When i desoldered all the caps , there was not a single leakage trace , only one smelt the famous odour...

I won't cannibalise my sweet ! I bought it new in the days ,sold it to a friend and just got it back. I've already killed my lovely J08 wich used to have logic controls issues too not talking about the head alignment wich is...impossible(?).No it will stay like it is ,since i can use it ,the rew function is slow ,well ,i will live with it !

You could do it the other way round- get another units and swap the good internals into your favorite one, but keep the casing. I did this several times for my Zen Vision M. (DAP repair is SOOO much easier than walkman repair)

Sure , but it's not completely dead ,it has no wow and flutter ,a good sound ,just a small malfunction i can live with.

I bet this is the cam ,it may be tired. Do you have photos of your JX849's ? As you know how each behaves ,may be we could see how the cam looks like for each of them ? Of course if it's the cam there's no way to do something unless we take a good one and mold some new ones.A friend of mine did that for small gears now unavailable in a PCDP and it did worked pretty well.

Nothing to do with cam wear. Most likely board problem.

I don't know... i've changed all caps ,not any leakage trace ,but as you said it could be elsewhere ,my board is clean ,like new.

Would you please tell me more , what model is it(same mechanics?) , did you regreased,have you checked the solenoids(with a multimeter) or swaped them ? I'd really like to solve the issue with mine ,i think i will re-open it one day ,what is strange is that it seems to need some multiple mechanical moves(after a day's rest) before acting ok (only talking about the playback mode),just after the rest the playback function goes immediatly reverse then get back to forward mode then stops ,after 3 or 4 tries it finally goes ok.Again something seems weak to move the tape. The player was fine when my friend left it for years in a closet ,when i got it ,it would play only in the forward mode but showed some weakness to move the tape ,of course the belt was tired but was changed ,the caps were changed ,the mechanics were regreased at best but i didn't dismantled it ,so what could be subject to wear other than belt and caps ? I mean due to years of rest. 

Edit: from what i know ,some gears that are moving free on their axis can only be well regreased by removing them , cleaning the axis from old dry grease.

What a solenoid is supposed to do exactly ?

http://fr.wikipedia.org/wiki/Sol%C3%A9no%C3%AFde

Thanks for the french link ! But.... what i wanted to know was what does it do exactly ,i suppose it pulls some mechanical parts ,do you know if it's also supposed to keep those parts ? Just trying to figure how this works.Don't forget to tell me what you did with your JX having the same problem ,about mine what wasn't done was cleaning the board because it was clean to my eyes , some said erratic behaviour should be solved by cleaning it.

The thing is opened again , let's check what's wrong...

First of all , the cam was in the correct reset position so it wasn't that ,albeit i notice something different in my JX , yet your photo is not clear enough ,but it could be the cause(yet i'm not sure actually) but check your photo -ok no- your solenoid beeing removed it seems too there is that missing metal lever i'm talking about wich is attached to the lower solenoid ,it seems you've removed it , you should see the end near the solenoid and i don't see it on your photo ,this lever seems to be used to lift the head and rollers AND you can see  that little upright metal rod between the two black wheels AND this is where is the clutch i suppose , in our case it won't declutch ,i must check this in action now.

Next episode....

lots of things here , well i wanted to open the unit again because i wasn't fully satisfied , remember the rew function in forward playback mode(and vice versa) ,plus the fact that at "cold-start" it needed a sort of complete cycle when play was pressed ,it would go forward ,then reverses then stops ,sometimes i had to press play multiple times before the tape runs ,once done it would be ok after ,but the day after this would repeat... That's why i decided to open it again.

Once opened , i soldered little wires to see how it operates inside but there is so many switches that's it's impossible...

I've cleaned the board without removing any fresh caps ,i too decided to better line up one of the cap and also put the mechanics in the correct reset position(may be it was not finally...).Then new problems occured , the play function then went crazy ,it would go forward then immediatly reverse then immediatly go forward and stop...

One of the solenoid pin went a bit loose so i was afraid the solenoid was killed , but the tester still gave the exact same value for both.I decided to remove the caps i lined up better for a new one , i closed the thing and now the play function(or reverse) are OK anytime(cold or hot) ,the rew function is working a bit better but not all the time.Alas i'm back with wow and flutter on the recording mode and at certain point of the tapes.

I just have received a PX747 wich cosmetically talking must be the JX849 brother ,it works fine ,one diffence i've noticed is the left thing that carries the tape reel is as smooth as the other ,in my JX this one shows resistance.So i wonder if this would not be a greasing problem , mainly dry grease somewhere.But this is strange since i had solved the wow and flutter issue and here it comes again so may be i'm wrong...

Rew and FF functions fixed !

Hi, here's what you're looking for ! I hope this is just a belt issue for you... Changing the belt improved a bit two of them but there are still unsolvables issues as now.Good luck!

http://imageshack.us/photo/my-...solderingpoints.jpg/

The big problem as you said is dessoldering the board ,unless you're a pro as Plop , i did broke some tracks and had to put very small wires instead. The big problem with this model is that you can't check your works unless you solder/unsolder the board multiple times , the problem is not only the belt with those , even with new caps ,new belt ,board cleaning(hey,board was clean) there are still unsolvables issues , i will try to solve that one day,but keep in mind that those are VERY difficult to work on. 

via Google translate

Sua única opção é dessoldar da placa de circuito impresso para substituir a correia para o JX849 eo JX707. O JX707 é muito delicada, e nas mãos erradas pode ser facilmente danificada.

Você pode querer uma mensagem privada retrodos membros S2G e ver se ele é capaz e disposto a realizar esse reparo, se você não está confiante para fazer isso sozinho.

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Your only option is to desolder the printed circuit board to replace the belt for the JX849 and the JX707. The JX707 is very delicate, and in the wrong hands can be easily damaged.

You may want to private message S2G member retrodos and see if he is able and willing to perform this repair if you are not confident to do this yourself.

Plop : one question , did you ever changed the door battery on your JX849 or the likes having the same troubles ?

I don't own a JX849. I have changed the battery on JX303 and JX707 though. When I get around to it, I will also change it for the JX505 too.

Yes i know you don't own a 849 but you said some of his cousins had the same kind of issues ,of course if those are players only it's not a faulty battery issue. I was just wondering if a new battery in the 849 could help solving unsolvable issues as it helped on my JX505 ? I will give it a try some day.

It's worth a try I suppose. The JX849 has an easy access to the memory battery doesn't it?

You've confirmed there is no issues with the tape mech? If you still have problems, then it may be contamination on the PCB, or even worse. A failing component on the logic circuit.

It's a real mystery , boards seem too young to have a cap concern , for both of the two i own , there's no cap issue ,boards are clean , no smell when you desolder caps ,for sure there is the belt problem , now why won't they work perfectly with a new belt(for one and new belt+new caps for the second) , for one of them , what i know is that it was stored working ,a few years later out of the closet appeared the mechanical issue , new belt , new caps is not the solution so what ? I haven't yet taken appart the whole drive , that's what i want to do but i need time enough ,it's a lot of work... Some say a good cleaning should be the solution , but there's nothing to clean ,really. As i said ,it's like there's something weak somewhere but what ??? One of his cousins i own , acts like something very powerful in mechanical term , so i wonder if the problem is not dried grease somewhere(some axis ?) ??

I am not referring just to the capacitors when I point to the components, there are also the transistors and IC chips too. Also don't rule out cold solder joints on the PCB causing circuit faults too.

You can rule out the tape mech since you have two JX849, by swapping parts from the good known working JX849 to find out if it is the PCB or the tape mech that is at fault.

If it is the tape mech, then it could be the clutch assembly not running freely when the motor flips from forwards to reverse.