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CPC 464 not turning on. [solved]

Started by Godmil, 23:26, 07 November 21

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Godmil

Hello,
I just found my old 464 and was keen to show it to my son, however it doesn't power up.  I have minimal electronics experience, but I have a multimeter and soldering Iron and a will to try stuff out. I was just wondering if anyone could give me tips as to what to try first.

I have a new power supply and the voltmeter says its working fine.  When its plugged in the light doesn't turn on and poking around the board I'm not seeing anything with power getting to it.  I tried the connectors on the power switch (circled in red in one of the attached pictures) but the voltmeter isn't detecting anything across them.

I read someone say that the power switches can break, if I wanted to bypass it could I literally just make a connection between those two contacts?  Or is there a way to check if power is getting past the powersocket at all? (I couldn't see anything I could prod with my multimeter, would I need to take the board off the case and check the back of the board?)

Any tips would be greatly appreciated.
Thanks.

eto

The power switch itself is often the culprit. You can open it and clean it and the contacts and check if that helps.


When I was a kid I tended to turn on/off my CPC with the monitor only and kept the CPC switch in "on"-position - I guess that's like bypassing the on/off switch in the CPC. Not sure though if that can have any side effects.

Bryce

Could you confirm the voltage and polarity of the new power supply you have first? 5V, at least 2A and the negative on the outside of the barrel?


Bryce.

Godmil

#3
Thanks for the replies.  I'm still trying to remember how the multimeter works :)
I bought this powersupply https://coolnovelties.co.uk/coolnovelties/amstrad-power-cables/27-amstrad-cpc-464-tv-connection-kit-0705693506418.html

With the multimeter when I stick the red end in the center and touch the black end to the outside I'm getting 5.1V.... but when checking the current it seems to cycle from 0 to about 1.6A back and forth every 5 seconds or so... is that normal?

I checked the resistance across my power switch and when its OFF its infinite, and when its ON its like 0.01 Ohms, which I think sounds like its good. I gave it a spray of Contact Cleaner just incase. This is interesting though. When I plugged it back in, I noticed the voltage across the PowerSwitch was 0 when set to ON, and when I turned it OFF the voltage would increase from 0 by about 0.1V every second. When it got to about 2.5V I unplugged it (worried about breaking something), when I tried it again the same thing happened. 

EDIT: tried the voltage across the switch again and its just giving me 0V all the time now, not sure what's going on :/  I think I'll take the board off the case to check the back of it.

Godmil

#4
I tried taking the board off so I could check the back, and tested the power connector with the multimeter.  I tried puting the Black connector at point X, then the Red one at point A, which gave me 5V.  I then moved the red one to point B and got 0V.  I tried the leg on point C at the front and still 0V.

I'm guessing that I should have still been able to see 5V at those other points, so does that mean the internal wiring on the board could be broken?  :(

EDIT: I tried testing the resistance between various points on the board that I could see are internally connected, and they all seemed fine.  Even from point B to the little dot at the end of that line.  But the resistance between points A and B is infinite.  Could that be my whole problem?  I could connect those points with a wire.  But I'll hold off until someone says something cause I'm really just guessing at how things work :)

Bryce

Crack in the trace? If so, solder a bridge wire between A and B.

Bryce.



Godmil

Awesome. Thanks I'll do that now.... or as soon as I can find some wire :)

Godmil

OMG It's lighting up! Gatta see if I can get a video signal now  ;D

eto

Quote from: Godmil on 14:10, 08 November 21
OMG It's lighting up! Gatta see if I can get a video signal now  ;D

Nice! Press the DEL key, you should hear a sound if the CPC is working (make sure the volume is not set to 0).


Godmil

I thought it wasn't working... then I remembered to change the video input on my TV  :D
Thanks for the help everyone, I'm so excited it's working!(also I'm so greatful that if one wire was to be broken that it would be the very first one on the board)
How awesome is it that there is such an active forum for something like this  :)

Skunkfish

Awesome result, have fun!

It's always satisfying when you can fix a problem yourself  ;D
An expanding array of hardware available at www.cpcstore.co.uk (and issue 4 of CPC Fanzine!)

Animalgril987

And another CPC brought back to life :D

chinnyhill10

Quote from: eto on 08:16, 08 November 21
The power switch itself is often the culprit. You can open it and clean it and the contacts and check if that helps.


When I was a kid I tended to turn on/off my CPC with the monitor only and kept the CPC switch in "on"-position - I guess that's like bypassing the on/off switch in the CPC. Not sure though if that can have any side effects.


Might be rubbish but I was always told not to do that in case the PSU in the monitor delivers a surge. Turn the monitor on first then the computer. The other way doesn't matter as much but I always turned the computer off first.
--
ChinnyVision - Reviews Of Classic Games Using Original Hardware
chinnyhill10 - YouTube

Bryce

Quote from: chinnyhill10 on 23:08, 08 November 21

Might be rubbish but I was always told not to do that in case the PSU in the monitor delivers a surge. Turn the monitor on first then the computer. The other way doesn't matter as much but I always turned the computer off first.

It's not rubbish. When you turn on a power supply it can react in two ways: 1. It ramps up to the desired voltage - This can cause problems if it ramps too slow that some chips may not start in the right order, although that's why the CPC and other computers have a reset circuit. 2. It overshoots, ie it goes above the desired voltage for a few milliseconds - This could damage the CPC. So the reasoning behind using the switch is that you don't connect the PSU to the electronics until the PSU has stabilised at 5V.

Bryce.

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