Building a replacement MTX PSU

About original Memotech hardware.
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1024MAK
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Re: Building a replacement MTX PSU - Sneak Preview

Post by 1024MAK »

More photos...

Image

Image

Image

I'll put more up on Sunday :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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Dave
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Re: Building a replacement MTX PSU - Sneak Preview

Post by Dave »

Interesting !

It looks like you're putting DC out?

regards
Dave
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1024MAK
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Re: Building a replacement MTX PSU

Post by 1024MAK »

Outputs:
Two 7.5V AC feeds (for feeding to the diodes that in turn go to the +5V regulator and the -5V zener diode supply circuitry)
One +16V DC feed, for feeding to one of the diodes that in turn supplies the +12V regulator.

The +16V DC supply is generated by a LM2577 based step up DC to DC converter, which in turn is supplied by two diodes and a 2200uF 16V smoothing capacitor, which gets it's supply from the two 7.5V AC feeds.

Because I am using a 50VA transformer with a 230V primary, the two 7.5V AC outputs actually produce a bit more than the specification suggests when used at my house (where the "230V" mains supply is at, or close to 240V).

Schematic will be made available, along with a parts list when I get around to it :mrgreen:

Also when I demonstrated it at Memofest 2014, Claus asked me about the performance when operating at 230V. So as I have a mains isolating transformer with various tappings, I will see if I can set it up to give 220V and 230V outputs, I can then test my MTX PSU using these voltages.

Code: Select all

My replacement MTX power supply unit
Test and set-up of LM2577 based step up DC to DC converter:-
LM2577 based step up DC to DC converter
Test input 8.01V at 19.7mA. Output (no load) 16.015V

Unit constructed, test load data:-
DIN  Wire      Output        No load
Pin. Colour    Name          Voltage
 1.  Yellow.   +16V DC       16.025V DC, 6mV ripple (meter)
 2.  Green.    7.5VH AC       8.93V AC
 3.  Red.      0V
 4.  Black.    0V
 5.  White.    7.5VL AC       8.92V AC

Internal DC supply (feeds LM2577 module):- 11.45V DC, 33mV ripple (no load).

Unit constructed, test load data:-
DIN  Wire      Output      Lamp          Current  Voltage  
Pin. Colour    Name                   
 1.  Yellow.   +16V DC     Two 24V 5W    360mA    15.785V DC, 28.2mV ripple (meter)
 2.  Green.    7.5VH AC    One 12V 21W   1.37A     8.15V AC
 3.  Red.      0V
 4.  Black.    0V
 5.  White.    7.5VL AC    One 12V 21W   1.38A     8.18V AC
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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Crazyboss
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Re: Building a replacement MTX PSU

Post by Crazyboss »

Mark

I think more people could be interested, cause people always miss the power unit.

As mentioned at the Memofest 2014, I am interested to buy one.

I am sure more people will be interested, so you can start a production line ;)

Around what price can you produce one of those?
//CLAUS - Webmaster at www.mtxworld.dk
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1024MAK
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Re: Building a replacement MTX PSU

Post by 1024MAK »

All in good time ;)

Timing and cost is directly proportional to how much use I get of a TARDIS, should one be made available :P

The prototype has a mains switch which glows red when on and a green "output on" LED. For the "production version", I am open to suggestions as to the colour of this LED.

How many people are interested in buying one?
If you are a "maybe", but are going to remain undecided until the cost is known, please say so.

Also, for those people who would prefer to build their own, I will post up the details once I have drawn the schematic in a eye friendly form :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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Dave
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Re: Building a replacement MTX PSU

Post by Dave »

mmm, what colour should the LED be . . .

Difficult question, maybe 1 led is too restrictive, maybe we should have 1 LED per output voltage? :lol:
:roll: Even better, 2 LEDs per output, that flash at a frequency proportional to the voltage :roll: :lol: :lol:

It could replace my Christmas tree lights then :-)

OK - interested in buying, depending on price

(If you want me to draw the schematic for you, send me your "drawings" and I'll KiCad them)

regards
Dave
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1024MAK
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Re: Building a replacement MTX PSU

Post by 1024MAK »

Construction Details

First, the DC board:
DC board 1.jpg
DC board 1.jpg (216.42 KiB) Viewed 10004 times
DC board 2.jpg
DC board 2.jpg (149.08 KiB) Viewed 10004 times
DC board underside.jpg
DC board underside.jpg (582.78 KiB) Viewed 10004 times
Diodes:
Two 1N4001 or 1N4002 or a higher voltage rating.
Capacitors:
The small blue capacitor is a 100nF ceramic multilayer type, 5mm spacing.
The large capacitor is a 2200uF 16V electrolytic.
Fuse:
PCB fuse clips, 5mm pins, suitable for a 20mm type fuse.
1A anti-surge (A/S) / time delay (T) 20mm x 5mm glass fuse

More tomorrow (sorry it's slow, I'm a bit time poor...)

Mark
Last edited by 1024MAK on 16 Jul 2015 17:52, edited 2 times in total.
:!: 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:
User avatar
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 »

DC board 3.jpg
DC board 3.jpg (157.87 KiB) Viewed 9999 times
Step up DC to DC converter:
Step up DC to DC converter.jpg
Step up DC to DC converter.jpg (237.97 KiB) Viewed 9999 times
Inside:
Inside #01.jpg
Inside #01.jpg (227.42 KiB) Viewed 9999 times
:!: 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:
User avatar
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 »

Inside #02.jpg
Inside #02.jpg (202.07 KiB) Viewed 9999 times
Inside #03.jpg
Inside #03.jpg (155.21 KiB) Viewed 9999 times
Inside #04.jpg
Inside #04.jpg (198.62 KiB) Viewed 9999 times
:!: 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
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Joined: 13 May 2013 23:16
Location: Upstate New York. USA.

Re: Building a replacement MTX PSU

Post by wyerd »

Looking good Mark! Will you be posting circuit diagrams and a parts list as I'd like to make a 110v version?
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