tezza

Hi, I followed Bryan's instructions and successfully added the UAV to my NTSC Atari 800. Even here in PAL-land I now get a great picture on composite video! I'm not sure why as the UAV is not an NTSC-->PAL converter. Perhaps my TV/monitors are simply "modern" enough to allow it? Anyway, I wrote about the experience for those who might be interested. Tez

Found the cause. Atariksi was right. It was the GTIA chip. I had a spare working scruffy ATARI 800XL that I'd kept in case I need parts. I swapped out the GTIA chip in the 400 with the one in the 800XL. The problem now no longer exists on the 400 but the junk 800XL now exibits the symptom. The latter being a parts machine, this is of no concern. My 400 is fuly working again! Thanks for the assistance. Tez

If it is stuck on, it is probably the mechanical key spring. Try tapping it several times and seeing if it seems to rebound. No, its a 400. Membrane keypad. Also it is a replacement keyboard as I thought the problem was the original keyboard. It would seem not, as this new keyboard does exactly the same thing. Tez

Hmmm. I swapped out the keyboard with a replacement one but the problem with SELECT still exists. However I have discovered my initial assessment was wrong. The SELECT key is not non-working. It appears to be stuck ON !! Oh well, a disassembly and diagnosis awaits after Xmas. Maybe it is GTIA after all? Tez

I tend to write these fixes up after they are done and this one is no exception. It's at the URL below for anyone whose interested. http://www.classic-computers.org.nz/blog/2010-09-04-fixing-an-atari-400-screen-issue.htm Tez

Yes, I would tend to agree. The SELECT and OPTION keys would have been thrashed in the day and I wonder if the membrane has just had it as far as those two keys are concerned. If it was a ribbon connection issue, I would have expected a few more keys to be down. They are the ONLY keys which don't respond, even if you clasp the membrane keyboard between thumb and forefinger and squeeze hard. RESET and START are fine. Tez

I hear (and understand) what you're saying. It might be physically difficult to do though. I always worry that brittle ribbion which is the keyboard cable is going to snap if I play around with the innards with it still connected. It's hard to position the naked keyboard without putting strain on the ribbon. I seem to recall in my last thread regarding the ANTIC chip someone mentioned an a 800XL GTIA might be backwards compatible with a 400 one? Anyone know for sure? I could then do a swap over and check that way as I have a 800XL (in fact I have two..one is a parts machine which could be a donor). Tez

Hi, I just repaired a screen issue mentioned in another thread. The problem? A faulty ANTIC IC. Anyway, on testing the unit after reassembling I noticed another unrelated issue. The SELECT and OPTION keys don't work. I'm not sure it they were working before I disassembled the machine, as I've never really given this micro a good once-over until now. They many have never worked in the time I owned the machine! All other keys work including Shifted keys plus RESET and START. Would a good assumption be a problem with the keyboard membrane or maybe that brittle (and bastard to get in and out) keyboard connector? I'm assuming that if all other keys work apart from those two the keyboard driver chips are likely to be ok...but then I could be wrong? Anyone else had this problem or have any thoughts on the issue? Tez

Just closing this up. The problem was indeed the ANTIC chip. A new one arrived today. I replaced, reassembled and the Atari 400 is working as it should! Well...almost. I've just noticed the OPTION and SELECT keys don't work. Every other key does including RESET and START! These were probably existing problems as I never really had a good look at this computer until the screen issue. Most likely suspects are the membrane or maybe keyboard cable I guess. These two keys would have been hammered in the day. I might post a separate note about this and get some opinions? Thanks to everyone who contributed to this screen fix. Tez

Interesting. Had I known this I would have tried it when I had my Atari 800XL open to swap out the CPU. It may have given me a definitive answer as to whether ANTIC was the problem. Anyway, both the XL and the 400 are closed up now and I've ordered the part. Hopefully that's the cause. I can't think of what else it might be. Vintage computers never fail to surprise me though. I've had problems with a couple of my machines where the failed parts were static components namely a greencap capacitor and a resistor pack! Tez

Yes that was the first thing I did, along with reseating all the chips. No, it doesn't have enough lines. The bottom border is much larger than it should be. I know it is part of the border as it can be changed with POKE command. Tez

Where are you located? Perhaps, may be cheaper to pick-up a 800XL if you need multiple chips. New Zealand. Problem is the ANTIC chip is different in the Atari 800XL. I do have a spare Atari 800XL. Many of the other chips are the same but not the ANTIC unfortunately. I sent a paypal order off about 30 mins ago. I'll let the forum know if a replacement solves the problem. Many thanks to everyone who assisted. Tez

Right, I reassembled the machine... yes, it does. It changes the black areas (the top and side border and huge (1/3 screen) border at the bottom) a grey colour. There is a beep with every keypress. Holding START down when switching on causes beeping. I tried a few game carts. The screen is differet from No cart and BASIC, which are virtually the same. The game carts all show different symptoms but the result is always random coloured bars or squares on the screen with a dark background. Given that BASIC commands seem to work, the keyboard beeps when it should, and the fact the attract mode kicks in, I guess this is further evidence of faulty ANTIC, rather than, say, ROM? Tez

Hi Kurt, Hehehe. Yes, I've got a few projects which need writing up so there will be a few appearing soon. This one among them once I get the machine fixed. One of the entries which may be of interest to this community will contain a restoration project on an Atari 800XL which includes some retr0Brighting and the hazards of a dodgy power supply. Anyway..I digress... It was fun taking the Atari 400 apart. The design is like no other I've seen with two plug-in boards, one containing the RAM and the other the CPU and other propriety chips. For someone like me, used to single board computers like Apple IIs, more modern Atari's, PETs etc., this was an interesting design. It must have been expensive to make. No wonder prices for the 400 stayed so high for so long in the early 1980s. It's an artifact. The camera just picked up a bit of the scan line. Well, I just got a quote for a ANTIC chip. The email came through while I was writing this. $10 plus $15 shipping priority mail (or $6 "slow boat" mail). US dollars of course. One other question from those who might know? Could this symptom be possibly be caused by the CTIA chip? My feeling is that if this chip had failed I would be unlikely to get a clear picture at all. However, I'm thinking that if there is doubt, it might be wise to order both, given shipping costs. Tez

Here is the unit when it was working. http://www.classic-computers.org.nz/collection/atari-400.htm Tez

The pattern is not static. As soon as the screen is visible the letters/characters all change rapidly (and seemingly randomly) many times a second. It's so fast you cannot tell what the initial pattern was. The colours don't change though. Wait, I better qualify that. The character and background colours do change, but only every 15-20 mins or so. However, I noticed the Atari 400 did this if you had it in a BASIC loop displaying something for a long period of time, even when it was going properly. I'd assumed this was normal behaviour (is it?). Tonight I'll try reconnecting the keyboard and see if I get a beep with start, and also try pressing return with the BASIC cartridge in. Thanks for the replys. I've got to order the ANTIC chip from the US and given shipping costs from there to New Zealand, I want to make sure that's the problem before committing myself to that course of action. Tez

Thanks for those replys. Yes, I've detached the keyboard and no change. The symptom is the same whether a cart is inserted or not. I'll reconnect the keyboard and try pressing the RETURN with the BASIC cartridge inserted as suggested. The unit has only 16k. Tez

Hi, While exercising my Atari 400 the other day the machine suddenly developed a fault. The bottom 1/3 of the screen is black and the top 2/3 is full of random characters all changing very quickly. You can see a photo here: I've swapped out the RAM and almost all of the logic chips (except the 74LS158s on the RAM board...I didn't have any spares....however, I did transpose the two that were there and that didn't make a difference). I've also swapped out the CPU. No change. Power voltages to the board are fine. Has anyone come across this before on a 400 or 800? I suspect a fault in the ANTIC IC. Before I go and order one however, I'd be interested in what others think? I've been using the 400/800 field service manual as an aid to diagnosis but it doesn't specifically mention this symptom. Tez

Just to make it clear, in the sentence above I'm talking about 2 heaped tablespoons of Arrowroot prior to heating , NOT two tablespoons of Oxi. As I re-read it it struck me it could be ambigious. I just used a pinch of Oxi-magic Tez

Yes, it was mixed very well, although I had to dilute it first in a little bit of water, as initially the Oxy did not dissolve in the paste at all, no matter how long I mixed it. I'll leave out the Glycerine next time and see what happens, although I may need to buy a better brand of Oxy as this was a Tesco "cheapo version" for about £1.70. The better brands where about £5 plus. Hmm..interesting. I stirred it quite vigourously when I added the Oxi. I used 2 heaped tablespoons to get a really thick paste, and stirring after it had formed (i.e. after heating) helped thin it a little as well as to thouroughly mix in the Oxi. I found the Oxi didn't so much dissolve (as you'd see it dissolve if it was in water), but the mixture started to lighten up a little. Become light and frothy, and in fact it was impossible to see into it to see if Oxi lumps where there or not. I only used a tiny bit of Oxi. About 1/5 of a teaspoon. Strange that you didn't get any kind of reaction? I guess there are different brands of Oxi as you say, and maybe the glycerine also had an effect. The good thing is that it worked, regardless! Tez

Thanks for that feedback. Interesting. With 6% I got a mild foaming (you can see it in the Vic blog post). One other person over at the Vintage Computer Forums who did this with 12% said it foamed a lot..so much so it spilled over the side of the container. Hence Merlin's warning about foaming on the wiki. I think he might have overheated the mixture though and it was very hot. He had a 1000W microwave and it's diffcult to get the timing right, especially with just a small amount of liquid. One thing I did was to stir the mixture fairly vigourously after I added the Oxi, just to make sure it was well-distributed in the paste. Did you do this? If this wasn't done, perhaps it doesn't foam much. Alternatively, perhaps the glycerine has an anti-foam effect? Yes, I agree re-application due to drying out is a pain, and if I had had a blacklight I would have used that. I found that even though my units spent a lot of time "dry" during the process it still worked! (The paste dried in about 30 mins but I generally only re-applied 4x a day or so). I can only conclude either the thirty minutes at the time the units were wet under the strong UV we have here was enough bursts at a time, or the reaction continued under the dried flakes (probably the latter). But yea, using the sun is the el-chepo option and I would only recommend it if people had a very small number of cases, and didn't want to buy a blacklight for a one-off use. Tez

Well done, Looks like a pretty good result to me. Similar to what I found with my Atari 130XE. How did you get on with the Arrowroot recipe? Did you find it thickened up enough this time with some heating? From memory I think others use glycerine to help smooth out the lumps from Xanatan gum? I found with the arrowroot , providing you mixed it well (and broke up any lumps) before heating you didn't need glycerine. Personally I wouldn't go for higher concentration peroxide, unless you are going to dilute it. It may be a trade off between peroxide strength and time, but lower conc. peroxide is far safer. My treatments worked well at 6%. H2O2. Tez Tez

Sounds interesting if it is already in the form of a gel. Do you have a junk case you could try this cream on? Tez

For me it took a bit of managing. In the hot NZ sun, the paste would dry out in about 30 mins. It kind of formed a "scale" or large flakes over the case. You can see what it looked like here. I didn't apply another coat immediately it was dry (this was just unmanagable) but each unit did get a re-application about 3 to 4 times a day. I just painted over the scale (actually most of it flaked away as I was painting). I also rotated the physical positioning of the computers while I did this. In other words, if one side had been out of the sun, I turned the case around so it WAS in the sun. Even with the strong sunlight, one day usually wasn't enough. Most units got two days. The Atrari 130 XE got a third day several days after the main treatment, as I'm sure I could still see a tinge of yellow/green on one side (the extra day's treatment fixed that). The VIC-20 seemed fully done after one day. This was quite remarkable as there was cloud cover that day and it was actually quite dull! However, the paste didn't dry so quickly either which perhaps contributed to the great result. I used the sun (and Arrowroot), as I was looking for a method someone could use with a minimum expense i.e. without buying hard-to-get/find products or investing in a blacklight, setting up a room etc. . Really for people like myself who had less than 5 machines that needed the treatment, with no one machine being particularly rare or valuable. However, if I had lots of cases to do, or they were very valuable machines I would have explored the blacklight option rather than the sun, simply because you can control the variables much better. Horses for courses I guess. I'd be interested to hear of any results with the Arrowroot variation of the recipe and Blacklight exposure as opposed to sunlight. Anyone tried this, or intend to try it? Tez

Err...yes it's about 200 mls. Is that 1/2 pint, or less? It's a long time since I visited the UK, so I'm just trying to visualise in my head the size of the pint of beer. I consumed quite a few of these when I was there, but (perhaps understandably) I don't remember much about it (-: Tez