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Old 18 September 2016, 21:21   #1
Wrangler
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Amiga power light blinking

Just posting it here in case someone in the future wants the quick answer (whereas I couldn't find it anywhere on the internet ):

If your Amiga won't boot and power light flashes 5 short and 1 long, then that means the PSU is not supplying a TICK signal.
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Old 18 September 2016, 22:10   #2
idrougge
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Thanks.
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Old 20 September 2016, 21:04   #3
Toni Wilen
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(Short explanation if someone is interested in boring details)

It keeps reseting forever because missing tick (or vsync if Amiga without power supply tick or jumpered to vsync) stops CIA-A TOD counter which early boot code uses to detect if it counts vsync or ticks and if it is 50Hz or 60Hz PSU tick. If test fails (cause is always hardware fault), it tries to show Guru message but unfortunately it also fails because it is too early in boot phase (intuition.library is not initialized yet). Finally it resets the system.

btw, exact same problem can happen when Amiga counts vsyncs (not PSU ticks), has unbuffered VGA adapter and monitor that has too high load on sync signal lines. This combination can cause system to detect connected genlock. Genlock mode gets enabled: Vsync line becomes input, CIA-A TOD stops counting.

Power led flash count is not an error code, it only shows that something has gone wrong and gives few moments to start ROM built-in serial debugger.
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Old 20 September 2016, 21:38   #4
Wrangler
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That is really helpful Toni, thanks! What I take from this is:

1. The number of power light flashes is actually not a way to diagnose what's wrong - to some extent it's random depending on what's caused the problem etc. True?

2. This might also explain why my A4000T won't boot if a 15kHz monitor is plugged in but not turned on: load too high -> continual rebooting. I'd always wondered!
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Old 20 September 2016, 21:49   #5
Toni Wilen
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Quote:
Originally Posted by Wrangler View Post
That is really helpful Toni, thanks! What I take from this is:

1. The number of power light flashes is actually not a way to diagnose what's wrong - to some extent it's random depending on what's caused the problem etc. True?
It is always 6 flashes. (Unless different ROM versions have different delay?)

Quote:
2. This might also explain why my A4000T won't boot if a 15kHz monitor is plugged in but not turned on: load too high -> continual rebooting. I'd always wondered!
Practically guaranteed reason if it boots without monitor but reset loops when monitor is connected.
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