Yet Another not running CPC464 ^^' (LED doesn't light up)

GhostLine · 13:49, 14 June 22

Hi guys !

I've collected from a friend of mine a CPC464, who ... don't run.

I've already detected (and corrected) a +5V continuity problem, and I've also dismantled and cleaned the power switch, but still ...

I've no idea what to check in order to continue my diagnosis : when I turn on the CPC, I can catch a fluctuating voltage from the LED connection on the "tape PCB" (from 0.20v to 0.50v) and the voltage measured on the switch go to 0v, but nothing else.

GhostLine · 14:26, 14 June 22

Addition : I've separately tested the LED, who is ok, and just to be sure, I've connected the CPC to my OSSC : no signal when turned on.

JupiterJones · 15:35, 14 June 22

Hi!

Most usual culprit is the switch itself. Check its continuity with the multimeter, if no continuity or high resistance, it can be disassembled with pliers and thoroughly clean and re-assemble it again.

GhostLine · 15:52, 14 June 22

Thanks for your answer !

I've already done this, and even tried to shortcut it, without any success so far.

JupiterJones · 16:06, 14 June 22

Sorry, just read the message too quickly

Audronic · 00:05, 15 June 22

Can you without any thing else connected measure with an Ohm Meter from +5 Volt point on the motherboard to 0 Volt line to check that there is not a short ??

Keep Safe

Ray

GhostLine · 16:17, 15 June 22

Hey Ray,

Here are the results. Sorry if the measurements are not all logical, I'm a beginner at this

Audronic · 01:14, 16 June 22

@GhostLine

It Looks like you have a Short on the 5 Volt power line ??
These can be difficult to Trace.

Unplug the Tape deck and repeat test

Good luck

Keep Safe

Ray

Bryce · 11:18, 16 June 22

Quote from: Audronic on 01:14, 16 June 22@GhostLine

It Looks like you have a Short on the 5 Volt power line ??
These can be difficult to Trace.

Unplug the Tape deck and repeat test

Good luck

Keep Safe

Ray

How do you work that out? 2-3 (which is a visible piece of wire) gives the result .0, meaning the meter gives .0 for a short and 1. for open circuit, so everything is measuring at it should.

Bryce.

Audronic · 13:41, 16 June 22

@Bryce

Hmmnnn

1 and 2 = 1 which I assume is 1 Ohm

But 4 and 5 = 0 Which is Odd

Keep Safe

Ray

GhostLine · 13:53, 16 June 22

@Bryce : that was my way of reading it too ... I guess I've to found someone to test the chips (I don't know how to use an oscilloscope ^^').
@Audronic : there's a capacitor on top of that, if I'm not mistaken.

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Yet Another not running CPC464 ^^' (LED doesn't light up)