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Old 03 November 2010, 01:17   #1
ffunk
 
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Amiga 500 resurrection help

First of all greetings to all of you Amiga lovers, this is a wonderful place!
I am passionate Amiga lover and previous owner of a500 (15 years ago). I decided to buy Amiga once again, so I did. It was bought from domestic auction site, and was marketed very clever (the title was "good, old amiga") and I fell for the trick, though I payed 15EUR for it.
The A500 is unfortunately faulty. But very apart form that some very strange things happened in these days of my recovery tryouts.

First when I plugged it I couldn't tune it at all. My TV set could not find the channel. I hooked it up with A520 to composite out in composite in jack on my tv and still no picture. After numerous hard resets, military(dark) green screen appeared. I knew about the error codes and got the reference for faulty chip ram. Nevertheless I got impression it had to be light green not dark...
Ok, now I hooked the tuner again and found the signal at around 550MHz. It was always the same, dark green. I turned it off and forgot about her for a day.

Next day I opened her, and found that she is in a good cosmetic condition (custom chips in place, never opened, leads ok). The one thing I had noticed immediately was the trapdoor expansion memory, which has barrel Ni-Cd battery and it leaked destroying the memory module. I barely removed it, because of the oxidation, but fortunately no acid residue was spilled on the motherboard (on one picture below, an acidic residue can be seen only on the pins of the trapdoor expansion slot).

Then I gave it a try, and from that moment till now the situation got worse. No green screen, just black with a little of moving flicker lines. I push the power button on psu and I get some signal (voltage rises from A520) but every time I power it on it was the same.
In anger, I hard reseted the psu unlimited number of times and something strange happened. The screen went from a solid stable black (possible start of the boot sequence) to usual blackness with some slight moving flicker

Next, I inserted the composite cable to monochrome output and tried the same thing again. I got the usual blackness with something moving, but suddenly after countless resets I got white screen. It isn't probably white because it is on monochrome output.

Now pulled up my sleeves, got the tools and done the usual faulty Amiga checks.

1. I changed the amiga PSU to my ATX PC PSU... No change
2. I pulled out all custom chips, including agnus. Cleaned and reseated them firmly... No change
3. I swapped the places of CIA chips... No change
4. Inspected all connections, leads, capacitors... All visually look ok.

The things I noticed strange apart from all this are:
- keyboard acts normally, power led is on solid, caps lock key is lit for a second when I power on the psu.
- i can light the caps lock key exactly 6 times (12 presses total), and it won't lit again.
- floppy drive doesn't click, I presume it is faulty or something else is the problem.
- when I put diskette in the FDD it detects it immediately and starts to spin very sluggishly and does nothing. Very weird behavior... I also unplugged the data cable left it only on power and the FDD did the same thing all over again :|

That is probably all I tried to do, and I need your help. I am desperate to make this one work, can't wait for another auction or anything :|
Can someone please tell me what can I do next?

Thanks in advance


Here are some pictures of my A500







 
Old 03 November 2010, 03:09   #2
Loedown
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Welcome to EAB and there's a few clues in what you write.

1. Judging by the photo of the expansion port and trapdoor port, I would say it's had something go bad on both.

2. If the battery acid has leeched into the board layers and I haven't got an A500 apart in front of me to check and I am too sick to have a look at mine here, then there's no telling what sort of damage has been done and indeed what sort of 'hybrid' pathways have been created by the acid leak on the trapdoor pins.

3. Most likely there is going to be some sort of issue between some Address / Data pins on the trapdoor expansion, either an unusual resistance or inadvertent short.

If I were you then I would actually clip the pins off as close to flush with the motherboard as I could on the trapdoor expansion port, they are ruined anyway then clean up the whole area using something like CRC Contact Cleaner and a toothbrush. Oddly enough after that it will most likely boot.
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Old 03 November 2010, 03:51   #3
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Lemon juice for the trapdoor pins. Then wash with tap water and let it dry for a couple of days on a vented cupboard.

Then sack out and reinsert the Agnus chip.

With the Amiga turned on put your finger over every chip to feel if one is oddly way too warm.

Check voltage rails on the power supply connector internally.

If everything fails, then you'll have to find someone with an A500 or A2000 near your place to swap the custom chips, one at a time. Chances are you have a busted Paula or CPU.
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Old 03 November 2010, 06:55   #4
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Swap the CPU first..
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Old 03 November 2010, 08:13   #5
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Stupid question time: Have you taken a good look under the motherboard? Maybe there's some acid attacks under there... or maybe you can see a sign of something. Super dried solder joints, acid attacks etc.
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Old 03 November 2010, 10:33   #6
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Quote:
Originally Posted by 8bitbubsy View Post
Stupid question time: Have you taken a good look under the motherboard? Maybe there's some acid attacks under there... or maybe you can see a sign of something. Super dried solder joints, acid attacks etc.
A500 doesn't usually suffer from dry joints, certainly not to the degree to cause the faults described, logic dictates that the acid from the A501 expansion or whatever it was will be the culprit, just look at the state of the pins.
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Old 03 November 2010, 12:54   #7
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Thank you for all your replies.

The trapdoor port isn't the problem. I will take another picture from beneath for you too see that everything is ok. Battery acid ate only the expansion card, it hadn't leaked on the motherboard at all, so all is clean beside the pins on the slot.

Agnus had been taken out, cleaned and reseated.

Voltage rails are doing ok with 2 different power supplies.

As for the heating, I noticed normal heat up on denise, cpu, agnus and gary (i think). But all this this lukewarm heat up, and it is normal. It gives the sign that something is alive

I can be 100% positive that the battery acid isn't a culprit, I am thinking of some faulty custom chip...

Just a thought, should I try to construct a rgb to composite adapter, to check if the A520 is faulty and cannot give a picture? Because, as I said, on monochrome output there is a white picture on many resets. All this is for me to see if there is an actual color that indicates the problem.

What do you think?
 
Old 04 November 2010, 03:27   #8
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If you live in Europe (where is Nis?) all you need is an Amiga SCART cable to hook it to a TV set to have full colour glory, then the inspection can go deeper.

As the CPU, that's a thing you can swap without prejudice. Buy one from a local Ebay-a-like for a few money and test again.
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Old 04 November 2010, 11:41   #9
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Nis is in Serbia

Tnx for the tip! Will try this today, and see if there is any color on the screen.
As for the cpu swap, I'm not sure where to get one cheap... Hmmm...
 
Old 04 November 2010, 13:25   #10
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eBay is your best bet I think...

http://cgi.ebay.com/1pcs-Motorola-MC...-/180582645219

$14.99 and free shipping


Btw, check the IC socket pins for cracked/dried solder joints on the bottom of the motherboard.
EDIT: Loedown, I read your post, but I have actually read about a dude on this forum that got his A500 working after resoldering a dried pin on an IC socket.

Last edited by 8bitbubsy; 04 November 2010 at 13:49.
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Old 04 November 2010, 20:14   #11
ffunk
 
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Ok, so I constructed a RGB to SCART adapter and turned on the PSU... It gave a blue screen (of death lol) :/

What now?

I'm currently checking dried solder joints and possible broken leads under the microscope...

EDIT: On some resets it gave me a turquoise color. wtf...

Last edited by ffunk; 04 November 2010 at 20:19. Reason: added info
 
Old 05 November 2010, 00:18   #12
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Old 07 November 2010, 22:21   #13
ffunk
 
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@s2325
that is for amiga 1000, but tried to connect 2 different floppies and no go...

most of the times (90%) it gives me blue screen
 
Old 08 December 2010, 13:28   #14
ffunk
 
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didn't manage to repair this, but i would like to personally thank the guy behind user name Orange for giving me his working A500

thank you friend!
 
Old 10 December 2010, 02:29   #15
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Now you can swap one chip at a time to see if you can locate the culprit.

But I can point first to CPU, then Paula. Gary & Agnus are the other suspects.

Did you ever put your finger over the memory chips on the bottom of the board? One really warm RAM chip indicates it is busted.
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Old 10 December 2010, 11:10   #16
ffunk
 
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will try swapping.

almost all are lukewarm, but not hot or oddly warm... though i think gary or paula is dead cold.
 
Old 10 December 2010, 13:42   #17
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I accidently plugged the floppy drive ribbon cable in the wrong way once causing my A500 not to boot until i corrected it. Check the floppy cable is the correct way round on both the floppy drive and the motherboard
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