I'm trying to repair a nice Onkyo DX-6550 (sony chipset), it's built like a tank and isn't in a bad optical shape, also looks quite clean inside, so I'd really hope to repair it, but it's a tough one. The player turns on, all normal, drawer works, but CD doesn't spin. It moves the head (it's a magnetic pickup) if I manually put it away from centre, so radial movement/tracking seems ok, also focus coils move up and down (so, focus circuitry apparently working) and there IS a small red dot indicating that the laser is alive. Can't tell anything about it's health condition, though, as I can't get it to output eye pattern (disc doesn't spin). This seems to be because it can't get focus - the Focus OK signal never comes on.
I did all the obvious checks: laser lens cleaning, power supplies all measure perfect, no obviously damaged components in sight, CD appears to be correctly secured in place (although I have no way of confirming that distance is ok, but it's not adjustable, the platter motor is direct and fixed in height. CD also turns freely if done by hand.
The platter spindle motor is working, there's no voltage present (because of no focus) but when measuring around the microprocessor, I somehow got it to suddenly start spinning (wrong speed and didn't read anything) for a second, probably I induced some wrong signal to upc which decided to let it spin for a second.
Also, tray open and close switches work fine, i checked them, but I guess that would be obvious, otherwise I think it wouldn't try to focus after loading disk.
The "Laser ON signal" sent by microprocessor is also alright - 5V for a couple of seconds and then goes down again.
I hooked up my oscilloscope, obviously no relevant RF signal, as disc is not spinning.
But I could see amplitude changes of focus out testpoint (goes low and then high again, with amplitudes of about 0,5V, then stays again at 0,5V offset). Lens can be seen moving well up and down and all this seems about right (in a Philips CDM service manual this is described, I think it applies to most mechanisms).
I also had a look at the Laser out, before the driver transistor it has more amplitude, clearly goes on and off (don't remember if negative, but it doesn't matter for this), after transistor (PNP) it's inverted with less amplitude change (Still around 1,3V amplitude, looks normal to me) and when laser goes off, it returns slower to original amplitude (probably because of the cap at the base of the transistor). As I didn't know if this was normal, I exchanged that cap (100uF) with a new one. No change. Also took out the driver transistor (2SA950), to test it (wouldn't measure correct in circuit), it's fine. Put it back in. Also exchanged the filter cap at the abcdef diode array to GND, it's also 100uF. No change.
As this player has been tinkered with (the power chord is cut off, but inside someone got the leads out for testing, which made my life easier) and I don't know the history, I tried putting all adjustment trimmers to middle position (first I annotated down the values of resistance I measured, so I could get back later!), as normally this is starting point for adjustment procedure, but no luck, as it doesn't focus, all other settings are impossible.
Checked that clocks and oscillators are working - for what I could find with scope, yes. Can't figure out how to check the VCO, though. They refer to frequency counter, my DMM does have this function and I've used it in other players for similar purpose, but no display is shown here. Is it relevant for the laser unit working? Could this be the problem?
Had a look at the laser power trimmer on pickup, wasn't at any extreme position, measured it - 560 ohms. But there was a black mark and the thing wasn't adjusted to it, was slightly more to the left (more resistance), I tried putting to black mark - no difference. Put it back where it was.
Now a couple of things I find strange (but I'm still struggling with understanding the whole way of functioning of the APC circuit, photo diode array and everything, so maybe they are normal):
- measured 2,64V DC over the two parallel 33 ohm resistors at laser driver transistor (emitter), that would translate to 162mA being drawn from transistor (which only powers the laser diode, obviously), does that mean laser is being driven with that high of a current, adjusted by APC?!?! Is this an indication of a dying laser? Or malfunction of APC? Or am I doing the measurement/maths wrong?
- Monitor photo diode (PD) of OPC circuit outputs -7,62V when laser is on (0V otherwise), I found that strange, if the whole circuit only works with +-5V power rails??? I'm measuring at anode of diode, where it is connected to laser power trimmer.
-At the outputs of the photo diode array abcdef (inputs of RF amp), I can only see very small amplitude signals, is that normal? If measured with DMM, they change in polarity when laser is ON, for example: -3mV goes to +3mV and then back, when laser is off and it stops trying to focus.
So, resuming: although the laser looks ok to me (I look at it through mobile phone, always, for safety), looks similar to what I've seen in other players, could it be weak? As I've measured that strange 162mA... but maybe wrong way of measuring.
Could the focus circuitry be bad, although it seems to work?
Could the RF amp (CXA1081S) be bad, so not amplifying photo diode array output well?
Could it be the VCO, not working?
Could the APC for laser not be working, although components measure ok? Maybe the photo diode? Those -7,6V...
Could there be some weird problem in the surrounding circuitry, not allowing focus circuit to have correct functioning? I'm referring to the circuit with all the adjustment trimmers.
Last idea I have: maybe the focus and tracking driver chip is defective, although it seems to work?
Maybe even some strange mechanical problem I haven't spotted which makes the lens not being at right distance of disc? I had this with a B&O player which came back to life after adjusting disc height. But this one has no adjustment.
Please, share your thoughts, I'm kind of lost here... thanks!
I did all the obvious checks: laser lens cleaning, power supplies all measure perfect, no obviously damaged components in sight, CD appears to be correctly secured in place (although I have no way of confirming that distance is ok, but it's not adjustable, the platter motor is direct and fixed in height. CD also turns freely if done by hand.
The platter spindle motor is working, there's no voltage present (because of no focus) but when measuring around the microprocessor, I somehow got it to suddenly start spinning (wrong speed and didn't read anything) for a second, probably I induced some wrong signal to upc which decided to let it spin for a second.
Also, tray open and close switches work fine, i checked them, but I guess that would be obvious, otherwise I think it wouldn't try to focus after loading disk.
The "Laser ON signal" sent by microprocessor is also alright - 5V for a couple of seconds and then goes down again.
I hooked up my oscilloscope, obviously no relevant RF signal, as disc is not spinning.
But I could see amplitude changes of focus out testpoint (goes low and then high again, with amplitudes of about 0,5V, then stays again at 0,5V offset). Lens can be seen moving well up and down and all this seems about right (in a Philips CDM service manual this is described, I think it applies to most mechanisms).
I also had a look at the Laser out, before the driver transistor it has more amplitude, clearly goes on and off (don't remember if negative, but it doesn't matter for this), after transistor (PNP) it's inverted with less amplitude change (Still around 1,3V amplitude, looks normal to me) and when laser goes off, it returns slower to original amplitude (probably because of the cap at the base of the transistor). As I didn't know if this was normal, I exchanged that cap (100uF) with a new one. No change. Also took out the driver transistor (2SA950), to test it (wouldn't measure correct in circuit), it's fine. Put it back in. Also exchanged the filter cap at the abcdef diode array to GND, it's also 100uF. No change.
As this player has been tinkered with (the power chord is cut off, but inside someone got the leads out for testing, which made my life easier) and I don't know the history, I tried putting all adjustment trimmers to middle position (first I annotated down the values of resistance I measured, so I could get back later!), as normally this is starting point for adjustment procedure, but no luck, as it doesn't focus, all other settings are impossible.
Checked that clocks and oscillators are working - for what I could find with scope, yes. Can't figure out how to check the VCO, though. They refer to frequency counter, my DMM does have this function and I've used it in other players for similar purpose, but no display is shown here. Is it relevant for the laser unit working? Could this be the problem?
Had a look at the laser power trimmer on pickup, wasn't at any extreme position, measured it - 560 ohms. But there was a black mark and the thing wasn't adjusted to it, was slightly more to the left (more resistance), I tried putting to black mark - no difference. Put it back where it was.
Now a couple of things I find strange (but I'm still struggling with understanding the whole way of functioning of the APC circuit, photo diode array and everything, so maybe they are normal):
- measured 2,64V DC over the two parallel 33 ohm resistors at laser driver transistor (emitter), that would translate to 162mA being drawn from transistor (which only powers the laser diode, obviously), does that mean laser is being driven with that high of a current, adjusted by APC?!?! Is this an indication of a dying laser? Or malfunction of APC? Or am I doing the measurement/maths wrong?
- Monitor photo diode (PD) of OPC circuit outputs -7,62V when laser is on (0V otherwise), I found that strange, if the whole circuit only works with +-5V power rails??? I'm measuring at anode of diode, where it is connected to laser power trimmer.
-At the outputs of the photo diode array abcdef (inputs of RF amp), I can only see very small amplitude signals, is that normal? If measured with DMM, they change in polarity when laser is ON, for example: -3mV goes to +3mV and then back, when laser is off and it stops trying to focus.
So, resuming: although the laser looks ok to me (I look at it through mobile phone, always, for safety), looks similar to what I've seen in other players, could it be weak? As I've measured that strange 162mA... but maybe wrong way of measuring.
Could the focus circuitry be bad, although it seems to work?
Could the RF amp (CXA1081S) be bad, so not amplifying photo diode array output well?
Could it be the VCO, not working?
Could the APC for laser not be working, although components measure ok? Maybe the photo diode? Those -7,6V...
Could there be some weird problem in the surrounding circuitry, not allowing focus circuit to have correct functioning? I'm referring to the circuit with all the adjustment trimmers.
Last idea I have: maybe the focus and tracking driver chip is defective, although it seems to work?
Maybe even some strange mechanical problem I haven't spotted which makes the lens not being at right distance of disc? I had this with a B&O player which came back to life after adjusting disc height. But this one has no adjustment.
Please, share your thoughts, I'm kind of lost here... thanks!
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Hi . Had tried to repair a Sony CD player decade ago , and some others , most problem is laser related ... If focus coil does move up and down ,as it should, but "no disc" , check laser lens , if its not scratched , and cable from receiver matrix to PCB . Did you tried clean optical pickup with compressed air ? Also you can try increase laser current ,just for testing for short time. I saw many laser pickups ,where current increase makes laser to work for short time , then you will know you need to replace pickup ,and other parts are functioning.
162mA laser current,sorry but the laser is dead. The best option should be to measure the laser power, but all indicates laser dead.
0.5V when is focusing is a not enough amount of signal.
0.5V when is focusing is a not enough amount of signal.
I wanted to say that the best way of knowing the laser diode health, is to measure the current when is on. The APC is performing well, but the laser is worn out. The APC tries to keep the nominal power, but the diode laser is worn out, and the APC forces the laser diode, but the current is at maximun, and the power out is lower than the necesary to perform correctly.
Thanks for the quick replies. Just a quick update and correction: unmounted the whole transport to check below, make sure flex cable was ok, and it is. There I noticed that I was measuring wrongly the pins of the connector, somehow I managed to count pin 1 on the wrong end, so I wasn't measuring PD output correctly. It's not -7,6V, that was for the sledge. It's -5V, so also that value checks out. I also managed to adjust the VOC, frequency counter finally worked (trick was to measure before the resistor, not at testpoint). But in the meantime I read some docs and understand that this not related to the problem.
For what I understand from your reply, ManoloMS, you're saying that I'm measuring correctly the laser current (as I couldnt' be sure, no indication in SM, this was just guess work from logic assumption that current drawn from driver transistor would be laser current), then the APC is trying to drive it at max current because it's basically at end of life and still it doesn't provide enough light to get focus and read the disc, am I understanding you correctly?
Well, seems I will have to find a replacement pickup (stumbled across a thread where they show how to adapt a KSS-152A. But also these probably are not too easy to find these days... let's see).
Btw, I tried to adjust the laser current on trimmer to max (I first got it wrong, and set it to minimum, even then at the resistor I still measured about 2V (125mA) and dot looked dimmer through mobile phone camera, then I set to other extreme and it got a bit brighter but still wouldn't focus, so it's confirmed, I guess. So sad. Would be the first player I encounter of many, which in fact is the laser that's at end of life...
For what I understand from your reply, ManoloMS, you're saying that I'm measuring correctly the laser current (as I couldnt' be sure, no indication in SM, this was just guess work from logic assumption that current drawn from driver transistor would be laser current), then the APC is trying to drive it at max current because it's basically at end of life and still it doesn't provide enough light to get focus and read the disc, am I understanding you correctly?
Well, seems I will have to find a replacement pickup (stumbled across a thread where they show how to adapt a KSS-152A. But also these probably are not too easy to find these days... let's see).
Btw, I tried to adjust the laser current on trimmer to max (I first got it wrong, and set it to minimum, even then at the resistor I still measured about 2V (125mA) and dot looked dimmer through mobile phone camera, then I set to other extreme and it got a bit brighter but still wouldn't focus, so it's confirmed, I guess. So sad. Would be the first player I encounter of many, which in fact is the laser that's at end of life...
that's a shame looks a lot like my 2nd CD player, in the USA it was called the DX-5700. 'twas a very nice machine; used PCM-58 DACs, responded very well to a better clock, sounded great.
Yes, it is so.
I've read the threads about to modify this Onkyo/nec laser pickups with another KSS-152A.
It's a mess of cables, but if it works, OK.
I'd try to replace the laser diode. I don't have any cd like this, but I suppose it should be like the others KSS I've repaired with the same method.
Notes - Google Photos
KSS - Google Photos
Wow, you're a rocket scientist! 😎 Congrats. I've come across some of the very rare cases where this has been done successfully and reported, so I knew it is possible. But unfortunately I don't think I have the capacities of succeeding at this, lack of equipment (only 1 scope), lack of time (it's not my day job), lack of understanding and experience in some of the points (altough I've got quite some experience with repairing cd players and have successfully repaired quite a few, I'm not an engineer not even a trained tech). And for the very last, possibly most important: for me it's as difficult (and maybe even higher in cost) to get hands on a quality and appropriate (and not ESD damaged) laser diode as it would be to get a good kss-152a replacement pickup, with the difference that the time and work required to change and adapt the pickup seems to be much, much lower. So, thanks for sharing and again thanks for your insights, but this player is going back to the drawer for some time, until I happen to find a cheap kss-152a. Might even come from some donor player, but it has to be worth it (also in terms of money, I'm not intending to keep the player, I've got three already 😀).
If I get a Onkyo CD faulty like this and cheap in Ebay, I hope to try to replace its diode laser. It looks to be very similar to KSS-151a and 190.
Sure, I understood your idea, but I don't have your experience with this. Still, if I don't manage to find a suitable (and inexpensive) direct replacement (which appears to be the kss-152a), I might try to adapt a working laser diode from some similar pickup and take my chances... but I fear that I won't be able to properly align the diode (or the photo diodes)... also this will take a lot of time, even just for trying, which I don't have right now...