1040 STe power supply question

[Randy]

Hi all, are the power supplies in each of the ST(e) computers usable with all voltages, i.e., can I use a UK machine on US voltage (220 VAC to 120 VAC) with it's existing power supply?  In other words, does the power supply "switch" like many of today's devices to provide proper output regardless of the input mains voltages?  I am thinking not, but just wanted to make sure.  thanks

[MasterMotorola]

If you want to use a UK machine in the US then a universal power adapter would be your best option.  Or are you trying to repair a faulty PSU?

[Randy]

Not sure what you mean here, are you saying to buy an outboard voltage converter to step up the US voltage to UK voltage, in other words, step up from 120 VAC to 220 VAC?

[bfollowell]

No, they are most definitely not multi-voltage compatible. They will only work with the normal voltage from the country of origin for the ST. You will need to either purchase some sort of Step-Up transformer or replace the power supply.

 

I recently did a full conversion on a U.K. 1040 STE to U.S. STE and I replace the power supply with a cheap one I purchased from Digi-Key for about $20. It works great.

 

I also replaced the TOS roms and the keyboard, but those aren't really necessary if you don't want to do them.

 

[Colleton]

As bfollowell said, you'll need a US PSU.  I bought a UK STE and put a US PSU in it, works like a champ.

 

There are 3 choices for the PSU that I know of:

 

1.  An old US ST PSU.  I don't see too many on ebay.

2.  A new PSU from Exxos.  They're nice, but expensive.  I have one and like it.

3.  A Mean Well RD-50A.  You can get them from DigiKey or Amazon, among other places.  DigiKey has them in stock.  I have one of these installed in my Mega ST2, works very well and is an easy install.

 

Good luck!

[bfollowell]

I used the Mean Well RPD-60A, also from Digi-Key.

[Randy]

Thanks guys, that is what I thought.  However, something else has cropped up with this STe.  I pulled the old supply out and noticed that the caps are Rubycons and Nichicons, I have never seen any power supply in an ST with that grade of cap, mostly cheap-ass chinese caps, which these are most definitely not.  A quick check of the output lines with this power supply unloaded (out of the case) shows 2 x 5 VDC and 1 x 12 VDC, even though the bottom of the PS plate says 220VAC!  Looks like I need to check with the seller (in the UK) to see if he changed out the supply for a lower input voltage one for the US.  BTW, its an Misumi RS98.  And another thing, I notice that there are Atari Roms 2.06 in it.  Also, the motherboard board has the usual cheap-ass chinese caps on it, nothing like the power supply caps.  Hmm, a mystery for sure!

[MasterMotorola]

41 minutes ago, Randy said:

I pulled the old supply out and noticed that the caps are Rubycons and Nichicons, I have never seen any power supply in an ST with that grade of cap, mostly cheap-ass chinese caps, which these are most definitely not.

The previous owner probably recapped them at one point.  Most of the reconditioned retro computers get the capacitors replaced as they are one of the first things to go.  I once had a capacitor blow in my PSU while I was using the computer and it sounded like a gunshot went off next to me.  It shot upward with such force that it dented the inside of the metal shielding and caught the interior dust bunnies on fire.  I cleaned it, replaced the PSU, and it was fine.

[bfollowell]

Yes, and those voltages are perfectly normal. The purpose of a power supply is to supply your device with a regulated, much lower DC voltage that all the components require, regardless of what the source voltage is. In your case, the PSU is designed for 220VAC, 50Hz provided in the U.K., while in the U.S. the PSU is designed for 120VAC, 60Hz. They both provide 5VDC and 12VDC to your STE.

 

[Randy]

5 hours ago, bfollowell said:

Yes, and those voltages are perfectly normal. The purpose of a power supply is to supply your device with a regulated, much lower DC voltage that all the components require, regardless of what the source voltage is. In your case, the PSU is designed for 220VAC, 50Hz provided in the U.K., while in the U.S. the PSU is designed for 120VAC, 60Hz. They both provide 5VDC and 12VDC to your STE.

 

 Hi b, yes, I understand that, but it's a marked 220 VAC therefore I would have expected much lower DC voltage coming out from the power supply unless the power supply has been changed in some fashion to work with 120 VAC in which case the +5 & +12 is correct.  The seller indicated that he did not know as he apparently is a reseller and has no knowledge of the power supply.

[bfollowell]

OK, I'm confused. 5VDC & 12VDC have been very common internal voltages for computers for decades, regardless of the input voltage. Modulated video aside, STs from various parts of the world are virtually identical from a hardware standpoint. I'm not sure why you would have expected to see much lower DC voltages to the motherboard.

 

Either way, all STs, regardless of their country of origin, require 5VDC and12VDC internally, to the motherboard.

[Randy]

29 minutes ago, bfollowell said:

OK, I'm confused. 5VDC & 12VDC have been very common internal voltages for computers for decades, regardless of the input voltage. Modulated video aside, STs from various parts of the world are virtually identical from a hardware standpoint. I'm not sure why you would have expected to see much lower DC voltages to the motherboard.

 

Either way, all STs, regardless of their country of origin, require 5VDC and12VDC internally, to the motherboard.

 

 you are correct IF the correct mains voltage is used, i.e., if a 220 VAC supply is connected to a 220 VAC mains.  IF a 220 VAC supply is connected to a 120 VAC mains, I would expect the DC voltage outputs to be around HALF of what would be expected as the input voltage is around HALF of the required input (mains) voltage. FWIW, I did connect the power supply back into the STe to load down the supply and then measured the +5 and +12 VDC rails, and they were +5 and +12 VDC, indicating that this supply has been changed from a 220 VAC UK supply to a 120 VAC NA supply.  That is the only thing that makes sense, otherwise I would not get the full DC out from a UK supply unless it had been changed at some point to a NA supply, does that make sense?

[bfollowell]

Well, that's the point. You can't connect a 220VAC item to 120VAC supply unless you wish to damage the item that you're plugging in. That's just not a very smart thing to do. Sometimes, nothing much will happen other than the item won't work. Oftentimes, you risk serious damage to the item you're plugging in.

 

I get what you're saying though, and I think I missed it the first time through. You plugged the 220VAC U.K. PSU into 120VAC U.S. and expected to see some smaller VDC output, but were surprised that you still had 5VDC and 12VDC output.

 

First of all, where did you buy this machine? Where did it come from? My U.K. machine came directly to me from the U.K. from the person I purchased it from. Everything about it was factory U.K. before I stared converting it. If you got your U.K. machine from someone in the U.S., then I would think there's every reason to believe that they had already swapped the PSU to a U.S. type. Otherwise, they wouldn't have been able to use it. If your STE came to you from the U.K., I can't think of any reason that anyone there would have switched to a U.S. style PSU, because then they wouldn't have been able to easily use it there. Also, if it is in fact a U.S. PSU, it is all more likely that they swapped out the U.K PSU for a U.S. PSU. The circuits would've been different, more than just a few different value components. It's extremely doubtful that someone would've converted the PSU itself. If it was converted, then it is almost certain that they converted the machine by swapping the PSU, not converting the PSU itself.

 

First of all, have you been able to successfully boot this machine at all? Secondly, please humor me, post a picture of the bottom case label from your machine and another of the uncovered PSU, if you don't mind.

 

Thanks.

 

Edited June 5, 2020 by bfollowell

[Randy]

Hi b, I did install the power supply and everything works fine, well except for the floppy drive, will have to pull that one and see if I can get it working!  It was kind of strange that the power supply tag read 220 VAC (this is a UK machine for sure) but after looking over the caps it was apparent that someone had worked on the power supply, a power on test revealed the DC vales to be correct.

[bfollowell]

That is really odd, to say the least. I certainly wouldn't have thought you could just change a few components on the PSU and get it to work that way.

 

And the drive not working probably has nothing at all to do with anything else other than being a 30+ year-old drive that is probably dead, or at the very least needs some maintenance.

 

[Colleton]

3 hours ago, bfollowell said:

That is really odd, to say the least. I certainly wouldn't have thought you could just change a few components on the PSU and get it to work that way.

 

The only thing I can think is that he bought it from someone in US and the UK PSU board had already been swapped out with a US PSU board?  I don't see how you could plug 110v into a circuit designed for 220v and get the desired output voltages.

 

Switching power supplies don't like to be run without a load attached either, something to keep in mind.

[JohnnyCage]

On 6/4/2020 at 8:23 PM, Randy said:

Hi all, are the power supplies in each of the ST(e) computers usable with all voltages, i.e., can I use a UK machine on US voltage (220 VAC to 120 VAC) with it's existing power supply?  In other words, does the power supply "switch" like many of today's devices to provide proper output regardless of the input mains voltages?  I am thinking not, but just wanted to make sure.  thanks

I bought an ST from a guy a couple of months ago toghether with a PVM. The PVM is 220v.

I was pretty sure the ST was 220V but since I wasnt 100% sure I wrote to the seller. He didn't reply soon enough ,so I said to myself: if you plug it into 220V and the ST is 110v, bye bye ST expecting to receive 10-24v instead of the required 5-12v. So I plugged it in a 110V outlet. It turn on and worked flawlessly.

An hour later the seller answers me back: Dont use 110V, it is 220V.

To my surprise, I connected it to a 220v outlet and it continues to work flawlessly.

 

At this point I am believing your first thought was correct and STs come with dual voltage PSU: no other explanation.

[JohnnyCage]

On 6/4/2020 at 8:23 PM, Randy said:

Hi all, are the power supplies in each of the ST(e) computers usable with all voltages, i.e., can I use a UK machine on US voltage (220 VAC to 120 VAC) with it's existing power supply?  In other words, does the power supply "switch" like many of today's devices to provide proper output regardless of the input mains voltages?  I am thinking not, but just wanted to make sure.  thanks

I bought an ST from a guy a couple of months ago toghether with a PVM. The PVM is 220v. I was pretty sure the ST was 220V but since I wasnt 100% sure I wrote to the seller. He didn't reply soon enough ,so I said to myself: if you plug it into 220V and the ST is 110v, bye bye ST expecting to receive 10-24v instead of the required 5-12v. So I plugged it in a 110V outlet. It turn on and worked flawlessly. An hour later the seller answers me back: Dont use 110V, it is 220V. To my surprise, I connected it to a 220v outlet and it continues to work flawlessly. At this point I am believing your first thought was correct and STs come with dual voltage PSU: no other explanation.

After a couple of years, did you reach other conclusion?

[bfollowell]

49 minutes ago, JohnnyCage said:

I bought an ST from a guy a couple of months ago toghether with a PVM. The PVM is 220v. I was pretty sure the ST was 220V but since I wasnt 100% sure I wrote to the seller. He didn't reply soon enough ,so I said to myself: if you plug it into 220V and the ST is 110v, bye bye ST expecting to receive 10-24v instead of the required 5-12v. So I plugged it in a 110V outlet. It turn on and worked flawlessly. An hour later the seller answers me back: Dont use 110V, it is 220V. To my surprise, I connected it to a 220v outlet and it continues to work flawlessly. At this point I am believing your first thought was correct and STs come with dual voltage PSU: no other explanation.

After a couple of years, did you reach other conclusion?

 

I'm pretty sure they did NOT come with universal PSUs. I have no explanation for your situation other than possibly it isn't an original PSU. I do know for certain that not all PSUs were universal, even if yours is. It is definitely a mystery.

[ijor]

9 hours ago, JohnnyCage said:

I bought an ST from a guy a couple of months ago toghether with a PVM. The PVM is 220v.

I was pretty sure the ST was 220V but since I wasnt 100% sure I wrote to the seller. He didn't reply soon enough ,so I said to myself: if you plug it into 220V and the ST is 110v, bye bye ST expecting to receive 10-24v instead of the required 5-12v. So I plugged it in a 110V outlet. It turn on and worked flawlessly.

An hour later the seller answers me back: Dont use 110V, it is 220V.

To my surprise, I connected it to a 220v outlet and it continues to work flawlessly.

 

At this point I am believing your first thought was correct and STs come with dual voltage PSU: no other explanation.

 

The original PSUs were certainly NOT dual voltage. You would likely kill a 110V PSU if you connect it to 220V. However, a 220V PSU usually works at 110V, it is not ideal and not very healthy to the PSU in the long term, but usually it works. And no, it won't output half the voltage.

Edited December 12, 2023 by ijor

[351cougar]

I dont think even Falcons had a universal supply. I have seen a few schematics for st PS's with a jumper for 120 240, but it was internal, not like the slider seen on PC enclosures of the era.