Building a replacement MTX PSU

About original Memotech hardware.
wyerd
Posts: 88
Joined: 13 May 2013 23:16
Location: Upstate New York. USA.

Re: Building a replacement MTX PSU

Post by wyerd » 17 Jul 2015 18:30

Oh, BTW, my last name isn't quite spelled correctly. The R & E need to be transposed so it reads WYER. Thanks. :D

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Dave
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Joined: 11 Aug 2012 18:16
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Re: Building a replacement MTX PSU

Post by Dave » 17 Jul 2015 20:22

Hi David,

sorry! - I knew that :oops: - spelling corrected.

Fuse note added

A couple of mods to the label
Mark - can you confirm/correct the specs please?

regards
Dave
Attachments
label_240v.png
label_240v.png (24.08 KiB) Viewed 2084 times
label_115v.png
label_115v.png (39.92 KiB) Viewed 2084 times

wyerd
Posts: 88
Joined: 13 May 2013 23:16
Location: Upstate New York. USA.

Re: Building a replacement MTX PSU

Post by wyerd » 17 Jul 2015 20:26

Dave wrote:sorry! - I knew that :oops: - spelling corrected.
Dave
TY!

What do you use to create the labels?

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Dave
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Joined: 11 Aug 2012 18:16
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Re: Building a replacement MTX PSU

Post by Dave » 17 Jul 2015 20:43

Hi David,

just a graphics editor - PAINT.NET, it's free.
http://www.getpaint.net/download.html

It can create most graphics formats (.png, .jpg., .gif, etc.)

I am sure there are specific label creation programs around, but this does the job and can create output that could be used by any of the cheap ebay label printers

regards
Dave

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1024MAK
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Joined: 24 Dec 2012 03:01
Location: Looking forward to summer, in Somerset, UK

Re: Building a replacement MTX PSU

Post by 1024MAK » 21 Jul 2015 16:39

Hmm, it's a pain working out how to rate a PSU with a mix of two AC and one DC outputs.

If we want something similar to the original MTX PSU, try this:

220V/240V version, Power 50VA
15V AC (tapped at 7.5V AC) at 2.3A
16V DC at 450mA

115V version, Power 43VA
16V AC (tapped at 8V AC) at 1.68A
16V DC at 450mA

I will have to do some measuring before I can suggest a size for the label...

Mark

wyerd
Posts: 88
Joined: 13 May 2013 23:16
Location: Upstate New York. USA.

Re: Building a replacement MTX PSU

Post by wyerd » 23 Apr 2017 22:20

A few months back I purchased a USA spec MTX 512 and have just got round to setting it up. It came with the RS232 expansion card as the original owner had it connected to the FDX, but somehow it was lost and wasn't part of the purchase, or was the original PSU. So I hooked it up to the 110v PSU I built with Marks help, but unfortunately nothing happened, no green LED on the PSU and no sign of life from the MTX as the 1A fuse had blown. Plugging in an original 240v PSU connected to a step-up transformer made the MTX boot, so I thought the serial card may be causing the problem. I disconnected the card and tried the 110v PSU with the same result of the 1A fuse blowing again.

@Mark, what could be causing the 1A to blow when using the USA 512, but not with the UK 500? Is there anything I can test for on the board?

Thanks,
David.

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1024MAK
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Location: Looking forward to summer, in Somerset, UK

Re: Building a replacement MTX PSU

Post by 1024MAK » 24 Apr 2017 15:49

David, which fuse?
The mains input fuse (F1, in the panel mounted fuse holder)?
Or the the 1A fuse (F3) inside mounted on the strip board (protecting the DC supply)?

If you mean F3, I recommend you try a T 1.25A (T or A/S for time delay / anti-surge) fuse. The problem is the inrush current to the electrolytic capacitors plus the extra current required for the serial board.

If that does not do the trick, shout out ;)

Mark

wyerd
Posts: 88
Joined: 13 May 2013 23:16
Location: Upstate New York. USA.

Re: Building a replacement MTX PSU

Post by wyerd » 28 Apr 2017 04:30

It's the 1A fuse (F3)

Changing the fuse to a 1A slow blow fuse solved the problem.

Thanks,
David.

Edit. I've just checked the USA spec BOM and it does say F3 should be a slow blow fuse, so I must have used the wrong type in the first place somehow.

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