Very forceful isn't it 🙂 I remember that feeling of the arm holding on and keeping on track as you try and stop it.
Its difficult to diagnose this at a distance... could we possibly be looking more at a problem with the arm sticking.
Have you tried watching the wobbling arm to see if it wobbles less as it approaches the point where it is going to skip?
Its difficult to diagnose this at a distance... could we possibly be looking more at a problem with the arm sticking.
Have you tried watching the wobbling arm to see if it wobbles less as it approaches the point where it is going to skip?
I observed the arm for a while. It does not change the style of movement before it skips – the skipping itself can be a little "jump" forward of the arm.
I'll have to get a lot of work done tomorrow (real work, not fun work like this here), so it might take me a while to pursue the fault research here. Thanks so much for the help today!
I'll have to get a lot of work done tomorrow (real work, not fun work like this here), so it might take me a while to pursue the fault research here. Thanks so much for the help today!
You can use the small screw at the bottom of the motor to adjust the distance between disc and laser if that is what you want. Also it's possible to adjust the arm bearing too tight: make sure it moves enough freely but without play. Hitting it with the finger should make the arm bump against the limit and move back a little bit. Be careful to not touch the contacts of the laser as the slightest static could cause damage. BTW my 303 stops after reading the TOC but my 304MK2 spins for ever: seems there are firmware versions which are like that...
Last edited:
Its not an easy one to diagnose.
No real thought process here but ifyou observe the RF.......
What happens if you:
1/ Pause the player for a several minutes while it is playing correctly. Does it stay paused?
2/ Do the same again but this time in that few seconds when you see the RF reducing. Does it pause correctly and stay paused at that point?
Thanks @jpk73 , the input on spinning after reading the TOC is very helpful. So maybe nothing to further think about.
As to the caps, I wrote in the first post that I did a complete recap, no electrolytic (including tantalums) has remained – apart from the two 0.47 tantalums decoupling each TDA1540.
Pretty improbable that they have anything to do with the symptoms, but they will have to go now as well. The tantalums are easy to confuse with the MKT films as both are orange.
As to the caps, I wrote in the first post that I did a complete recap, no electrolytic (including tantalums) has remained – apart from the two 0.47 tantalums decoupling each TDA1540.
Pretty improbable that they have anything to do with the symptoms, but they will have to go now as well. The tantalums are easy to confuse with the MKT films as both are orange.
Good morning!
I'll try what you suggest and will report back immediately.
The style of the fault makes me suspect it in some aging-related fault which is typical for early Philipses (like cold solder joints or tired caps with high ESR or "griplets" – only that I have controlled those already so many times. Another candidates is broken cores in one or few of the myriad connection wires, but maybe this would give more constant symptoms.
A good thing of all this is that I am again seeing how useful the scope is and that i am getting more familiar with it. I'll keep it switched on 😎
The single beam philips pickups are very reliable and don't usually show laser output losses in the manner the OP describes, especially if the eye pattern is within spec when checking the amplitude before adjustment to compensate. A definite culprit can be sagging of the lens suspension, which cannbe adjusted for with either spindle height, focus offset and/or a combination of the two. Focus gain will interact with these settings as well, but if the player reads the disc at all, there are other possible issues to eliminate first as culprits. An excessively warped disc will show the limits of the focus offset setting in conjunction with the mechanical status of the suspension. Most of the time its aging electrolytic and tantalum caps, but sometimes noise on the power supply rails or failing servo drive transistors.
Check the tracking gain and offset adjustments. The trim pots can get flaky and drift or just show wiper noise due to age and oxidation. If theres a greater tendency for the unit to skip either forward or backwards, there can be an issue with the tracking gain feedback (dampening RC network), especially so if the player will remain parked at the exact frame of track where its paused as Mooly stated.
Monitoring the control voltage from the servos will show if theres an issue in the lens tracking servo. Suspect the filtering in the servo feedback if there's a creeping increase in tracking coil drive voltage when the player is paused. If the correction goes consistently back and forth in both directions, a mechanical binding or excess bearing play of the swing arm can be suspect.
Last edited:
Thanks @profiguy. Sounds very reasonable. Could you explain where to measure what exactly? I cannot extract a go-to plan from your explanations with my limited experience in fault-finding in CD players.
It would be great to have a measuring point to control/adjust the setting of the focus offset and gain pots with a given value (range) which should be attained (like the SM gives it for the laser in order to set the laser trim pot). Did not find those, though.
What you say about the laser I think is spot-on.
I'll report in a minute on @Mooly 's suggestions to check what happens when hitting "pause".
It would be great to have a measuring point to control/adjust the setting of the focus offset and gain pots with a given value (range) which should be attained (like the SM gives it for the laser in order to set the laser trim pot). Did not find those, though.
What you say about the laser I think is spot-on.
I'll report in a minute on @Mooly 's suggestions to check what happens when hitting "pause".
if you have a copy of the SM pertaining to the transport control block, I can point to those measurement points.
It stays paused at that point. If I unlock pause, it plays from that point on without skipping.
It pauses correctly and stays at the point. When I hit "pause" immediately after the "pre-skip-twitter" starts (not easy to do in time as then it's only about a second until it skips), the RF amplitude immediately goes back to normal (1.2V)
After doing the "pause – unlock pause" cycle a couple of times the player has stopped doing me the favour (for fault finding's sake) of skipping – for the moment.
Can't upload neither the full CDM-0 service manual (with the many iterations of that transport) nor the CD-204 service manual. Too large. Got those from Hifiengine.
You want to monitor radial motor drive at connector A13 (floating ground - do not earth scope on either point) for spikes in output while playing and when paused and trying to nudge the arm manually by tapping with the eraser end of a pencil. If you get any spikes (which you should), they have to go in opposing driver direction. The correction should look like a smooth jump without any noise. If you see noise, proceed to the next step below, otherwise suspect mechanical binding of the arm (suspension and bearing). When the player is powered is off, you should see a smooth floating of the arm that reacts to the slightest change in tipping the player like a higher end turntable arm. Reference the preload adjustment procedure in the SM. This can be a very fussy adjustment and take a lot of time to get right.
If the tracking correction response is incorrect or sporadically shows up without provocation of the swing arm, first check the ribbon cable next to the arm motor output at A13. These tend to fail on these older units causing all sorts of weird symptoms. One scenario is the intermittent connection causing back EMF of the motor freaking out the error feedback amp.
If that checks ok, look at the error amp output and follow it back until you find the area where weirdness originates from. Thats at A17 pin 3+4 on back to IC6107 and IC6101. You'll need to reference the schematic to pinpoint the exact path from back to front of the arm servo. I recommend trying some freeze spray on the 6 x TO92 transistors to see if theres a reaction. Its going to be tricky playing a CD while trying to measure these hard to reach locations so you'll need to solder some extension cables for this in some cases.
If the tracking correction response is incorrect or sporadically shows up without provocation of the swing arm, first check the ribbon cable next to the arm motor output at A13. These tend to fail on these older units causing all sorts of weird symptoms. One scenario is the intermittent connection causing back EMF of the motor freaking out the error feedback amp.
If that checks ok, look at the error amp output and follow it back until you find the area where weirdness originates from. Thats at A17 pin 3+4 on back to IC6107 and IC6101. You'll need to reference the schematic to pinpoint the exact path from back to front of the arm servo. I recommend trying some freeze spray on the 6 x TO92 transistors to see if theres a reaction. Its going to be tricky playing a CD while trying to measure these hard to reach locations so you'll need to solder some extension cables for this in some cases.
Interesting. I think all this still points to a 'tracking' issue.
I'm still looking for non invasive ways of trying to get a handle on where the problem might be. If you get it playing correctly and then lift one end up on say a book or two so the player is at an angle (which will alter the weight distribution on the arm bearing) does it continue to play normally or not?
To me, an intermittent electrical fault in the servo for example would just instantly cause it to go nuts and its not doing that. Its all a little bit like a traditional sled system that sticks except here there is no sled of course, the lens is moved by the radial motor (the arm).
Thanks so much @profiguy and @Mooly . These are great tracks to follow. I'll manage to do the "lift one side" trick now, but then will have to seriously dive into today's (paid) work. So results for the procedures @profiguy suggests a bit later. Thanks again for that deep "Old Philips" expertise. Just what I had hoped for.
I can say right now that the swing arm moves pretty lightly and returns immediately. I did not touch it directly with my finger but would say that I can perceive some sort of light friction. The tonearm on my turntable moves definitely more lightly, you just need to look at it and it moves.
I found something – but not the fault.
Three years ago I had swapped the orange cap 2228 on the servo PCB with a 1uF WIMA film. In the SM it is marked as 0.1uF. It seems to be part of a filtering circuit. No idea why I put the wrong value – or was there one of the infamous tantalums with that deviating value and I substituted it 1:1? See shot from the schematics.
In any case behaviour went unchanged. I was already hoping. I remember that after the recap in 2020 I had some skipping and then found that I had left one tantalum on the servo board (they are as orange as the MKTs there). But maybe it was 2217.
Now I'll do the lift trick and will report back. Below the shot of the area of the Servo board where I changed the cap back to 100nF. I can swap back the 1uF in order to keep conditions for fault finding stable if you think that's better.
I can say right now that the swing arm moves pretty lightly and returns immediately. I did not touch it directly with my finger but would say that I can perceive some sort of light friction. The tonearm on my turntable moves definitely more lightly, you just need to look at it and it moves.
I found something – but not the fault.
Three years ago I had swapped the orange cap 2228 on the servo PCB with a 1uF WIMA film. In the SM it is marked as 0.1uF. It seems to be part of a filtering circuit. No idea why I put the wrong value – or was there one of the infamous tantalums with that deviating value and I substituted it 1:1? See shot from the schematics.
In any case behaviour went unchanged. I was already hoping. I remember that after the recap in 2020 I had some skipping and then found that I had left one tantalum on the servo board (they are as orange as the MKTs there). But maybe it was 2217.
Now I'll do the lift trick and will report back. Below the shot of the area of the Servo board where I changed the cap back to 100nF. I can swap back the 1uF in order to keep conditions for fault finding stable if you think that's better.
No changes if I moderately tilt the player (tested with both back and front up and with each of the four corners raised).
At least I know now why I bought the original Philips Test CD.
At least I know now why I bought the original Philips Test CD.
I was thinking a bit more of an angle tbh, perhaps 30 maybe 40 degrees or so. Quite a lot 🙂
(These are just random ideas to try and get an idea of what is happening though)
(These are just random ideas to try and get an idea of what is happening though)
Ok I was already afraid you meant that. Need to find a space where to do this without getting electrocuted while raising the open machine 🙂
It needs to be on the speakers as I can't hear every little skip only by the noises the RAFOC makes.
Will report back in a minute (and further neglect my work...)
It needs to be on the speakers as I can't hear every little skip only by the noises the RAFOC makes.
Will report back in a minute (and further neglect my work...)