Technics SL-P770 CD Player Not Reading Discs

[SuperMaryo]

Hello,

First, excuse my English.
I just noticed this thread. My approach would be like this, been there (anti-electrostatic discharges measures taken into account):

1.clean lens with diluted isopropyl alcohol or glasses napkins and blow quality (no residue) canned compressed air below it (from some distance);
2.clean and re-lube with siliconic grease the guide for the laser head (the little stainless steel rod);
2'.clean the linear potentiometer inside the mechanism;
2''.one drop of light oil for the turntable motor will not hurt;
3.replace electrolytics in the servo stage (mostly top right in your photo);
4.replace electrolytics in power supply stage of the servo stage (middle/middle right);
5.check and eventually re-do adjustments exactly as in service manual using an analog oscilloscope (or a, probably, USD 2500 digital one) and a frequency counter; schematic of that 'servo gain adjuster' is available, I'll look for it, if interested; also, you'll need a tool for mechanical adj., I don't know its name in English, I'll post a photo if someone else doesn't chime in;
6.measure power output of the laser diode thru the lens with specialized device and eventually... replace it; once decided to replace it and found the replacement, you can start fiddling with the infamous potentiometer and start over from point 5.

After each step check functionality, maybe is not necessary to go any further. Use good quality CD pressings (big record houses from late 80s to early 2000s) for testing. Do not expect playabillity of CD-Rs, although not impossible.
If your player can do the revers search (using that dial) flawlessly than you can consider that you did a great job.

Best regards, good luck,
Cosmin

Cosmin, thank you very much for your time and suggestions. Please see my other reply to the thread where I added some information in RED.

 

[Iomis]

Hello,

I must iterate that I'm just a hobbyst and the list I put together is about what I would (should?) do after my experience with my own P770 and never completed (the list) because I don't have an analog oscilloscope. Cannot decide which one to buy as it will be used just a few hours and then... My Tek TDS320 shows something that resemble an eye pattern... But I have the luxury of owning a new old stock laser ass'y.
My conclusion is that it is a must to have a nice, wide, as clean as possible, correct eye-pattern of the RF signal and after that, move to the next adjustments.

At point 2'., yes, that's the one.
3. Main board. Personally, I replaced all of them in the CDplayer, except for the 'deluxe' ones (Elna, Nichicon) but I have the replacements ready for attack (I don't want to admit an extremelly possible failure of those; they're in the audio analog stage and its psu so their approach can wait until the servo-mech part is done).
5. Took a while to find it... Check service manual of SL-P210. For that opamp I used a cheap RC4558 from T.I., didn't bother with those diodes once I realized that without visualising a clean RF signal there's nothing I can do.

Once again, consider my approach with a grain of salt. It's based on my limited experience gained on my own devices, my own builts and experiments. But mostly thanks to the members of different forums willing to share their steps along personal journeys. I really hope a professional will amend my thoughts.

Best regards.

 

[SuperMaryo]

Hello,

I must iterate that I'm just a hobbyst and the list I put together is about what I would (should?) do after my experience with my own P770 and never completed (the list) because I don't have an analog oscilloscope. Cannot decide which one to buy as it will be used just a few hours and then... My Tek TDS320 shows something that resemble an eye pattern... But I have the luxury of owning a new old stock laser ass'y.
My conclusion is that it is a must to have a nice, wide, as clean as possible, correct eye-pattern of the RF signal and after that, move to the next adjustments.

At point 2'., yes, that's the one.
3. Main board. Personally, I replaced all of them in the CDplayer, except for the 'deluxe' ones (Elna, Nichicon) but I have the replacements ready for attack (I don't want to admit an extremelly possible failure of those; they're in the audio analog stage and its psu so their approach can wait until the servo-mech part is done).
5. Took a while to find it... Check service manual of SL-P210. For that opamp I used a cheap RC4558 from T.I., didn't bother with those diodes once I realized that without visualising a clean RF signal there's nothing I can do.

Once again, consider my approach with a grain of salt. It's based on my limited experience gained on my own devices, my own builts and experiments. But mostly thanks to the members of different forums willing to share their steps along personal journeys. I really hope a professional will amend my thoughts.

Best regards.

Thanks again for your help, especially with the diagram for that servo gain adjuster. I still think there is something wrong with my CD player that needs "fixing" (replacing) more so than tuning those optical adjusters. I'll have to go through the board diagrams and see if there are any specific capacitors that are associated with the optical portion and try replacing more of those first and get a TOC before I go trying to make it perfect.