A wise old tech once told me, "Mech it first." He meant that the first step in troubleshooting after confirming the customer's complaint is to look for obvious mechanical clues to the root cause of the failure -- blown fuses, burned resistors and the like. If I'd done that last night when I was working on my Magnavox CD player, I could have saved an hour's worth of frustration. Live and learn ...
The player is a late-1980s Magnavox with the TDA1541 dual DAC, the 4x oversampling digital filter, and the CDM2 disc drive. It had developed a skip that was only evident near the end of the CD. It also had trouble seeking to the last tracks on long CDs with a large number of tracks. I opened it up, cleaned the lens and confirmed that the load drawer and clamp were working properly. The problem was still there, so I swapped in the CDM from a junker CDB-650. That drive also had problems, so I went to put the original drive back in and noticed something that I would have caught if I'd done a thorough mech inspection first.
The CDM2 uses a rotary actuator (swing arm) instead of the linear sled that other manufacturers use for the laser diode, phototransistor and optics. The swing arm on this CDM2 had the tiniest bit of friction -- a barely perceptible catch -- near the outer limit of its travel. The counterweight for the swing arm rotates in a trough that's molded into the CDM's top plate, and the flex circuit from the pickup head routes along the base of this trough. The flex circuit had lifted just slightly at one end and was barely touching the counterweight. The plastic clip that holds the flex circuit's tail where it routes to the servo board had come loose at one end and allowed the flex circuit to shift. I removed the clip, repositioned the flex circuit and snapped the clip back in, making sure that it locked tightly in place. That eliminated the catch in the swing arm's motion. I put the player back together, checked it out on the bench to verify that the seek and skip problems were gone, and moved it into a system as a final check. It passed with flying colors.
This may be something to keep in mind if any of you are working on an old swing-arm Philips or Magnavox CD drive with a baffling skip problem. Check the swing arm for free motion and take a close look at the flex circuit dress and retention clip if the swing arm doesn't move freely. You may save yourself a lot of time and aggravation.
The player is a late-1980s Magnavox with the TDA1541 dual DAC, the 4x oversampling digital filter, and the CDM2 disc drive. It had developed a skip that was only evident near the end of the CD. It also had trouble seeking to the last tracks on long CDs with a large number of tracks. I opened it up, cleaned the lens and confirmed that the load drawer and clamp were working properly. The problem was still there, so I swapped in the CDM from a junker CDB-650. That drive also had problems, so I went to put the original drive back in and noticed something that I would have caught if I'd done a thorough mech inspection first.
The CDM2 uses a rotary actuator (swing arm) instead of the linear sled that other manufacturers use for the laser diode, phototransistor and optics. The swing arm on this CDM2 had the tiniest bit of friction -- a barely perceptible catch -- near the outer limit of its travel. The counterweight for the swing arm rotates in a trough that's molded into the CDM's top plate, and the flex circuit from the pickup head routes along the base of this trough. The flex circuit had lifted just slightly at one end and was barely touching the counterweight. The plastic clip that holds the flex circuit's tail where it routes to the servo board had come loose at one end and allowed the flex circuit to shift. I removed the clip, repositioned the flex circuit and snapped the clip back in, making sure that it locked tightly in place. That eliminated the catch in the swing arm's motion. I put the player back together, checked it out on the bench to verify that the seek and skip problems were gone, and moved it into a system as a final check. It passed with flying colors.
This may be something to keep in mind if any of you are working on an old swing-arm Philips or Magnavox CD drive with a baffling skip problem. Check the swing arm for free motion and take a close look at the flex circuit dress and retention clip if the swing arm doesn't move freely. You may save yourself a lot of time and aggravation.
