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Old 09 February 2011, 21:52   #1
manmaschine
 
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Problems with laid up A500

I've got an A500 which I've had since new in 1991, I retired it in 1994 when I got my first PC and occasionally brought out the Amiga when I felt like a little nostalgia, this is one of those times only to find that my classic 20 year old machine has developed a problem, and I was wondering if any of you guys had came across it before. The amiga after it's been running for a while suddenly reboots itself and shows the classic 'Guru Meditation' warning so I click the left button and sometimes it will come up with a white screen then go back to guru meditation, or it will stay with a blank white screen with no noise coming from the disc drive (they always make a noise periodically when on the insert disc screen, as most of you know!), and while it will recognise a disc and load it during this, it is hit or miss as to whether it will load or not ,if I switch it off for a while it will come right, insert disc screen, clicky drive, stick a disc in and off we go, only for it to reboot again 10 mins later and go through the white screen and guru meditation thing again. I ran the Amiga with the cover off and the screening can off and managed to play Lotus Turbo Challenge 2 all the way through without a problem, none of the chips seemed to get particularly hot, Fat Agnes got quite warm and the rest were barely skin temperature, so while heat might be an issue, I'm not sure. I'm thinking power supply now, had my dad check it out (Electronics Engineer of 40+ years experience!) and he said there were a couple of resistors that wern't long for this world but the rest of it looks fine, same with the actual motherboard on the amiga, everything looks fine, no evidence of burning or anything. So to save a lot of faffing about I just wondered it this was a common fault on our elderly machines or maybe an obscure problem that someone else had and cured. Thanks in advance! Remembered another curious thing, the caps lock light sometimes starts flashing and the keyboard stops working but oddly enough you can do the ctrl-A-A reboot with it no matter what.

Last edited by manmaschine; 09 February 2011 at 22:09.
 
Old 09 February 2011, 22:48   #2
kipper2k
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Originally Posted by manmaschine View Post
I've got an A500 which I've had since new in 1991, I retired it in 1994 when I got my first PC and occasionally brought out the Amiga when I felt like a little nostalgia, this is one of those times only to find that my classic 20 year old machine has developed a problem, and I was wondering if any of you guys had came across it before. The amiga after it's been running for a while suddenly reboots itself and shows the classic 'Guru Meditation' warning so I click the left button and sometimes it will come up with a white screen then go back to guru meditation, or it will stay with a blank white screen with no noise coming from the disc drive (they always make a noise periodically when on the insert disc screen, as most of you know!), and while it will recognise a disc and load it during this, it is hit or miss as to whether it will load or not ,if I switch it off for a while it will come right, insert disc screen, clicky drive, stick a disc in and off we go, only for it to reboot again 10 mins later and go through the white screen and guru meditation thing again. I ran the Amiga with the cover off and the screening can off and managed to play Lotus Turbo Challenge 2 all the way through without a problem, none of the chips seemed to get particularly hot, Fat Agnes got quite warm and the rest were barely skin temperature, so while heat might be an issue, I'm not sure. I'm thinking power supply now, had my dad check it out (Electronics Engineer of 40+ years experience!) and he said there were a couple of resistors that wern't long for this world but the rest of it looks fine, same with the actual motherboard on the amiga, everything looks fine, no evidence of burning or anything. So to save a lot of faffing about I just wondered it this was a common fault on our elderly machines or maybe an obscure problem that someone else had and cured. Thanks in advance! Remembered another curious thing, the caps lock light sometimes starts flashing and the keyboard stops working but oddly enough you can do the ctrl-A-A reboot with it no matter what.

Does it have an expansion Ram card in, if so, check the expansion ram battery, see if it has leaked and damaged any traces. Capacitors will degrade over time as most people on here will tell you so a swapout may be in order of the caps on the motherboard. The capacitors in the power supply are also suspect. The IC's are normally durable and i would consider low on the list. A capacitor doesnt need to look physically damaged in order for it to stop operating correctly. Due to the fact it has been stored for a long time, for me, the first thing would be to replace the capacitors (only the electrolytic can type)
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Old 09 February 2011, 23:32   #3
DDNI
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Hi if you got it new in 1991 then it may be an A500+. These have onboard rtc batteries that leak and destroy the motherboard.
Can you check and let us know.
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Old 10 February 2011, 03:16   #4
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As DDNI said.

You can also do a very hard push over all the socketed chips (but the Agnus) to see if some did try to pop off.

Also, can you please insert a blank line between phrases/paragraphs? Reading a block of test on internet is really bad.
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Old 10 February 2011, 09:09   #5
manmaschine
 
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Hi, thanks for the replies

My machine is definately an A500 non plus, I know 1991 was the changeover but I think mine is one of the very last of the original A500s, it has a B52 Rock Lobster motherboard. The memory expansion board was fitted and yes the battery is starting to leak, we wern't sure if removing this would cause a problem, I know it's to keep the clock alive but wasn't sure if the board needed it to be there. My dad has a capacitance tester which I'm going to try on it as I'm aware that capacitors do indeed dry up with age and cause problems, especially electrolytics. I had heard about the motherboard having a backup battery, but does this apply to original machines, I didn't see one when I had the computer opened up but it could be hidden, where is it located?
 
Old 10 February 2011, 19:06   #6
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http://amiga.resource.cx/mod/a500.html

http://amiga.resource.cx/photos/gallery/a500rev8a.jpg
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Old 10 February 2011, 22:31   #7
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Only the A500+ have a built-in battery on the motherboard, that's why so many of this model had an horrible death.

At the time the 500+ was made, C= also sold A500 using the same board & 2Mb-capable Agnus, but without a TTL chip to demux the RAM lines and (obviously) without the other 512kb onboard.

Those boards (8A or 8A1 revisions) have placement for all the missing parts, including the f-word battery. They also sports the A500+ name on the mobo.
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