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One friend from Head-fi 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.
Inspection: when play is pressed, no response, no laser beam, no mechanical movement, no display. Rotate the turntable, it patters.
Open the cover, it looks intact and no evidence that it lacks anything. Maybe it just broke something.
 
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.
As usual, the caps of power supply must be replaced totally. It’s the area above two white sockets.
After replacing all the caps and cleaning the each side of the power supply board, also lubricated the volume VR, it looks quite clean.
After testing all the buttons, most of them cannot response exactly; therefore, they will be dissembled and cleared.
As experience, the variable resistors used to determine the main parameters like TB, FB, TG , and FG are easy to get problems. For example, bad contact, resistor broken and poor lubrication. All should be replaced by brand new VRs.
Testing again, no response.
Check the power supply of the 54th pin of the CPU. It should be +3.8V coming from the DC-DC power supply circuit (Q803 Ba9700 core); however, 0V. The power supply of the BA9700, 0V as well. Then check the source of the BA9700, Q801 TL499. It’s another DC-DC step-up switching power generator, it raises both battery and power base voltage inside of BA9700 and BA9700 generates the power of CPU. Further inspection indicates that the power from the base has been sent to the Q801; however, the ground of the Q801 is disconnected from the base. The P21 controls the whole power supply by a power switch by cutting the ground line. Unfortunately, it has been corroded inside. After repairing the switch, it powers on.
 
It has been dissembled.
Mechanical module and laser head.
The main motor must be replaced. The turntable must be taken down from the original motor.
The model is Rf410, same with the notorious motor of SONY D303/35 only it has a longer spindle.
The spare motor is a RF410CH D/V4.0, a little different with the original D/V5.9. The figure of 4.0 and 5.9 stands for the working voltage. It means when the 4.0 motor is installed into the circuit designed for 5.9 motor, it will run faster. However, the rotation speed is under control of a closed loop. Because the speed of the linear velocity of the disc is precisely controlled at 1.3M/s, 210r-540r/m, the increase of the rotation will be detected and be offset by decrease the drive voltage of the main motor. So the replacement of the motor is possible. Actually, I tried replacing the RF410 D/V5.9 by another RF410 D/V2.0. Guess what? It works fine! It seems the control range of the motor is wide.
In order to extend its life, both the upper and lower bearings should be lubricated. So the small hole on the bottom of the motor is drilled to add oil. The drill bit is also showed in the pic.
Install the turntable to the new motor; determine the height of the table by inserting name cards. The height should be measured before taking it down. Because the spindle of the new motor is a little shorter than the original one, the glue is necessary to be added into the hole of the table.
Testing the original laser head. Both RF waveform of the commercial cd and CDR are 0.4Vp_p, far less than technical requirement: Commercial CDs: 1.2Vp_p, CDR:0.8Vp_p.
The RF waveform of reading topic of CDs.
After testing, the laser head is sentenced aged. Dissemble the laser head, check and clean inside, then replace its laser diode.
Replace the original laser diode by a brand new ROHM RLD78MD. It’s a 780nm red laser diode. Because it's used in MD player/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.
After replacing the laser diode, the beam path changed. The precisely adjustment is necessary. Readjust the photo diodes IC.
Zooming in the surface of the photo diode IC and display it on the wall by a DELL projector using specific microscope. The laser spot fails to locate at the middle of the PD IC.
Adjusting the PD IC in order to pinpoint the laser point location, re-assemble all and test.
Awesome! The RF waveform of CDR reaches to 1Vp_p! Decrease the laser power immediately to 0.8Vp_p.
Recheck and readjust all the VRs replaced just now.
A pretty young lady, 23 yrs old, naked.
Lubricate the main mechanical parts.
 
 
Stainless steel chassis, beautiful craftwork!
The difference of the laser VR between the original and the new one.
Young lady comes back to life again!
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Post time 2015-10-28 12:28:22
Post time 2015-10-28 17:17:43
Author
david-ease 
2015-11-13 06:46