Laser diode replcement in Toshiba P21 - diyAudio
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Old 30th June 2012, 07:57 PM   #1
kaosun is offline kaosun  United States
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Default Laser diode replcement in Toshiba P21

One friend sent me a Toshiba XR-P21 for repair.
It’s an vintage portable cd player made around 1988, comes with a power supply base and looks cute. However, it has no response when it is plugged in and pressed play. It’s a challenge for me because the famous three models of XR series, including P20, P21, and P22, none of them is easy to handle. Therefore, I recorded the progress with cellphone to show you how a cd player is repaired.
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Inspection: when play is pressed, no response, no laser beam, no mechanical movement, no display. Rotate the turntable, it patters.

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Open the cover, it looks intact and no evidence that it lacks anything. Maybe it just broken something.
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The whole circuit is divided into 2 boards. The upper one includes power supply, DAC/audio, and CPU/LCD. The lower one includes drivers, DSP, and RF amp.
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As usual, the caps of power supply must be replaced totally. It’s the area above two white sockets.
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After testing all the buttons, most of them cannot response exactly; therefore, they will be dissembled and cleared.

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As experience, the variable resistors used to determine the main parameters like TB, FB, TG , and FG are easy to get problem. For example, bad contact, resistor broken, poor lubrication. All should be replaced by brand new VRs.
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Click the image to open in full size.

Testing the original laser head.
Both RF waveform of the real cd and CDR are 0.4Vp_p, far less than technical requirement:
Real CDs: 1.2Vp_p, CDR:0.8Vp_p.
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After testing, the laser head is sentenced aging.
Dissemble the laser head, check and clean inside, then replace its laser diode.
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Click the image to open in full size.

Replace the original laser diode by a brand new ROHM RLD78MD. It’s a 780nm red laser diode. Because it's used in MD play/recorder, it has more laser power (10mw) than CD laser diode (5mw). It means the diode can extend its life under less working current, it will work at lighter working load.
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After replacing the laser diode, the beam path changed. The precisely adjustment is necessary.
Readjust the photo diodes IC.
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Amplify the surface of the photo diode IC and display it on the wall by projector by using specific microscope. The laser spot fails to locate in the middle of the PD IC.
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Adjust the PD IC in order to guarantee the precise laser location, reassemble all and test.
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Awesome!
The RF waveform of CDR reaches to 1Vp_p! Decrease the laser power immediately to 0.8Vp_p.
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A pretty young lady, 23 yrs old, naked.
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Young lady comes back to life again!
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Last edited by kaosun; 30th June 2012 at 08:52 PM.
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Old 9th July 2012, 01:02 PM   #2
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This is pretty cool. Now add a S/P DIF output (or maybe it already has one), and listen how it "sounds"....
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Old 9th July 2012, 05:20 PM   #3
Mooly is offline Mooly  United Kingdom
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Excellent work and it just goes to show what you can achieve when you set your mind to it.

Well done
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