CPC464 no audio from output jack - Speaker works

[Vyper68]

Hi
As it states in the header i have a CPC464 where the speaker works but i get no audio from the jack from either the Powered RGB SCART lead or Headphones. The 464 was a bit battered when i got it but it did work after a good clean and some fettling.
The socket does not feel slack when using a 3.5mm jack either, so does anyone have any ideas on where i should look as this is my first CPC.

The PCB is Board: PT NO Z70374, MC0044B

Thanks in advance.

[Bryce]

Most likely physical damage somewhere near the audio socket. There are two rows of resistors directly behind the socket. All of these are part of the sound circuitry. Check that none are broken or have dry joints and check for dry joints on the socket itself. Also check that none of the tracks in this area are damaged.

Bryce.

[Vyper68]

Thanks Bryce, i will have a look at the PCB again more closely to see if there is any damage around that area.

[Audronic]

@Bryce


Is there a Spec for the output voltage coming out of the Audio socket ?


The signal is attenuated by 10 to 1 initially and then is fed Via either a 10K or 22K resistor .
The load would have to be Hi impedance 50 - 100K and you would loose another 1/10th of the signal even then ?


It looks like it is meant to feed an amplifier ? 10 - 100 Millivolt input ? with a Hi Impedance input ?




Thanks


Ray 

[pelrun]

It's line-level audio, which should be (roughly) 1V peak to peak (i.e. +/- 0.5V.) It's definitely intended to be connected to an amp.

[Audronic]

@pelrun


OK. Thanks


Ray

[Vyper68]

It's line-level audio, which should be (roughly) 1V peak to peak (i.e. +/- 0.5V.) It's definitely intended to be connected to an amp.

Hi, does this mean i the socket will not work with my SCART lead?

[pelrun]

No, a SCART input takes line-level audio too.

[Bryce]

@Bryce


Is there a Spec for the output voltage coming out of the Audio socket ?


The signal is attenuated by 10 to 1 initially and then is fed Via either a 10K or 22K resistor .
The load would have to be Hi impedance 50 - 100K and you would loose another 1/10th of the signal even then ?


It looks like it is meant to feed an amplifier ? 10 - 100 Millivolt input ? with a Hi Impedance input ?




Thanks


Ray

As pelrun says. They "manually" bring the sound to RCA / Line-level, which should be around 1Vpp and is designed to feed an amplifier or the RCA inputs of a SCART port. However, as it's done manually (no op-amp), it can be off and depends on several analogue factors: Exact voltage on the 5V line, exact values of those resistors (they are +/- 10% parts). So in worst case (4.6V supply and 10% resistor variance) it could be a lot lower.

Bryce.