New project: Onkyo DX-120 CD player from 1986. What intrigues me about this unit is the TAOHS laser pickup (made by Olympus?) and the use of several Yamaha IC chips for servo control, data decoding & recovery, & DAC.
I recently dug it out of my storage unit. Current status:
It powers on.
Tray opens and closes.
The carriage drive is functional.
The machine performs a focus search but fails to detect the presence of a disc.
Next I measured IR light intensity. It was 150 mW. Service manual says it should be >250mW. Another post on diyAudio suggested 300mW for this particular optical pickup (TAOHS series). I raised the light output in tiny increments until I reached about 275mW.
At this point it displays the TOC information rapidly and will play a CD which is in perfect condition. However it won’t play through the damaged areas of “less-than-perfect” discs that have scratches. These same discs plays without interruption in other machines.
The service manual describes a “skew adjustment screw” and states “adjust it for best eye pattern.” Adjusting this revealed that the adjustment must be all the way at one end to get the best eye pattern.
I am able to get a decent looking RF signal eye pattern. The service manual shows 3V P-P and that’s what I’m getting.
However I don’t think the carriage is moving smoothly enough. It sometimes seems “sticky.” I’ll have more on this after I post photos of the carriage assembly. Some sections of it look very well-made and precise, but some other parts in it look really crude to my eye.
I’d like to get this Onkyo DX-120 into a condition where it will play most of my discs.
-EB
I recently dug it out of my storage unit. Current status:
It powers on.
Tray opens and closes.
The carriage drive is functional.
The machine performs a focus search but fails to detect the presence of a disc.
Next I measured IR light intensity. It was 150 mW. Service manual says it should be >250mW. Another post on diyAudio suggested 300mW for this particular optical pickup (TAOHS series). I raised the light output in tiny increments until I reached about 275mW.
At this point it displays the TOC information rapidly and will play a CD which is in perfect condition. However it won’t play through the damaged areas of “less-than-perfect” discs that have scratches. These same discs plays without interruption in other machines.
The service manual describes a “skew adjustment screw” and states “adjust it for best eye pattern.” Adjusting this revealed that the adjustment must be all the way at one end to get the best eye pattern.
I am able to get a decent looking RF signal eye pattern. The service manual shows 3V P-P and that’s what I’m getting.
However I don’t think the carriage is moving smoothly enough. It sometimes seems “sticky.” I’ll have more on this after I post photos of the carriage assembly. Some sections of it look very well-made and precise, but some other parts in it look really crude to my eye.
I’d like to get this Onkyo DX-120 into a condition where it will play most of my discs.
-EB
Here are photos of the TAOHS-DG2 optical pickup from this Onkyo DX-120 CD player.
In order to get this unit to play a disc it was necessary to adjust the light output from the laser.
It was only 50% of what it should be.
Also the initial laser current was lower than expected.
Perhaps the APC control circuit drifted?
After all this CD player is 35 years old.
Only a very modest increase in laser current was needed to obtain plenty of RF-signal (eye pattern).
I'm listening to the CD player now while editing this post.
This PC board contains the APC circuit (automatic power control), the adjustment trimpot, and a 15 ohm resistor for measuring laser current.
Laser current is directly proportional to the voltage drop across the resistor.
For a typical laser current of 50mA there will be 0.75V (750mV) across the 15 ohm resistor.
Laser diodes are incredibly non-linear. A 5% increase in current can double the brightness.
And because the APC circuit maintains a specified light output level (uW), the laser current itself will vary with time & temperature.
Optical pickup manufacturers often labeled the initial laser mA & uW.
If a laser gets weak or fails from old age then the measured current will be much higher than the mA value given on the factory label.
In that case the only practical repair is to replace the entire optical pickup.
This sticker on the side of this TAOHS-DG2 gives the original factory values for laser current (42.9mA) and the corresponding light output level (218uW).
My first measurement of the pickup showed only 150uW of light output. And the laser current was only 30mA. So, both light output & laser current were lower than the original factory setting. I concluded the laser diode was probably OK, but because of long-term drift and aging the APC circuit was out of adjustment.
Here is an interesting bit of information from the Onkyo service manual:
It states >250uW of laser light is required to initialize a disc.
Other data I obtained for the TAOHS-series of optical pickups suggests 300-400uW for the target light output.
Based on this I decided to increase the laser current in small increments while monitoring both laser current & the light output.
For now I am using 275uW of light output.
This requires a laser current of 54.8mA, which is only 25% above the original factory current.
Evidently that original factory setting of 218uW was lower than what Onkyo specifies in the service manual (>250uW).
At this time the RF-level (eye-pattern) is slightly >3V P-P. This is close to the value given in the Onkyo service manual:
My next step will be to learn why this player still can't play discs with scratches on them.
I have a bunch of "shop" discs which are in less than perfect condition.
The other disc players I've had on the bench recently were able to play these discs without complaining.
This isn't the case (yet) with the Onkyo DX-120.
I haven't checked out its tracking & focus servo circuits yet.
There are several trimpots and tons of small electrolytic capacitors.
At 35 years of age every small electrolytic must be checked for ESR.
Also I'm suspicious that the focus/tracking mechanism might be "loose" in one way or another.
This optical pickup uses flat steel springs to support the focus/tracking coils and the objective lens:
The lens can move up and down about 3mm in total.
When at rest with no power the weight of the lens and tracking coils causes the mechanism to sag down close to the lower stop.
I observed the effect of gravity by rotating the pickup 180 degrees (lens facing down). This moves the lens close to the upper stop.
When on its side the focus springs are in a straight (neutral) position.
I don't know whether or not this represents a problem?
When the player is powered up, the focus servo "biases" the focus coil with a steady current which raises the lens close to the correct position for playing a disc.
There is a "focus offset" control on the main PC board which has a very strong influence on the vertical position of the lens. This trimpot has only a narrow range where the lens isn't hitting the top or bottom stop. This is without a disc in the tray and in stop mode.
I need to do more research about this.
Is it an indication of a fault, or just the way this particular CD player works?
But, for now, it plays discs which are in good condition.
-EB
In order to get this unit to play a disc it was necessary to adjust the light output from the laser.
It was only 50% of what it should be.
Also the initial laser current was lower than expected.
Perhaps the APC control circuit drifted?
After all this CD player is 35 years old.
Only a very modest increase in laser current was needed to obtain plenty of RF-signal (eye pattern).
I'm listening to the CD player now while editing this post.
Warning:
It's critically important to monitor the laser current while making any attempt to adjust the trimpot.
Also the light output must be monitored with a laser light meter such as my Leader LPM-8000.
This procedure is best left to experienced CD player technicians.
It is far too easy to permanently destroy the laser diode by altering the trimpot setting.
So follow along with what I'm doing but don't try it yourself!
It's critically important to monitor the laser current while making any attempt to adjust the trimpot.
Also the light output must be monitored with a laser light meter such as my Leader LPM-8000.
This procedure is best left to experienced CD player technicians.
It is far too easy to permanently destroy the laser diode by altering the trimpot setting.
So follow along with what I'm doing but don't try it yourself!
This PC board contains the APC circuit (automatic power control), the adjustment trimpot, and a 15 ohm resistor for measuring laser current.
Laser current is directly proportional to the voltage drop across the resistor.
For a typical laser current of 50mA there will be 0.75V (750mV) across the 15 ohm resistor.
Laser diodes are incredibly non-linear. A 5% increase in current can double the brightness.
And because the APC circuit maintains a specified light output level (uW), the laser current itself will vary with time & temperature.
Optical pickup manufacturers often labeled the initial laser mA & uW.
If a laser gets weak or fails from old age then the measured current will be much higher than the mA value given on the factory label.
In that case the only practical repair is to replace the entire optical pickup.
This sticker on the side of this TAOHS-DG2 gives the original factory values for laser current (42.9mA) and the corresponding light output level (218uW).
My first measurement of the pickup showed only 150uW of light output. And the laser current was only 30mA. So, both light output & laser current were lower than the original factory setting. I concluded the laser diode was probably OK, but because of long-term drift and aging the APC circuit was out of adjustment.
Here is an interesting bit of information from the Onkyo service manual:
It states >250uW of laser light is required to initialize a disc.
Other data I obtained for the TAOHS-series of optical pickups suggests 300-400uW for the target light output.
Based on this I decided to increase the laser current in small increments while monitoring both laser current & the light output.
For now I am using 275uW of light output.
This requires a laser current of 54.8mA, which is only 25% above the original factory current.
Evidently that original factory setting of 218uW was lower than what Onkyo specifies in the service manual (>250uW).
At this time the RF-level (eye-pattern) is slightly >3V P-P. This is close to the value given in the Onkyo service manual:
My next step will be to learn why this player still can't play discs with scratches on them.
I have a bunch of "shop" discs which are in less than perfect condition.
The other disc players I've had on the bench recently were able to play these discs without complaining.
This isn't the case (yet) with the Onkyo DX-120.
I haven't checked out its tracking & focus servo circuits yet.
There are several trimpots and tons of small electrolytic capacitors.
At 35 years of age every small electrolytic must be checked for ESR.
Also I'm suspicious that the focus/tracking mechanism might be "loose" in one way or another.
This optical pickup uses flat steel springs to support the focus/tracking coils and the objective lens:
The lens can move up and down about 3mm in total.
When at rest with no power the weight of the lens and tracking coils causes the mechanism to sag down close to the lower stop.
I observed the effect of gravity by rotating the pickup 180 degrees (lens facing down). This moves the lens close to the upper stop.
When on its side the focus springs are in a straight (neutral) position.
I don't know whether or not this represents a problem?
When the player is powered up, the focus servo "biases" the focus coil with a steady current which raises the lens close to the correct position for playing a disc.
There is a "focus offset" control on the main PC board which has a very strong influence on the vertical position of the lens. This trimpot has only a narrow range where the lens isn't hitting the top or bottom stop. This is without a disc in the tray and in stop mode.
I need to do more research about this.
Is it an indication of a fault, or just the way this particular CD player works?
But, for now, it plays discs which are in good condition.
-EB
I set up the Onkyo DX-120 to play a disc on repeat yesterday. Checked it today and the disc is still playing.
This “repeat play of entire disc” test may turn out to be useful. This Onkyo DX-120 tends to go into the “stop” state when it encounters a bad spot on a disc.
I have several “somewhat scratched” discs which play perfectly in newer disc players. But they don’t play properly in some of these early vintage (before 1990) CD players. The
When they encounter a bad spot on a disc these older CD players tend to skip or stutter first, then they mute the audio, and after that the carriage may jump around all over the place. Eventually they either recover sufficiently to restart playing the disc from track 1, or else they revert to the “stop” state.
It’s plausible their control logic simply isn’t as refined as newer players.
That said, my goal with this vintage 1986 Onkyo DX-120 is to get it to play “less than perfect” discs without skipping or stopping. I’ll also compare it to my collection of other 1980’s CD players which contain other type of optical pickups. I have four old CD players which contain Philips swing-arm optical pickups. It will be informative to play the same “less than perfect” disc in several CD players to learn how well they can play through the bad spots on the disc.
-EB
This “repeat play of entire disc” test may turn out to be useful. This Onkyo DX-120 tends to go into the “stop” state when it encounters a bad spot on a disc.
I have several “somewhat scratched” discs which play perfectly in newer disc players. But they don’t play properly in some of these early vintage (before 1990) CD players. The
When they encounter a bad spot on a disc these older CD players tend to skip or stutter first, then they mute the audio, and after that the carriage may jump around all over the place. Eventually they either recover sufficiently to restart playing the disc from track 1, or else they revert to the “stop” state.
It’s plausible their control logic simply isn’t as refined as newer players.
That said, my goal with this vintage 1986 Onkyo DX-120 is to get it to play “less than perfect” discs without skipping or stopping. I’ll also compare it to my collection of other 1980’s CD players which contain other type of optical pickups. I have four old CD players which contain Philips swing-arm optical pickups. It will be informative to play the same “less than perfect” disc in several CD players to learn how well they can play through the bad spots on the disc.
-EB
The simple fact that you had to increase the laser power adjustment that much points at a problem with the laser itself.
There are mostly two possibilities:
1. the laser diode is bad
2. the laserlens is dirty
Seeing the age of the Onkyo, I suspect both may be true, but the first possibility is the most likely. These laserdiodes do wear out and simply dialing up the power doesn't help, because with the degradation the pick-up assembly loses focus.
If you have the service manual or things are marked properly on the main PCB, look for the eye-pattern test point. Hook a scope unto that and the sinus waveforms should be crisp, the more they are "out of focus", the worse the condition of the pick-up assembly.
I see you've already done that, my bad. That RF-output does not look good. I fear your pick-up assembly is on it's last legs.
There are mostly two possibilities:
1. the laser diode is bad
2. the laserlens is dirty
Seeing the age of the Onkyo, I suspect both may be true, but the first possibility is the most likely. These laserdiodes do wear out and simply dialing up the power doesn't help, because with the degradation the pick-up assembly loses focus.
If you have the service manual or things are marked properly on the main PCB, look for the eye-pattern test point. Hook a scope unto that and the sinus waveforms should be crisp, the more they are "out of focus", the worse the condition of the pick-up assembly.
I see you've already done that, my bad. That RF-output does not look good. I fear your pick-up assembly is on it's last legs.
Last edited:
Perhap the insufficient light level (150uW) resulted from long-term drift in the APC control system?
The cause could have been a dirty APC trimpot.
There are also 3 small electrolytic capacitors located on the APC PC board which is attached to the optical pickup. I will check their uF & ESR before proceeding further. My experience is that tiny electrolytics have a high failure when >10 years old. This CD player is 35 years old. No electrolytic capacitors inside it have been replaced (yet).
Reviewing my testing procedure up to the point where I decided to adjust the APC trimpot:
1) My initial measurements: Light output: 150uW. Laser current: 30mA. CD player will not initialize any disc.
2) Factory label on optical pickup: 218uW, 42.9mA
3) Onkyo service manual: “>250uW is required to initialize a disc.”
4) A search of this forum and others suggested the desired IR light output from TAOHS-style optical pickups is 300-400uW.
5) Onkyo service manual: RF level (eye-pattern): 3V P-P
At this point I cautiously adjusted the APC trimpot to obtain 275uW.
Laser current is now 54.8mA. I believe this is a safe level of laser current.
At this time the machine is able to initialize every disc. The only remaining issue is that it won’t always play through bad spots (scratches) on some discs.
To confirm the laser diode itself is still in perfect condition I plan to conduct the following test:
I will set the APC trimpot for 42.9mA of laser current and measure the light output. This should be 218uW according to the original factory label.
I also plan to perform a final adjustment of the APC trimpot to obtain an RF level (eye-pattern) of 3V P-P averaged among several discs.
But first I intend to check every small electrolytic capacitor for ESR & uF. In addition to those 3 tiny electrolytics mounted on the optical pickup APC PC board, there are >20 located on the main PC board. Some of these capacitors perform critical functions in the servo control circuitry.
-EB
I'm sorry but that pick-up assembly is toast. That power rating on the side of the assembly is mandatory, you should never exceed that.
Just look at the RF-output pattern: those sinus waves should be clear and crsip, with very sharp cross-points, this one simply isn't, which means the focus isn't sharp.
With some of the Sony KSS-150 and successors you can adjust the tilt of the laserlens ever so slightly, therefore correcting the focus somewhat. I don't know if this pick-up has that correction possibility.
But there's another thing you mentioned: the laserlens appears to sag. With the old Pioneer cd-players that was an automatic fail: the power needed to compensate for that tiny amount of sag is already too much for the circuit.
Those old pick-up assembly's are delicate constructs with not much tolerances. Everything added up tells me this pick-up assembly is done for.
Just look at the RF-output pattern: those sinus waves should be clear and crsip, with very sharp cross-points, this one simply isn't, which means the focus isn't sharp.
With some of the Sony KSS-150 and successors you can adjust the tilt of the laserlens ever so slightly, therefore correcting the focus somewhat. I don't know if this pick-up has that correction possibility.
But there's another thing you mentioned: the laserlens appears to sag. With the old Pioneer cd-players that was an automatic fail: the power needed to compensate for that tiny amount of sag is already too much for the circuit.
Those old pick-up assembly's are delicate constructs with not much tolerances. Everything added up tells me this pick-up assembly is done for.
Seriously? That's a bad manual then.
I've repaired CD-players for years and a good RF-pattern will show each sinus wave with very crisp and sharp lines. The cross-points between the sinus waves should be very clear and sharp as well.
This is a subject I wish to learn more about.
Is there a phenomena or failure mechanism which causes an IR laser diode to emit “noisy” light which degrades the quality of the RF signal (eye-pattern)?
Is this an entirely different fault than simply not generating a sufficient amplitude of IR light?
With this Onkyo DX-120 the initial light output (150uW) was insufficient for the player to achieve “focus lock.” At this stage of initialization the disc hasn’t begun to rotate yet.
During “focus search” the CD player is measuring the peak light level received from the ABCD photo-detectors inside the optical pickup. If there is a disc in the tray, then this peak will be above a preset threshold at the moment when the lens focuses the light beam on the data layer of the disc.
Prior to adjusting the APC trimpot I observed a small peak in the received light level, but it wasn’t sufficient for the machine to detect that “a disc is present.”
-EB
That Onkyo service manual was published in 1986. Onkyo would have used a photo of an eye pattern displayed by an analog oscilloscope. I think they put that photo into the service manual mainly to establish that the P-P amplitude of the eye pattern should be 3V. I don’t think Onkyo intended it to be studied in detail.
-EB
The laser diode emits light of a precise wavelength. That light bounces of the cd disc and is being received within the pick-up assembly.
So that gives you a couple of failure points:
1. the laser diode itself. If it degrades beyond a certain point, the wavelength may not be precisely right anymore meaning there's less reflection. It can also be that the light that's being emitted is no longer as sharply bundled as it used to be, causing scattering of the light which also means less reflection.
2. the receiving part in the assembly has degraded (as well). Which in essence causes the same problems as with the emitting part.
3. the lens is dirty/damaged/slightly opaque due to aging. Again the same problems.
4. the rubber suspension of the lens has sagged, meaning it's lost part of it's flexibility and the focussing circuit has to try and correct that with the focussing coils. As we're talking signals in the mV's here, that's also very limited.
So basically it doesn't really matter which part or parts have degraded, it all leads to the same outcome: less light to convert into an electrical signal. The consequence can be seen in the RF-signal, when that loses it's crispness, it's the beginning of the end. You can prolong that end somewhat by boosting the laser power, but as you've already noticed that doesn't help that much and it's a very short term solution, as the laser diode will degrade even faster.
The only hope you have is finding a replacement pick-up assembly, but even if that has rarely or even never been used, it will already have the degredation of the rubber suspension parts due to age. Unless Onkyo can provide you with a brand new pick-up assembly, which is not very likely, this player is doomed.
So that gives you a couple of failure points:
1. the laser diode itself. If it degrades beyond a certain point, the wavelength may not be precisely right anymore meaning there's less reflection. It can also be that the light that's being emitted is no longer as sharply bundled as it used to be, causing scattering of the light which also means less reflection.
2. the receiving part in the assembly has degraded (as well). Which in essence causes the same problems as with the emitting part.
3. the lens is dirty/damaged/slightly opaque due to aging. Again the same problems.
4. the rubber suspension of the lens has sagged, meaning it's lost part of it's flexibility and the focussing circuit has to try and correct that with the focussing coils. As we're talking signals in the mV's here, that's also very limited.
So basically it doesn't really matter which part or parts have degraded, it all leads to the same outcome: less light to convert into an electrical signal. The consequence can be seen in the RF-signal, when that loses it's crispness, it's the beginning of the end. You can prolong that end somewhat by boosting the laser power, but as you've already noticed that doesn't help that much and it's a very short term solution, as the laser diode will degrade even faster.
The only hope you have is finding a replacement pick-up assembly, but even if that has rarely or even never been used, it will already have the degredation of the rubber suspension parts due to age. Unless Onkyo can provide you with a brand new pick-up assembly, which is not very likely, this player is doomed.
I’m curious to learn why the label on the optical pickup (218uW, 42.9mA) doesn’t match up with the Onkyo service manual stating “>250uW is required to establish focus lock.”
In addition, after adjusting light output to 275uW I’m getting 3V P-P of RF signal. This does match up with what Onkyo specifies in their service manual.
Furthermore I found some charts giving target light output levels (uW) for several optical pickups. It listed 300-400uW for the TAOHS family of optical pickups.
This Onkyo DX-120 does have a “skew” adjustment which tilts the plane of the optical pickup from left to right as viewed from the front of the CD player. I have adjusted it for the best eye pattern.
I’m beginning to think this is normal for the Onkyo DX-120.
The Onkyo service manual specifies a “resting” DC offset of 400mV for the drive voltage applied to the optical pickup focus actuator coils. This is measured in stop mode and/or when there is no disc in the tray.
This amount of offset is exactly the proper amplitude to compensate for the “sag.” It positions the lens at the same height as when it is playing a disc. This offset voltage is present at all times while the machine is powered up, whether or not a disc is in the tray or currently playing.
I’m continuing to study all of these items.
-EB
This optical pickup contains no internal “moving parts” made of plastic or rubber. The suspension system for the focus/tracking lens is provided by flat steel springs.
The Onkyo DX-120 disc loading mechanism and tray assembly is roughly 50% plastic and 50% metal. All parts are functioning at this time. Its mechanical parts look enormous in comparison to newer disc players. This Onkyo DX-120 was manufactured in 1986.
I’ve been collecting/restoring vintage audio gear for a long time. As a general rule, the manufacturers provide no parts or support after about 5 years. Therefore some of my restorations require “parts donor” machines.
I also collect and restore tube (valve) radios made from 1948-1965. In other words some are >70 years old. Fortunately there is a large community of antique radio collectors and restorers.
I’m comfortable restoring items which are only 35 years old. I know what to expect. I also understand that some items may be unrepairable.
-EB
The eye pattern from my Onkyo DX-120 looks like this on a DSO:
It will probably look much cleaner when viewed with an analog CRT oscilloscope. It's difficult to configure the "persistence" feature of a DSO to emulate a CRT. Eye patterns viewed with digital scopes often look "noisier" due to random pixelation.
I'll set up one of my analog scopes soon for comparison. My DSO takes up very little space on my crowded workbench. Plus it is simple to copy screen images and raw data files onto a PC for detailed analysis. So I rely on it. My analog scope only gets used occasionally. Right now I'm thinking that viewing eye patterns is a good reason to bring an analog scope back to my workbench for a while.
The most important item to observed from viewing the eye pattern with a digital scope is its peak-to-peak amplitude. Digital scopes do a great job with amplitude measurement. For example my Tektronix TDS2002B measures and displays the P-P amplitude of the eye pattern in real time (3.22V P-P for the attached screenshot).
I also confirmed the Onkyo DX-120 goes into an "error state" when it cannot resolve scratched portions of a disc. Its "error" display looks like this:
This occurred near the end of a "less than perfect" disk which had some rather large scratches. Therefore I can keep a disc playing in repeat mode for a lengthy burn-in test. If the CD player encounters a problem it will stop and display the "Ed" error message. That means I don't need to watch it continuously or listen to the audio.
Interesting item: I decided to try a CD-R in the Onkyo.
It plays!
The RF level is lower (about 2V P-P) but the eye pattern itself looks similar to factory pressed discs. I wan't expecting this. I've read that some "first generation" CD players won't play burned discs.
-EB
It will probably look much cleaner when viewed with an analog CRT oscilloscope. It's difficult to configure the "persistence" feature of a DSO to emulate a CRT. Eye patterns viewed with digital scopes often look "noisier" due to random pixelation.
I'll set up one of my analog scopes soon for comparison. My DSO takes up very little space on my crowded workbench. Plus it is simple to copy screen images and raw data files onto a PC for detailed analysis. So I rely on it. My analog scope only gets used occasionally. Right now I'm thinking that viewing eye patterns is a good reason to bring an analog scope back to my workbench for a while.
The most important item to observed from viewing the eye pattern with a digital scope is its peak-to-peak amplitude. Digital scopes do a great job with amplitude measurement. For example my Tektronix TDS2002B measures and displays the P-P amplitude of the eye pattern in real time (3.22V P-P for the attached screenshot).
I also confirmed the Onkyo DX-120 goes into an "error state" when it cannot resolve scratched portions of a disc. Its "error" display looks like this:
This occurred near the end of a "less than perfect" disk which had some rather large scratches. Therefore I can keep a disc playing in repeat mode for a lengthy burn-in test. If the CD player encounters a problem it will stop and display the "Ed" error message. That means I don't need to watch it continuously or listen to the audio.
Interesting item: I decided to try a CD-R in the Onkyo.
It plays!
The RF level is lower (about 2V P-P) but the eye pattern itself looks similar to factory pressed discs. I wan't expecting this. I've read that some "first generation" CD players won't play burned discs.
-EB
The following post is where I found data suggesting 300-500 uW for TAOHS-style optical pickups:
I'm still not 100% sure what the optical pickup inside this Onkyo DX-120 actually is.
The Onkyo service manual refers to it as TAOHS-DG2.
But there is no brand name or part number on the actual pickup itself.
I've seen numerous photos of other TAOHS-style pickups which look totally different.
So I don't know how much the name "TAOHS" actually defines who made the pickup.
Onkyo always had a very close relationship with Toshiba. And Toshiba manufactured both CD players & optical pickups during the 1980's.
Who manufactured the optical pickup inside my Onkyo DX-120?
Was it Olympus or Toshiba?
-EB
I'm still not 100% sure what the optical pickup inside this Onkyo DX-120 actually is.
The Onkyo service manual refers to it as TAOHS-DG2.
But there is no brand name or part number on the actual pickup itself.
I've seen numerous photos of other TAOHS-style pickups which look totally different.
So I don't know how much the name "TAOHS" actually defines who made the pickup.
Onkyo always had a very close relationship with Toshiba. And Toshiba manufactured both CD players & optical pickups during the 1980's.
Who manufactured the optical pickup inside my Onkyo DX-120?
Was it Olympus or Toshiba?
-EB
I know what you are talking about.
I've observed textbook-perfect eye patterns in the past.
But I was using analog oscilloscopes then. I intend to get out one of my analog scopes (I own several) and see what they can tell me about eye patterns.
I also have plenty of CD players to compare with. This Onkyo DX-120 is just one of many which have been in my storage cache for years. I'm either a collector or a hoarder of vintage audio gear.
-EB
Something else just occurred to me:
My scope probe ground clip wasn’t attached to the “ground” pin of the tiny 4-pin white plastic header on the main PC board where the RF signal test point is located. Instead my scope probe was grounded at the audio output jack PC board. Although a low noise level would be expected from the audio output ground bus, this might not be true while monitoring the RF signal.
My plan is to replace the 4-pin factory test point connector with a standard male header which has tall .025” square posts. This will simplify connecting the scope probe for cleanly observing the RF signal.
The original test point connector is unlike anything I’ve seen before. I’ll post a photo of it. It was probably selected for the testing procedures used at the Onkyo factory. But it isn’t easy to use when one doesn’t have the proper connector to plug into it.
Current status:
Once again I kept a disc playing overnight on repeat. It is still playing today.
The Onkyo DX-120 plays both factory-pressed & CD-R discs perfectly as long as the discs are clean and free of scratches.
Disc initialization is amazingly fast: Less than 2 seconds. The disc rotates only a couple of turns before the TOC data is displayed on the front panel.
Moving from track to track by pressing front panel buttons is somewhat slow, probably due to the (rather slow) worm gear drive system used for moving the carriage.
The Onkyo DX-120 plays both factory-pressed & CD-R discs perfectly as long as the discs are clean and free of scratches.
Disc initialization is amazingly fast: Less than 2 seconds. The disc rotates only a couple of turns before the TOC data is displayed on the front panel.
Moving from track to track by pressing front panel buttons is somewhat slow, probably due to the (rather slow) worm gear drive system used for moving the carriage.
-EB
The “sticky carriage” issue was caused by rotating the “skew adjustment screw” all the way to one end of its adjustment range.
This “skew adjustment” is accomplished by a plastic cam with a ramped surface. Rotating it raises or lowers the right hand side of the optical pickup carriage.
The cam itself slides along with the carriage, pressing down against a flat fixed plastic rail which is part of the lower section of the disc transport mechanism. The ramped surface of this cam touches the fixed rail. This is a “plastic against plastic” sliding mechanism. It isn’t as precise as the precision machined steel rod and nylon slider located on the left hand side of the carriage assembly.
Rotating the “skew” adjustment all the way to the end presses the vertical portion of the plastic cam against the outer edge of the slide rail on the fixed chassis. This causes a great deal of unwanted friction.
The solution was to back off the “skew” cam adjustment just enough to prevent unwanted interference between the vertical surface of the cam and the fixed slide rail.
At this point the carriage moves very smoothly over its entire range of motion.
When I get a chance I will see if the exploded diagram in the service manual will show the relationship between the cam and the fixed rail.
-EB
The Onkyo DX-120 continued to play overnight in "disc repeat" mode.
Today I'm testing it with some of my "less-than-perfect" discs.
Interestingly it is playing them today without skipping or stopping.
I intend to check the carriage drive motor for "dead spots."
More to come...
-EB
Today I'm testing it with some of my "less-than-perfect" discs.
Interestingly it is playing them today without skipping or stopping.
I intend to check the carriage drive motor for "dead spots."
This is a "worm drive and gear" type carriage drive. This motor rotates very slowly except when returning the carriage from the end of a disc back to the start position. It is a small DC motor with brushes and commutator.
Small DC motors which rotate very slowly do tend to develop dead spots between the brushes and commutator.
Applying sufficient DC voltage (9-12V) to spin the motor at 2-3,000 RPM for a few seconds is usually sufficient to clean the commutator and eliminate the dead spots.
I haven't done this yet.
But perhaps the "medium speed" motor rotation which occurs while returning the carriage from the end of a disc to the first track was sufficient to clean up this motor?
Small DC motors which rotate very slowly do tend to develop dead spots between the brushes and commutator.
Applying sufficient DC voltage (9-12V) to spin the motor at 2-3,000 RPM for a few seconds is usually sufficient to clean the commutator and eliminate the dead spots.
I haven't done this yet.
But perhaps the "medium speed" motor rotation which occurs while returning the carriage from the end of a disc to the first track was sufficient to clean up this motor?
More to come...
-EB