You might have some ripple on the psu and the rf amp is going crazy, a recap never hurts, perhaps to check where the fault could be you could try first only the servo board without the lens pickup and also go removing the wires from the connector one at a time (those connectors have locking tabs) to see which signal o part of the circuit is driving you CDP crazy
I have desoldered a couple of caps in the servo board and they are indeed on their way out (roughly 60% of nominal capacity). But I also tried removing only the RF pin from the servo to main board connector and nothing changed, still weird behaviour.
I suspect a fault in the focus and tracking servo, but I'm in the dark as to what might be the cause...
I suspect a fault in the focus and tracking servo, but I'm in the dark as to what might be the cause...
Normally a cd player will start doing "things" when focus is detected, this is when an RF signal reaches 2v in amplitude, then stops the search and the servo activates and starts working, if some of the potentiometers for calibration are all the way to one of the sides can do that exact failure since it compensates so much that the servo goes crazy and detects an RF signal all the time.
Another thing could actually be capacitors on the RF amp non blocking the DC signal and having a clipped on high RF signal resulting in a misdetection of focus and of course in a completely wrong servo operation. A scope will make it easier to get to the problem, but beign blind i'd go for a recap and a recalibration of what it is posible with a multimeter (0v for focus/tracking bias/offset is a good start point to rule out servo failures)
Another thing could actually be capacitors on the RF amp non blocking the DC signal and having a clipped on high RF signal resulting in a misdetection of focus and of course in a completely wrong servo operation. A scope will make it easier to get to the problem, but beign blind i'd go for a recap and a recalibration of what it is posible with a multimeter (0v for focus/tracking bias/offset is a good start point to rule out servo failures)
I'm testing the player without a disc so I would expect the following:
1) lens starts moving up and down in search of focus (2 or 3 times)
2) no focus found, then stop and wait.
Some older players do start disc rotation during focus search, this might be one of those so I would expect just a couple of spin attempts and then nothing.
What I get is instead (no disc inserted):
1) lens just move up&down one time.
2) lens is moved all toward one side (tracking coil receives roughly 7 volts)
3) spindle motor starts rotating quickly in both directions (one turn CW and one turn CCW)
If I press eject, the spindle motor starts rotating at full speed, and it can only be stopped by removing power. It behaves the same also if the optical pick-up is completely disconnected (no photo-diodes, no laser, no coils) or if the RF pin is disconnected from main board (the RF DC voltage level is indeed correct at 1.8V). Acting on the focus offset potentiometer moves the lens up & down, but acting on the tracking offset does nothing (i have marked all potentiometers so I can go back to factory settings)
Surely there are tired capacitors but unless one is completely short I do not think they are causing those problems.
thanks for your help
1) lens starts moving up and down in search of focus (2 or 3 times)
2) no focus found, then stop and wait.
Some older players do start disc rotation during focus search, this might be one of those so I would expect just a couple of spin attempts and then nothing.
What I get is instead (no disc inserted):
1) lens just move up&down one time.
2) lens is moved all toward one side (tracking coil receives roughly 7 volts)
3) spindle motor starts rotating quickly in both directions (one turn CW and one turn CCW)
If I press eject, the spindle motor starts rotating at full speed, and it can only be stopped by removing power. It behaves the same also if the optical pick-up is completely disconnected (no photo-diodes, no laser, no coils) or if the RF pin is disconnected from main board (the RF DC voltage level is indeed correct at 1.8V). Acting on the focus offset potentiometer moves the lens up & down, but acting on the tracking offset does nothing (i have marked all potentiometers so I can go back to factory settings)
Surely there are tired capacitors but unless one is completely short I do not think they are causing those problems.
thanks for your help
DC blocking caps tends to fail by going fully shorted or completely open, they are subject to much more stress than regular smoothing capacitors, check the non polarized caps first.
You are correct, this player spins a little the disc in order to aid the focus search.
From what i recall this was a quite dumb player, not everything was controlled by the main CPU, so you can expect this kinds of behaviors of things working when they should be stopped.
By reading the Service Manual on the block diagram it states that CLV servo is controlled by the PLL circuit and IIT servo, which is fed with RF DEL signal.. which is odd but okay i guess... you might try to remove that signal to see if that behavior corrects and also recap the focus servo which is also the RF preamp/mixer
You are correct, this player spins a little the disc in order to aid the focus search.
From what i recall this was a quite dumb player, not everything was controlled by the main CPU, so you can expect this kinds of behaviors of things working when they should be stopped.
By reading the Service Manual on the block diagram it states that CLV servo is controlled by the PLL circuit and IIT servo, which is fed with RF DEL signal.. which is odd but okay i guess... you might try to remove that signal to see if that behavior corrects and also recap the focus servo which is also the RF preamp/mixer
Today I had time to do a quick test and run the player with the RF-DEL pin removed from the connector. As expected it now behaves normally, it tries to focus once and then stops. Disc tray open and closes when pressing a button, so i guess the RF-DEL always low was confusing the CPU into believing the pickup was reading something, but culd not decifer anything. Now the next step, why the RF-DEL is always low ? Bad RF amp IC ? just a matter of bad capacitors ?
Well that's a huge advance, normally a failing IC would go short by going high or open and get a high impedance but if it's always low you might be lucky and can be a matter of capacitors, from the service manual IC internal diagram it looks like it heavily relies on external components.
best luck!
best luck!
... and faulty caps it was !!
Replaced all electrolytic in the servo board and now it reads CD's perfectly.. those old pick-up's are quite robust as they were over-engineered with huge operative margins. A full recap would then be highly suggested or at least the PSU should have all new caps.
One question: the PSU regulators run pretty warm in few minutes, is that normal ?
thanks for all your hints and suggestions, it really helped !
Replaced all electrolytic in the servo board and now it reads CD's perfectly.. those old pick-up's are quite robust as they were over-engineered with huge operative margins. A full recap would then be highly suggested or at least the PSU should have all new caps.
One question: the PSU regulators run pretty warm in few minutes, is that normal ?
thanks for all your hints and suggestions, it really helped !
That's amazing! so cool you can bring it back to life. indeed those old pickups are build to last, i'm pretty positive you will have it working for a lot more time now you recapped that.
As for the regulators yes, they are pretty steamy, it wont hurt if you want to improve the cooling with a hefty headsink from a dead CRT TV or a computer power supply.
Also, a good recap might help to cool it down a little bit since now the ESR of those PSU caps has to be very wrong
As for the regulators yes, they are pretty steamy, it wont hurt if you want to improve the cooling with a hefty headsink from a dead CRT TV or a computer power supply.
Also, a good recap might help to cool it down a little bit since now the ESR of those PSU caps has to be very wrong
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