A500: Green Screen/11 blinks, reseating chips didn't help...

[DanAdamKOF]

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.

[DanAdamKOF]

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?

[DanAdamKOF]

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?

[DanAdamKOF]

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.

[DanAdamKOF]

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.

[DanAdamKOF]

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!

[DanAdamKOF]

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).

[DanAdamKOF]

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.

[DanAdamKOF]

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

[DanAdamKOF]

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.

[DanAdamKOF]

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.