mattlacey Posted June 18, 2014 Share Posted June 18, 2014 Hey Everyone, I recently picked up an 800XL from eBay that was described as for parts / not working. It didn't come with any cables apart from the power, so I fixed up a 5pin DIN to Composite, and I also have an RF cable from my 2600 to hand. When connecting the computer to my TV via either method the screen is just a mess, looks as though it's not synced right even though I fancy I can see a white patch where the cursor would be in the buffer as it jumps around. I'd love to learn how to fix this, but I'm not entirely sure where to start. There's no visually obvious issues when the machine is opened up, and the PSU is delivering 5.1V on all lines which drops to around 4.7 when the machine is powered on... is that about normal? If so, what are the next steps to take? I've got a multimeter and scope to hand. For reference, it's a PAL Rev C. Quote Link to comment Share on other sites More sharing options...
Paul Westphal Posted June 19, 2014 Share Posted June 19, 2014 Are you connecting it to a PAL TV? PAL and NTSC are 50hz and 60hz respectively. Quote Link to comment Share on other sites More sharing options...
Rybags Posted June 19, 2014 Share Posted June 19, 2014 Does the video just roll or does it appear scrambled (like diagonally distorted) ? Check the COxxxx number on Antic, ensure it's a PAL part. If it's an NTSC Antic then the system will generate NTSC refresh/scanline count video with PAL encoding. Another possibility is the 4050 IC - it receives the 4 luma bits + CSync from GTIA. Quote Link to comment Share on other sites More sharing options...
mattlacey Posted June 19, 2014 Author Share Posted June 19, 2014 It's definitely a PAL machine and has the PAL chip numbers according to a table I found linked on another thread. It's not just rolling, it's probably distorted and crazy I didn't realise that the pot you can adjust was for colour and thought that might be to do with the timing; it seemed to have a pretty big effect on the display but didn't get anything close to working really. I'm guessing I'll need another machine so that I can start part swapping to work out what's up, and need to get a few tools like an IC puller too. I really don't know much about electronics but that's partly why I bought the thing, I want to start learning more about the hardware side. Managed to replace the real time clock chip on my Falcon successfully! Quote Link to comment Share on other sites More sharing options...
Rybags Posted June 19, 2014 Share Posted June 19, 2014 You can pull ICs by prizing each end in turn with a small precision screwdriver. The trick is don't lift one side too much higher than the other each time. Pulling and reseating the GTIA and 4050 is probably a good idea, there might just be oxidation on some pins causing a poor signal. I'd say chances are the CSync signal is somehow being corrupted, not sure if the voltage drop you mention is within what'd be called normal, but it'd be handy to try an alternate power supply. If you have the soldering skills you could use a USB wall-wart, so long as it can supply 1 Amp it'd be OK for the Atari - of course >1.2 Amps would be the optimum. Quote Link to comment Share on other sites More sharing options...
mattlacey Posted June 19, 2014 Author Share Posted June 19, 2014 I was expecting the power supply to be quite complicated, got a pleasant surprised when it was just 5v on 3 lines and ground elsewhere! Will definitely give that a try. Looking at the legs of the GTIA this morning I could see a lot of oxidation on the outside, so perhaps popping them out and giving them a quick once over will help. Will take a crack at it tonight and let you know now I get on. Quote Link to comment Share on other sites More sharing options...
Rybags Posted June 19, 2014 Share Posted June 19, 2014 Usually just prying the chip up 1 mm then reseating is sufficient. The power supply, I resoldered the plug a few years back, there's only actually 2 pins used. Quote Link to comment Share on other sites More sharing options...
mattlacey Posted June 19, 2014 Author Share Posted June 19, 2014 Resat pretty much everything and cleared up a little oxidation but it's not really made a difference. This is what the display looks like with the colour pot wound down towards the colour end (or what seems to be the colour end on this machine): https://vine.co/v/MTA5aQa16et Quote Link to comment Share on other sites More sharing options...
mattlacey Posted June 22, 2014 Author Share Posted June 22, 2014 Kinda tried everything I can think of with this thing but to no avail... think the next step might be ordering a new GTIA and ANTIC chip from Best Electronics unless anyone else has some ideas? Quote Link to comment Share on other sites More sharing options...
+Larry Posted June 22, 2014 Share Posted June 22, 2014 If the keyboard is ok ( and I don't really know how you would tell with the current issue other than you can hear a "click"), you may be better off in the long-run to buy a new mobo from BEST for $39.95 (IIRC). Mine are all late-model Taiwan mobo's, and then you can use the old board as a possible donor for the future. I wouldn't throw money at a bad board, not knowing if it will fix the issue. -Larry 1 Quote Link to comment Share on other sites More sharing options...
BillC Posted June 22, 2014 Share Posted June 22, 2014 A different power supply should be the first step, the voltage specification of the ICs is 5.0V +-5%, which means 4.75V is the minimum voltage which they are designed for. Some may work corrrectly at lower voltage but it's unlikely that all will, and it only takes one IC not working properly to cause problems. You could also check the power supply for AC voltage, I built a power supply from scratch once and the 800XL I tested it with wouldn't work, I checked and found AC ripple on the +5VDC( I can't remember how much since this was about 25 years ago). After replacing a couple of capacitors it was, and still is, good. Quote Link to comment Share on other sites More sharing options...
russg Posted June 22, 2014 Share Posted June 22, 2014 (edited) Resat pretty much everything and cleared up a little oxidation but it's not really made a difference. This is what the display looks like with the colour pot wound down towards the colour end (or what seems to be the colour end on this machine): https://vine.co/v/MTA5aQa16et That looks like a sync problem, not using the right display format, PAL for NTSC or whatever down under. Can you try a different monitor, or a different setting or input jack? Looks almost like a horizontal hold out of sync. .... You mentioned a 2600 RF cable. Does the 2600 work? (That video you show, is turned sideways?, it isn't vertical like that.) Edited June 22, 2014 by russg Quote Link to comment Share on other sites More sharing options...
mattlacey Posted June 23, 2014 Author Share Posted June 23, 2014 That looks like a sync problem, not using the right display format, PAL for NTSC or whatever down under. Can you try a different monitor, or a different setting or input jack? Looks almost like a horizontal hold out of sync. .... You mentioned a 2600 RF cable. Does the 2600 work? Yeah I thought Vine knew which way up my camera was, but ho-hum 2600 works fine, I get similar results using a composite monitor lead and RF :/ Quote Link to comment Share on other sites More sharing options...
mattlacey Posted June 23, 2014 Author Share Posted June 23, 2014 A different power supply should be the first step, the voltage specification of the ICs is 5.0V +-5%, which means 4.75V is the minimum voltage which they are designed for. Some may work corrrectly at lower voltage but it's unlikely that all will, and it only takes one IC not working properly to cause problems. You could also check the power supply for AC voltage, I built a power supply from scratch once and the 800XL I tested it with wouldn't work, I checked and found AC ripple on the +5VDC( I can't remember how much since this was about 25 years ago). After replacing a couple of capacitors it was, and still is, good. It shows a steady 5v when the machine is powered on, when I flick the swtich though it drops to 4.7V... is that about normal? Quote Link to comment Share on other sites More sharing options...
mattlacey Posted June 24, 2014 Author Share Posted June 24, 2014 Right, so I got to test using a friend's power supply and with his the video is not scrabled. It is however, a solid screen of dark red. So that means a) I need a new PSU and b) something else must be screwed. Correct? Quote Link to comment Share on other sites More sharing options...
1050 Posted June 26, 2014 Share Posted June 26, 2014 Yes? Not real sure what your voltage is even after you've said three times now. When you turn it on it goes from 5.1 to 4.7 I'm hoping. What does your friends power supply give? Visuals are helpful and show a clear difference between power supplies it seems, but it's the voltage measurement with clear statements as to when that voltage was read that will help the most. But I like pictures too, so take more if you want. And Kudos for your meter use right off like that, some are not so helpful in that regard. You may have one or several ram chips shorted from yet another power supply in the past that sent overvoltage onto the board. This extra load from shorted ram chips would be enough to take a good 5.1 volts down to below proper standards. Seems to fit so far. To check if this might be the problem you can turn it on with either power supply and leave it on for five minutes and then you touch each ram chip to see if your skin is melting on the end of your finger. Just kidding, but a bad ram chip will be so hot that you will look to see if you still have fingerprints afterwards so don't be careless about it just in case you do have a couple shorted ram chips in there, they are really, really hotter than the rest. Which run quite warm even when they are working perfect. These would be the eight, 16 pin chips all in a column on the left side of the board, each one needs to be checked. And a IR thermometer might be just the ticket if you have one handy, instead of the melted finger thing. If this is the case then you just pull those extra hot chips and replace them, and you are probably fixed. The overvoltage condition does not get to effect the larger 40 pin chips because the ram chips fail so quickly and bring the voltage back down to a level that it rarely hurts any other chips on board. Built in safety valves you might think of them. Number one failure mode too, so never use a power supply until you first put a meter on it to see if it isn't a system killer first. And they are out there... Quote Link to comment Share on other sites More sharing options...
mattlacey Posted June 27, 2014 Author Share Posted June 27, 2014 Yes? Not real sure what your voltage is even after you've said three times now. When you turn it on it goes from 5.1 to 4.7 I'm hoping. What does your friends power supply give? Visuals are helpful and show a clear difference between power supplies it seems, but it's the voltage measurement with clear statements as to when that voltage was read that will help the most. But I like pictures too, so take more if you want. And Kudos for your meter use right off like that, some are not so helpful in that regard. Yeah, you're right with the 5.1 to 4.7 drop when powering the machine on. I built a USB -> 7pin DIN cable yesterday and am running that from a 2.1A Apple USB wallwort... the machine is showing a solid red with that too, but at least that's better than the original PSU. The interesting thing is, when I measure the voltage across the power lines now, it goes for 5.1v with the machine off to ~4.4 when it's powered on. I left the machine on for a while last night (around 20 minutes) and a few chips were warm but not too far above ambient temp. As for the ram chips, the bottom 3 (closest to the front of the machine) were definitely warmer than the rest but they weren't hot in the slightest. Is there a way to work out which chips are FUBAR short of swapping them with known good ones? I don't have another machine to hand and not sure my mate will like me stealing his Quote Link to comment Share on other sites More sharing options...
1050 Posted June 27, 2014 Share Posted June 27, 2014 No, not really, swapping them out is the easiest way to go, which is why most of us have spare machines to pull from when needed. You can buy those chips on FleaBay for not a lot, you are looking for 150 nanosecond speed 4164 dram chips which are 64k by 1 bit wide often abbreviated as 64k x 1. But now it doesn't sound much like bad ram if they aren't hot in the slightest. You could almost cook eggs with them if this was the problem and you had a decent power supply. Maybe there is something else stealing the power? Careful what ever it is will be hot. Try the power switch for heat, check everything you can think of. Hey!! An idea! Remove the ram chips and try measuring voltage again to see what you get. Machine won't work without them of course but if they are bad then the voltage should stay close to 5 when they are removed from the board. Start with those bottom three warm ones while leaving the rest in and if the voltage stays around 5 then you caught them red handed. Might be your power supply isn't really putting out those amps or the juice is getting lost in supply wires a tad too small to carry a real good load? Shorted rams might draw as much as 4 amps from a standard 1 amp power supply, but the voltage will be way down. Quote Link to comment Share on other sites More sharing options...
mattlacey Posted June 27, 2014 Author Share Posted June 27, 2014 I've not found anything hot in the machine so far... will try measuring the voltage without those chips tonight though. I know the supply and cables are good for the stated 2.1A as I checked that out with the multimeter after putting it together. Will let you know how I go testing without the chips. Problem with being in Australia is spare machines are hard (and expensive) to come by. I guess I could get a US machine if I just want RAM and things which won't be different there to here (as opposed to the NTSC GTIA etc.). Quote Link to comment Share on other sites More sharing options...
Rybags Posted June 27, 2014 Share Posted June 27, 2014 If you want to get rid of it, I'd probably take it. I've got a loose non-working 800XL motherboard here which needs a home, I might be able to get a working machine with what's at hand. Quote Link to comment Share on other sites More sharing options...
mattlacey Posted June 28, 2014 Author Share Posted June 28, 2014 (edited) So today I found this field service manual: http://www.atarimania.com/documents/Atari_800XL_Sams_Computerfacts_Technical_Service.pdf and started following it through with an oscilloscope to work out what might be bad. Didn't find anything in the guide so got to the logic charts and started checking the ICs starting with the RAM. Finally got to U3 (I wasn't going in order) and was not getting the expected values on any of the legs Stood up to take a better look and the top leg, #20 wasn't in the socket but wedged off to the side! I must have installed it badly (shame on me) last week when I was trying to work out what was wrong but had the bad PSU. Reseated that chip, took it over to the TV to try it out and POW! Nice blue screen and the READY prompt. Did the ROM and RAM test and all clear so we're looking good. Appreciate all the input guys... next step, retr0bright! Edited June 28, 2014 by mattlacey 2 Quote Link to comment Share on other sites More sharing options...
1050 Posted June 28, 2014 Share Posted June 28, 2014 (edited) Bad link, looks like you added some text to it and that got cut off while it messed up the link too. Great news, still wondering what chip though. OK, I'll play: http://www.atarimania.com/documents/Atari_800XL_Sams_Computerfacts_Technical_Service.pdf Now where is the missing text? Edited June 28, 2014 by 1050 Quote Link to comment Share on other sites More sharing options...
mattlacey Posted June 28, 2014 Author Share Posted June 28, 2014 Gah, I could have sworn I fixed that with the edit button but now it won't let me edit again! Full text: So I found this service manual (http://www.atarimania.com/documents/Atari_800XL_Sams_Computerfacts_Technical_Service.pdf) and started following it through with an oscilloscope to work out what might be bad. Didn't find anything following the guide so I started working through the chips checking each leg using the logic tables in the back of the book. When I got to U3 (I wasn't going in order) I found that none of the pins had the right p/h/l values, and when I stood up to take a closer look I saw that the last pin (20) wasn't in the socket but splayed out over the side! I must have reseated it badly (shame on me) when trying to work out what was wrong with the machine when I was using the bad PSU. Reseated that chip once more, took it over to the TV to try it out and POW! Nice blue screen and the READY prompt. Did the ROM and RAM test and all clear so we're looking good. Appreciate all the input guys... next step, retr0bright! Quote Link to comment Share on other sites More sharing options...
russg Posted June 28, 2014 Share Posted June 28, 2014 Gah, I could have sworn I fixed that with the edit button but now it won't let me edit again! Full text: So I found this service manual (http://www.atarimania.com/documents/Atari_800XL_Sams_Computerfacts_Technical_Service.pdf) and started following it through with an oscilloscope to work out what might be bad. Didn't find anything following the guide so I started working through the chips checking each leg using the logic tables in the back of the book. When I got to U3 (I wasn't going in order) I found that none of the pins had the right p/h/l values, and when I stood up to take a closer look I saw that the last pin (20) wasn't in the socket but splayed out over the side! I must have reseated it badly (shame on me) when trying to work out what was wrong with the machine when I was using the bad PSU. Reseated that chip once more, took it over to the TV to try it out and POW! Nice blue screen and the READY prompt. Did the ROM and RAM test and all clear so we're looking good. Appreciate all the input guys... next step, retr0bright! What chip? Quote Link to comment Share on other sites More sharing options...
tregare Posted June 28, 2014 Share Posted June 28, 2014 he said it was U3 Quote Link to comment Share on other sites More sharing options...
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