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Ericsson MC12 Schematic

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spacesmurf Page Icon Posted 2021-10-19 10:00 PM
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Hi, for context... I enjoy watching electronics repairs videos as somewhat of an unrealized dream.

I also grew up in the 90s, and when I saw this device in an auction for next to nothing (it does not start), I had to buy it.

Before this, I lucked out with a 'for parts' Amstrad that turned out to be an easy fix.

So indeed, it does not boot but draws power even before I press the on button, and when pressed, nothing happens.

I took it all apart down to the mainboard, and it draws precisely the same. There's voltage going to the CPU, but nothing appears on the screen. I was able to find the pinout for the CPU, and as far as I can check with a multimeter, it looks ok. I don't know what I am doing, but I will keep going and see how far I can get; hence, I now have a Logic Probe on order to see if this will reveal anything.

...anyway, I am looking for a schematic/repair manual if such a thing even exists.

It's also missing the stylus and a tray right in the middle below the keyboard.
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C:Amie Page Icon Posted 2021-10-20 12:14 PM
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To my knowledge, none were published externally to hp.

If you do any tracing, please do write it up and publish your findings.

Have you tested all of the capacitors?
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spacesmurf Page Icon Posted 2021-10-20 9:12 PM
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Thank you C:AMIE, sure thing though not sure when I am going to get to it.

In the meantime, I will share some board pics should someone be curious.

https://postimg.cc/p9h7Q8JM
https://postimg.cc/y3BbzG47
https://postimg.cc/FfM6TRTd
https://postimg.cc/V58f6Lzk
https://postimg.cc/nCVn4Rj8
https://postimg.cc/FkZnFxN3

Edit: Couldn't get the IMG tag working.

Edited by spacesmurf 2021-10-20 9:14 PM
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WallyB110 Page Icon Posted 2021-10-21 7:39 AM
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Thanks for the photos :-)
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andrej2112 Page Icon Posted 2021-10-21 12:55 PM
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Hi
Is it drawing power from battery or charger?
check all capacitors, on mine I have short circuit across caps
Andrej
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systremor Page Icon Posted 2021-10-29 3:28 PM
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By coincidence, I've also won an auction on a non-working Ericsson MC12. It arrived today :-D

The symptoms were the same; no display or anything on batteries or the AC adapter, but mine also had a decent amount of corrosion from leaky batteries.

It turned out that the RAM board (underneath the keyboard) makes bad contact with the motherboard. This problem may happen at normal use, when the screen will get garbled. Reattaching the RAM board allowed it to turn on after being dead...
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spacesmurf Page Icon Posted 2021-11-01 5:37 PM
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systremor lucky you, I did reseat everything twice and checked for bent pins etc. as well as shorted caps but nothing so far.

I will have another look though, just in case so thanks for sharing.
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spacesmurf Page Icon Posted 2021-11-01 5:47 PM
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andrej2112 - 2021-10-21 12:55 PM

Hi
Is it drawing power from battery or charger?
check all capacitors, on mine I have short circuit across caps
Andrej


I think I did but then again this is my first attempt at something like this and my little to no knowledge is from youtube videos. I assume those black ones are not capacitors? They are short in my case.

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C:Amie Page Icon Posted 2021-11-01 6:13 PM
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I can't help but notice that there seems to be a patch wire there on the left side of your circle? Was that something you did? It seems a bit messy
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WallyB110 Page Icon Posted 2021-11-01 7:45 PM
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^ I agree. That doesnt look like stock.
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systremor Page Icon Posted 2021-11-01 9:18 PM
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C:Amie - 2021-11-01 6:13 PM

I can't help but notice that there seems to be a patch wire there on the left side of your circle? Was that something you did? It seems a bit messy


Can confirm that my MC12 has green patch wires on various places, as well. Looking at other board pics on Google yields the same patch wires

Edited by systremor 2021-11-01 9:29 PM
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spacesmurf Page Icon Posted 2021-11-02 5:53 AM
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Not my doing, this and couple of other bodge wires were already there.
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C:Amie Page Icon Posted 2021-11-02 7:36 AM
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It's not the wire, it's the fact it looks very badly soldered.
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spacesmurf Page Icon Posted 2021-11-21 5:16 PM
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The logic probe did not reveal anything interesting. There was no 'pulse' on the bus lines.

I also looked around with an oscilloscope and the only activity was on the clock which shows the expected 11 MHZ (bus speed) and chip select pins.

Address on the bus is stuck (bits on A0 - A25 don't change). I am throwing in the towel. Ordered a working one and will compare for anything obvious.

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WallyB110 Page Icon Posted 2021-11-21 6:56 PM
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Hmmm... I gotta go with what was said above. Solder work looks suspect.

-Walt B

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