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Amstrad CPC noisy tape player

Posted: Sat Jan 06, 2018 7:23 am
by danielj
So, I've just got the tape player in my CPC 464 back up and running after having burnt out the old motor and inductor (don't ask), and when the motor's running the speaker is generating a horrible buzzing noise. It's loading fine, so that rules out great swathes of the circuit, and the CPC's sound is also fine (that's amplified through the tape deck), so that rules out a load more I'd have thought. It's just when the motor's running.

I've replaced C322/C324, but it's still buzzing away... Any ideas? I'm thinking C304... Or is it not likely to be one of the caps?
cpc-tape.jpg

Re: Amstrad CPC noisy tape player

Posted: Sat Jan 06, 2018 7:36 am
by daveejhitchins
Have you replaced C323? - It's the one directly across the motor.

Dave H :D

Re: Amstrad CPC noisy tape player

Posted: Sat Jan 06, 2018 7:45 am
by danielj
That'd be sensible - it's ceramic so I just assumed it was probably OK...

d.

Re: Amstrad CPC noisy tape player

Posted: Sat Jan 06, 2018 9:20 am
by danielj
Nope :( that didn't fix it...

d.

Re: Amstrad CPC noisy tape player

Posted: Sat Jan 06, 2018 11:08 am
by daveejhitchins
C304/C315/C318/R306/R313 - Supply line decoupling - these work with L301 so they all need looking at.

Or - is it just a really noisy motor?

Dave H :D

Re: Amstrad CPC noisy tape player

Posted: Sun Jan 07, 2018 5:09 pm
by danielj
Just to follow up on this - I haven't changed those other caps, but it seems to have shut up now. Perhaps it was just a grubby motor and now it's been used a bit has calmed down!

d.

Re: Amstrad CPC noisy tape player

Posted: Sun Jan 07, 2018 5:17 pm
by daveejhitchins
danielj wrote:Just to follow up on this - I haven't changed those other caps, but it seems to have shut up now. Perhaps it was just a grubby motor and now it's been used a bit has calmed down!
Or the electrolytics have re-formed a bit!

Dave H :D

Re: Amstrad CPC noisy tape player

Posted: Sun Jan 07, 2018 5:19 pm
by danielj
Can that happen? :O

Re: Amstrad CPC noisy tape player

Posted: Mon Jan 08, 2018 5:26 pm
by daveejhitchins
danielj wrote:Can that happen? :O
It can and does.

There was an article explaining it, back in the mid 80's (I was working for Rank Hi-Fi, at the time, and had the job of improving reliability of the Leak 2000 series). What was noticed was that as capacitors 'aged', when not powered-up, was shrinkage. This separated, slightly, the internal winding of the capacitor - so reducing the capacitance. When powered-up again, the shrinkage was reversed thereby restoring the most of the lost capacitance. There were other factors involved too, however, the shrinkage was the main one.

Dave H :D