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About original Memotech hardware.
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1024MAK
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Re: No picture.

Post by 1024MAK »

1024MAK wrote: 21 Jul 2020 14:49 Does your multimeter have a diode test range?
If yes, with the power off and the PSU NOT plugged into the computer, test diodes D14 to D19 one at a time, each one with the leads around one way, then the other way round. One way the diode should conduct and the meter should show a voltage of 0.6V appropriately. The other way round, should give you an open circuit indication.

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:
Steven.G
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Joined: 18 Jul 2020 14:03

Re: No picture.

Post by Steven.G »

Tested all 3 times.

1 to 2 = 0
2 to 3 = OL
3 to 4 = 0
4 to 5 = OL

Diodes test.

Diode D14 = 555, OL
Diode D19 = 554, OL

Steve..
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1024MAK
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Re: No picture.

Post by 1024MAK »

Err “test diodes D14 to D19” meaning D14, D15, D16, D17, D18 and D19...

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

Re: No picture.

Post by 1024MAK »

1 to 2 = 0 = okay
2 to 3 = OL = not good :-(
3 to 4 = 0 = okay
4 to 5 = OL = not good :-(

Diodes test.

Diode D14 = 555, OL = good :-)
Diode D19 = 554, OL = good :-)

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:
Steven.G
Posts: 45
Joined: 18 Jul 2020 14:03

Re: No picture.

Post by Steven.G »

Oops sorry!
So would that be the cluster of diodes under and around C51?
Steven.G
Posts: 45
Joined: 18 Jul 2020 14:03

Re: No picture.

Post by Steven.G »

Anyway they all read about 555.

Steve..
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1024MAK
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Re: No picture.

Post by 1024MAK »

So all the diodes appear to be okay. Next would be to open the case of the PSU. I’m out at the moment, so can’t talk you through the actual method to open it. And the last time I opened one, was over ten years ago! Do make sure that the mains plug is NOT plugged into a socket. As long as it is unplugged, there are NO hazardous voltages inside (in fact, it will be completely dead).

Once open, check that the wires are connected as per the photo below:
Image

Again on the 200 ohm resistance range, test between the terminals with the coloured wires as below:
Yellow to green
Green to black / red
Black / red to white.

Be aware that the solder/terminals may need scraping to get a good electrical connection.

If all these have values less than 2 ohms, then it could be a cable fault.
In which case test as below (still on the same resistance range):

DIN plug pin - wire colour on the transformer
1 - yellow
2 - green
3 - red/black
4 - red/black
5 - white

These should all be less than 2 ohms.

Report back your findings.

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:
Steven.G
Posts: 45
Joined: 18 Jul 2020 14:03

Re: No picture.

Post by Steven.G »

So I opened the PSU to a big surprise,, it's nothing like the photo!!
However I did my best and got,,
blue to green gives 00.0 ohms
green to white gives 00.0 ohms
white to orange gives 00.0 ohms

1 - blue connects pins 1,2,& 5. 00.0 ohms
2 - green connects pins 1,2,& 5. 00.0 ohms
3 - white connects through an in-line T1.6a fuse(BLOWN I think we have a fault) to black & brown and connects to pins 3 & 4
4 - orange connects pins 1,2,& 5. 00.0 ohms

Hope all this makes sense..
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Dave
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Re: No picture.

Post by Dave »

Did it have a UK plug on it?

Apart from the dodgy fuse hack, it looks like it may be tapped for 110v!
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Dave
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Re: No picture.

Post by Dave »

I tried to get a closer look at your Facebook photos, it looks like it might have had a European plug on it? So maybe the input was tapped for 220VAC. I’ve never seen a European MTX power supply. A clearer photo of the PSU label would be nice.

In any event, that doesn’t look like a factory fitted fuse/holder
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