Building a replacement MTX PSU

About original Memotech hardware.
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1024MAK
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Building a replacement MTX PSU

Post by 1024MAK » 30 Jun 2013 16:07

Hi all :-)

Here are some preview pictures of the development and construction of a replacement mains PSU for MTX computers :D
New MTX PSU Sneakpic01.JPG
New MTX PSU Sneakpic01.JPG (41.45 KiB) Viewed 3753 times
New MTX PSU Sneakpic02.JPG
New MTX PSU Sneakpic02.JPG (27.23 KiB) Viewed 3753 times
New MTX PSU Sneakpic03.JPG
New MTX PSU Sneakpic03.JPG (38.2 KiB) Viewed 3753 times
Edited to add:
  • The schematic is here
  • A UK parts list (BOM) is here
  • A USA parts list (BOM) is here
The USA version uses a different transformer, so has a 2A mains fuse. Apart from that, it is essentially the same.
My thanks to forum member Wyerd for the USA BOM :D

Mark
Last edited by 1024MAK on 16 Jul 2015 18:02, edited 2 times in total.

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Dave
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Re: Building a replacement MTX PSU - Sneak Preview

Post by Dave » 30 Jun 2013 18:52

Hi Mark,

is the switch sat next to a cut-out in a case you are thinking about?

And why the "coils" in the LED and resistor leads? - Just to get a grip of for testing, or do they serve a porpose?

regards
Dave

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1024MAK
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Re: Building a replacement MTX PSU - Sneak Preview

Post by 1024MAK » 02 Jul 2013 01:55

Dave wrote:is the switch sat next to a cut-out in a case you are thinking about?
Yep, the cut-out was made for the switch :mrgreen:
Dave wrote:And why the "coils" in the LED and resistor leads? - Just to get a grip of for testing, or do they serve a purpose?
Makes the connection more robust and easier to solder :D
More pictures and hopefully some test results soon :D

Mark

EDIT 2013-11-11:- I now have some more parts that have arrived today. So hopefully this weekend I may find some spare time to (1) post some more details and (2) finish the testing ready for the final part of the build. But don't hold your breath ;)

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Crazyboss
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Re: Building a replacement MTX PSU - Sneak Preview

Post by Crazyboss » 11 Nov 2013 20:17

Hi Mark.

Look forward to see the final product ;)

Hopefully ist a bit more powerfull than the original MTX one ;)

Actually I didn turn my MTX (the one with Jims donated board), since a few days after the meeting in Jims house.

I think its a powersupply issue, sometimes it work good and sometimes not.

Not fun to play with the MTX when the colours are gone, only black white or gray (usely cause lack of power).
//CLAUS - Webmaster at www.mtxworld.dk

Martin A
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Re: Building a replacement MTX PSU - Sneak Preview

Post by Martin A » 11 Nov 2013 20:30

I have display issues with both of mine, if the RS232 is fitted, but without it they're both fine.

I suspect it's lack of juice on the 12v line.

However, I've only got the one PSU to share between the 2 systems, so I'm another user watching this with interest.

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Re: Building a replacement MTX PSU - Sneak Preview

Post by Crazyboss » 11 Nov 2013 23:23

Martin A.

I had this problem too, sometimes there is a fuse inside the PSU itself, but not always. The problem its hard to open the PSU without damage the psu-case. But in my case, i replaced the fuse cause it was blown, and then it worked.
//CLAUS - Webmaster at www.mtxworld.dk

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Re: Building a replacement MTX PSU - Sneak Preview

Post by Dave » 11 Nov 2013 23:53

Hi Claus,

that's interesting. The PSUs sold in the UK do not have fuses - but in the UK, mains plugs are fused (although I wonder how many have actually got appropriately sized fuses in, rather than the ubiquitous 13A).

I wonder if the fuse was an end-user mod, or something that Memotech did for products sold outside the UK

regards
Dave

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1024MAK
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Re: Building a replacement MTX PSU - Sneak Preview

Post by 1024MAK » 12 Nov 2013 00:02

If anyone wants a 13A fuse to blow themselves up with, I have zillions of the dammed things (from the days that UK 13A plugs only came with a 13A use, even though a large number of appliances were suppose to have a 3A or 5A fuse fitted in the plug...) :roll:

Mark

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Dave
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Re: Building a replacement MTX PSU - Sneak Preview

Post by Dave » 12 Nov 2013 00:40

Thanks for the offer Mark,

unfortunately, I found that the 13A fuse in my washing machine was too small.

However, I was able to cure the problem by going to the next size up

:-)
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