Quad CD66 Distortion - UK Vintage Radio Repair and Restoration Discussion Forum

PWH · 10th Apr 2019, 12:37 am

First time symptom; CD plays sounds great as it has done for years, then after a few CD's was very distorted on both channels. Not skipping or dropping out, just horrible audio distortion. You can't listen to it. Same and equal on both channels. Switched off, waited and turned on again and it sounds fine for maybe 30 seconds then slowly the distortion creeps back and 10 seconds later you can't listen to it.

In the past, all electrolytic caps have been changed. I recently fitted new bulbs to the display which I can now see works well as does the remote. No problems with spinning up the disc.

Any clues as to where to start looking would be appreciated I suppose it must be some common part after the DAC?

Thanks

Radio Wrangler · 10th Apr 2019, 6:32 am

Start by checking all the power supplies. Find out how the reference voltage for the DAC is arranged.

A lot of distortion is helpful, you should be able to record a test tone on a CD and see the distortion on an oscilloscope.

David

G8HQP Dave · 10th Apr 2019, 10:29 am

An opamp getting the wrong bias? Maybe a resistor has gone open circuit, so you are relying on leakage current to set DC conditions.

Chris55000 · 10th Apr 2019, 1:50 pm

Hi!

The Quad CD66 uses Philips–based electronics & CD mechanism – a basic S.M. with annotated component–level circuit–diagrams can be obtained from:–

https://elektrotanya.com/quad_66_cd_.../download.html

Have a look at all the power supply voltages first as Member Radio Wrangler suggests, if you find it's not a psu fault, you'll need to make yourself a tone–test disc recording (I think you can get signal generator apps for PC use to to this!) – and if it looks you're getting stuck, myself or other Members'll help you go thro' it to locate the trouble!

A defective pickup or laser would not cause distortion on it's own – you'd get other far more obvious symptoms if the pickup or laser is defective!

Chris Willams

TonyDuell · 10th Apr 2019, 7:20 pm

I once had something that sounded a bit like distortion in a CD player using an older Philips chipset. It turned out to be the RAM chip which was giving (intermittant?) bit errors.

PWH · 10th Apr 2019, 9:29 pm

Thanks for the replies. I am in the process of moving and all my equipment is in transit.
I will report back when I have tried the above.

PWH · 11th Aug 2019, 9:33 pm

Turns out that it was a dry joint(s)! Put it on the bench and tested it and didn't work. Took it apart and obviously jogged the bad connection as it came back to life. Reworked the joints around the PSU and it seems fine now.

Thanks everyone.

Lance G · 16th Jan 2020, 2:02 pm

Always good to get feedback when a solution is found. Well done !
Thanks.

barrymagrec · 16th Jan 2020, 4:32 pm

Quote:

Originally Posted by PWH

Turns out that it was a dry joint(s)! Put it on the bench and tested it and didn't work. Took it apart and obviously jogged the bad connection as it came back to life. Reworked the joints around the PSU and it seems fine now.

Thanks everyone.

It`s very often dry joints on Philips kit, TVs, Washing Machines, Testgear, whatever - my dad reckoned it had always been like that and he was familiar with pre war Philips Radios.

10th Apr 2019, 12:37 am	#1
PWH Heptode Join Date: Mar 2003 Location: Waiheke Island, New Zealand Posts: 503	Quad CD66 Distortion First time symptom; CD plays sounds great as it has done for years, then after a few CD's was very distorted on both channels. Not skipping or dropping out, just horrible audio distortion. You can't listen to it. Same and equal on both channels. Switched off, waited and turned on again and it sounds fine for maybe 30 seconds then slowly the distortion creeps back and 10 seconds later you can't listen to it. In the past, all electrolytic caps have been changed. I recently fitted new bulbs to the display which I can now see works well as does the remote. No problems with spinning up the disc. Any clues as to where to start looking would be appreciated I suppose it must be some common part after the DAC? Thanks

10th Apr 2019, 6:32 am	#2
Radio Wrangler Moderator Join Date: Mar 2012 Location: Fife, Scotland, UK. Posts: 22,899	Re: Quad CD66 Distortion Start by checking all the power supplies. Find out how the reference voltage for the DAC is arranged. A lot of distortion is helpful, you should be able to record a test tone on a CD and see the distortion on an oscilloscope. David __________________ Can't afford the volcanic island yet, but the plans for my monorail and the goons' uniforms are done

10th Apr 2019, 10:29 am	#3
G8HQP Dave Rest in Peace Join Date: Sep 2008 Location: Solihull, West Midlands, UK. Posts: 4,872	Re: Quad CD66 Distortion An opamp getting the wrong bias? Maybe a resistor has gone open circuit, so you are relying on leakage current to set DC conditions.

10th Apr 2019, 1:50 pm	#4
Chris55000 Nonode Join Date: Aug 2007 Location: Walsall Wood, Aldridge, Walsall, UK. Posts: 2,873	Re: Quad CD66 Distortion Hi! The Quad CD66 uses Philips–based electronics & CD mechanism – a basic S.M. with annotated component–level circuit–diagrams can be obtained from:– https://elektrotanya.com/quad_66_cd_.../download.html Have a look at all the power supply voltages first as Member Radio Wrangler suggests, if you find it's not a psu fault, you'll need to make yourself a tone–test disc recording (I think you can get signal generator apps for PC use to to this!) – and if it looks you're getting stuck, myself or other Members'll help you go thro' it to locate the trouble! A defective pickup or laser would not cause distortion on it's own – you'd get other far more obvious symptoms if the pickup or laser is defective! Chris Willams __________________ It's an enigma, that's what it is! This thing's not fixed because it doesn't want to be fixed!

10th Apr 2019, 7:20 pm	#5
TonyDuell Dekatron Join Date: Jun 2015 Location: Biggin Hill, London, UK. Posts: 5,213	Re: Quad CD66 Distortion I once had something that sounded a bit like distortion in a CD player using an older Philips chipset. It turned out to be the RAM chip which was giving (intermittant?) bit errors.

10th Apr 2019, 9:29 pm	#6
PWH Heptode Join Date: Mar 2003 Location: Waiheke Island, New Zealand Posts: 503	Re: Quad CD66 Distortion Thanks for the replies. I am in the process of moving and all my equipment is in transit. I will report back when I have tried the above.

11th Aug 2019, 9:33 pm	#7
PWH Heptode Join Date: Mar 2003 Location: Waiheke Island, New Zealand Posts: 503	Re: Quad CD66 Distortion Turns out that it was a dry joint(s)! Put it on the bench and tested it and didn't work. Took it apart and obviously jogged the bad connection as it came back to life. Reworked the joints around the PSU and it seems fine now. Thanks everyone.

16th Jan 2020, 2:02 pm	#8
Lance G Triode Join Date: Jan 2020 Location: Braunton, Devon, UK. Posts: 11	Re: Quad CD66 Distortion Always good to get feedback when a solution is found. Well done ! Thanks.