Hello members, was wondering if anyone can advise re. problem with the above player. Been having problems of it not reading discs so purchased a new sled for it from Singapore CDM 12.4. Put it in recently and now playing all CD,s even CDR,s which it never did but the motor doesn,t stop when it comes to the end of the disc. It starts to rotate anti clockwise sometimes erratically but normally slowly. Any help appreciated. Mikeymoo 🙂
Ah OK 😉
I take it you mean the platter keeps rotating. That's odd... and it didn't do this with the old pickup ?
The only thing I can think of is that the RF is to high and the servo is 'keeping hold' of the disc. You need a scope to check the level on a standard CD (not a CDR). It should be around the 1.5 volt mark as a maximum.
I fitted a Japanese sourced CDM12.4 to my Stage 2 many years ago now and the RF was very high on that, around 1.7 volts or more from memory.
I take it you mean the platter keeps rotating. That's odd... and it didn't do this with the old pickup ?
The only thing I can think of is that the RF is to high and the servo is 'keeping hold' of the disc. You need a scope to check the level on a standard CD (not a CDR). It should be around the 1.5 volt mark as a maximum.
I fitted a Japanese sourced CDM12.4 to my Stage 2 many years ago now and the RF was very high on that, around 1.7 volts or more from memory.
Mooly, thanks for this but don,t have scope and probably wouldn,t know how to use one if I did. Could I use a multi meter to check this? Excuse ignorance on this but really are a novice. Stretched myself by changing sled as had to change all the wires due to the new ones being too short. Have cleaned it also as you advised once. It did rotate (CD) with the old pickup from memory but might have done the odd rotation anti clockwise I think. Thanks
Its not really possible with a meter because you have no reference to work to and altering the laser power without knowing that means you could be increasing it beyond safe limits. You need to see the actual signal coming off the disc to know what is going on.
I'm trying to think back to when I had mine in regular service. If the signal from the disc isn't good or correct level wise then the servo makes a bit of a strange noise as it tries to let go.
I can't think of any easy way to do this. If the worst comes to the worst then mark the laser preset with a pen and turn it slightly one way and then the other (a few degrees, no more) and see if its better or worse. I shouldn't even be suggesting that because its really not the way to do it (its very unprofessional and courting disaster).
And I'm still trying to think back... is it to much signal that is causing this or to little... I'm not 100% sure thinking about it. Again... scope to see what is really going on.
The other big problem has been the quality of CDM12.4's offered for sale over the last few years. They have been out of production by Philips for a decade or so and the Chinese or wherever copies are very variable in quality.
Ultimately you need to get a scope on it to see 🙂
I'm trying to think back to when I had mine in regular service. If the signal from the disc isn't good or correct level wise then the servo makes a bit of a strange noise as it tries to let go.
I can't think of any easy way to do this. If the worst comes to the worst then mark the laser preset with a pen and turn it slightly one way and then the other (a few degrees, no more) and see if its better or worse. I shouldn't even be suggesting that because its really not the way to do it (its very unprofessional and courting disaster).
And I'm still trying to think back... is it to much signal that is causing this or to little... I'm not 100% sure thinking about it. Again... scope to see what is really going on.
The other big problem has been the quality of CDM12.4's offered for sale over the last few years. They have been out of production by Philips for a decade or so and the Chinese or wherever copies are very variable in quality.
Ultimately you need to get a scope on it to see 🙂
Mooly, is it possible for me to check the voltage with meter across the terminals of the spindle motor or the anywhere else? You could be right about the quality of CDM 12.4 as on close inspection it doesn,t look new but it plays CDR,s which the original never did. Cheers
The spindle motor voltage wouldn't tell you much really because its under control from the servo. I'm afraid there is very little you can do without a scope, and even then a fix isn't guaranteed but it would show what the signal quality was like. The CD12.4 has the laser controlled via the chip on the pickup and so monitoring the current to adjust it up or down isn't an easy option either.
If its unusable as it is then tweaking the power up or down to observe the effect is an option. The problem is with the pickup so in some way there is nothing lost to try, as long as you accept the risks.
If its unusable as it is then tweaking the power up or down to observe the effect is an option. The problem is with the pickup so in some way there is nothing lost to try, as long as you accept the risks.
Mooly, how could I tweak the power to the pickup? Is there any use in swapping any part(s) from the original? I,m keen to get it playing correctly as bit stretched to purchase new player and this did sound great. Thanks
The power is adjusted with the tiny preset resistor mounted on the pickup itself. Its small and delicate but a jewellers screwdriver will fit. All you can do is move it a few degrees and observe. And as you'll see, you can't adjust while its playing. Turn the power off to move it. And mark the original position first and don't go more than a few degrees each way from that point.
There are no other adjustments at all on the Micromega.
There also has to be a big question mark over the pickup itself though and I know what you mean when you say it didn't look new. The last one I saw even smelled old, as if it had come from some old equipment. There were signs of the brown fur that old equipment gets too when you looked in the nooks and crannies of the pickup. The chassis and motors did look new though. That must be 6 or 7 years ago now.
There are no other adjustments at all on the Micromega.
There also has to be a big question mark over the pickup itself though and I know what you mean when you say it didn't look new. The last one I saw even smelled old, as if it had come from some old equipment. There were signs of the brown fur that old equipment gets too when you looked in the nooks and crannies of the pickup. The chassis and motors did look new though. That must be 6 or 7 years ago now.
I tried it again and made a slight adjustment to the pickup. I presume it is a very small rotary switch on the back of the pickup itself facing backwards on a PCB??? Further more, the motor continues to spin anti clockwise when the draw is open with a slightly erratic motion like it is kind of pulsing. I put a circuit screwdriver on the chassis and it lite up. Is this odd?? Touching it I detect a minor vibration but didn,t get a shock. With the draw closed it also continues to rotate anti clockwise, like it never stops. Could it be something more fundamental like a switch not kicking in to turn the machine off? Thanks
I think the Micromega has an earthed chassis so you should check that the mains lead is a three core and not a two and that there is continuity from earth on the mains plug to the metal chassis. You will have to measure to the metal screw inserts as the heavy anodising on the case acts as an insulator.
A neon lighting and feeling a vibration all point to a missing earth... which might have been done deliberately to stop a ground loop.
The motor moving with the tray open is very odd indeed. You mentioned earlier it might have done the same with the old pickup fitted. The only switches involved are a microswitch on the mechanism that detects when the pickup is at the rest position. If that were a problem then the sled motor would keep going and the gears would be making a racket and getting the teeth stripped. Only others are on the drawer to detect fully in and full out. On something of this age its possible there could be some electrolytics starting to deteriorate, particularly if its always powered up. Leakage from a small cap somewhere on the servo board is another possibility causing slight conduction between traces or components.
A neon lighting and feeling a vibration all point to a missing earth... which might have been done deliberately to stop a ground loop.
The motor moving with the tray open is very odd indeed. You mentioned earlier it might have done the same with the old pickup fitted. The only switches involved are a microswitch on the mechanism that detects when the pickup is at the rest position. If that were a problem then the sled motor would keep going and the gears would be making a racket and getting the teeth stripped. Only others are on the drawer to detect fully in and full out. On something of this age its possible there could be some electrolytics starting to deteriorate, particularly if its always powered up. Leakage from a small cap somewhere on the servo board is another possibility causing slight conduction between traces or components.
Mooly, yes you are right with earthing, I made sure it was earthed as many of the sockets here in Portugal are not earthed so this took care of that issue. It seems to have resolved the issue of not stopping, for how long I don,t know but at this stage is working as it should. Stops when CD has finished and then powers off completely after about 8 mins of which I believe it goes into a sleep mode as never shuts down completely unless unplugged. As you mentioned re. age, could be other things starting to deteriorate but good to having it up and running for now. Thanks once again for your help and how is your knowledge with a Quad FM4? Just asking as I have one of these sitting around that started blowing the small fuse at the back of the unit, I took it to a shop to have repaired of which it lasted for a very short time and is in a state of not working what so ever.....Thoughts much appreciated. Regards Mikeymoo.
Its all sounding more promising. Yes they do go to sleep after a few minutes, so that's normal. These players are around 20+ years old now and so any that have been powered up continuously for that time might be starting to show signs of cap deterioration... maybe... its a not a definite.
The Quad. Does it work if the fuse is replaced or does it again blow instantly ? Blowing of primary fuses usually comes down to either a faulty mains filter cap (if it has one), an intermittent problem with the transformer (least likely) or poor mains quality which if there are brief interruptions can cause the tranny core to saturate and suddenly blow the fuse. Make sure the fuse is the correct type (normally anti surge for primaries).
The Quad. Does it work if the fuse is replaced or does it again blow instantly ? Blowing of primary fuses usually comes down to either a faulty mains filter cap (if it has one), an intermittent problem with the transformer (least likely) or poor mains quality which if there are brief interruptions can cause the tranny core to saturate and suddenly blow the fuse. Make sure the fuse is the correct type (normally anti surge for primaries).
Thanks. From memory the fuse did blow straight away and I,m not sure if it has a mains filter cap??? Mikeymoo
Should be easy to diagnose, whatever the reason. You could rig up a bulb tester to stop it blowing and that would then allow live voltage readings to be taken.
If you still have the original sled you may be able to fix it. There was a very common problem with the grease used on many of the Micromega sleds. After several years it gummed up the sled and it could not track accurately. A clean and decent light silicone grease applied to the gear and pinion solved the problem for most users.
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