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Old 01 September 2020, 01:51   #1
rabidgerry
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Amiga Power Supply Transplant - Meanwell RT-50B

Hello, just showing everyone the of a new PSU into an old Amiga MSU using a brand new Meanwell RT-50b.

I owe everything to Karl on this website https://www.retro32.com/amiga-resour...-rt-50b-rt-65b

I had toyed with the idea for a while now and when I saw that website above I was sold as it's really very easy to do.

Ok the old PSU. I bought a dead on on purpose




Inside the old PSU



PCB completely removed.


It is worth noting at this point that I checked all the capacitors on the PCB for charge and they were all discharged. I reckon it had been switched off for so long that the charge had faded over time. I could be wrong though. Always best to check these type of caps as anything over 10v should be discharged correctly.



The unboxed Meanwell RT-50b



Nice and compact little PSU



The wiring of the 5 wire end.

Note I checked every pin to see which pin was what wire, simply because on the original website I followed the guy mentions that don't take his wire colour labelling for granted. So I didn't and checked each one with multimeter.




Starting to wire up now.

These wires I didn't bother snipping and tripping to fit under the terminal screws. They had single end spade connectors and it was easy enough to place them under the screw terminal and screw down tight for s good connection.




I had spare mains cable lying around. I need these to extend from the terminals to the plug wires of the old Amiga PSU. The originals are to short to stretch.



Cut a piece of the mains cable, stripped it, and separated the three wires.




I ended up cutting the wires a little short so I had to cut longer ones.



Starting to wire those longer pieces of mains wire to the terminals and the connector blocks







I used mains wire as it obviously is connecting to the main side of the power supply cable.



As you can see here the reading on the 5v line was a little high. I know from the site that I followed originally when Karl the guy who did the mod first tied his PSU he got distortions in his display. As can be seen on his website he shows this and also mentions the important details to check the 5v rail and then adjust accordingly. So as you can see I am a bit over so I had to adjust the little trim pot inside.



The final adjustment, this took a few goes to get perfect, but nailed it in the end, tiny little adjustments to get a nice steady 5v




I couldn't be arsed showing you a video of my pluggin it into the Amiga and turning it on but what can I say? It works a treat. Now to put things into perspective, that power supply cost like £15 before postage! Excellent value.

Hopefully this is of some use to someone. And thanks to Karl on his website for the inspiration https://www.retro32.com/amiga-resour...-rt-50b-rt-65b
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Old 01 September 2020, 03:32   #2
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I did the same a month or so ago. Mean Well make excellent power supplies. I used Velcro pads to stick the power supply to the bottom on the case.
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Old 01 September 2020, 08:54   #3
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Originally Posted by rabidgerry View Post
The final adjustment, this took a few goes to get perfect, but nailed it in the end, tiny little adjustments to get a nice steady 5v
I would adjust the voltage under load (with Amiga connected) and in the Amiga itself, so voltage drop along the cable between PSU and Amiga is compensated.
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Old 01 September 2020, 09:32   #4
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Yes. 5.08 in idle doesn't mean very much.
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Old 01 September 2020, 09:54   #5
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Yes. 5.08 in idle doesn't mean very much.
Well it's not 5.08v now.
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Old 01 September 2020, 09:58   #6
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Quote:
Originally Posted by ExUnit View Post
I did the same a month or so ago. Mean Well make excellent power supplies. I used Velcro pads to stick the power supply to the bottom on the case.
I was thinking of doing something like this but it wedged in perfectly. I probably will go back and cut a little bit off the casing that is below the meanwell, but there is no urgency to do so. Just glad it works and nothing fried or blew up.
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Old 01 September 2020, 11:18   #7
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Originally Posted by rabidgerry View Post
I was thinking of doing something like this but it wedged in perfectly. I probably will go back and cut a little bit off the casing that is below the meanwell, but there is no urgency to do so. Just glad it works and nothing fried or blew up.

It is a snug fit isn't it It's so much lighter and runs quite a bit cooler as well, which is great. It doesn't matter how much you double, tripple check the pins, the moment you flick the switch is stressful Great feeling when it works though.
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Old 01 September 2020, 11:19   #8
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Quote:
Originally Posted by rabidgerry View Post
Well it's not 5.08v now.
Sorry, perhaps we didn't explain properly.

The PSU may give 5.08 in idle, but a perfect 5.00 when the Amiga is powered up.
Or it may give 5.00 in idle, and 4.92 when the Amiga is powered.
Or anything else in between and all around. Amigas and PSUs be quirky like that.

That is why Krashan said:

Quote:
Originally Posted by Krashan View Post
I would adjust the voltage under load (with Amiga connected) and in the Amiga itself, so voltage drop along the cable between PSU and Amiga is compensated.
It is best to measure the lines under load to get the idea of real numbers.
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Old 01 September 2020, 11:50   #9
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It is a snug fit isn't it It's so much lighter and runs quite a bit cooler as well, which is great. It doesn't matter how much you double, tripple check the pins, the moment you flick the switch is stressful Great feeling when it works though.
Yeah moments before I switched it on I said to my girlfriend "now I might blow my Amiga up"! I knew wouldn't but I still had that feeling like you said.


That's good about the heat, my current functioning older PSU heats up a lot and emits a smell, I'm sure you are familiar with that, most Amiga users probably have at one point or another!

Quote:
Originally Posted by Lord Aga View Post
Sorry, perhaps we didn't explain properly.

The PSU may give 5.08 in idle, but a perfect 5.00 when the Amiga is powered up.
Or it may give 5.00 in idle, and 4.92 when the Amiga is powered.
Or anything else in between and all around. Amigas and PSUs be quirky like that.

That is why Krashan said:



It is best to measure the lines under load to get the idea of real numbers.
So what plug it into the Amiga and take a reading from a 5v pin somewhere?
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Old 01 September 2020, 11:55   #10
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Yes. With the top open you should be able to access the lines.
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Old 01 September 2020, 12:44   #11
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What about from the 5v coming out of the RGB output? Pin 23?
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Old 01 September 2020, 16:18   #12
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I have often read that the floppy power connector is a good place to measure Volts.
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Old 01 September 2020, 16:25   #13
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Yep, the floppy connector is a decent spot. It takes into account both the losses in the cable, and in the 25+ year old power connectors, which will have a certain amount of resistance that means the voltage measured in the machine will vary with load, even if the PSU is outputting perfect 5V.

The ports are a reasonable place to measure too (video, parallel, external floppy and controller ports all have 5V available, though there are usually some noise suppression or current limiting components between them and the main 5V rail that could drop the reading slightly. It's probably negligible if you've nothing else connected to the port, so give it a go.

Most original Amiga brick supplies output 5.1V or 5.2V as standard, presumably in order to compensate for the cable and connector losses.
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Old 01 September 2020, 16:33   #14
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Quote:
Originally Posted by Daedalus View Post
Yep, the floppy connector is a decent spot. It takes into account both the losses in the cable, and in the 25+ year old power connectors, which will have a certain amount of resistance that means the voltage measured in the machine will vary with load, even if the PSU is outputting perfect 5V.

The ports are a reasonable place to measure too (video, parallel, external floppy and controller ports all have 5V available, though there are usually some noise suppression or current limiting components between them and the main 5V rail that could drop the reading slightly. It's probably negligible if you've nothing else connected to the port, so give it a go.

Most original Amiga brick supplies output 5.1V or 5.2V as standard, presumably in order to compensate for the cable and connector losses.
I could always bump it up a notch 0.1 of a volt.

I'll measure on the RGB out first and see what the crack is.
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Old 01 September 2020, 18:50   #15
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Got about 4.6v from the RGB output on pin 23. I will check the floppy connector also.

Should I get a little low on the volts side then is it best to dial in a little more on the PSU?
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Old 01 September 2020, 20:07   #16
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Got about 4.6v from the RGB output on pin 23. I will check the floppy connector also.

Should I get a little low on the volts side then is it best to dial in a little more on the PSU?
Yes, you should have at least 4.85V on the floppy power connector. So, dialing up slowly a bit would be good.

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Old 01 September 2020, 20:31   #17
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Ok haven't gone inside yet but I will later.

I did however measure my old PSU, another old original A500 brick. I got 5.32v from that without anything connected.

I shall take a reading from the floppy pin when I get the chance.
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Old 05 September 2020, 17:06   #18
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Originally Posted by Daedalus View Post
Yep, the floppy connector is a decent spot. It takes into account both the losses in the cable, and in the 25+ year old power connectors, which will have a certain amount of resistance that means the voltage measured in the machine will vary with load, even if the PSU is outputting perfect 5V.

The ports are a reasonable place to measure too (video, parallel, external floppy and controller ports all have 5V available, though there are usually some noise suppression or current limiting components between them and the main 5V rail that could drop the reading slightly. It's probably negligible if you've nothing else connected to the port, so give it a go.

Most original Amiga brick supplies output 5.1V or 5.2V as standard, presumably in order to compensate for the cable and connector losses.
I tested my original Amiga PSU and it output about 5.32v on my multimeter.

Ok so I'm, going to measure the NEW power supply at the floppy connector. Should I be looking for 5v at this point?

And if it is below 5v increase the trim pot on the Meanwell power supply?
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Old 05 September 2020, 17:40   #19
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Originally Posted by rabidgerry View Post
I tested my original Amiga PSU and it output about 5.32v on my multimeter.

Ok so I'm, going to measure the NEW power supply at the floppy connector. Should I be looking for 5v at this point?

And if it is below 5v increase the trim pot on the Meanwell power supply?
That is what I would do. And actually several of the original supplies specify 5.2V on the 5V rail, probably to compensate for the voltage loss across the cable and connector.
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Old 05 September 2020, 19:09   #20
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That is what I would do. And actually several of the original supplies specify 5.2V on the 5V rail, probably to compensate for the voltage loss across the cable and connector.
Ok well I connected it all up and made adjustments. I stopped ust shy of 5v on the floppy header.



on the PSU itself I got 5.32v which funnily enough is the exact same as the old original one that I own that still works. However the old one when connected only gave me 4.97v. I know that is bugger all really.



So I'm good to go now?
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