted February 4, 2018 Author Share Posted February 4, 2018 Not normally done is all, I don't have a recommendation either. But you'll need a 27256 equivalent, eprom speed should be rather slow 200ns, don't know about eeprom speed though. http://atariage.com/forums/topic/259483-xegs-game-rom/?do=findComment&comment=3639787 It's likely to be the ROM but ram is lower pin count. Will need a programmer for eeprom too but there are some good cheap USB universal programmers out there on eBay for example. $40, I'd get one myself but I already have such a version in parallel printer port style made a bit before USB took over like it has. This one could do the job? https://www.ebay.co.uk/itm/USB-Universal-Programmer-Support-13000-ICs-EPROM-FLASH-MCU-PIC-7pcs-Adapters/111631739482?epid=1588690105&hash=item19fdc52a5a:g:EU0AAOSw8-tWT92U And also which eprom will i need? Quote Link to comment Share on other sites More sharing options...
1050 Posted February 4, 2018 Share Posted February 4, 2018 Yes it will. A bit spendy but you get a bunch of programming sockets for the small square packages if that's something you wanted. https://www.ebay.co.uk/itm/Eprom-TMS-27C256-20JL-4-Pieces-IC-TEXAS-INSTRUMENT/232623130991 Download the datasheet for it to find speed rating of 200ns represented by the -20JL part of the number. 10F1 short for 100ns 12F1 short for 120ns and many other 'codes' used and each one should be looked up in it's own datasheet only. This is legwork and it should be done. I find that my 8bits appreciate 200ns speed OS ROMS. Faster ones have been flaky - sort of like what you have right now (!!!!!). So above, you buy 4 when you only need one because the slow ones aren't so popular anymore? I would here all day long and consider it an investment. Unless you can find one at 200ns at a reasonable price by spending a bit more time at it than my measly couple of minutes. Same programmer will handle eeproms and the number there is 28256, but again I don't know what speed would be best there. Commercial usable eproms are working but not same speed as eproms as I know the game to be played - don't understand that, haven't gone there so I can't suggest a thing except you are on your own. Quote Link to comment Share on other sites More sharing options...
stargazerf3a Posted February 5, 2018 Author Share Posted February 5, 2018 Thank you for your help,i've ordered the programmer and 5 eproms 1 Quote Link to comment Share on other sites More sharing options...
stargazerf3a Posted March 22, 2018 Author Share Posted March 22, 2018 (edited) Hello guys, With your help i was able to resurrect my atari xegs i've also made a sio2pc cable and now i am enjoying 8bit goodness All it took was a tl866 programmer and a blank eprom THANK YOU GUYS Edited March 22, 2018 by stargazerf3a 2 Quote Link to comment Share on other sites More sharing options...
+kheller2 Posted March 22, 2018 Share Posted March 22, 2018 Hello to all members , Yesterday i had a lucky find outside the trash, a XEGS always wanted an 8 bit computer and voila but, Oh do share the story.. I love these stories. Quote Link to comment Share on other sites More sharing options...
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