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Old 31 July 2015, 01:46   #1
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Location: Montevideo
Posts: 37
Amiga 500 keeps rebooting, then works fine

the problem is that the Amiga 500 keeps rebooting until it works fine.
It shows the light grey, white screen, the keyboard leds blinks, all this for a couple of minutes more or less, until it does a final reboot and everything works fine. It responds to the CTRL+A+A meanwhile is booting.
Video here: [ Show youtube player ]

It does this only the first time I power it up. It's like it needs to get 'warm'.

Things I've tried:
- re seating all chips
- cleaning motherboard with contact cleaning
- removing all chips, cleaning sockets
- removing 512k ram expansion (trapdoor)
- trying a different disk drive

Today I've replaced a couple of burned resistors (R401 and R408), a user told me that they were just for controlling voltage to the joy ports.
But the problem is still there.

Could this be the capacitors?
I have this Amiga since 1990, it's a rev 6A-A03
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Old 31 July 2015, 09:01   #2
Toni Wilen
WinUAE developer
Join Date: Aug 2001
Location: Hämeenlinna/Finland
Age: 44
Posts: 23,136
Works normally after warming up period usually is caused by bad capacitor(s), including PSU caps.

Do you have another PSU? Did you try swapping CIA chips (CIA-A to CIA-B and vice versa)?. Try also without display cable.

This kind of reset loop can be caused by stuck CIA timer (or timer that looks like it is stuck due to for example lack of proper clock signal) or boot code detecting non-existing genlock.
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Old 31 July 2015, 17:52   #3
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Location: Montevideo
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thanks Toni,

I don't have another PSU to test it. I'll swap the CIA chips as you say.
I forgot to mention that the last reboot before the A500 starts to work normally gives a guru meditation error, then you click the mouse and everything works fine.

thanks again
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Old 05 August 2015, 17:56   #4
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Location: Montevideo
Posts: 37
Today I've swapped the CIA chips and the problem persist.
Try booting without the display cable and same thing.

I don't have another PSU, so what I did is disconnect the PSU from the Amiga and power it on to warm up, then connect it, same problem.
I don't know if that's a way to test if the PSU is faulty or not.

So I think the only thing to try is to replace the motherboard caps?
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