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Old 08 May 2017, 03:52   #1
arkpandora
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Power supply questions (A500/600/1200)

Hi!

I would like to use my A500, 600 and 1200 again for the first time in about 10 years, but I would like to make sure they are safely powered. I don't know anything about electronics, electricity or the technical side of computers, so I need a bit of help!

I still have an original A500 PSU, plus an old (20-year-old) second-hand standard PC internal PSU that was modified with an Amiga connector and was still working fine ten years ago. So here is an anthology of questions:

1. Is there any risk of damaging the Amiga if I use them without checking them first?

2. If I need to check them first, can you direct me to any tutorial on the art of checking an Amiga PSU?

3. Should the capacitors of an original A500/600/1200 PSU be changed, like those of an Amiga motherboard (I know my Amigas' motherboards will have to be recapped as well)?

4. If I want to buy a new PSU that I can use without risk of damaging the Amiga, which type of PSU should I buy? It should be powerful enough to power an expanded Amiga 1200.

Thank you so much for any help!

Last edited by arkpandora; 08 May 2017 at 18:32.
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Old 08 May 2017, 07:41   #2
demolition
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It is rare that a broken Amiga PSU will damage the Amiga so I would just connect it up and try. A recap of the PSU might be needed. If the Amiga is unstable it might be a hint that the PSU needs recapping.

The A500 does not generally needs recapping, but A600 and A1200 should be recapped ASAP if it has never been done.
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Old 08 May 2017, 09:26   #3
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It’s pretty easy to check voltages of a linear (heavy brick) PSU with a multimeter.
Connect the negative lead to the shield, and test the rest with the positive probe.
Even a $5 multimeter is accurate enough to reasonably test the PSU.

If you have access to a scope, you can also check the power rails actually look like DC.

The lighter switchmode PSUs might have to have some load to even produce
the correct voltages in the first place.

The two large smoothing capacitors in a linear PSU,
especially that hasn’t been used in a decade could do with changing.
If you have access to a variac, you can run the PSU at a much lower voltage
(on it’s own) for a day or two. That’s about the nicest way to reform them,
but it’s a bit extreme, I’d just change them anyway.
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Old 08 May 2017, 13:20   #4
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I'm thinking of getting a PicoPSU as a psu replacement, would I have to use a laptop power brick along with it and would it matter what wattage it would be?
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Old 08 May 2017, 13:27   #5
ajk
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You don't have to specifically use a laptop supply, but yes you do need some kind of power brick. Despite the name, a PicoPSU is not really a power supply, it is an adapter.

Wattage should be at least equivalent to, or preferably exceed the rating of the PicoPSU model you intend to use.
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Old 08 May 2017, 13:35   #6
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Does it have to be a 12V power brick?
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Old 08 May 2017, 13:54   #7
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That also depends on the model of the PicoPSU. Some are 12V only, some have a fairly wide input range like 12V-25V or 12V-32V. Many recent laptop supplies are 19V or thereabouts so getting one of the wide input range models may be a good idea.
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Old 08 May 2017, 14:16   #8
demolition
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Quote:
Originally Posted by ajk View Post
Despite the name, a PicoPSU is not really a power supply, it is an adapter.
Why do you think it is not a power supply? Just because it runs off 12VDC instead of 230VAC doesn't mean it is not a power supply.

The reason that the smallest PicoPSUs can only run from 12VDC is that they simply pass through this voltage to the 12VDC output. To be able to run from a wider input voltage range, it would also need to regulate the 12V rail which would add cost and complexity. But as you mention, there are also PicoPSUs designed for this, e.g. for usage in cars where you will not find a stable 12V supply.
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Old 08 May 2017, 14:42   #9
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Because I am trying to keep this as clear as possible It can not by itself replace the original PSU.
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Old 08 May 2017, 14:46   #10
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Instead of a PicoPSU, you can use a Meanwell PSU that supplies +5V, +12V and -12V. That way, you don't need two power supplies and the main rail is +5V as intended.
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Old 08 May 2017, 16:37   #11
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For a Meanwell PSU, don't you require some form of housing in the form of the old Amiga PSU case?
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Old 08 May 2017, 16:41   #12
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Quote:
Originally Posted by wiz12 View Post
For a Meanwell PSU, don't you require some form of housing in the form of the old Amiga PSU case?
Sure, but unless you are installing the PicoPSU inside the Amiga, it should also be put inside a box. If you have more than one Amiga, it would be more convenient to just replace the insides of the original PSU and then it will look and work 100% like the original, just safer and with more power.

Edit: I put a PicoPSU including the 12V supply brick inside the original case as you can see here:
http://eab.abime.net/showthread.php?t=70315

Last edited by demolition; 08 May 2017 at 16:49.
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Old 08 May 2017, 17:47   #13
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A PicoPSU calls itself a power supply unit. So you can call it PSU. Adapter isn`t a better name. What you need to know is that it is a DC-DC converter what needs a DC input voltage to work.
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Old 08 May 2017, 20:04   #14
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Thanks! I don't understand everything yet, but your answers and chat are helpful.

Quote:
Originally Posted by xArtx View Post
It’s pretty easy to check voltages of a linear (heavy brick) PSU with a multimeter.
Connect the negative lead to the shield, and test the rest with the positive probe.
According to the power connector's schematics, the shield is the lower left pin. But what is the connector's outer square connected to, if it is? I apologize for my basic questions.

Quote:
Originally Posted by xArtx View Post
The two large smoothing capacitors in a linear PSU,
especially that hasn’t been used in a decade could do with changing.
If you have access to a variac, you can run the PSU at a much lower voltage
(on it’s own) for a day or two. That’s about the nicest way to reform them,
but it’s a bit extreme, I’d just change them anyway.
Is it safe anyway to supply an Amiga using an original Amiga PSU or my 20-year-old internal PC PSU that have remained inactive for 10 to 20 years without checking their voltage first or replacing their capacitors?

Also can you confirm that an original A1200/600/500 PSU is what you call a linear one, and that a standard internal PC PSU such as my 20-year-old one is not linear but what you call a "switchmode" one ?
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Old 08 May 2017, 20:14   #15
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It's never 100% safe to use an old, unknown power supply.

Only the very oldest and weakest Amiga power supplies were transformer based. Later A500 and (as far as I know) all A600/A1200 power supplies were switch mode. A transformer based supply past a couple tens of watts starts to get really big.
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Old 08 May 2017, 21:13   #16
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Quote:
Originally Posted by arkpandora View Post
According to the power connector's schematics, the shield is the lower left pin. But what is the connector's outer square connected to, if it is? I apologize for my basic questions.

Is it safe anyway to supply an Amiga using an original Amiga PSU or my 20-year-old internal PC PSU that have remained inactive for 10 to 20 years without checking their voltage first or replacing their capacitors?

Also can you confirm that an original A1200/600/500 PSU is what you call a linear one, and that a standard internal PC PSU such as my 20-year-old one is not linear but what you call a "switchmode" one ?
The shield (outer square) should be connected to Ground.

Switch mode supplies, even old ones, should be relatively safe since they have a built-in protection circuit, i.e. they will shut themselves off if the voltages cannot be kept within some defined range. This is in theory though and some cheap supplies can have badly designed regulation which cannot be trusted.

A linear supply is a transformer-based one which is very heavy. Switch-mode supplies are much lighter. I am not sure whether A1200 came with transformer supplies but I know that A500 and A600 did (I have a heavy PSU that came with one of my 600s). This is how my heavy A600 supply looks:
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Old 08 May 2017, 21:16   #17
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I got one like that with my A1200 as well.
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Old 08 May 2017, 21:20   #18
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Quote:
Originally Posted by idrougge View Post
I got one like that with my A1200 as well.
I guess you can never be sure how C= combined the hardware as their motto was 'just ship it'..
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Old 08 May 2017, 21:37   #19
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Quote:
Originally Posted by wiz12 View Post
For a Meanwell PSU, don't you require some form of housing in the form of the old Amiga PSU case?
Yes, but so does a PicoPSU. You can of course house it in something else, such as an ice cream carton.
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Old 09 May 2017, 00:03   #20
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Just use the heaviest brick you can get your hands on. There are differing views on the matter but when I tried to add a 3.5" 1GB hard drive to my 1200 and failed cus of the old lightweight power supply I was advised to get a brick. A heavy 500 brick. Same weight as the brick for the 590. I gathered quite a few. The A1200 now has powered external drives but also powers a VidiAmiga, XL Drive, BlizzardIV and internal 2.5" and PCMCIA ethernet plus the SCSIKIT so I have stuff flowing from every port on the machine and use a brick. Every Amiga that I have that has any kind of addition uses a brick.

Much heavier than the standard. There has been much discussion in my time on the matter. I have got several of those Goliaths and converted tower PSU's but I won't use them. On my 1200 tower the power is single blue wire going to the centre of the square connector. Works... but not good.

Amiga power supplies for the 500, 600 and 1200 all work. There is a heavier small power supply like the lightweight 1200 which I have used. But after more than 25 years of continuous use you really can't beat a brick. The kind that would take your toe off if you dropped it on your foot. Nothing any more technical than that. So if you see one on the Bay ask the guy how heavy it is.

http://www.scuzzscink.com/amiga/power/a258_power09.jpg

I couldn't provide a picture of the weight sadly.

scuzz
http://www.scuzzscink.com/amiga/a_amiga_inframe.htm

PS The A500 power supply came in two weights. One very light and then there was the brick.
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