suspicious_milk Posted December 30, 2012 Share Posted December 30, 2012 I've got a 64k coco2 with 8x 8042665 chips. I could use these in the 800xl? Haven't used the Coco in years, and dont' really plan to . . . Quote Link to comment Share on other sites More sharing options...
Joey Z Posted December 30, 2012 Share Posted December 30, 2012 (edited) bad ram would probably show up in the self test. to use a multimeter, you need to have it in voltage mode (for this) and you need to put the black lead on any ground pin on the motherboard. the bottom left pin of just about any chip will work. the top of the chip is always identified by a notch. you will also probably see a pretty big trace going to it if it is a ground pin. then the red lead goes to the pin in question. also, you want to check /BE when you start with OPTION pressed, and also when you start without OPTION pressed. Edited December 30, 2012 by Joey Z 1 Quote Link to comment Share on other sites More sharing options...
suspicious_milk Posted December 30, 2012 Share Posted December 30, 2012 (edited) bad ram would probably show up in the self test. to use a multimeter, you need to have it in voltage mode (for this) and you need to put the black lead on any ground pin on the motherboard. the bottom left pin of just about any chip will work. the top of the chip is always identified by a notch. you will also probably see a pretty big trace going to it if it is a ground pin. then the red lead goes to the pin in question. Other than than the pin notch & OPTION key, thing, that's all new to me - - - I'll giver her a go hopefully later today. I was leaning towards bad RAM because though the SELF TEST shows good, it is not testing all of it. The part it is not testing (I"m guessing) is the RAM in which BASIC is loaded to (but yet not come up). This is a spare unit, and if I have to solder/desolder anything chances are good I'll screw it up. But am willing to risk it for the experience. Been practicing (watched some how to videos) and the soldering part, I"m not *too* bad at for a noob, but desoldering - - - I've got a LOT more practice to do :-) I have a bad Apple IIGS board that will attest to that THANKS!! Edited December 30, 2012 by suspicious_milk Quote Link to comment Share on other sites More sharing options...
Joey Z Posted December 30, 2012 Share Posted December 30, 2012 Other than than the pin notch & OPTION key, thing, that's all new to me - - - I'll giver her a go hopefully later today. I was leaning towards bad RAM because though the SELF TEST shows good, it is not testing all of it. The part it is not testing (I"m guessing) is the RAM in which BASIC is loaded to (but yet not come up). This is a spare unit, and if I have to solder/desolder anything chances are good I'll screw it up. But am willing to risk it for the experience. Been practicing (watched some how to videos) and the soldering part, I"m not *too* bad at for a noob, but desoldering - - - I've got a LOT more practice to do :-) I have a bad Apple IIGS board that will attest to that THANKS!! well, if the RAM that is hidden under BASIC is bad, you won't know until you are able to get basic disabled. anyway, my money is on bad PIA or MMU, like the others said. if /BE changes depending on whether the OPTION key was pressed during power up or not, that points to a bad MMU. if it doesn't change, that points to a bad PIA. looking at the symptoms however, I am thinking bad MMU seeing as how BASIC doesn't start, although I suppose it could be that the BASIC ROM is bad in addition to one of the other things. anyway, we will know soon enough. Quote Link to comment Share on other sites More sharing options...
suspicious_milk Posted December 30, 2012 Share Posted December 30, 2012 (edited) well, if the RAM that is hidden under BASIC is bad, you won't know until you are able to get basic disabled. anyway, my money is on bad PIA or MMU, like the others said. if /BE changes depending on whether the OPTION key was pressed during power up or not, that points to a bad MMU. if it doesn't change, that points to a bad PIA. looking at the symptoms however, I am thinking bad MMU seeing as how BASIC doesn't start, although I suppose it could be that the BASIC ROM is bad in addition to one of the other things. anyway, we will know soon enough. Yes; without a doubt - - I lose voltage when booted with OPTION. So bad MMU? I'll have to scrounge a new one. That is one of the VERY FEW chips on this board in a socket, so I can save my mad soldering skills for another day ;0) I have a 65xe and an extra XEGS, I'll have to take a peek and see if either has a socketed one (or despite the 61618 number on them, are they internally different among different Atari models?). EDIT: nope, no sockets. Don't really want to risk either full working Atari with my unrefined desoldering. I'll pick up an MMU somewheres else. Thanks Again, to all who responded! Edited December 30, 2012 by suspicious_milk Quote Link to comment Share on other sites More sharing options...
Joey Z Posted December 30, 2012 Share Posted December 30, 2012 (edited) I don't think they are different, but I am not exactly the person to ask. I have only owned an atari for a few years, and have only recently explored the inner workings of the 64K+ machines. Until recently I only had a 48K machine, so that was all I was interested in. Even now, I don't have a machine with an MMU in it, I have a 400 with custom circuitry in it to do 64k... anyway, looking here: http://www.atarimax....org/achmmu.html, the XEGS MMU is a different part number, so I wouldn't try it since you have the 65XE to try. also, looking at the schematics, the 65XE should have an MMU that is compatible, but somehow I don't think it will be socketed in the 65XE. I think XE's rarely had anything except maybe the RAM socketed. I also doubt the XEGS would be socketed even if it does have an MMU that will work, so time to try out those desoldering skills anyway, good luck. I guess it has to be the MMU, because regardless of the state of /BE, you have 40 blocks on self test, right? so basic isn't getting disable, but the enable line is definitely changing if you got a voltage change. do you happen to remember the numbers you got for when you checked the voltage? I just want to make sure that they are definitively different logic levels before you desolder something you didn't have to. EDIT: OK I see you decided to not have an attempt at desoldering the MMU. but if you could give me the numbers you got on the /BE pin that would help to make sure that the MMU diagnosis is correct. and also, one last thing to check would be the RD4 and RD5 lines if you could. Edited December 30, 2012 by Joey Z Quote Link to comment Share on other sites More sharing options...
suspicious_milk Posted December 30, 2012 Share Posted December 30, 2012 (edited) No cart - RG reads a "1" on the MM while R4 reads 1018 (but fluctuates up to 1020). With a cart, I get no reading at all (the LCD display goes blank while connected). Darnit, sorry for double edit - EARLIER the BE line read "162" then dropped to "1" with OPTION., now I'm getting different numbers on it every time I test it with no apparent pattern. Edited December 30, 2012 by suspicious_milk Quote Link to comment Share on other sites More sharing options...
Joey Z Posted December 30, 2012 Share Posted December 30, 2012 are you sure there aren't decimal points somewhere in those readings? and you have it set on DC volts, right? Quote Link to comment Share on other sites More sharing options...
suspicious_milk Posted December 30, 2012 Share Posted December 30, 2012 (edited) are you sure there aren't decimal points somewhere in those readings? and you have it set on DC volts, right? No I wasn't sure. Sorry. OK this time, I cleared my work area, waited between resets, and was careful and methodic. My MM dial was set to V (20). With No Cart: R5 - 4.94 R4 - 0.00 With Cart: R5 - 4.94 R4 - 4.94 No OPTION Boot: BE - 0.17 With OPTION Boot: BE - 4.91 BASIC No OPTION Boot: 4.95 BASIC with OPTION Boot: 4.95 Thanks for your patience with me here. My head is not on straight, I'm down with the Flu and trying to stay busy. I'm normally a not such a moron ... Edited December 30, 2012 by suspicious_milk Quote Link to comment Share on other sites More sharing options...
Joey Z Posted December 30, 2012 Share Posted December 30, 2012 (edited) OK, hold the purchase of the MMU. RD5 should not be 5v with no cart. with the machine off, check the resistance (with the ohms setting) of R13 (ohms are measured from one side of the resistor to the other if you don't know) EDIT: it also looks like the RD5 pin on the cartridge port (pin 14) is right next to 5v (pin 13) visually make sure there is not a short between the two pins on the motherboard. look here for the pinout: http://www.hardwarebook.info/Atari_8-bit_Cartridge pin 1 is usually labeled on the motherboard. Edited December 30, 2012 by Joey Z Quote Link to comment Share on other sites More sharing options...
suspicious_milk Posted December 30, 2012 Share Posted December 30, 2012 OK, hold the purchase of the MMU. RD5 should not be 5v with no cart. with the machine off, check the resistance (with the ohms setting) of R13 (ohms are measured from one side of the resistor to the other if you don't know) should I unplugged the machine and turn it on to drain xs power 1st? Quote Link to comment Share on other sites More sharing options...
Joey Z Posted December 30, 2012 Share Posted December 30, 2012 I guess so, and also see the edit. Quote Link to comment Share on other sites More sharing options...
suspicious_milk Posted December 30, 2012 Share Posted December 30, 2012 OK, hold the purchase of the MMU. RD5 should not be 5v with no cart. with the machine off, check the resistance (with the ohms setting) of R13 (ohms are measured from one side of the resistor to the other if you don't know) EDIT: it also looks like the RD5 pin on the cartridge port (pin 14) is right next to 5v (pin 13) visually make sure there is not a short between the two pins on the motherboard. look here for the pinout: http://www.hardwareb...8-bit_Cartridge pin 1 is usually labeled on the motherboard. I cleaned the cart slot just to be on the safe side. Didn't see any problems on either side of the board. Machine off, MM on OHM @ 711 but fluctuates like crazy (up to 1200+). I'm still gonna try to get an MMU, wether or not its the issue (it wouldn't hurt to have an extra for testing). Is the resistor the problem or a symptom? Quote Link to comment Share on other sites More sharing options...
Joey Z Posted December 30, 2012 Share Posted December 30, 2012 (edited) I cleaned the cart slot just to be on the safe side. Didn't see any problems on either side of the board. Machine off, MM on OHM @ 711 but fluctuates like crazy (up to 1200+). I'm still gonna try to get an MMU, wether or not its the issue (it wouldn't hurt to have an extra for testing). Is the resistor the problem or a symptom? The resistor would have been the problem, but it seems to be fine. the resistor is there to keep the input pin on the MMU from 'floating' to a high state when there is no cartridge plugged in and the RD5 line is disconnected. OK, just one last thing to check, measure the resistance between pin 13 and 14 on the cartridge port. it will either read a low value (a problem) or it will read infinity (your meter may tell you OL for overload or it may behave differently. it depends on the meter) EDIT: remove the MMU when you do this in case the MMU is shorted internally so you don't get a reading that is erroneous. Edited December 30, 2012 by Joey Z Quote Link to comment Share on other sites More sharing options...
suspicious_milk Posted December 30, 2012 Share Posted December 30, 2012 MM set to ohms 2000; read 808 between pins 13/14 ( with or without MMU ) Quote Link to comment Share on other sites More sharing options...
Joey Z Posted December 30, 2012 Share Posted December 30, 2012 OK, LAST THING. power up the 800XL with the MMU removed and no cartridge inserted (it won't boot right in this state, but don't worry, it shouldn't damage anything) check the voltage between where RD5 normally is on the MMU socket, and ground. if it is 0, then the MMU is the problem. if it is at (or close to) 5v, then there is a problem elsewhere. otherwise, the MMU is probably defective. sorry about all this, I just like to be absolutely sure before I send someone off to spend money on a part they might not need. Quote Link to comment Share on other sites More sharing options...
suspicious_milk Posted December 30, 2012 Share Posted December 30, 2012 its like 0.1. so, bad MMU after all. Really appreciate your help!!! Quote Link to comment Share on other sites More sharing options...
Joey Z Posted December 30, 2012 Share Posted December 30, 2012 Your welcome. Let me know if the MMU fixes it then, and good luck. Quote Link to comment Share on other sites More sharing options...
thax Posted June 23, 2013 Share Posted June 23, 2013 Hello fellow atarians, I am having same problem with my 800xl, been fine for 30 years and suddenly it doesnt goto basic on boot up. followed your posts and its 40 ram blocks normal and 48 if hold down option. ive reseated the mmu and basic chips already and they were clean and probably didnt need it! Please let me know where to get a MMU chip replacement. Dont need to solder, my 800xl is REV A no. 034 so its a real oldie! the chips are socketed, so heres hoping to get a new mmu. Its funny, very very rare do I play cartridge games, but prob has been since I have done recently. Thinking of checking connections for dry joints ect. will liet you know! thanks again! Quote Link to comment Share on other sites More sharing options...
russg Posted June 25, 2013 Share Posted June 25, 2013 (edited) Hello fellow atarians, I am having same problem with my 800xl, been fine for 30 years and suddenly it doesnt goto basic on boot up. followed your posts and its 40 ram blocks normal and 48 if hold down option. ive reseated the mmu and basic chips already and they were clean and probably didnt need it! Please let me know where to get a MMU chip replacement. Dont need to solder, my 800xl is REV A no. 034 so its a real oldie! the chips are socketed, so heres hoping to get a new mmu. Its funny, very very rare do I play cartridge games, but prob has been since I have done recently. Thinking of checking connections for dry joints ect. will liet you know! thanks again! Best Electronics CO61618 MMU NML16L8LNJ/NC 408-243-6950 Mon-Fri PM hours Pacific time. Minimum order may be $15... then there's shipping. http://www.best-electronics-ca.com/ Edited June 25, 2013 by russg Quote Link to comment Share on other sites More sharing options...
Federico Musso Posted July 25, 2020 Share Posted July 25, 2020 Hi im having the same problem, the atari 65xe was working perfectly and one day I started having this same issue ill post the readings of the mmu Im getting 5V 5.14 S4 5.14 BE 0,18 RD4 nothing RD5 0,54 is my mmu faulty? Quote Link to comment Share on other sites More sharing options...
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