Hi Chris, Mooly, and everyone who posted here a message in this thread and is more cd player tech, pls help me with your individual answer and advices on this,
I have a Sony CDP 790 (made in Japan, its USA version?) and it have the next problems, i need very much your help:
1) When i press EJECT the cd holder gets out, with some mechanical noise sometimes to the end of the out movement; when i press EJECT again, the cd holder doesnt never gets in, remains out; when i press POWER OFF the cd holder remains out; when i press POWER ON, the cd holder gets in, but nothing else happend, like mechanical sound related to play, or to start playing;
2) When i press PLAY, the PLAY symbol appear on display, but no other sound is heared, and it doesnt play (the function CONTINUES and the other 3 functions with a red dot cannot be cleaned from display to dissapear completely) and when i press STOP, the PLAY symbol dissapear; i look inside, and the laser lights without a CD, so it works, and when i press PLAY without a CD inside, the symbol PLAY appear on display, but no mechanical sound or anything and all remains like this until i press STOP to cancel PLAY symbol. The laser head doesnt move along his track from center to outside of the CD disk position at all; what could be the problem? The motor board (2) switches Mooly cleaned in the first page of this thread or is also something electronically in this cd player?
Your individual experience and your individual cdtech answer-advice of everyone of you, given here, will help me very much, thanks a lot in advance, i really need your help before i start cleaning, dismantling this nice cd player, which also looks in good condition, and apparently doesnt seem to have electronic problems on the main board and display, but problems at cd holder and maybe related to laser head assembly - i also mention that the guy who solded to me, said it was working ok previously, and the malfunction it have now, is from not using it for years and not have any problems in the past (i dont know if this is true, but i thought is usefull to mention this to you - apparently wasnt done anything inside cd player from someone, but someone looked inside, because the case crews positions and some worn out on them)
Thanks, need very much your help, of everyone here individually which want to help
I have a Sony CDP 790 (made in Japan, its USA version?) and it have the next problems, i need very much your help:
1) When i press EJECT the cd holder gets out, with some mechanical noise sometimes to the end of the out movement; when i press EJECT again, the cd holder doesnt never gets in, remains out; when i press POWER OFF the cd holder remains out; when i press POWER ON, the cd holder gets in, but nothing else happend, like mechanical sound related to play, or to start playing;
2) When i press PLAY, the PLAY symbol appear on display, but no other sound is heared, and it doesnt play (the function CONTINUES and the other 3 functions with a red dot cannot be cleaned from display to dissapear completely) and when i press STOP, the PLAY symbol dissapear; i look inside, and the laser lights without a CD, so it works, and when i press PLAY without a CD inside, the symbol PLAY appear on display, but no mechanical sound or anything and all remains like this until i press STOP to cancel PLAY symbol. The laser head doesnt move along his track from center to outside of the CD disk position at all; what could be the problem? The motor board (2) switches Mooly cleaned in the first page of this thread or is also something electronically in this cd player?
Your individual experience and your individual cdtech answer-advice of everyone of you, given here, will help me very much, thanks a lot in advance, i really need your help before i start cleaning, dismantling this nice cd player, which also looks in good condition, and apparently doesnt seem to have electronic problems on the main board and display, but problems at cd holder and maybe related to laser head assembly - i also mention that the guy who solded to me, said it was working ok previously, and the malfunction it have now, is from not using it for years and not have any problems in the past (i dont know if this is true, but i thought is usefull to mention this to you - apparently wasnt done anything inside cd player from someone, but someone looked inside, because the case crews positions and some worn out on them)
Thanks, need very much your help, of everyone here individually which want to help
You need to sort out any mechanical issues before looking any further.
Dismantling and cleaning the two micro-switches related to the drawer open/close sensing would be the first place to start. Also make sure the belt is good. The fact the tray goes in when you cycle the power on/off also lend weight to the switch problem.
So you have to inspect and clean those to be 100% sure they are perfect.
Most problems like this are mechanical in nature. Electronic faults come way down the list of suspects.
Dismantling and cleaning the two micro-switches related to the drawer open/close sensing would be the first place to start. Also make sure the belt is good. The fact the tray goes in when you cycle the power on/off also lend weight to the switch problem.
So you have to inspect and clean those to be 100% sure they are perfect.
Most problems like this are mechanical in nature. Electronic faults come way down the list of suspects.
I did cleaned the microswitches, it were dirty, i took all ribbons out and put back, to check fault oxidised contacts, but all is like the usual; i think something is put reversed at the microswitches or the microswitches cable to be intrerrupted or something? pls help!!!
So, the cd player thinks the cd is inside even with the cd holder out, because he tries to play when i press play, the green arrow symbol for play is lighting, but nothing further, of course. What it can be??? The cd player seems to not know when cd holder is inside or outside very well...
Is normal that the laser head to be up all the time, even if is no CD inside? It is in the higher position, near a imaginary CD ready to read it, all the time when cd holder is not outside! The cd holder stil not get inside at the second press of EJECT button, and gets inside only when i restart the CD player; can be cold joints on the laser head assembly board or what? I never saw this malfunction on an another Sony cd player, until now, and i repaired some cd players until today, a few, with no major defects.
So what can be? Pls help, help ... Tnks for the help Mooly and advice, but what this can be? Something reversed at the mechanical parts of cd holder?!!?! it puzzles me...Help... pls (the laser head is always at center, dont move along his track and the no dISC message never appears on start on display as should be, after 5 seconds)
So, the cd player thinks the cd is inside even with the cd holder out, because he tries to play when i press play, the green arrow symbol for play is lighting, but nothing further, of course. What it can be??? The cd player seems to not know when cd holder is inside or outside very well...
Is normal that the laser head to be up all the time, even if is no CD inside? It is in the higher position, near a imaginary CD ready to read it, all the time when cd holder is not outside! The cd holder stil not get inside at the second press of EJECT button, and gets inside only when i restart the CD player; can be cold joints on the laser head assembly board or what? I never saw this malfunction on an another Sony cd player, until now, and i repaired some cd players until today, a few, with no major defects.
So what can be? Pls help, help ... Tnks for the help Mooly and advice, but what this can be? Something reversed at the mechanical parts of cd holder?!!?! it puzzles me...Help... pls (the laser head is always at center, dont move along his track and the no dISC message never appears on start on display as should be, after 5 seconds)
Is it posible to be a problem at the limit(s) of laser head, a laser head microswitch limit of end and start track not working? The laser lights sometimes, at the start, so it tries to read, but no other moves along his regular track from cd center to outside, just it stays at center firmly ...
Starting with the drawer shut and the power off, if you now move the laser manually (by turning the gears carefully and gently) so that it is around halfway along its track and then operate the power switch to turn the unit on, does the laser return back to the rest position and then perform the focus search operation (lens moving up and down 3 times) ?
I will try in a few moments and return with an answer; please tell me Mooly (tnks for answers 
) if i remove cd holder and all pieces there and remain with the cd put directly on the spindle motor and magnet above, i must keep pressed something to normally works, some microswitch from loading motor? I want to remove all so that the cd rest directly on spindle motor and then see what i can do to resurect... (ill be back in a few minutes) tnks
) if i remove cd holder and all pieces there and remain with the cd put directly on the spindle motor and magnet above, i must keep pressed something to normally works, some microswitch from loading motor? I want to remove all so that the cd rest directly on spindle motor and then see what i can do to resurect... (ill be back in a few minutes) tnksYupee!!! i succeeded to make the cd player to play audio, by moving the laser head forward and something unblocked and then showed - no dISC message, so i put a disc, i played and the first track works, but not all, seems to stop after 1 minut (is not due to disc problem) and also dont skip to track 2, 3 and so on, it wants only track 1 - so it must be something from wrong position of laser head, cause it makes some noise like it doesnt like to search other tracks, and is difficult for the cd player to find other tracks! So, good until now, when it plays, it plays correctly audio, probably someone setted wrongly the trimpots on the laser trying to adjust to make it works, what seems to be the problem now? tnks..........yupeee
Now i put the laser head to the outside of the cd (position) and seems to work more normally, and play all track on this cd, but starts playing track 1 after 10 seconds or so - please Mooly, can you tell me the distance in mm between laser head and the black rear portion of the cd holder to put the laser head in a more normal position? When you can measure, if you can, i will appreciate very much - or how i make to put the laser head in the right position which is normal when cd with cd holder is outside the case of cd player? Thank you very much...youpee, all works better and better, this cd player is really nice and how i can make the tracks to be read faster? The lens is cleaned from today already...
and how i can make the tracks to be read faster? The lens is cleaned from today already...When i repositioned the laser head, the cd holder start to work normally in and out, so it must be all about a wrong position of the laser head and thats why the center limit was pressed or something and wasnt functioning correctly - now it works, all tracks, but sometimes skips minutes in a track, plays all the tracks still...what next? The laser is not too powerfull in his actual setting, the tracking also and skipping maybe needs setting?!...what i must do now? (please read my last messages also)
Please guys, note this kind of malfunction somewhere (for other persons and to share), so when cd holder works wrongly or not want to be inserted back, and cd doesnt play, and dont see any no dISC message, only 0 zero (at sony cd players) this is a problem of laser head wrong position or blocked position, so you must adjust manually as Mooly kindly and smartly suggested - move the wheels of the laser head, to center or back until all begin to work, assuming is no other electronic problem (also i mention that i cleaned the microswitches of the loading motor, it must helped a little) - so please guys read my last messages and suggest me what to do next, for smooth playing and no minutes skips of current track or tracks skips accidentaly during audio play. tnks a lot!!!! Yupeee!!! Wait for you advice guys... let it be love
The only point of reference for the laser is the micro-switch located on the 'BD' board underneath the pickup. That detects when the laser is at the innermost point.
You need to make sure that everything is free mechanically and that there is no old hardened grease in any of the gears that drive the laser. Its also possible for there to be problems with the small motor that drives the pickup.
To take the diagnostics to the next level involves using an oscilloscope to view the RF signal when it does play, and to then make an informed decision as to what problems there could be.
When it does play, you could try monitoring the DC voltage across the sled motor and seeing if it tries to increase (with the sled not moving). If it does then that points to a problem with the motor or possibly excess friction in the drive train from motor to laser.
You need to make sure that everything is free mechanically and that there is no old hardened grease in any of the gears that drive the laser. Its also possible for there to be problems with the small motor that drives the pickup.
To take the diagnostics to the next level involves using an oscilloscope to view the RF signal when it does play, and to then make an informed decision as to what problems there could be.
When it does play, you could try monitoring the DC voltage across the sled motor and seeing if it tries to increase (with the sled not moving). If it does then that points to a problem with the motor or possibly excess friction in the drive train from motor to laser.
Hi, its me again... In my desire to help others which have the same Sony CDP 790 cdplayer and have problems with it, i will say, that the skippings of my cdplayer are probable due to laser head ribbon as i can observe, so the next step will be to dissasemble all the laser head assembly, all electronics and all to see whats the problem - in rest, the cdplayer works pretty well, except skippings... so in a few days i hope to give to you all an answer if this was the problem with tracks and minutes skippings (sometimes), it can also be related to the dirty contact limits of the laser head. If someone have other good suggestions regarding the skippings, pls help, advice, tnks to everybody in advance.
Hello 'me again'
Well the original skipping on the original player that this thread is based on was caused by a definite poorly soldered joint on the pickup itself (see pics post #1) so I suppose you never know what you might find.
The clues are always in test and measurement though... use of an oscilloscope to observe the signals... use of a meter to determine if anything untoward is happening with the sled drive (sticking).
Good luck though.
Well the original skipping on the original player that this thread is based on was caused by a definite poorly soldered joint on the pickup itself (see pics post #1) so I suppose you never know what you might find.
The clues are always in test and measurement though... use of an oscilloscope to observe the signals... use of a meter to determine if anything untoward is happening with the sled drive (sticking).
Good luck though.
I finally managed to repair the cd player, so the problem with skiping was due the ribbon intermittent contact (one wire from it was partially intrerrupted) and i found some cold joints on the laser head electronic board, repaired also. Until now, the player works fine, so all is good. If something new appears, i will let you know, all the best for all, tnks to all also.
and thanks for the update. Intermittent connections are always tricky to find... you have done well.
I worked for a Sony agency in SA and used to repair CD players there - and I wasn't aware of these differences!
I used to own a CDP790, and I had fond memories of the good sound.
However a couple of years back (and having moved to the UK) I bought another CDP790, and was disappointed with the sound - I guess the one I had in SA had the AD1860 DAC that's why!
I thought most of the Sony products in SA were products intended for the UK market, but perhaps this CD player was an exception?