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 »

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 »

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 5086 times
label_115v.png
label_115v.png (39.92 KiB) Viewed 5086 times
wyerd
Posts: 88
Joined: 13 May 2013 23:16
Location: Upstate New York. USA.

Re: Building a replacement MTX PSU

Post by wyerd »

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 »

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
Posts: 648
Joined: 24 Dec 2012 03:01
Location: Looking forward to summer, in Somerset, UK

Re: Building a replacement MTX PSU

Post by 1024MAK »

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 »

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

Re: Building a replacement MTX PSU

Post by 1024MAK »

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 »

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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gunrock
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Joined: 28 Oct 2020 21:17

Re: Building a replacement MTX PSU

Post by gunrock »

Hi all,

I've been silly enough to buy an MTX512 with a PSU, so now need to build my own PSU. I'm having some trouble sourcing replacements for some of the missing items in the UK BOM (I'm in Denmark). I think I have now sourced alternatives for the ones that are now obsolete.

However, the main problem is the price - currently looking at around 90 GBP! That is, of course, because the minimum order for quite a few of the parts (resistors, diodes, fuses, shrouds and strain reliefs, etc.). Is there anyone out there in Europe, who'd be willing to sell me at around cost (i.e. added hassle charge) plus postage the bulk order items, perhaps? I'm not a regular hardware builder, thus don't really need a full set of part bins.

Or does someone have a cheaper source for some of these parts (in small numbers)?

Many thanks,
Steve
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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 »

Which items are you after? Or which parts are you having trouble getting?

Unfortunately the cost of postage is often a limiting factor.

Mark
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