Marius Posted December 16, 2013 Share Posted December 16, 2013 Hi, Due to a lightning strike very near my house (thank god nog IN my house) I have some equipment that needs repairment. One is my Atari 850. It has a very strange defect: it does do RX, but no TX. When I switch on a good Lantronix (The other one was dead too due to lightning) I get all the needed data on my screen. But as soon as I want to type something, it fails. With another 850 it works immediately. Also tried R2: on that defective 850, but that also fails. Since I do not have schematics of atari 850 it is getting trial and error. Perhaps someone an idea, or schematics? Thanks in advance! Quote Link to comment Share on other sites More sharing options...
BillC Posted December 16, 2013 Share Posted December 16, 2013 Hi, Due to a lightning strike very near my house (thank god nog IN my house) I have some equipment that needs repairment. One is my Atari 850. It has a very strange defect: it does do RX, but no TX. When I switch on a good Lantronix (The other one was dead too due to lightning) I get all the needed data on my screen. But as soon as I want to type something, it fails. With another 850 it works immediately. Also tried R2: on that defective 850, but that also fails. Since I do not have schematics of atari 850 it is getting trial and error. Perhaps someone an idea, or schematics? Thanks in advance! The Jerzy Sobola schematics are available on this webpage: http://republika.pl/jsobola/ The 850 Interface Service Manual is here. Quote Link to comment Share on other sites More sharing options...
Joey Z Posted December 17, 2013 Share Posted December 17, 2013 Hi, Due to a lightning strike very near my house (thank god nog IN my house) I have some equipment that needs repairment. One is my Atari 850. It has a very strange defect: it does do RX, but no TX. When I switch on a good Lantronix (The other one was dead too due to lightning) I get all the needed data on my screen. But as soon as I want to type something, it fails. With another 850 it works immediately. Also tried R2: on that defective 850, but that also fails. Since I do not have schematics of atari 850 it is getting trial and error. Perhaps someone an idea, or schematics? Thanks in advance! it sounds like maybe the power supply circuit is screwed up. the fact that it receives means 5V must be good, but there are also 10V and -8V supplies. specifically Q102 is used for -8V regulation, so that could be the culprit. otherwise, the LM324's are used to amplify the TTL signal to RS232 levels, so that may also be the problem. It could also be one of the diodes related to the RS232 voltages, like CR112, CR113, CR118, CR119. Quote Link to comment Share on other sites More sharing options...
thorfdbg Posted December 17, 2013 Share Posted December 17, 2013 One is my Atari 850. It has a very strange defect: it does do RX, but no TX. When I switch on a good Lantronix (The other one was dead too due to lightning) I get all the needed data on my screen. But as soon as I want to type something, it fails. With another 850 it works immediately. Also tried R2: on that defective 850, but that also fails. Probably one of the 1488 (RS232 line drivers) is defective and requires replacement. Quote Link to comment Share on other sites More sharing options...
Rybags Posted December 17, 2013 Share Posted December 17, 2013 (edited) I once fixed a PC that had suffered lightning strike via the phone line. Turned out the dialup modem PCI card copped it and you could see the fried component. If you open up the 850 you might be able to actually see physical damage from a surge. Seems I don't have schematics or a FSM for it, unsure if they even exist. If you're doing modem dialup, a surge protection device for the phone line is probably a good idea, I've got a surge powerboard that has one built in, you should be able to get phone ones seperately and pretty cheap. Edited December 17, 2013 by Rybags Quote Link to comment Share on other sites More sharing options...
Joey Z Posted December 17, 2013 Share Posted December 17, 2013 (edited) Probably one of the 1488 (RS232 line drivers) is defective and requires replacement. no 1488 in there. they use op amp on TX and transistors with clamping diodes for RX (assuming jerzy's schematics are correct) my 850 seems to have 324 and 3086 in it, so it would make sense. Edited December 17, 2013 by Joey Z Quote Link to comment Share on other sites More sharing options...
BillC Posted December 17, 2013 Share Posted December 17, 2013 Probably one of the 1488 (RS232 line drivers) is defective and requires replacement. According to the schematic the 850 uses LM324 Op-Amps for RS232 output, and LM3086 Transistor Arrays for RS232 input. Most likely it is one or both of the LM324 blown, but it could also be the +10V supply as all of the op-amps have the +terminal connected to it through R164, a 10K resistor. Quote Link to comment Share on other sites More sharing options...
Marius Posted December 17, 2013 Author Share Posted December 17, 2013 Thanks guys for all your help. I'm going to unscrew the 850 open soon, and investigate. The damage happens through our LAN here, and not through the power-supply. Everything that was connected with a RJ45 connector was fried, and everything else was good. The Atari 850 was connected to the LAN with the Lantronix at the moment it happened. I think that the +10 (+12?) V theory supply is an interesting one, since also the R2: port is not doing TX, and R2: was not connected at the moment of trouble. I'll give it a shot soon. I am very fond of my Atari 850's so I hope I can repair this one. Quote Link to comment Share on other sites More sharing options...
Marius Posted December 25, 2013 Author Share Posted December 25, 2013 (edited) I replaced the LM324 on Serial1 and it's working again. Is the metal shielding inside very important btw? It was very rusty and dirty so I decided to remove it. I know a lot of atari equipment has such a shielding, and they all work fine without... but I was wondering is this also the case in the 850? Thanks for your help folks! Prowizard p.s. how come that the LM324 has not that info on the IC printed? It shows: LM349... is that equal to LM324? Edited December 25, 2013 by ProWizard Quote Link to comment Share on other sites More sharing options...
Marius Posted December 25, 2013 Author Share Posted December 25, 2013 (edited) Sigh... that darned Jerzy Sobola with his full-of-failure schematics all the time. It is NOT a LM324, but a LM349 ... sigh, I ordered wrong IC now. Ok... but now I know more. Thanks anyway Pro Edited December 25, 2013 by ProWizard Quote Link to comment Share on other sites More sharing options...
AtariGeezer Posted December 26, 2013 Share Posted December 26, 2013 The LM324 and LM349 are both quad op-amps and pin compatible. Guess he thought they were suitable subs... Quote Link to comment Share on other sites More sharing options...
Marius Posted December 26, 2013 Author Share Posted December 26, 2013 The LM324 and LM349 are both quad op-amps and pin compatible. Guess he thought they were suitable subs... Perhaps they are... but I have tried several of those schematics in the past, and they all had mistakes; from smaller to serious mistakes. Although it's nice there are digital PDF versions of the schematics, I need to be able to trust the schematics. If it's a typo, ok... but if he is going to change parts, because they are compatible, it's dangerous; why not stick to the original, used parts, and let someone else (the user of the schematic) decide whether it wants to use the original parts, or substitutes. But ok, that's another discussion. I'm glad I found the problem (thanks again for all the help here guys) and I'll order LM349. I am also going to try the LM324 I ordered. If it works I'll let that know too. Quote Link to comment Share on other sites More sharing options...
Mathy Posted December 26, 2013 Share Posted December 26, 2013 Hello ProWizard If you're a member of the ABBUC, you can download most of the original schematics from the ABBUC website. Sincerely Mathy Quote Link to comment Share on other sites More sharing options...
Marius Posted January 7, 2014 Author Share Posted January 7, 2014 Today I had some spare time to test LM324, and at first sight I thought: ah it works. But it doesn't work very well. When I type slow to my modem (typing A......T......Z..... enter works). But when I type fast: ATZ ... it misses characters. This also happens when I'm on a telnet BBS and typing a message; it sometimes sends the wrong character (byte) through the RS232. Strange enough: receiving works perfect with the LM324, so it is only on the TX. When I replace it with a good LM349 the 850 works perfect. So indeed: LM324 is a mistake in this schematic. 1 Quote Link to comment Share on other sites More sharing options...
thorfdbg Posted January 10, 2014 Share Posted January 10, 2014 Today I had some spare time to test LM324, and at first sight I thought: ah it works. But it doesn't work very well. When I type slow to my modem (typing A......T......Z..... enter works). But when I type fast: ATZ ... it misses characters. This also happens when I'm on a telnet BBS and typing a message; it sometimes sends the wrong character (byte) through the RS232. Strange enough: receiving works perfect with the LM324, so it is only on the TX. When I replace it with a good LM349 the 850 works perfect. So indeed: LM324 is a mistake in this schematic. The 324 is a quad op-amp that should be pretty hard to break. Unfortunately, the 324 is also pretty slow (very bad slew-rate). If you have no replacement available, you could try to add pull-ups from the output of the op-amp (3.9K to VCC) to add some load on the line. This helps *a bit*. Output pins are 1,7,8,14 IIRC. I wonder why they used an Op-amp for this instead of dedicated RS232 receivers (i.e. the 1488/1489). I need to check what I have in my 850XL - it is almost but not completely a 850 rebuild. Quote Link to comment Share on other sites More sharing options...
drac030 Posted January 10, 2014 Share Posted January 10, 2014 Sigh... that darned Jerzy Sobola with his full-of-failure schematics all the time. Jerzy is a very experienced hardware-man, and a senior gentleman at the same time, so you might think one could forgive some mistakes. I also do not think that he would refuse accepting corrections, if you decide to point them out to him. 3 Quote Link to comment Share on other sites More sharing options...
Marius Posted January 10, 2014 Author Share Posted January 10, 2014 Jerzy is a very experienced hardware-man, and a senior gentleman at the same time, so you might think one could forgive some mistakes. I also do not think that he would refuse accepting corrections, if you decide to point them out to him. Ok you are right; My apologies for my not so kind words about the schematics. But on the other side: when you are into electronics you have to rely on the accuracy of the schematic. I have had too many times with these schematics that things were wrong. I can remember in one case, this lead into serious damage of my PCB. So when there was again this failure (I still do not understand why someone replaces a component with a possible substitute in a schematic of an obsolete device like the 850) I was frustrated because I already ordered the part, which now indeed turns out to be a wrong part. I'm not experience enough to conclude for myself I ordered the wrong part. I trusted the schematic. On the other side, since I'm not experience enough indeed, I'm also not in the position to judge the overall quality of his work (the schematics), and I shouldn't have used the words I used. So if mr. Sobolo is reading this: Sorry, I hope you'll accept. Quote Link to comment Share on other sites More sharing options...
Marius Posted January 10, 2014 Author Share Posted January 10, 2014 I bought LM349 in France, which were here lightning fast (within 2 days!) ... replaced the wrong parts in the 850, and it works like new again. So end of story: I'm happy again! Quote Link to comment Share on other sites More sharing options...
BillC Posted January 10, 2014 Share Posted January 10, 2014 Jerzy is a very experienced hardware-man, and a senior gentleman at the same time, so you might think one could forgive some mistakes. I also do not think that he would refuse accepting corrections, if you decide to point them out to him. I believe Jerzy also makes his schematics through examination of the device in question, I have noticed that some of his schematics don't list components that are missing from different revisions. This means he could have used an 850 in which the 349s had already been replace by 324s as the basis of his schematic. Quote Link to comment Share on other sites More sharing options...
Marius Posted January 10, 2014 Author Share Posted January 10, 2014 I believe Jerzy also makes his schematics through examination of the device in question, I have noticed that some of his schematics don't list components that are missing from different revisions. This means he could have used an 850 in which the 349s had already been replace by 324s as the basis of his schematic. Perhaps other components are replaced then too (like someone mentioned in this topic). Just replacing the LM349 with LM324 is not working very well. Well, anyway... I have my 850 back up running again, so I'm hoping lightning strikes will not happen the next 37 years (it was the first one in 37 years for me, so I'd say: let's repeat that). Quote Link to comment Share on other sites More sharing options...
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