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]

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]

same problem

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]

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.

 

[Mooly]

I'm very familiar with the CDM12.4
It is a dc motor. Can you feel any play in the bearing if you move the platter? The CDM12.4 has a small plastic "bar" that presses on the motor shaft to prevent wear in the bearing causing excessive jitter on the signal... the CDM12.4 was technically a CD ROM drive. The "lesser" 12.1 doesn't get this feature, crude though it is. A consequence of this tensioner is that it wears the bearing in a definite plane, front to back.
The motor itself is the same as on cdm12.1's etc but be aware that the "grey" and "black" platters are not interchangeable. The polarity of the magnetic clamp is opposite for each.
You replaced the laser... again be aware that there are lots of poor quality parts out there, particularly the complete mech and laser. It's a well documented issue.

If the motor is electrically faulty... usually worn/dirty commutator then a quick fiddle can be to power the motor from a 9 volt battery for a few seconds each way but make sure you disconnect the wires first so as not to apply voltage to the main pcb.

 

[jimmytwos]

i have changed the motor on the mech. i had to modify the mech as the new motor is slighty deeper which would have jammed the mech. so i've made some rubber stand offs out of old cable sleeving to make a gap between where the motor sits when the drawer is open and the board underneath. so far so good, on track 8 and its playing fine, hopefully its sorted? cheers mooly

 

[jimmytwos]

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.

hi, as regards to the tray operating aabnormally, mine has done this also from time to time. im pretty sure it may be down to the software in the player/ and /or preamp. also in my case, excess static in the area where the components are sited can cause the cd player display to show garbled digits or the buttons to glow orange? also my amp was affected by static, which caused the software to turn the amp volume up to maximum and blow fuses. it seems that the software can be erratic at times, hovever since i moved my hifi to a different location its been fine.

 

[Mooly]

Pleased to hear you seem to have sorted it

 

[jimmytwos]

Pleased to hear you seem to have sorted it

yep, it's had a load of cd's play from start to finish without any audio dropout, so far! thanks again mooly as i would have never thought of replacing the motor, and just would have probably stuck it in the loft,along with all the other 'projects' i'll never get done

 

[tiefbassuebertr]

Which of this two loaders is in use?

 

[jimmytwos]

its the one on the left with the metal clamp

 

[tiefbassuebertr]

its the one on the left with the metal clamp

I see. This is the same loader used by the newer cd player devices from Thule Audio's "SPIRIT" series (I make the service for Thule's formerly German distributor).

I don't know typical cd audio player from Philips, where this loader was inside. The main application was cd-rom devices for personal computer and CDI devices (CDI = Compact Disc Interactive). This loader was equipped both with laser units only with integrated APC circuit (CDM12.1 with Sharp TO outline Hologram LTOH30P and VAM1201, VAM1202 with Sharp Hologram in resin compact outline) and laser units with additional integrated RF amplifier stages (best known model is the CDM12.4 with Sharp Hologram LTOH30P and TDA1302, but there are various other types without model number and with RF amps from "TEA" series).

 

[macbuse]

Hi

I've run the CDP for a week, after changing the quadlink, and there are the odd clicks
but there are no more silent passages. Maybe I should invest in a more stable
power source. The french electric supply out of the wall is pretty variable and we have
a couple of micro power cuts every week.

On the other forums I discovered that people had moved on from CD players
and so I bought a Squeezebox. When it arrives I'll have the time to play
about with the CD player pickup and the motor.

BTW where did you source the motor ?
I ripped a CD drive apart but the spindle motor isn't suitable.

 

[jimmytwos]

seems i have a new problem with this cd player. been working fine, now though it refuses to play if i skip track. it plays fine if i dont try to skip past track 3 or 4 but after that it just spins up really fast then stops? if i slow the cd down with my finger it 'locks on' track and plays. the laser is quite new, but just to check i removed it and put it in a naim cd player and it played fine with none of the above faults.
any ideas?