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  • Joined: 13 Jun 2017
  • Posts: 93
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SMS AC adapter 3025-18 problems
Post Posted: Mon Mar 08, 2021 1:00 pm
Hello,

I've got the EU SMS 1 AC power adapter that always worked ok.. lately I found strange that using it on the SMS2 having the same voltage requirement (and I suppose lower current one) two console has given problems, the modded SMS2 had visual GFX strange colors, the second SMS2 both EU seems to not boot up anymore.
I checked the AC adapter and found out that without any load it give out 13,4 volts on the exit!
How is that possible? Is it possible I might have broken both SMS2 consoles or which components might be broken? Should I try with some third party adapter?

Thanks
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  • Joined: 10 Jun 2020
  • Posts: 26
  • Location: Norfolk, uk
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Post Posted: Mon Mar 08, 2021 3:42 pm
My first thoughts would just be it's heading to its end of days.

I do not tend to use any original power supplies these days and instead use the same model of multi way 9v 600Ma power supply on my MS1 & 2 (along with the majority of other machines of that era),the old ones are in a drawer so can be put with machines if I ever wanted to sell them as complete.

They are under £10 each and far cheaper than replacing machines. :)

I'm sure you can get similar in all countries if you are not UK, just make sure it's regulated in the description as some i had off ebay in the past caused interference, where these have never had a problem.

This is the one i use:

https://www.tlc-direct.co.uk/Products/SK661400.html


386DX wrote
Hello,

I've got the EU SMS 1 AC power adapter that always worked ok.. lately I found strange that using it on the SMS2 having the same voltage requirement (and I suppose lower current one) two console has given problems, the modded SMS2 had visual GFX strange colors, the second SMS2 both EU seems to not boot up anymore.
I checked the AC adapter and found out that without any load it give out 13,4 volts on the exit!
How is that possible? Is it possible I might have broken both SMS2 consoles or which components might be broken? Should I try with some third party adapter?

Thanks
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  • Joined: 19 Oct 1999
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  • Location: London
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Post Posted: Mon Mar 08, 2021 3:49 pm
The adaptors have capacitors like most electronics and these degrade with age. The Master System passes this into a voltage regulator which converts down to a steady 5V, but may not be happy with much more than 12V - but it’s likely the adaptor voltage drops when under lid anyway. At a higher voltage it’s likely to get rather hot. If your system doesn’t work, replacing the voltage regulator may be a good first step.

Beware cheap AC adaptors, many (especially in the USB power adaptor space, which is not what you want here anyway) are somewhat dangerous (failure modes may include flames and/or passing mains voltage into you or your console).
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  • Joined: 05 Sep 2013
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Post Posted: Mon Mar 08, 2021 6:24 pm
386DX wrote
I checked the AC adapter and found out that without any load it give out 13,4 volts on the exit!


what it gives without any load should be irrelevant, check the voltage when it's working
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Post Posted: Mon Mar 08, 2021 10:28 pm
Thanks for the answers. I imagined that without the hardware load the voltage might be a bit higher but I wasn't expecting ..that high. Something strange that was suspecting already before was that the adaptor became a bit warm even when just plugged with the console off.

Anyway before trying I might buy a modern one too for both the SMS1 and 2 and maybe also for the Mega Drive II. Are there any technology differences I might consider from these old psu? Cause modern power switching ones are much lighter for similar voltages (considering how heavy these original ones are for 9V-1A only).
Also to repair them can they be opened without cutting plastic or breaking the case?
Thanks.
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  • Joined: 14 Aug 2000
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  • Location: Adelaide, Australia
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SMS AC adapter 3025-18 problems
Post Posted: Wed Mar 10, 2021 11:20 am
13.4V is fine.

I power my SMS 1 with the power supply of my MD1 and unloaded the output of the MD power supply is 13.9V.

I would try an alternate power supply to confirm or rule out that the suspected power supply first.
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  • Joined: 13 Jun 2017
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Post Posted: Sat Mar 27, 2021 12:14 pm
UPDATE: I tested today that original PSU and once the SMS II is powered with the SMS I psu, its output voltage goes down to 11,3<->10,8 volts as imagined! I checked also the voltage regulator that is a standard Motorola 7805CT but I've seen some other datasheet that seems to support up to 35V (???) in input as maximun so I suppose there's no problem also considering the regulator itself stays quite cold or just a bit warm. On the regulator output I measured 4,8 volts.
I'll continue to use this one without opening it because I suppose I should break the plastic and I don't like that.
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