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Amiga computer related discussion => Amiga Hardware Issues and discussion => Topic started by: DanAdamKOF on March 17, 2012, 09:26:01 PM
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I recently bought an NTSC Amiga 500 with a version 6 motherboard, that won't boot up. It shows a green screen on the TV, and the Power light blinks 10 times short, 1 time long, then repeats. The caps lock light can be toggled 11 or 12 times then stops being toggleable.
Except for the Denise and CPU, I pulled every chip carefully with chip pullers, cleaned the chip legs and socket, and reseated them, and I went over the Denise and CPU legs with a generous amount of alcohol as well, but there was no change. I let the A500 run for about an hour, the Fat Agnus was warm but not hot, and the RAM chips were cool.
I also visually inspected the board and saw no cold joints, scraped traces, burned-out components, or bad capacitors. The previous owner was the original owner and only opened it once just out of curiosity, but never did anything on the inside.
I've been doing all this without any trapdoor RAM installed by the way.
It looks like I've done all there is to do when the A500 is acting like this. But if any of you guys have suggestions about other things to try, I'm all ears.
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agnus is properly seated?
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agnus is properly seated?
It seems like it. I pulled it with a PLCC puller and put it back securely twice. I could try it over and over I guess?
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Almost certainly a bad Chip RAM IC. It'll be difficult to diagnose without removing each of the RAM chips I'm afraid!
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green is chip ram error. . have you looked here?
http://wiki.classicamiga.com/Amiga_boot_error_code_colours
lost
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green is chip ram error. . have you looked here?
http://wiki.classicamiga.com/Amiga_boot_error_code_colours
lost
I did run across a similar page saying that the green screen is either a chip RAM issue or an issue with something on its bus. As far as I could tell, people were saying to test chip ram by feeling it and if it's too hot to touch, it's bad. Is there another way to test RAM, such as with a multimeter? Will bad RAM show certain points being abnormally shorted/open internally or anything like that?
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here is another link with a similar problem.. just reading it now.. might have some insight for you..
http://www.amiga.org/forums/showthread.php?t=20817
lost
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here is another link with a similar problem.. just reading it now.. might have some insight for you..
http://www.amiga.org/forums/showthread.php?t=20817
lost
Ooh, great link! I didn't run across this before, thank you for pulling up something new. I'm wondering how exactly piggy-backing works to test RAM, I guess I will need to pull up some more info, if this is something I want to do. I may just do the below:
Almost certainly a bad Chip RAM IC. It'll be difficult to diagnose without removing each of the RAM chips I'm afraid!
Missed this earlier. I'm no stranger to soldering and the board is the wonderful 80s spaced out through-hole non-rohs type, so replacing the RAM outright seems simple enough, I'd probably just put in some sockets and buy new RAM, could upgrade it to 1MB while I'm at it.
Do you think this is a guaranteed fix? I sort of dislike the shotgun approach to fixing things, but I guess it's worth a try.
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My self, a500's are cheap and a dime a dozen, I have even had 2 just given too me.. I keep them for spares.. might be just as easy just to source out a another a500 and keep the chips off this one just for parts. As for a guaranteed fix i dunno.
lost
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Do you think this is a guaranteed fix? I sort of dislike the shotgun approach to fixing things, but I guess it's worth a try.
The green screen means that the power on write then read test to memory has failed, which doesn't always mean that there is an issue with the memory ICs. Can also be related to anything that shares the memory bus. You can probably do some more tactical fault finding if you have an oscilloscope and the skills to use it.
Another quick thing to try is exchanging the two 8520 CIAs. I've seen faults where one of them being bad, I forget which one, causes a green screen error.
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It also might be that: if there is no expansion card, that may have been installed as chip RAM (just a couple for pads to cut/solder) and now without the card, it's missing half of the chip RAM. If that's what happened, all you will need to do is pop in the RAM expansion card.
The green screen usually means chip RAM, not just RAM.
I hope this helps....
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It also might be that: if there is no expansion card, that may have been installed as chip RAM (just a couple for pads to cut/solder) and now without the card, it's missing half of the chip RAM. If that's what happened, all you will need to do is pop in the RAM expansion card.
The green screen usually means chip RAM, not just RAM.
I hope this helps....
Is this something that comes like this from the factory? I didn't notice anything like that, that would have been done by hand. Could you elaborate on this some more? I'm an Amiga newbie if that's not obvious:nervous:
The A500 came with a dodgy-looking trapdoor card (no identification on it at all, cheap-looking PCB) that I took out since it has a leaked battery on it. I checked near there on the A500's board and it's unaffected. The trapdoor board seems unaffected by the battery too, I should probably remove that though. If getting pictures would help I can take some.
I'll exchange the CIAs a bit later, thank you Castellen.
As for getting a new Amiga, I guess I could, but I already spent sort of a lot to get this A500 and a C64 with a fair amount of accessories and hardware, and I prefer to fix things rather than replace them if possible. I'm OK with spending a few bucks on old RAM, or more than a few bucks on two chip pullers (which I can reuse later so that's OK), but I'd like to hold back on buying a totally different Amiga if I can help it.
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I don't have an A500 here to jog my memory, but there are three solder pads just inboard (to the left, look from the front) that need to be joined/cut in a different configuration to use the 512Kb card as chip RAM.
I'll try to find a photo of a 6a mobo to show you which pads...
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No photos, BUT this covers what I am talking about. It lists the pads involved.
http://www.amibay.com/showthread.php?t=4722
See if this helps
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I made an 1MB chip RAM MOD on my A500, if you can take pics of the jumper/pad areas we can identify if the mod was performed.
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did the battery damage the pcb? remove the battery and repair or jump what ever broken tracers on it.. better to have a 1meg machine then a 512k machine if reversing. Is there a 1 meg agnus in there?
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http://eabmobile.abime.net/attachment.php?attachmentid=13726&d=1177615199
1 meg hack
lost
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Swapped the CIA chips, no change.
I checked the jumpers and they are for sure unmodified.
The A500 board is not damaged from any leakage.
I had apparently overlooked branding on the trapdoor board, it's a "JEC 512k" (918000) http://amiga.resource.cx/exp/jec512 The battery on it has leaked but it doesn't appear to have done anything to the PCB. With the trapdoor board installed and the switch closed, the screen goes black when the LED is doing its long pulse, and when the switch is open, there's only a tiny black line interrupting the green for a brief second (same behavior as when the board is disconnected entirely).
I dunno what more I can do right now. If you guys could shine some light on this piggyback RAM test method (the link was broken in the thread this was linked from, here's a mirror: http://us4.aminet.net/aminet/docs/hard/Trouble.txt ), I could try that out.
Thank you all for your help so far!
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recapping it should be a no brainer. PM Cosmos and he can whip together a bag of caps for cheap. Just because they don't look fried doesn't mean they aren't.
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This is nice link for Amiga troubleshooting:
http://home.arcor.de/kickstart/TKA/Tutorials/troubleshooter/trouble1.html
According to the table possible problems are: Agnus, Gary, DRAMS, U2 socket.
You may need at least a spare Agnus and Gary to troubleshoot the problem.
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Some more behavior to report: When you power on the A500, you can press the caps lock button 12 times, and it won't respond to further presses.
If you press Ctrl+A+A you can only toggle caps lock 8 times after a reset.
recapping it should be a no brainer. PM Cosmos and he can whip together a bag of caps for cheap. Just because they don't look fried doesn't mean they aren't.
Is that a pretty common cause of this issue? I want to avoid the shotgun approach if I can help it. Then again, recapping is real cheap.
This is nice link for Amiga troubleshooting:
http://home.arcor.de/kickstart/TKA/Tutorials/troubleshooter/trouble1.html
According to the table possible problems are: Agnus, Gary, DRAMS, U2 socket.
You may need at least a spare Agnus and Gary to troubleshoot the problem.
I can at least say that the U2 socket looks sound. None of the pins are bent, none have oxidation or corrosion, the Agnus is held tight, the pins on the bottom are connected perfectly, and the plastic on the socket looks fine (no cracking or any funny business).
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Hi,
By golly that Amiga 500 knows it is St. Pats day, thats all
smerf
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You can boot the A500 without the keyboard attached. You will not be able to three-finger-reset of course.... but the caps-lock problem might be a bad CPU on the keyboard.
Az
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You can boot the A500 without the keyboard attached. You will not be able to three-finger-reset of course.... but the caps-lock problem might be a bad CPU on the keyboard.
Az
I've booted without the keyboard plenty of times. I don't think the keyboard is defective per se, I saw in another "green screen" thread either here or on another Amiga board that someone noticed you could only toggle caps lock a few times.
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The number of times toggling the cap lock is related to the buffer in the keyboard. The keyboard buffer can only hold so many keystrokes before it needs to be emptied by the CPU.
So, that can only tell you that the buffer is not being emptied.
The CPU should be good because you are getting Error codes, if the CPU was bad then there will be no display and no error codes.
Maybe try to boot w/o floppy drive cable and see what happens, it may take little longer, just leave it on w/o floppy drive for a minute.
Some more behavior to report: When you power on the A500, you can press the caps lock button 12 times, and it won't respond to further presses.
If you press Ctrl+A+A you can only toggle caps lock 8 times after a reset.
Is that a pretty common cause of this issue? I want to avoid the shotgun approach if I can help it. Then again, recapping is real cheap.
I can at least say that the U2 socket looks sound. None of the pins are bent, none have oxidation or corrosion, the Agnus is held tight, the pins on the bottom are connected perfectly, and the plastic on the socket looks fine (no cracking or any funny business).
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Way back in the day we isolated bad ram by feeling for the one hotter than the rest. Worth a try.
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Is that a pretty common cause of this issue? I want to avoid the shotgun approach if I can help it. Then again, recapping is real cheap.
No, bad caps rarely if ever cause this specific problem. It's some where in the chip RAM or custom chips or the pads I mentioned being re-configured.
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I can't believe I can't find any pics on the internet!! Here is a video that shows you the exact pads I was talking about. Maybe you can tell if yours have been fiddled with.
http://www.youtube.com/watch?v=swt2-JiLYt8
I sure hope something in the mess helps.
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look at above post with pdf file. It has CLEAR pic's of the mobo and what to look for, just watched that video , its ok but pdf is more detailed with close ups.
lost
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Piggy-backing chips often is worth a try - just stick the known good chip on top of the chip to be tested, such that all the pins are making contact correctly between the two. That way, if one chip has lost a connection internally, the good chip will set the output correctly as it'll be floating in the dead chip.
Testing for heat is not reliable. If it works, great, but the only time a dead chip will get hot is if there's a short circuit somewhere. If it's just a lost connection it'll be normal temperature.
The only surefire way to check for RAM being bad is to take the chip out and put it in a known good machine. One thing you can try though is to check the data line out of the RAM chip against ground - each of the chips should have roughly the same resistance between it and ground. If one is different, check that chip first.
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I had compared the PDF to my A500 earlier, it's for sure unmodified.
Piggy-backing chips often is worth a try
Thanks a lot for this! At the least I'm going to check the chips with a multimeter.
So just to make sure about piggybacking, if I were to just reuse the RAM chips already in the A500, would it boot with only 2 chips in there normally + the dead chip with a good one piggybacked? If I did this, would I need to do anything with those capacitor in the slot of the now-disconnected chip?
Again, thank you guys for your help :)
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An update, I checked each chip's pins' resistance against ground (and VCC), and found no difference in resistance from chip to chip. They were left in the board for what it's worth.
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I had EXACTLY the same problem as you with an amiga 500 (rev 6A). I replaced all possbily bad ic's with good ones of another working amiga. I also checked the ohm resistance of all 4 ram chips like you,and found no difference from chip to chip. It seems like a "dead end"...
NOT QUITE!
I finally found what the problem was, by "thermal" testing the ram chips! I simply felt with my finger the temperature of each ic on motherboard. Normally after some time on power, there must be SOME heat on every ic .I take this as a practical way to see if an ic is dead or not. If it's too hot OR no hot at all this probably means there is a problem.
Anyway, what i noticed was that one of the 4 ram chips was slightly warmer than the other 3 (3 was ~30-35c and 1 about ~40-45). This temp difference put me in thoughts: although none of the ram chips was too hot or no hot at all (which normally indocates a problem), this difference seems very suspicious. So i took off a ram chip from a spare A502+ ram expansion i have, place it above the "suspicious" chip and then press it down untill it wedged and couldn't move.
Power up, and... NO MORE BLINKING POWER LED! :)
Amiga worked like new!
Funny thing is that the ram chip sitted so well and tight above the dead one (i also cut the ground pin of the bad chip, so that will not heat up the good one above it), that i left it as is! To unsolder the bad one and solder back the working chip requires a lot of trouble if you only have a soldering gun and a suction pump. First you must remove the aluminum back plate (which requires to unscrew all the connectors on the back side of amiga) in order to have access to the back side of motherboard, as the 20pins of each ram chip is soldered on both sides of mb. Then you must do 40 unsolderings and 40 solderings (20pins on both sides of mb=40)!
I hope this info will help you too. Power up your amiga, and after 3-4 minutes check how warm are the ram chips. If you notice any temp difference then you might have found the "culprit"! ;)
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snip
Hey, that's promising. As I recall, I did thermal test, but none varied greatly in temperature. Maybe I didn't give it long enough, maybe I'm less sensitive in my fingertips than I assumed, in any case, it's something I should look into again.
An online friend has a half-working A500 he said I could have, but we haven't arranged shipping or anything like that. Truthfully I'm not 100% sure I'd hold onto the Amiga stuff after I move soon (more of a c64 guy) but I do like repairing things regardless. Hopefully we can arrange shipping and I can cobble together one fully-working A500 in the future.
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The temperature test is a good trick to start with but it doesn't work all the time. (It's surprisingly good though - I've repaired a couple of machines w/o any schematics that way!)
If everything else fails, there's no hint of bad contact on Agnus' socket, no bad solder points on the RAMs or the buffers (U34/35 - thermal?) you'll be left with desoldering each RAM chip and test it elsewhere...
Dunno if it's been covered before: doing the 1 MB chipram mod doesn't require you to have the RAM expansion in place all the time. If it's not present there's simply no difference to an unmodded board.
Then you must do 40 unsolderings and 40 solderings (20pins on both sides of mb=40)!
Don't really get that - you desolder und resolder from both sides?
Actually, 20 pins is pretty fast if the vias aren't too tight and you've got a bit of practice - once you know which one's wrong.
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Don't really get that - you desolder und resolder from both sides?Actually, 20 pins is pretty fast if the vias aren't too tight and you've got a bit of practice - once you know which one's wrong.
Every pin is soldered on BOTH sides of motherboard,so you must unsolder/solder each pin twice. For unsoldering, maybe you can heat up with soldering gun many pins together (since they are very close to eachother) and then push the ram chip underneath with a small flat screwdriver to get it off. To tell you the truth, it wasn't the unsolder/solder procedure, but rather the tedious task of unscrewing/rescrewing all the connectors on the back of the amiga, in order to remove the aluminum back plate! Amiga really has a "hell of an armor" around her! :)
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Every pin is soldered on BOTH sides of motherboard,so you must unsolder/solder each pin twice.
No. The pin's soldered into the via. The through hole has a metal rivet inside, connecting all layers (there may be more than two). For a reliable solder joint you need to solder a pin in one piece. Anything else may trap air in the via and/or cause a cold joint, leading to various trouble!
I can't even imagine desoldering in one step - how do you get a clean via without heating it thoroughly? And how do you desolder from the component side? :confused: No offense, but I've never ever seen that before.
For unsoldering, maybe you can heat up with soldering gun many pins together (since they are very close to eachother) and then push the ram chip underneath with a small flat screwdriver to get it off.
Wouldn't exactly try that either. It's a good way to tear off traces that haven't completely separated yet. If you're using a special desoldering tip or an air gun, that's something completely different of course.
To tell you the truth, it wasn't the unsolder/solder procedure, but rather the tedious task of unscrewing/rescrewing all the connectors on the back of the amiga, in order to remove the aluminum back plate! Amiga really has a "hell of an armor" around her! :)
Yeah - and then disassemble an A3000 for a change - and you'll never complain about the 500 again... ;)
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Yes i know all that my friend...
The thing is, that i DONT have any "special desoldering tip or an air gun" to do the job properly,and surely i'm not going to spent any money for any of these tools, just to unsolder a f@cking ram chip! :laugh1:
So the "never heard before" procedures i was describing to you, was the "alternatives" I had, which of course are dangerous and crappy methods, an so that's why i didnt even try to practice them on my precious amiga! ;)
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Reread the post: I said unless using special tooling I wouldn't recommend the methods you described...
I've been working with a suction pump for most of my 'career' - a 20€ iron and a 5€ pump - and think I'm fairly acquainted with it. And I can't really make out what you're doing...
Doing it the right way, desoldering with a suction pump isn't overly dangerous or crappy. Provided the solder points in question are somewhat cooperative is doesn't take too long either, you won't need more than maybe 10 seconds per point.