Building a replacement MTX PSU

About original Memotech hardware.
wyerd
Posts: 93
Joined: 13 May 2013 23:16
Location: Upstate New York. USA.

Re: Building a replacement MTX PSU

Post by wyerd »

I can't make out the wires!

I've magnified the PDF and numbered the terminals:-

Image
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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 »

wyerd wrote:I can't make out the wires!
In my photos, they are very thin silver coloured wires that come out of the black plastic body of the switch and connect to the terminal very close to the black plastic of the body. Yes, very difficult to see. Your switch may not be the same.
wyerd wrote:I've magnified the PDF and numbered the terminals:-

Image
Based on this, terminals numbered 1 and 4 are the inputs and terminals 2 and 5 (are your sure this is 5 and not 3?) are the outputs. It does not matter which side is live/line and which is neutral, but both live/line wires need to be on one side of the switch. So I suggest 1 be used for live/line input, 2 be live/line output. 4 would then be neutral input and 5 (3) would be neutral output.

Mark
:!: Standby alert :!:
“There are four lights!”
Step up to red alert. Sir, are you absolutely sure? It does mean changing the bulb :!:
Looking forward to summer in Somerset later in the year :D

Not as many MTXs as Dave! :lol:
wyerd
Posts: 93
Joined: 13 May 2013 23:16
Location: Upstate New York. USA.

Re: Building a replacement MTX PSU

Post by wyerd »

OK, thanks. 3 is shown on the rear, together with 6 on the right, but there isn't a terminal in the space.
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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 »

wyerd wrote:OK, thanks. 3 is shown on the rear, together with 6 on the right, but there isn't a terminal in the space.
Ahh, yes, the plastic body would also be used with DPDT (double pole, double throw) and DPCO (double pole, change-over) type switches which will use six terminals.

Mark
:!: Standby alert :!:
“There are four lights!”
Step up to red alert. Sir, are you absolutely sure? It does mean changing the bulb :!:
Looking forward to summer in Somerset later in the year :D

Not as many MTXs as Dave! :lol:
wyerd
Posts: 93
Joined: 13 May 2013 23:16
Location: Upstate New York. USA.

Re: Building a replacement MTX PSU

Post by wyerd »

Thanks for the assistance Mark. Mains side is now wired up and ready to connect to the transformer. Continuity checks out as well this time which alerted me to the wiring issue on the switch.

Image

Image

The switch reminds me of the one on the FDX.
wyerd
Posts: 93
Joined: 13 May 2013 23:16
Location: Upstate New York. USA.

Re: Building a replacement MTX PSU

Post by wyerd »

Mark,

How do you set the output voltage?

Code: Select all

LM2577 step-up DC-DC converter.                             eBay/che'261211800    1 £1.63 £1.63   1     1 LM2577 DC to DC Adjustable Converter Step-up Cir
           I used a Chenyao19870517 LM2577 DC to DC adj                                                                             
           Set the output voltage to 16V before fitting
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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 »

Connect a temporary DC supply to the input terminals. I used a DC power supply set to 8V, but a 9V battery would be fine. If using a PP3 [NEDA 1604, IEC 6F22, MN1604, 6LR61], best use a brand new one.
Connect a digital multimeter to the output terminals.
Now locate the preset (variable resistor) on the board. On mine, it is a square blue coloured item, with a small gold adjusting screw. Turn the screw until the meter indicates between 16V and 16.1V. Note that the preset is a multi turn type, so don't worry if you have to keep turning it. The value of 16V is nowhere near the end stop.

Disconnect, and install. Job done :mrgreen:

Mark
:!: Standby alert :!:
“There are four lights!”
Step up to red alert. Sir, are you absolutely sure? It does mean changing the bulb :!:
Looking forward to summer in Somerset later in the year :D

Not as many MTXs as Dave! :lol:
wyerd
Posts: 93
Joined: 13 May 2013 23:16
Location: Upstate New York. USA.

Re: Building a replacement MTX PSU

Post by wyerd »

Connected it to a 9v battery. Adjusted the screw until mulimeter read 16v. Job done!
wyerd
Posts: 93
Joined: 13 May 2013 23:16
Location: Upstate New York. USA.

Re: Building a replacement MTX PSU

Post by wyerd »

Mark,

Can you confirm the ouput connections of F2 please?

Red connection to DIN Plug 3
Black connection to DIN Plug 4
Black connection to R2 of LED
Black connection to black output of strip board - This is the connection I can't see in the photos.

Thanks.
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1024MAK
Posts: 757
Joined: 24 Dec 2012 03:01
Location: Looking forward to summer, in Somerset, UK

Re: Building a replacement MTX PSU

Post by 1024MAK »

wyerd wrote:Mark,

Can you confirm the ouput connections of F2 please?

Red connection to DIN Plug 3
Black connection to DIN Plug 4
Black connection to R2 of LED
Black connection to black output of strip board - This is the connection I can't see in the photos.

Thanks.
Yes, what you have listed is correct. On the strip board, the black wire from the fuse goes to the "0V" track. This track is the one that is the negative connections for the two capacitors. And another black wire goes from this track to the -V input of the DC-DC converter board.

I hope that helps :mrgreen:

Mark
:!: Standby alert :!:
“There are four lights!”
Step up to red alert. Sir, are you absolutely sure? It does mean changing the bulb :!:
Looking forward to summer in Somerset later in the year :D

Not as many MTXs as Dave! :lol:
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