problem with quad cd 77 help needed

[jimmytwos]

i have a strange problem with a quad 77 cd player. when playing, the sound will randomly cut out but the cd is still playing and display still counts down. i replaced the laser but i still have the same problem. if i make the cd skip by tapping the case the sound cuts back in. so far i have re-soldered connections to the motherboards with no effect. i have also changed the small caps on the dac board. anyone have any suggestions?


thanks, jim

[Mooly]

Hard to say. Is it the self powered standalone 77 or the one that is part of a system ?
Not that that helps much I guess.

Intermitent problems need a proper approach. You need to be able to work on it "live" measuring PSU rails etc. It's always a good idea to confirm the integrity of the RF from the pickup. The unit may mute if the quality is really poor yet still be able to maintain servo lock and update the time counter.

It could be a rail dropping out, it could be the mute operating... it could be anything tbh.

[jimmytwos]

thanks for the reply, i have ran it removed from its case and the laser seems fine. if i slow the disc down with my finger it actually slows the music until it drops out, so im guessing the laser is outputing correctly. its the bus version, into 77 amp. its become extremely annoying as it can play for hours fine then suddenly drop out.

[Mooly]

Are you sure the fault is actually in the player? In the absence of test gear, scope etc, perhaps a first step would be to use headphones (conected via resistor and cap) and carefully probe and confirm if audio is actually present or not in the player when the fault occurs.

[tiefbassuebertr]

Originally Posted by jimmytwos

i have a strange problem with a quad 77 cd player. when playing, the sound will randomly cut out but the cd is still playing and display still counts down. i replaced the laser but i still have the same problem. if i make the cd skip by tapping the case the sound cuts back in. so far i have re-soldered connections to the motherboards with no effect. i have also changed the small caps on the dac board. anyone have any suggestions?
thanks, jim

The reason therefore cannot be the mechanism so as the RF/PCM-dec/servo/operating MCU units for focus and tracking. In such cases the disc goes in "STOP"/"ERROR" modus and don't longer rotate.
Unfortunately there is no outdoor connection for S/P-DIF resp. DOBM signal as to see at the pics about Quad
When such interface is inside (e. g. a PIN at the PCM decoder IC - check out the appropriate datasheets), you can nevertheless create a connection for connecting a coax lead (digital cable) to an external (outdoor) DAC. SAA7220 e. g. uses such pin. Use additional a terminator resistor of 91 ohms and in front of this resistor a capacitor to avoid dc effects. RF transformer, as usual in use, is not necessary in most cases
What happens, if you check this?

[macbuse]

I have a Quad 77 cd with a pre amp on quad bus.

I have exactly the same problem but I'm thinking about.
The sound is still prety good apart from the embarassing silences.

I took the transport out and cleaned the lens but this doesn't seem
to help. So I am thnking about replacing the pickup -- it's a cdm 12.1 ?

[jimmytwos]

i have discovered something rather strange. if i load 2 discs into the player, one on top the other it plays with no dropouts? maybe the clamping mech is worn? there is a small spring on the back of the clamping arm that may need replacing. i played the cd player last night for hours, with different discs and it played fine!

[Mooly]

Originally Posted by jimmytwos

i have discovered something rather strange. if i load 2 discs into the player, one on top the other it plays with no dropouts? maybe the clamping mech is worn? there is a small spring on the back of the clamping arm that may need replacing. i played the cd player last night for hours, with different discs and it played fine!

This is what I was wondering when I commented in post #2 (not so much any specific issue) but rather that poor RF from the pickup can give these symptoms.

So it seems you are on to something... and without actually having the unit in front of me it's hard to comment. Basic checks start with making sure the platter and clamp is clean and that the disc rotates freely.
Adding a second disc increases the rotational mass (flywheel effect) so it may be a problem with the spindle motor. Not sure what these use. Is it a DC motor or a hall effect type?

[macbuse]

I bought the CD 77 in 1999 and I didn't use it for a
a few years (when the kids were babies) so I
only really noticed this problem over the last year or so
since I moved to a new house.

Where I lived previously, the CD tray used to go into "epileptic fits"
jumping in and out all the time. This hasn't happened for a while
and I have the dropouts instead. I've been doing what you had done for
a while -- "gently" lifting and dropping the player to get it to play --
imagining that it was some problem with dust. Finally I stripped the
transport out over Xmas, dusted everything (there was surprisingly little)
and cleaned the lens.

This week I had decided to change the pickup and, although this hasn't worked
for you, I might try it too.

This morning, I dug out another quadlnk cable I have and switched
it over and I'll see if that works any better. If I don't get a positive
result then I'll try switching the spring for a stronger one.

Or buy this

CD stabilizer The Mat [English]

Thanks.

[jimmytwos]

hi mooly, its a very cheap and nasty cdm 12.4 i think, i'll check, but it has a cheap and nasty spindle motor. dc i'd imagine. i have removed the insides of the cd player and have it playing in front of me. the clamp mech seems fine and holds the disc ccorrectly. it all spins freely. i think you may be onto something with the spindle motor as i only changed the laser.