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Old 04 January 2018, 19:55   #1
Sim085
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Amiga 1200 abnormal restarts

Hello, today I experienced something strange; when I switched on the A1200 this booted from the CF card and then as soon as it loaded Workbench it restarted. It then booted again, this time I could do some things but after some time it restarted again.

With another CF card it never booted in Workbench, keeping on restarting.

Am I correct in assuming this is either power or capacitor related or it might be something worse?

The reason I ask is that yesterday while trying to a CF card adapter I plugged this the other way round. Could this be the result of this mistake? i.e. - something got friend?

My A1200 motherboard is Rev 2B with Blizzard MK4.

If I disable the Blizzard MK4 everything loads fine. If I enable the Blizzard Mk4 and unplug the floppy everything looks to work fine too.

That said up until a couple of days ago I didn't have any issue.
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Old 04 January 2018, 21:58   #2
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How is your PSU performing? Has your motherboard been re-capped? Looking at sympthoms, the issue is most likely in the power circuits.
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Old 09 January 2018, 18:56   #3
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Yep, sounds like a power issue. It could be capacitors in the machine, though it's unlikely they're directly the cause of the issue. Their leakage can however cause all sorts of problems as it corrodes the nearby tracks and components, so if that hasn't been done already, get it done now.

More likely the direct cause of the spontaneous restarts are the capacitors in the PSU. When they get old, they're less good at smoothing out the power, meaning you start to get more ripple and noise in the supply, some of which can trigger spontaneous instability or resets. Reducing power consumption will lessen the issue in this case, which matches what you're seeing. So I would have the PSU checked and recapped if necessary, or alternatively rebuilt with a modern PSU module.

Before all that though, simple things: are you sure the PSU is connected correctly, and a slight movement of a loose connection isn't causing the reset?
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Old 09 January 2018, 21:14   #4
Sim085
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Ok, have been waiting for too long to do this so I am planning to take my A1200 to technician some day this week. I just hope they'll do a good job.

Quote:
Originally Posted by Daedalus View Post
It could be capacitors in the machine, though it's unlikely they're directly the cause of the issue. Their leakage can however cause all sorts of problems as it corrodes the nearby tracks and components, so if that hasn't been done already, get it done now.
What I am cannot understand is why the ATX Power Supply is only outputting 4.8V! I got the same even when I tried another ATX power supply.

What is the best option to power up an A1200? It looks like using ATX power supplies will get me nowhere with this A1200...

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Yep, sounds like a power issue.
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Old 10 January 2018, 01:19   #5
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Quote:
Originally Posted by Sim085 View Post
Ok, have been waiting for too long to do this so I am planning to take my A1200 to technician some day this week. I just hope they'll do a good job.



What I am cannot understand is why the ATX Power Supply is only outputting 4.8V! I got the same even when I tried another ATX power supply.

What is the best option to power up an A1200? It looks like using ATX power supplies will get me nowhere with this A1200...
Was this on a single 5v rail or did you use multiple 5v rail. A couple of guides I read recommend to use multiple 5v line twisted together.
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Old 10 January 2018, 07:45   #6
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Quote:
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...What I am cannot understand is why the ATX Power Supply is only outputting 4.8V! I got the same even when I tried another ATX power supply...
Under what scenario did you measure the voltage? Flyback switched mode power supply only gives correct and steady voltage when under load.
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Old 10 January 2018, 11:22   #7
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Indeed, the Amiga doesn't use enough power to effectively regulate with many modern ATX supplies, especially with many of them using the 12V rail as the primary output.

Also, where are you measuring the 4.8V? You could be getting a voltage drop due to tarnishing of the Amiga's power connector, for example. Try measure it at the ATX connector itself and see if it's 5V there - a drop of 0.2V due to poor connection quality is easily possible.
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Old 10 January 2018, 13:10   #8
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I feed two 5V lines, one from an HDD connector coming from the ATX power supply and another from the floppy connector coming from the ATX power supply.

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Was this on a single 5v rail or did you use multiple 5v rail. A couple of guides I read recommend to use multiple 5v line twisted together.

I switch on the amiga and take the measure.

Quote:
Originally Posted by mpattonm View Post
Under what scenario did you measure the voltage? Flyback switched mode power supply only gives correct and steady voltage when under load.

I get the reading from where I join the ATX connectors to the Amiga connector (the china-connector). Up to a month or two ago this was reporting 4.84V but now I get 4.8V. Could it be that dying capacitors are putting less request for power from the power supply?

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Also, where are you measuring the 4.8V?
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Old 11 January 2018, 12:31   #9
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I feed two 5V lines, one from an HDD connector coming from the ATX power supply and another from the floppy connector coming from the ATX power supply.
Hmmm, that may not be enough, you might also need to link together the 5V lines on the ATX connector itself. The 12V supplies should also be linked (but only to the same +12V supply - some PSUs have more than one rail), and also the 3.3V lines. But this is ignoring the fact that the PSU might be underloaded, causing all rails to be unstable.

Quote:
I get the reading from where I join the ATX connectors to the Amiga connector (the china-connector). Up to a month or two ago this was reporting 4.84V but now I get 4.8V. Could it be that dying capacitors are putting less request for power from the power supply?
No, capacitors don't change the overall consumption of a machine. To increase the load on the machine you need to add more devices or a dummy load. A dummy load can be a resistor of a suitable value - 5 ohm would probably suit the 5V line, but needs to be rated for ~10W to handle the power.

Alternatively, adding hard drives and fans will also increase consumption and might be worth a try.
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Old 14 January 2018, 11:25   #10
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I still have to get the new capacitors and replace these. However in the meantime I managed to get an old Amiga 500 PSU. I plugged the A1200 to this and it is running normally, boots immediately, no crashes.

How is the A500 power supply different from an ATX power supply? Also, I would like to take care of this PSU (my original A500+ poped a couple of years ago). Is there any maintenance I have to consider?
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Old 14 January 2018, 11:55   #11
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For me it looks like PSU is losing parameters. How old is that PSU? If it's "old enough" You'll gradually lose parameters (sometimes until complete failure).

If it's a problem, better don't use this PSU. You can have problems with hardware, e.g. if power loss occurs while writing data on HD/CF/whatever.

Last edited by Solo Kazuki; 14 January 2018 at 12:07.
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Old 15 January 2018, 10:48   #12
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There are a few different designs of A500 PSUs. Some are quite similar to an ATX supply, but less powerful and less sophisticated. They're made to use the lower power consumption of the Amiga, so their minimum loads will be well below what the Amiga uses. Other types are far more primitive, simple linear power supplies that don't have a minimum load, but are heavy and inefficient.

The main thing is really the capacitors in the PSU - these should probably be replaced in order to keep it working well...
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