With respect to std., Red Book CD players ....
Which observation is more correct? Or are there other modes of failure that are common?
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One reason for this query is due to two Radio Shack portable CDPs, "in-the-shop", that are misbehaving. They both have low hours, and have mostly sat in storage since purchase in early-mid 1990s.
Thx in advance for any feedback you can provide!
- Some say the laser diode deteriorates over time -- and you may get symptoms with lasers that are "going bad" : poor tracking, errors "ERR", stops play all-of-sudden and enters STOP mode, etc.
- Others say that because the laser is a DIODE, it will either work or not work at all (this does not, of course, include physical damage to the lens or focusing mech/electronics).
Which observation is more correct? Or are there other modes of failure that are common?
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One reason for this query is due to two Radio Shack portable CDPs, "in-the-shop", that are misbehaving. They both have low hours, and have mostly sat in storage since purchase in early-mid 1990s.
- Optimus CD-3450 (1995) model sat mostly in storage until a few mos. ago when it was tested. it worked fine. It was re-tested (by someone else), after shipment across country, and it began to STOP playback after randomly. Most suggest it is electro cap(s) that have dried out, but I have not tested.
- Optimus CD-3400 (1994), the infamous "audiophile" model. Plays back with a mysterious cyclical + soft "thumping" distortion over its Line Out and Headphone Out. Have not tested Digital (SPDIF) out yet. Some have suggested RAM issue, such as weak solder joint. This unit had no issue when tested about 4 years ago.
Thx in advance for any feedback you can provide!
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Lets be clear...
Laser diodes can "deteriorate" over many hundreds or thousands of hours use. Deterioration here meaning a reduction in optical output for a given current... in other words the laser brightness can fall off. That is just one of several reasons why all laser diodes are run from an APC (automatic power control) circuit. This maintains the optical output of the laser by monitoring the light output internally within the laser diode chip. The APC circuit gradually increases the diode current as the diode deteriorates maintaining the exact same light output.
Optical output as measured externally to the pickup can fall due to contamination of the internal optics. That is a totally different problem to the above.
As to whether the laser works/does not work. That really falls into the first description. It can "work" but the output may be so low that the APC circuit is unable to correct the issue. A damaged laser diode can also still "glow red" but in that state is little more than a side emitting LED. It can also do that with too little current for the lasing action to start.
As to the specific models... normal fault-finding applies. i.e. you need to look with a scope to see the quality of the RF signal and identify any problems.
Laser diodes can "deteriorate" over many hundreds or thousands of hours use. Deterioration here meaning a reduction in optical output for a given current... in other words the laser brightness can fall off. That is just one of several reasons why all laser diodes are run from an APC (automatic power control) circuit. This maintains the optical output of the laser by monitoring the light output internally within the laser diode chip. The APC circuit gradually increases the diode current as the diode deteriorates maintaining the exact same light output.
Optical output as measured externally to the pickup can fall due to contamination of the internal optics. That is a totally different problem to the above.
As to whether the laser works/does not work. That really falls into the first description. It can "work" but the output may be so low that the APC circuit is unable to correct the issue. A damaged laser diode can also still "glow red" but in that state is little more than a side emitting LED. It can also do that with too little current for the lasing action to start.
As to the specific models... normal fault-finding applies. i.e. you need to look with a scope to see the quality of the RF signal and identify any problems.
Mooly:
Thx! I have not scoped either of these PCDPs yet. These devices are "ancient" and I have other projects that must take priority -- I was hoping for QUICK+LOW-COST fix.
About the reduction of output ... and that being the cause of frequently-encountered problem seen by repair techs. But what are its END-USER symptoms? Skipping, stopping, ERR, etc., as I noted in the OP?
Thx! I have not scoped either of these PCDPs yet. These devices are "ancient" and I have other projects that must take priority -- I was hoping for QUICK+LOW-COST fix.
About the reduction of output ... and that being the cause of frequently-encountered problem seen by repair techs. But what are its END-USER symptoms? Skipping, stopping, ERR, etc., as I noted in the OP?
Pickups suffer many problems and the symptoms vary player to player. Low optical output with a perfect disc and otherwise perfect optics may create no symptoms. Many pickups suffer from problems with the lens suspension system which in some pickups can be a just a loop of neoprene type material (like a tiny elastic band) securing the lens from below. Any change in the characteristics of that affects the lens/servo ability to track the disc.
There's never a quick or cheap fix as such. You have to look at the problem logically. If it stops or skips after a while then monitor the voltage across the sled drive. If it starts to rise unexpectedly then that indicates the sled has stuck. As the voltage rises higher the motor eventually has enough torque to overcome the friction and the sled jolts forward. You hear it as skip or jump.
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