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Can I use this power supply with Kaypro 2 (1983)?

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seaken

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Following this thread


I learned that I can buy a Mean-Well RT-85B power supply to replace my Aztec power supply in my Kaypro 2 from 1983 (I have the Kaypro 2 that was a rename of the Kaypro II and uses the full-height single-sided drive mounted horizontally just like the Kaypro II).

I was going to go ahead and purchase one but then I found I already had an unused power supply that may be a suitable replacement. But I don't know enough about power supplies to know for sure, so I am asking here in hopes that someone can give me some guidance.

I ended up with power supply pictured below by accidentally ordering it as a replacement for a power supply for an Acer small form factor I picked up at a surplus store. I clicked the wrong button and ended up with the wrong part. This part was for the models that supply the power to the drives through the motherboard instead of directly from a power connector to the drive. Anyway, I ended up with this supply that I couldn't use. After researching the RT-85B I am wondering it this unused PS may work for me.

This is an FSP220-30FABA. The DC outputs are

+12V 18.0A
+5Vsb 2.5A
-12V 0.3A

and looks like this:

IMG_20240225_143114194.jpg
IMG_20240225_143037525.jpg
IMG_20240225_143027726.jpg

Obviously it does not have the same connection header as the RT-85B and I would have to rewire to make it adapt to the Kaypro.

But what I wanted to know is if this PS will even work? It has +12V, +5V, and -12V just like the RT-85B but the Amps are listed differently. I don't know if this PS has the right specs. Can you help me understand the Amps and how these numbers either do or do not match what I need for the Kaypro?

The RT-85B has these DC outputs:

+12V 3.5A
+5V 8A
-12V 0.5A

Thank you for any help you can give me.

Seaken
 
If you're going to start a thread about this, it would be polite to include the original power supply spec so that everyone else doesn't have to chase it down. From the linked thread:
Picture in my book shows:
ASTEC Model AA12350
Output 65 Watt Max
+12 VDC 3.5A
+5 VDC 5A
-12 VDC .25A
Click to expand...
I switched the order to match your message. All the numbers are greater than or equal, so it ought to work.

Other things might matter, like if it has or needs soft power (a power-on / power-off signal from the computer), but otherwise the main question is if there is room for it. I don't have any specs on the sizes, but it would be good if all three dimensions were equal or smaller.
 
seaken said:
This is an FSP220-30FABA. The DC outputs are

+12V 18.0A
+5Vsb 2.5A
-12V 0.3A
Click to expand...
I think this is what he is wanting to use not the RT-85B so it doesn't have enough 5V.
 
Ok, thanks @Bruce Tomlin. The problem is I don't really know what I am talking about! I try to be polite but I messed up because I don't have a handle yet on what I am looking at.

Maybe I have a clue now from @djg. The 5V line is not enough?

Okay, I will just buy the RT-85B.

So, the Amps has to be higher than or equal to the original? Does it matter how much higher? Or is it only enough to be a higher number?

Thank you both for your help.

Seaken
 
Same for my Kaypro - Cracked solder around the pin that the power connector goes into... Resoldered them and it started working.

The 5v line is a little low. If you measure the 5V draw, you can probably get away with 2.5A though... I can't recall how much the Kaypro draws, but I think it's less than that.

You need to have more "amps" than the computer draws. If your computer draws 2A, then any power supply above this should be OK. If you want something more reliable, then you should aim to have the PSU capable of delivering twice what the computer requires.

The original power supply could provide 5v and 5A, so if you were comparing it, then the one you showed might or might not be suitable, depending on the draw.

It is possible to measure the draw with a multimeter if you put the ammeter function between the PSU and the Computer.
 
I'm sure the PSU can be fixed. But I am not good at soldering and I don't yet have the right equipment. If I was a real nerd I would fix the PSU. But I am more inclined to throw money at it. Or maybe I'll decide to set up a proper soldering workstation and learn to solder better.

Seaken
 
@cj7hawk thanks for the tips on amps. So, if I understand you I need to have a PSU that provides same voltage and at least the same, or more, amps.

What will happen if the amps are not enough? The computer just won't boot? Or would it damage the PSU?

Seaken
 
seaken said:
I'm sure the PSU can be fixed. But I am not good at soldering and I don't yet have the right equipment. If I was a real nerd I would fix the PSU. But I am more inclined to throw money at it. Or maybe I'll decide to set up a proper soldering workstation and learn to solder better.

Seaken
Click to expand...
Dont throw it away. I can repair it! Those arent exactly plentiful anymore. soldering is easy, like bowling. But it takes lots of practice to get good at it.. No matter what you do that ball is going down the alley.. know what I mean? I started soldering when I was a kid so I have decades of experience.. but honestly its something that anyone can learn at any time. Ill even tell you which starter iron and solder to begin with. Buy a few build it yourself kits (XT-IDE v 4 is a good one) and go from there.. its worth it if you plan on doing this hobby.
 
@VERAULT, yes, you are not the only one who has told me this. I am planning to attend the soldering training at VCF East in April. Then I will start getting the proper materials together. One of the problems I have is that my hands are not as steady anymore and I struggle to hold small parts. But I think I can work through that with the right equipment.

I won't throw out the PSU even if I replace it with a RT-85B.

Seaken
 
I get it. I never had shakey hands (not yet anyway) but a guy i worked with started getting shakey hands in his 50s. Doctor put him on low dose blood pressure meds to help with the hand shaking. He said it helped a bit.. for me its pain. As i get older my hands get stiffer and less precise.. they are basically painful lobster claws when i wake up... Is that the bell ringing on imminent arthritus? Probably.
 
Yes, I have the dead arm and aching hands from bursitis and arthritis. Some days I just can't work on small items. But I have enough days where I am fine. But the days where my hands work better don't always coincide with my days in my computer lab.

Seaken
 
seaken said:
So, the Amps has to be higher than or equal to the original? Does it matter how much higher? Or is it only enough to be a higher number?
Click to expand...
It gets complicated when you look at the details. For your RT-85B it also has minimum load requirements. For 5V you need to draw minimum of 2A and can draw up to 10A if your don't exceed the total supply wattage.

Screenshot from 2024-02-26 11-27-41.png

All the details won't be on the label. You need to find the datasheet for the supply. Didn't see one for FSP220-30FABA. If you don't meet the minimum load that output or another output may not regulate the voltage properly.

May not be able to find what minimum and maximum currents a machine draws without measuring it. Difficult to measure without a working power supply. Some supplies don't have minimum load requirements though they may be more expensive. If you stay same to somewhat higher current rating to existing supply normally you will be OK. Much higher you may have minimum current issues.

seaken said:
What will happen if the amps are not enough? The computer just won't boot? Or would it damage the PSU?
Click to expand...
Depends on the power supply design. Power supply damage is possible.
 
Thank you @djg, that was just the info I needed. That seems to indicate that this FSP220-30FABA will not be suitable. At least not for me since I don't know how to test this stuff. But I have read that the RT-85B is a suitable replacement for the Kaypro 2. I will get one and try it out. If that doesn't help get my Kaypro going I'll be back with more questions on where to go from there.

Seaken
 
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