Another Quad CD66 with distortion - Page 2 - UK Vintage Radio Repair and Restoration Discussion Forum

PWH · 22nd Oct 2020, 12:01 am

DAC supply voltages, measured with a meter
Pin 28: +5.01v
Pin 26: -5.89V
Pin 15: -15.15V

Via the digital out, and the DAC left out of circuit, (I presume it isn't needed for digital out) the sound is just as distorted and the same sort of distortion..

Red to black · 22nd Oct 2020, 12:17 am

Meter readings here are usually pretty inconclusive unless you have either a dead short/missing supply line and even then that usually manifests itself in other ways like a blown CP or fusible resistor, even scope checks are not really much use except at the two ADC output pins. the only way I know of was to check the supply lines first and then start swapping chips (educated guesses

).

Bear in mind way back when I was repairing these in the day job I had plenty of known good chipsets to try at will from machines (Philips) that had been scrapped for other reasons for example being dropped etc. although we did buy the chips too to replace stock, CD was fairly new back then and not many people would touch them! you could charge premium rates and the players were still expensive enough for people to pay to get them fixed, it seems like such a long time ago now.

PWH · 22nd Oct 2020, 1:01 am

The supply to the 7220p seems a bit low at 4.8V. The other side of the part circled in the photo is 5.1v. The part measures 3ohms. It may be one of those components with a strange symbol? 3 Ohms would not seem consistent with the markings??

Radio Wrangler · 22nd Oct 2020, 4:55 am

The same distortion via a digital output and presumably an external DAC must point the finger at the decoder or RAM device.

David

dave cox · 22nd Oct 2020, 5:38 pm

I don't think the pickup itself is off the hook yet?

I always imagined that with all that redundancy, error detection & correction in the media, that you would either get a perfect data stream or nothing at all, once an unrecoverable error was detected. But that never seems to happen in practice, it will do its best to fix up errors but when it can't it will just pass the data through anyway! As long as the TOC can be read then some 'sound' will be produce no matter what ...

dc

PWH · 22nd Oct 2020, 9:03 pm

Quote:

Originally Posted by dave cox

I don't think the pickup itself is off the hook yet?
dc

I took the entire CD mechanism from the distorted machine and substituted it into the good machine. It played perfectly, so the mechanism/laser can be ruled out (phew!).

So, I am left with 3 chips to try and source

SAA7220P
SAA7210
MN4264P-15
Unless there is any practical way of checking between these chips to try and identify the culprit..

dave cox · 23rd Oct 2020, 9:53 am

MN4264P-15 is DRAM, I seem to have every other variant of 64Kx1 in my junk-box but not that one!
Its a bit of a way to post in any case!

Diagnosis will be very difficult, and not practical.
I've certainly seen DRAM fail in the past, no experience of the other 2 ICs.

dc

Red to black · 23rd Oct 2020, 4:22 pm

It take it you have another identical machine, so I would swap the relevant chips across one at a time until you know which one is actually faulty that way you only need to try and source the only one you need, if any.

PWH · 23rd Oct 2020, 8:47 pm

I have ordered the DRAM and will order the other 2 chips when I can.
I don't want to swap out the chips as the PCB tracks lift very easily.
Thanks to all for your help. I will report back once something has changed..

Radio Wrangler · 23rd Oct 2020, 10:34 pm

Question.... which do you value the most, the chips or the board?

If the answer is the board, I score along the IC's legs where they enter the package until the body comes free without straining the pads on the board. Then I desolder and remove one pin at a time.

The chip is wrecked, but there is least risk to the board.

David

PWH · 24th Oct 2020, 12:32 am

The board.. Thanks for the tip I'll do that. I'll also put sockets in - if there is enough headroom.

Red to black · 24th Oct 2020, 11:13 am

I don't remember having any difficulty with the print on these boards, they weren't particularly fragile and besides the chips are normal DIL types not SM.
Decent quality solder wick and a half decent soldering Iron (I think I had a 25W Antex XS at the time) and the chips could be removed/replaced very quickly and easily, no need to cut the legs on these.

PWH · 28th Nov 2020, 5:05 am

The DRAM has arrived and been fitted..
Sounding superb on the digital out so fitted the DAC.
Sounds superb as well, so just to put it back together.
Thank you everyone for your assistance, I am very pleased and learnt a lot.
I still think this is the best CD player I have ever hard.
(and there is no room for the DIL socket unfortunately)

22nd Oct 2020, 12:01 am	#21
PWH Heptode Join Date: Mar 2003 Location: Waiheke Island, New Zealand Posts: 503	Re: Another Quad CD66 with distortion DAC supply voltages, measured with a meter Pin 28: +5.01v Pin 26: -5.89V Pin 15: -15.15V Via the digital out, and the DAC left out of circuit, (I presume it isn't needed for digital out) the sound is just as distorted and the same sort of distortion.. Last edited by PWH; 22nd Oct 2020 at 12:16 am. Reason: added digital out info

22nd Oct 2020, 12:17 am	#22
Red to black Nonode Join Date: Mar 2010 Location: Sunderland, Tyne and Wear, UK. Posts: 2,474	Re: Another Quad CD66 with distortion Meter readings here are usually pretty inconclusive unless you have either a dead short/missing supply line and even then that usually manifests itself in other ways like a blown CP or fusible resistor, even scope checks are not really much use except at the two ADC output pins. the only way I know of was to check the supply lines first and then start swapping chips (educated guesses ). Bear in mind way back when I was repairing these in the day job I had plenty of known good chipsets to try at will from machines (Philips) that had been scrapped for other reasons for example being dropped etc. although we did buy the chips too to replace stock, CD was fairly new back then and not many people would touch them! you could charge premium rates and the players were still expensive enough for people to pay to get them fixed, it seems like such a long time ago now. __________________ I don't suffer from Insanity. I enjoy every minute of it.

22nd Oct 2020, 1:01 am	#23
PWH Heptode Join Date: Mar 2003 Location: Waiheke Island, New Zealand Posts: 503	Re: Another Quad CD66 with distortion The supply to the 7220p seems a bit low at 4.8V. The other side of the part circled in the photo is 5.1v. The part measures 3ohms. It may be one of those components with a strange symbol? 3 Ohms would not seem consistent with the markings?? Attached Thumbnails

22nd Oct 2020, 4:55 am	#24
Radio Wrangler Moderator Join Date: Mar 2012 Location: Fife, Scotland, UK. Posts: 22,867	Re: Another Quad CD66 with distortion The same distortion via a digital output and presumably an external DAC must point the finger at the decoder or RAM device. David __________________ Can't afford the volcanic island yet, but the plans for my monorail and the goons' uniforms are done

22nd Oct 2020, 5:38 pm	#25
dave cox Nonode Join Date: Jan 2009 Location: Bristol, UK. Posts: 2,061	Re: Another Quad CD66 with distortion I don't think the pickup itself is off the hook yet? I always imagined that with all that redundancy, error detection & correction in the media, that you would either get a perfect data stream or nothing at all, once an unrecoverable error was detected. But that never seems to happen in practice, it will do its best to fix up errors but when it can't it will just pass the data through anyway! As long as the TOC can be read then some 'sound' will be produce no matter what ... dc

23rd Oct 2020, 9:53 am	#27
dave cox Nonode Join Date: Jan 2009 Location: Bristol, UK. Posts: 2,061	Re: Another Quad CD66 with distortion MN4264P-15 is DRAM, I seem to have every other variant of 64Kx1 in my junk-box but not that one! Its a bit of a way to post in any case! Diagnosis will be very difficult, and not practical. I've certainly seen DRAM fail in the past, no experience of the other 2 ICs. dc

23rd Oct 2020, 4:22 pm	#28
Red to black Nonode Join Date: Mar 2010 Location: Sunderland, Tyne and Wear, UK. Posts: 2,474	Re: Another Quad CD66 with distortion It take it you have another identical machine, so I would swap the relevant chips across one at a time until you know which one is actually faulty that way you only need to try and source the only one you need, if any. __________________ I don't suffer from Insanity. I enjoy every minute of it.

23rd Oct 2020, 8:47 pm	#29
PWH Heptode Join Date: Mar 2003 Location: Waiheke Island, New Zealand Posts: 503	Re: Another Quad CD66 with distortion I have ordered the DRAM and will order the other 2 chips when I can. I don't want to swap out the chips as the PCB tracks lift very easily. Thanks to all for your help. I will report back once something has changed..

23rd Oct 2020, 10:34 pm	#30
Radio Wrangler Moderator Join Date: Mar 2012 Location: Fife, Scotland, UK. Posts: 22,867	Re: Another Quad CD66 with distortion Question.... which do you value the most, the chips or the board? If the answer is the board, I score along the IC's legs where they enter the package until the body comes free without straining the pads on the board. Then I desolder and remove one pin at a time. The chip is wrecked, but there is least risk to the board. David __________________ Can't afford the volcanic island yet, but the plans for my monorail and the goons' uniforms are done

24th Oct 2020, 12:32 am	#31
PWH Heptode Join Date: Mar 2003 Location: Waiheke Island, New Zealand Posts: 503	Re: Another Quad CD66 with distortion The board.. Thanks for the tip I'll do that. I'll also put sockets in - if there is enough headroom.

24th Oct 2020, 11:13 am	#32
Red to black Nonode Join Date: Mar 2010 Location: Sunderland, Tyne and Wear, UK. Posts: 2,474	Re: Another Quad CD66 with distortion I don't remember having any difficulty with the print on these boards, they weren't particularly fragile and besides the chips are normal DIL types not SM. Decent quality solder wick and a half decent soldering Iron (I think I had a 25W Antex XS at the time) and the chips could be removed/replaced very quickly and easily, no need to cut the legs on these. __________________ I don't suffer from Insanity. I enjoy every minute of it.

28th Nov 2020, 5:05 am	#33
PWH Heptode Join Date: Mar 2003 Location: Waiheke Island, New Zealand Posts: 503	Re: Another Quad CD66 with distortion The DRAM has arrived and been fitted.. Sounding superb on the digital out so fitted the DAC. Sounds superb as well, so just to put it back together. Thank you everyone for your assistance, I am very pleased and learnt a lot. I still think this is the best CD player I have ever hard. (and there is no room for the DIL socket unfortunately) Last edited by PWH; 28th Nov 2020 at 5:13 am. Reason: added comment