Vintage CD player repair --> Technics SL-PJ25 (Linear Motor Inside (c) )

[Vince]

Hello people,

20 months ago I bought 20 old defective cheap CD players to get some hands on experience on this type of device.... I now know enough to know that's it's not worth repairing, at least not if one is trying to make a living from it...
Managed to fix and flip a third of them, another third was not economically repairable and were trashed/scrapped for part. Another third, I decided to keep for myself because they have old Philips swing arm CDM4-11 in them and I like those.  Then there is this last one, object of this thread, that I kept because of it's exotic engineering. The pickup is moved using a linear motor rather than the usual worm screw.

"Of course"  it does not work, like all the others before it.

Problem is that I am trying to make space in the lab... and if I can't fix it then I fear I will find it hard justifying to myself that I should keep it...

So either I can fix it, or I take the difficult but rational decision to scrap it.

Problem is that I am failing at fixing it, so before I resort to scrapping it, I want to give it one last chance and decided to bother yuo all about it here.... hoping maybe some vintage CD player guru might know these beasts and recognize a common fault. I don't intend to spend 200 hours on it. I spent a few hours on it already,doing the easy / reasonable stuff.   I am only posting here in case it's a common problem the experts already know about and which could lead to a quick fix.


Anyway, so it's a Technics SL-PJ25 as the title says.
Linear motor as I said.. .though in this particular case I am not sure it's relevant here.

Symptoms : when you insert a disc, it fails to spin the disc, hence does not detects it / reads the TOC.

If I close the tray with no disc present, so I can see what the pickup is doing, I can see that the drive does the usual / expected dance :

- pickup is moved to the center of the disc
- laser is turned on (I can see that easily with the digital camera)
- laser is moved up and down twice, to try to focus.
- laser is turned off.

It's everything I would expect it to do... except that at the same time it's supposed to spin the disc of course, and it does not.

I attached the block diagram and schematic pertaining to the spindle motor.

   

There is IC402, an op-amp, that drives a push-pull BJT pair, Q403 / Q404 that drive the motor.

Then there is a "digital transistor" (as its datasheet calls it...) Q351 that turns the 5V power on or off to the op-amp.

Control signals : I see two lines coming out of that big "Digital Signal Processing" chip, IC301.

Pin #64, "PC" operates the switching transistors that turns the 5V power to the op-amp. So it's a digital output only.
Pin #65, "EC" OTOH must be analog, it operates between 0 and 2.5V and drives the inputs of the op-amp.


What I did

1) Measured the 5V rail = Good.
2) Measured +8V and -8 rail : good. more like 9 or 10 volts but hey, the more the betterer...
3) Shorted collector and emitter of the upper transistor, Q403, so as to send 8V directly to the motor, to make sure the motor works. It does.
4) Noticed that when I do that, after a few seconds the transistor starts to emit smoke, no kidding ! I am shorting it, how could it possibly go up in smoke, there is no current flowing through it ?! 
5) checked Q351 : it's not turned on, hence not supplying 5V to the op-amp.
6) However its base is at 5V so of course it's not conducting.
7) Now back to the start of the command chain : the two pins from the big IC, that make it all happen.
That's were the problem is apparently there is zero activity on these pins when I insert a disc.

Because the drive is otherwise doing what's it's supposed to be doing with the pick-up, we can be sure that the drive knows it is supposed to spin the disc / power the motor.. but it does not.

So:

1) These two pins are fried, the chip is kaput, dead end.
2) The chip requires some more input/signals from the outside world in order to spin the discs.... and maybe this is jot working because of some discrete external component, hence fixable.... but too complex to trouble-shoot.  That's where the gurus here might help : does this problem ring a bell, something I could check ?


Not holding my breath really, but I can't possibly scrap this player without at least TRYING to get some help from the forum, you never know !


Thanks for reading...

[SoundTech-LG]

Having repaired hundreds...  most of the issues are electro-mechanical. Most of those, are Laser modules, or spindle motors. Replaced lots of both lasers, and motors.
In order to get a spindle motor signal, the laser has to get a good focus on the CD platter first...  then if it does, it will then send a signal to spin the spindle motor. If it does not like the focus, it will never try to spin the spindle motor.
Have never seen much of any circuitry go bad other than maybe power supply on rare occasions. Hope that helps.

[FIXITNOW2003]

the only one i have seen was a SL-PJ28A from my notes it was not reading CD I Replaced 3X 47uf /25V caps on pcb under laser. but this was a long time ago so remember little about it

[Runco990]

Indeed, the laser has to get focus before it will spin the disc.  It's extremely unlikely there is anything wrong other than the optical pickup.  I have repaired thousands of CD and DVD players.

On old units there are usually 2 things that happen.  The laser itself drops in output, because they are not made to last, unlike the original Philips swing arm units.

OR, if the laser diode is good, (You need a Leader Laser power meter to measure it) the plastic optics in modern 3 beam pickups get cloudy, preventing enough light to reach the photo-detector.

Both are fatal, as no one here myself included has the surgical gear needed to rebuild an optical block.

In some cases, I was able to CLEAN the lens and mirror INSIDE the block.  Usually from a smoker's house.  Some pickups can be taken apart enough to do this without ruining the alignment.

I have been toying with the idea of doing an Ultrasound cleaning with some type of non-residue fluid, but so far have not picked up any sacrificial candidates due to the plain unprofitability of such endeavors.  I'd do this fore myself, sure.  Nothing to loose.

Some very old CD players will have several bad small value capacitors in the optical amplifier or the laser current source, such as the Philips CDM units with the infamous 33uF capacitor that gives a weak laser diode symptom.  I doubt this is the case in your player as it is still "too new", but it wouldn't hurt to check.  However, UNPLUG the optical block if you go poking near it with a meter or ESR meter.  There is enough voltage to possibly damage it.  I often see bad caps around the optical assembly on the very early silver Technics players, though.

[TheMG]

Just on the off-chance... are you using a commercially stamped music CD? I had this same player way back and remember that it did not like CD-RW at all (would act like there was no disc), and some CD-R were also problematic with this player.

[tooki]

CD-RW can’t be read by drives not explicitly designed to support reading them (the contrast between pits and lands is much lower), which for audio CD players didn’t begin to be added until nearly the early 2000s IIRC. CD-R, on the other hand, is intended to mimic the playback characteristics of a stamped CD, with the intent that they be readable on any drive. But if the writer, reader, or disc are marginal, you sometimes run into cases where playback fails.

[andy2000]

I found this discussion on replacing laser diodes and realigning the optics at home:

https://www.diyaudio.com/community/threads/kss-190a-with-new-laser-diode-applicable-for-the-kss-151a-too.366374/

I haven't personally tried to replace a laser diode, but I was able to realign the photo diode array on a very early CD pickup after partially disassembling it to clean the optics.  I had to remove the laser diode, and the photo diode array to clean everything.  The end result was much improved from where it started. 

I used a simplified setup compared to the person in that discussion.  Just a  hp 33120A to drive the focus coil with a low frequency sine wave, and a 4 channel oscilloscope to view the 4 photo diode outputs.  I used the CD player itself to power the laser diode.

[SoundTech-LG]

Well that's great news! Now instead of piling them up in the trash heap, serious repair enthusiasts can spend more of their time attempting to restore these dinosaurs!

[Vince]

Thank you very much everyone for your input ! 

OK so.... from what you say, it's most likely yet again a pick-up problem... "of course" 
Will try to confirm that by looking in the service manual, see if it tells me what signal I could check to see if what comes out of the pick-up, short of seeing an eye pattern, is correct or not, or present at all.

I am not in love enough to spend any significant money or time on it, so optical surgery is probably not on the cards, especially with my big fat fingers.

However I might consider replacing the pick-up or complete transport, if like the Philips CDM12 I replaced a couple times, they are easily available and for dirt cheap. Think I paid 10 or 15 Euros shipped, for the CDM12.

Need to look at reference / label on the pick-up.

Anyway, I will now  redirect my investigations toward the pickup.

Test CD : yes, I used a "proper" commercial / pressed music CD, that's in good nick and I know works just fine.

Thanks again 

[Runco990]

The CDM-12 is one optical block I have successfully cleaned after removing the photodetector to gain access.  Dust likes to settle on the angled mirror.  The epoxy that holds it in stays with the photo-diode making exact reassembly very easy.    

[Vince]

OK spent a bit of time on it this morning. It's not promising, I give up on this thing. Searched ebay, these players are worth squat (IIRC I paid 10 Euros for mine), and I can't even find a pickup for sale for it ?!
As I said if it were available and super cheap I might have considered throwing a new pickup at it, but since they aren't even available, that closes the case.

I just don't have enough love or financial incentive to save this player, I have a gazillion other things to repair that I actually care a lot more about, and are much more valuable to me, or valuable at all as well, which would be a much better use of my limited time.

So it is with regret but with a rational mind at play, that I give up. I will salvage what I can from it so that it's not a total loss, and move onto the next repair. A mile long list of instruments to repair in the lab...

Thanks for your help...

[Haenk]

You'll need a SOAD70A. It is available, however not cheap. Makes no sense for the otherwise not that great (audio-wise) SL-PJ25. Unfortunately, it has the same pickup as the SL-P999 (and a couple of others) - which is a fixworthy player. So that drives prices up a lot.

After all, it's destined to be dumped, I'm afraid. Which always makes me feel sorry.

[Vince]

Thanks for the info  ...... even if as you said, it's bad news for my particular player, which clearly won't get fixed.

You can't save them all.. actually after having gone through my pile of 20 old cheap defective players I bought to get some hands on experience on these things.....99% of the time they aren't worth fixing. Even if they required no parts at all somehow (but they always do, broken plastic gears and tired belts...), they aren't worth fixing if just for the labour involved, pain of packing them for shipping, and next to zero profit once sold. My time is worth a lot to me as I get older and have plenty other projects I want to do, so I am not gonna spend countless hour on some random dirt cheap CD player.... at some point reality has to kick in 

If one day I do get excited again about CD drives with a linear motor, to the point that I would want to own one, then I would just do some research to figure out what brand and models had them, knowing the list if probably kinda short, then actively hunt for them on Ebay and spend 40 quid for one in working condition and be done with it.

But right now, I have a million other pieces of gear in the lab that need my attention urgently, so let's get back to work...