The laser unit i received from ebay didnt work.It was rusty and oxidized.thankfully i got a refund.I was pointing the phones camera on the laser and no light would come out.So i unsoldered the small ribbon that goes to the PD,LD and tested both of the diodes with the diode tester.they seemed ok but no light coming out of the laser (iam looking with my phones camera)so i made a small current source around 35ma as the one on the schematic of kss240 and tested again.no light out of the laser diode.I was wondering whether it is easy to replace the diode itself and get it working as there are quite cheep at alliexpress.the old diode came out pretty easily as it was glued.
I found some potential replacements.
RLD78MRA1
QL78D6S
SLD105VL
RLD78MD-K
RLD78MRA1 pdf, RLD78MRA1 description, RLD78MRA1 datasheets, RLD78MRA1 view ::: ALLDATASHEET :::
QL78D6S-A datasheet
HTTP 301 This page has been moved
https://www.google.com/url?sa=t&rct...rld78mdk.pdf&usg=AOvVaw3eVB3Xbc6z8n0pYKh2UdW_
I found some potential replacements.
RLD78MRA1
QL78D6S
SLD105VL
RLD78MD-K
RLD78MRA1 pdf, RLD78MRA1 description, RLD78MRA1 datasheets, RLD78MRA1 view ::: ALLDATASHEET :::
QL78D6S-A datasheet
HTTP 301 This page has been moved
https://www.google.com/url?sa=t&rct...rld78mdk.pdf&usg=AOvVaw3eVB3Xbc6z8n0pYKh2UdW_
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A diode tester probably wouldn't be any use on a laser diode because the current needed for lasing to start is probably much higher than the test current. There is also the real risk of damaging the LD due to transient spikes which happens in nano seconds and can damage the facets of the diode chip.
The diodes do come out of most pickups very easily but whether a replacement will work without the internal optics being aligned to it is another matter.
There is a thread here which is long and spans a few years:
Dead Laser Pickups - why not replacing the Diode only?
The diodes do come out of most pickups very easily but whether a replacement will work without the internal optics being aligned to it is another matter.
There is a thread here which is long and spans a few years:
Dead Laser Pickups - why not replacing the Diode only?
Mooly, thanks for the thread - it's still valuable years later! Using it to check my Arcam CD92 eye pattern. I don't think i'm hitting the right test point (i have been using 'ADATA'). I'm getting to grips with using a new digi scope at the same time, so i wanted to check i was on the right track and my scope would actually do it. I checked my Arcam Delta 170.3 and i can get a nice pattern from it - so i know i can do it and the scope will show the trace
Level seems pretty high on the CD92, so I don't think i've got the proper point, but it is a KSS240A mech.
Level seems pretty high on the CD92, so I don't think i've got the proper point, but it is a KSS240A mech.
Pleased to hear you are finding the thread useful 
ADATA certainly sounds wrong. The RF on the KSS240 is as shown here and any player using this pickup will be the same. The RF appears on pin 18 of the chip on the pickup and is available on pin 4 of the ribbon.
ADATA certainly sounds wrong. The RF on the KSS240 is as shown here and any player using this pickup will be the same. The RF appears on pin 18 of the chip on the pickup and is available on pin 4 of the ribbon.
Attachments
I have several CD players which use the KSS-240A optical pickup:
Among these are two Sony CDP-491 units and one Sony CDP-591.
I also have a couple of 5-disc changers which use the KSS-240A.
Today I encountered unusual and intermittent faults with one of the CDP-491 units. I’ve never observed anything quite like it.
The RF signal amplitude, which was about 1V P-P to start with, is mysteriously changing from 500mV P-P to over 1.3V P-P and back.
It changes abruptly when this happens.
Once it dropped so low that it wouldn’t initialize a disc.
Later it began working again.
The RF amplitude simply isn’t stable.
Also the sled motion is “nervous.” This is a gear drive system. The motor will suddenly move the pickup substantially outwards (towards a higher track) but then reverse and back up slightly. Sometimes there is a skip in the audio output when this happens. I don’t think it is a mechanical fault though. The sled drive runs very smoothly when moving from track 1 to track 10 and back.
Sometimes it will play several tracks perfectly but then it will get really “skippy” for a while.
Earlier in this thread there is a discussion of broken solder joints on the KSS-240A and on other PC boards in the player. I intend to closely inspect the soldering on both the tiny KSS-240A PC board and on the servo PC board attached under the transport.
I also plan to temporarily substitute a different KSS-240A because I have several on hand. I might even sub entire transports because I have two CDP-491 units. This is very easy to do because Sony used a single flat flex cable between the transport and the main PC board. I prefer to isolate intermittents to just one section or PC board first, followed by tracking down the precise location of the fault.
-EB
Among these are two Sony CDP-491 units and one Sony CDP-591.
I also have a couple of 5-disc changers which use the KSS-240A.
Today I encountered unusual and intermittent faults with one of the CDP-491 units. I’ve never observed anything quite like it.
The RF signal amplitude, which was about 1V P-P to start with, is mysteriously changing from 500mV P-P to over 1.3V P-P and back.
It changes abruptly when this happens.
Once it dropped so low that it wouldn’t initialize a disc.
Later it began working again.
The RF amplitude simply isn’t stable.
Also the sled motion is “nervous.” This is a gear drive system. The motor will suddenly move the pickup substantially outwards (towards a higher track) but then reverse and back up slightly. Sometimes there is a skip in the audio output when this happens. I don’t think it is a mechanical fault though. The sled drive runs very smoothly when moving from track 1 to track 10 and back.
Sometimes it will play several tracks perfectly but then it will get really “skippy” for a while.
Earlier in this thread there is a discussion of broken solder joints on the KSS-240A and on other PC boards in the player. I intend to closely inspect the soldering on both the tiny KSS-240A PC board and on the servo PC board attached under the transport.
I also plan to temporarily substitute a different KSS-240A because I have several on hand. I might even sub entire transports because I have two CDP-491 units. This is very easy to do because Sony used a single flat flex cable between the transport and the main PC board. I prefer to isolate intermittents to just one section or PC board first, followed by tracking down the precise location of the fault.
-EB
That does sound strange. If the RF retains clarity but simply reduces in amplitude then that suggests the optical output from the pickup is changing.
Perhaps rig a couple of leads up to the LD current monitoring resistor and leave a DVM connected to see if it varies. Dicky preset on the KSS maybe (it would be a first though). Worth checking it for dries.
Same can be done for the sled motor. Monitor the volt across the terminals and see if the voltage needs to build up before the motor kicks forward whilst in play mode. It could just be a sticky motor. If it over corrects by jumping to far forward then it will reverse but obviously if the jump was to much then you hear that as a skip.
Normally the motors are 'twitchy' edging forward and backward in very small steps.
Perhaps rig a couple of leads up to the LD current monitoring resistor and leave a DVM connected to see if it varies. Dicky preset on the KSS maybe (it would be a first though). Worth checking it for dries.
Same can be done for the sled motor. Monitor the volt across the terminals and see if the voltage needs to build up before the motor kicks forward whilst in play mode. It could just be a sticky motor. If it over corrects by jumping to far forward then it will reverse but obviously if the jump was to much then you hear that as a skip.
Normally the motors are 'twitchy' edging forward and backward in very small steps.
I experienced the RF output of a KSS-150a/KSS-210a oscillating up and down on a Sony CDP-710. The oscillation was more of a sawtooth type pattern, it would increase slowly then suddenly drop, then start increasing again.
It turned out that the previous owner had turned the laser power right the way up.
I cleaned the optics and reduced the laser power back to sensible level and then it worked fine. I can also assume the previous owner had wound the laser power up to try and compensate for the dirty optics and to get the player 'working' enough to sell it.
It turned out that the previous owner had turned the laser power right the way up.
I cleaned the optics and reduced the laser power back to sensible level and then it worked fine. I can also assume the previous owner had wound the laser power up to try and compensate for the dirty optics and to get the player 'working' enough to sell it.
Bingo! They definitely fail. Especially after being connected/disconnected several times.
With my CDP-491 I already subbed different flex cables without improvement. I do have a decent stock of replacement flex cables. Digi-Key sells them in many different lengths, pin-pin spacing, & pin counts.
It’s looking more and more like something is intermittent inside my KSS-240A. At the beginning of this thread Mooly reported his CDP-790 exhibited intermittent faults much like my CDP-491. The cause was a dry solder joint on the tiny PC board attached to the side of the KSS-240A.
I expect to ID this issue today.
-EB
My Sony CDP-491 is working perfectly with a generic replacement KSS-240A optical pickup.
All of its intermittent issues are gone.
I will move it to one of my upstairs audio systems and listen to it for a week or two to confirm that.
I've looked very closely at the original Sony KSS-240A but haven't confirmed any bad solder connections on it yet. Its laser control circuitry (APC) is embedded into the transparent clear epoxy 24-pin IC which also functions as the ABCD EF optical sensors and RF signal preamplifier. The original Sony KSS-240A contains an elaborate "flexible" PC board with very thin traces. It winds all around 3 sides of the optical mechanism. This is one thing that's different about modern generic KSS-240A units: They have a separate IC chip containing the RF preamps and laser control circuitry. That's why the optical sensor IC on modern generic pickups has fewer pins: It contains only the ABDC EF optical sensors.
I think I will leave this generic KSS-240A pickup installed and use this CD player for a while. These generic KSS-240A pickups cost me only $11 USD each. I bought 3 of them as a trial to see whether or not they were in any way "good enough to use." So far I put two of them into CD players and both work 100% perfectly. I may get a chance to try the third generic pickup soon. I have a Denon 5-disc CD player labeled "faulty KSS-240A." I haven't inspected it yet.
As far as comparing plastic vs. sintered bronze guide rod bushings, the old original Sony KSS-240A pickup had considerably more friction slidng along the guide rod than the plastic bushings in the new generic pickup. The sled moves much more smoothly with the new pickup and there is no jumpiness in its motion. I have played several discs without hearing a single skip. The old pickup never made it all the way through a disc without skipping once or twice in random locations.
-EB
All of its intermittent issues are gone.
I will move it to one of my upstairs audio systems and listen to it for a week or two to confirm that.
I've looked very closely at the original Sony KSS-240A but haven't confirmed any bad solder connections on it yet. Its laser control circuitry (APC) is embedded into the transparent clear epoxy 24-pin IC which also functions as the ABCD EF optical sensors and RF signal preamplifier. The original Sony KSS-240A contains an elaborate "flexible" PC board with very thin traces. It winds all around 3 sides of the optical mechanism. This is one thing that's different about modern generic KSS-240A units: They have a separate IC chip containing the RF preamps and laser control circuitry. That's why the optical sensor IC on modern generic pickups has fewer pins: It contains only the ABDC EF optical sensors.
I think I will leave this generic KSS-240A pickup installed and use this CD player for a while. These generic KSS-240A pickups cost me only $11 USD each. I bought 3 of them as a trial to see whether or not they were in any way "good enough to use." So far I put two of them into CD players and both work 100% perfectly. I may get a chance to try the third generic pickup soon. I have a Denon 5-disc CD player labeled "faulty KSS-240A." I haven't inspected it yet.
As far as comparing plastic vs. sintered bronze guide rod bushings, the old original Sony KSS-240A pickup had considerably more friction slidng along the guide rod than the plastic bushings in the new generic pickup. The sled moves much more smoothly with the new pickup and there is no jumpiness in its motion. I have played several discs without hearing a single skip. The old pickup never made it all the way through a disc without skipping once or twice in random locations.
-EB
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I will search for something like that "special plastics grease." It may have a different name here in the USA.
-EB
I will probably do this at some point in the future. I don't discard old optical pickups.
But at this point I'm totally satisfied with the performance of the $11 USD generic KSS-240A which I installed in place of the original Sony pickup.
Interestingly the portion of the servo control circuit (CXA1372Q) which drives the sled motor is 100% analog.
The same analog tracking output signal which goes to the tracking/focus actuator is low-pass filtered with a tiny 47uF 6v3 electrolytic (C107 on schematic) and then amplified to drive the sled motor.
I check both ESR & uF of all electrolytics on the these servo boards. But I didn't check this particular machine (yet). My experience is tiny electrolytics often dry out. This CD player is 30 years old! If C107 dries out then the signal driving the sled motor won't be low-pass filtered at all.
I also suspect part of the "jumpy sled" issue with the original Sony KSS-240A was that its sintered bronze bushings were a rather tight fit against the polished steel guide rod. I don't know why because it wasn't dirty, corroded, or covered with dried out sticky grease. The new generic pickup with its plastic bushings moves very smoothly and freely in comparison. It isn't loose or wobbly either. Evidently the manufacturer of these $11 USD generic pickups does possess some degree of skill.
-EB