A600 Obscure Fault Of The Day, Takes 15 Minutes To Switch On

Loedown · 01 January 2013, 01:12

Symptom it takes 15 minutes to start up but will start immediately on a keyboard reset.

U14 controls Amiga hard / soft reset, simple NE555 timer through Q511.

C612 eats out the traces and leaves R611 missing Vcc, so the voltage to pin 2 of U14 ( Trigger ) VERY slowly rises until Amiga boots.

Similar circuit used in A500.

FOL · 01 January 2013, 01:15

Quote:

Originally Posted by Loedown

Symptom it takes 15 minutes to start up but will start immediately on a keyboard reset.

U14 controls Amiga hard / soft reset, simple NE555 timer through Q511.

C612 eats out the traces and leaves R611 missing Vcc, so the voltage to pin 2 of U14 ( Trigger ) VERY slowly rises until Amiga boots.

Similar circuit used in A500.

What rev cause some revs are completely different in layout.

Loedown · 01 January 2013, 02:05

Rev 1.5

Arnie · 01 January 2013, 09:12

Hmm, interesting. Is it the same (u14) for a A1200?

Loedown · 01 January 2013, 09:57

A1200 uses a different method of reset. If you suspect a reset line fault look at the status of the line, should be drawn high after a short period of time or high - low - high.

FOL · 01 January 2013, 13:41

Quote:

Originally Posted by Loedown

A1200 uses a different method of reset. If you suspect a reset line fault look at the status of the line, should be drawn high after a short period of time or high - low - high.

I remember a nightmare of an A600 where it had been eaten away effecting the power on. Took me ages to find all damaged track as it destroyed copper through hole links by the expansion connector.
I think it also damaged Q555 or the U14 IC, cant remember now though.

I have seen on a few A4000 where the post amp gets damaged by the leakage, so even after repairing all track fault still shows until IC is replaced.

Loedown · 02 January 2013, 09:55

Quote:

Originally Posted by FOL

I remember a nightmare of an A600 where it had been eaten away effecting the power on. Took me ages to find all damaged track as it destroyed copper through hole links by the expansion connector.
I think it also damaged Q555 or the U14 IC, cant remember now though.

I have seen on a few A4000 where the post amp gets damaged by the leakage, so even after repairing all track fault still shows until IC is replaced.

I hope people read this post and get scared because it's a bastard job to repair a badly corroded main board. I won't be repairing any more A600 because of it.

The one I had needed about 6 traces replaced or repaired.

01 January 2013, 01:12	#1
Loedown Precious & fragile things Join Date: Feb 2009 Location: Victoria, Australia Posts: 1,946	A600 Obscure Fault Of The Day, Takes 15 Minutes To Switch On Symptom it takes 15 minutes to start up but will start immediately on a keyboard reset. U14 controls Amiga hard / soft reset, simple NE555 timer through Q511. C612 eats out the traces and leaves R611 missing Vcc, so the voltage to pin 2 of U14 ( Trigger ) VERY slowly rises until Amiga boots. Similar circuit used in A500.

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01 January 2013, 02:05	#3
Loedown Precious & fragile things Join Date: Feb 2009 Location: Victoria, Australia Posts: 1,946	Rev 1.5

01 January 2013, 09:12	#4
Arnie R.I.P Smudge 18-08-16 Join Date: Aug 2005 Location: Leicester/UK Age: 66 Posts: 3,968	Hmm, interesting. Is it the same (u14) for a A1200?

01 January 2013, 09:57	#5
Loedown Precious & fragile things Join Date: Feb 2009 Location: Victoria, Australia Posts: 1,946	A1200 uses a different method of reset. If you suspect a reset line fault look at the status of the line, should be drawn high after a short period of time or high - low - high.

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