This DVD player has a strange fault. There is a motor which, via a belt, closes the drawer and, upon doing so, then raises the laser block. However, this motor does not switch off upon completion of the sequence, and nor does it reverse direction if eject is pressed - so you have to manually remove the disc.
There are no sensors at all on this part of the mech, no leaf switches to indicate the drawer is closed. Not only that, but the motor is fed directly from the power supply pcb.
Any thoughts before I dig further into that pcb? TIA
I'm sure that you must be missing something here. I don't think that I have ever seen a loading motor driven directly from a power supply. If that were the case, how would the system control IC look after running it, stopping it, and determining which direction it has to run (open / close) ? They are invariably driven via a custom motor driver IC. Sometimes, this is a through-hole SIL device with a heatsink tab - looks a bit like a car radio audio IC - and sometimes, it is a DIL or s.m. job. Very occasionally, they are driven by low level logic feeding a four-transistor bridge.
As to there being a switch, there almost always is, although it may be hidden deep in the mech somewhere. Look for a couple of wires from the main deck loom, which seem to disappear somewhere that you can't see the ends of them. The alternative, that I have seen used a couple of times over the years, is to sense the motor stall current when the unload or load operation completes.
And on that tack, are you *absolutely sure* that the loading cycle *totally* completes ? If the motor is still running at the (perceived) end of the cycle, and it's driving a belt, then that would imply that at this time, that belt is slipping on the motor's pulley. This is a common scenario that I see probably once a month in various players. The loading mech has to do a lot of work at the end of the cycle, not the least of which is lifting the weight of the deck, and (and this is key) often moving a latch bar that secures the tray closed. The sense switch is sometimes at the end of this bar, so although the loading cycle *appears* to complete in that you see the deck go up, it actually *doesn't* complete in that the belt slips under the load of trying to move that bar into place.
I would replace the loading belt with a new one, slightly tighter than what's on there now to allow for stretch. Clean the pullies with IPA at the same time. I would say that there is a better than 50% chance that this will clear the problem.
I'm sure that you must be missing something here. I don't think that I have ever seen a loading motor driven directly from a power supply. If that were the case, how would the system control IC look after running it, stopping it, and determining which direction it has to run (open / close) ? They are invariably driven via a custom motor driver IC. Sometimes, this is a through-hole SIL device with a heatsink tab - looks a bit like a car radio audio IC - and sometimes, it is a DIL or s.m. job. Very occasionally, they are driven by low level logic feeding a four-transistor bridge.
As to there being a switch, there almost always is, although it may be hidden deep in the mech somewhere. Look for a couple of wires from the main deck loom, which seem to disappear somewhere that you can't see the ends of them. The alternative, that I have seen used a couple of times over the years, is to sense the motor stall current when the unload or load operation completes.
And on that tack, are you *absolutely sure* that the loading cycle *totally* completes ? If the motor is still running at the (perceived) end of the cycle, and it's driving a belt, then that would imply that at this time, that belt is slipping on the motor's pulley. This is a common scenario that I see probably once a month in various players. The loading mech has to do a lot of work at the end of the cycle, not the least of which is lifting the weight of the deck, and (and this is key) often moving a latch bar that secures the tray closed. The sense switch is sometimes at the end of this bar, so although the loading cycle *appears* to complete in that you see the deck go up, it actually *doesn't* complete in that the belt slips under the load of trying to move that bar into place.
I would replace the loading belt with a new one, slightly tighter than what's on there now to allow for stretch. Clean the pullies with IPA at the same time. I would say that there is a better than 50% chance that this will clear the problem.
It did seem very unusual to me that a motor would be connected to the psu; as you say , what about the issue of control of the voltage? That said, the psu in this unit is a huge pcb with what appears to be several circuits so I didn't suspect it too much. The load cycle was OK and the laser came on/disc played after its completion, with just the constantly running/straining motor as an indication all was not well.
Well, I just took another look at it in the cold light of day and the answer was staring me in the face. The Phanton Twiddler had obviously been at this player before it reached me. There was a motor connector on the logic /processor pcb but someone had connected the motor to a vacant identical one on the psu which was supplying a fixed 5v line. changed 'em over and all OK....
can't believe I was so stupid not to have noticed that - I blame these nocturnal fixing sessions!
Glad it turned out to be a simple one - heaven knows, we all need a few of those from time to time !! And don't beat yourself up too much about not spotting it right off - I think we've all been there more than a few times d;~}
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