Technics SL-P770 CD Player Not Reading Discs

[SuperMaryo]

Hi - I got a Technics SL-P770 CD Player from ebay "powers on otherwise untested" which of course meant it wasn't working. So, it does power on an all the display lights come on as they are supposed to. It will power on and load a disc, but it will either not spin, or it will sometimes spin and then slowly come to a stop. I replaced the spindle motor with an identical one, but it has the same problem. I measured the voltage to the spindle (connector with two white wires almost dead center of the board), and it usually starts up around 1.3v and slowly goes to zero. I'm really not sure what to check next. Some research makes it seem as if some of the capacitors could be bad - I found a Japanese YouTube video with a similar issue where he replaced a bunch of capacitors, but he didn't really show which ones he replaced, but it looked like most of the smallish red ones on the bottom half of the board. If anyone could provide any next steps or ideas, I would be really grateful. Thanks in advance!

 

[drp1003]

Does it load a CD? Does the machine spin a CD right away after the tray closes? Does it read a CD? Then after it reads the CD, does the display light up with the number of tracks that are on the CD like it's ready to play?

 

[drp1003]

If it is trying to read a CD by spinning a CD but it fails to read a CD, then it's possible that the LASER is dying.

 

[drp1003]

If it is not reading a CD then do this next:

Take a close-up photo of the six adjustment pots on the main board - the six yellow things kinda grouped together with the phillips head screw tops.

Now, look up in the service manual which two are the two for LASER FOCUS and LASER POWER, or whatever they are called in the service manual Usually there are two of them.

You can adjust them a little bit at a time to see if anything changes and hopefully a CD will get read. Every time you make a small adjustment, try to load a CD to see if it will work.

If this does not work, then you can alway turn the adjusters back to their original locations by using the photo that you took. BE CAREFUL AND TRY NOT TO TURN THEM VERY FAR.

 

[SuperMaryo]

Hi, thanks for the quick responses. The first problem is that it doesn't always even spin the CD, and when it does, it doesn't seem like it's spinning as fast as it should. It loads it, and sometimes it will spin it, sometimes it will not, and if you manually try to spin it with your fingers, it will sometimes spin slowly then slowly stop. That's why I assume it was either the spindle motor or a problem with the voltage to the spindle, and being that the spindle says it should be ~6v and it was only reading a max of about 1.3v initially, it likely had to do with voltage issues, or bad capacitors, a voltage regulator or ??

 

[drp1003]

Check polarized electrolytic capacitors C15,C16,C17,C18,C19,C20. Those are the ones that seem to be part of the power supply that are related to the DC spindle motor.

 

[SuperMaryo]

I see the ones you are referring to. I'll check and replace them and report back. I think I have replacements for these already. Thanks!! Fingers crossed.

 

[drp1003]

I think I remember watching a YouTube video of a CD repair, and the culprit ended up being bad solder joints on a transistor. Check the solder joints on Q351/352/353.

And Q12 and IC11 and Q15

 

[SuperMaryo]

I don't have replacement caps in my parts, so I ordered new ones from Mouser. Again, I'll keep you posted, thanks for the advice.

 

[SuperMaryo]

So, I replaced C15,C16,C17,C18,C19,C20. 2 of the 47uF were only reading about 25uF, so I was hoping that would do the trick, but unfortunately not. There has been an improvement where the CD is spinning faster and you can hear and see the laser diode moving and searching and trying to read the disc, but it's still not reading. I checked the solder joints when I was replacing those caps and still nothing. The voltage to the spindle seems to go up and down from about 1.0 to 2.0 v as it's searching for tracks. There is a youtube video in Japanese that I obviously can't read where he replaced all 18 of the maroon colored Caps such as C818, C814, C802, C808, etc. (All in that corner of the board.) I'm not sure if those Caps are typically problematic or not, but any other ideas on this?

 

[KeithD]

The SL-P770 has the SOAD60A CD mechanism. I don't know if the spindle motor board is the same as the SOALP1200 found in the previous generation of Technics players (x20 series and the 1200). But if it is, a common problem with the SOALP1200 is two capacitors on the motor board go bad. I've shown these in the yellow oval on the picture below. I think it's mostly the 1 µF cap that goes bad, but people tend to replace both. I have an SL-P120 that was slow to spin up, and replacing those two caps solved the issue.

 

[SuperMaryo]

Mine does not have that board or SMCs under the CD player/transport.

 

[SuperMaryo]

Ok, I hooked up my cheap-o oscilliscope and tried fiddling with the different settings but then just realized the turntable height one needed a resistor and capacitor "filter" so that looks off. First picture is "Best Eye (PD Balance) Adjustment TJ301+ and TJ302-. The ones with both channels are the Focus and Tracking Offset. None of these look anything like what the manual says, so I'm at a loss at this point. If anyone has any other suggestions, TIA. I can't get any discs to read.

 

[SuperMaryo]

Well if no one has any suggestions of what else to check or any capacitors that might need replacing other than the ones I already did, I guess this will go in the closet of the unrepairable for the foreseeable future. I was really hoping I could get this one back to life since it's a fairly higher-end player by Technics. I can't find any S0AD60A/SOAD60A lasers to buy anywhere and try and replace that, so I'm out of guesses on this and it's been sitting on my workbench too long.

 

[KeithD]

Sorry, I have no experience with the SL-Pxx0 line, just the x20 line and earlier. I agree this is a higher end player. You might search for information on others in this series such as the 990, 550, 350, or 250 as they likely use the same laser/mechanism. This was true throughout the x20 line.

 

[SuperMaryo]

From what I could find, the SL-P350, SL-P550, SL-P770, and SL-P990 all use the S0AD60A laser mechs, I just can't find any at a decent price. There's a 350 on ebay right now for almost $100 but I don't know if I really want to keep dumping money into this one. I'd almost rather pick up something like a Yamaha CD-S303 for $400 and be able to play USB Flac files on it and just call it a day. I just have a nostalgia for old Technics stuff. I have an SA-700 and SA-404 along side a recapped SL-220 turntable that sound wonderful.

 

[KeithD]

From what I could find, the SL-P350, SL-P550, SL-P770, and SL-P990 all use the S0AD60A laser mechs, I just can't find any at a decent price. There's a 350 on ebay right now for almost $100 but I don't know if I really want to keep dumping money into this one. I'd almost rather pick up something like a Yamaha CD-S303 for $400 and be able to play USB Flac files on it and just call it a day. I just have a nostalgia for old Technics stuff. I have an SA-700 and SA-404 along side a recapped SL-220 turntable that sound wonderful.

I was thinking more along the lines of search for repair videos or threads on other players in that series. Maybe someone as successfully solved your issue on a different player in the line. Maybe you've done this already, but seems strange there is nothing addressing the issue you are having on at least one player in that series. That's how I solved my issue with the 120, I found a video or thread for the same problem on a 320.

 

[Iomis]

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

 

[SuperMaryo]

I was thinking more along the lines of search for repair videos or threads on other players in that series. Maybe someone as successfully solved your issue on a different player in the line. Maybe you've done this already, but seems strange there is nothing addressing the issue you are having on at least one player in that series. That's how I solved my issue with the 120, I found a video or thread for the same problem on a 320.

I did look at every video and article I could find. I pride myself in finding information in hidden corners of the internet and the closest I found on this is a Japanese video on YouTube where he replaced a bunch of capacitors, but he didn't say why. I've found many other videos of the same line of CD players, but most of those are due to the spindle not spinning at all. I replaced the spindle motor with a new one and the caps that were recommended earlier in this thread. It's spinning nice and fast and the laser moves around but it just won't find the TOC. Iomis (Cosmin) just responded with more ideas, so maybe I'll get back to work on this one more time.

 

[SuperMaryo]

Cosmin, thank you very much for your time and suggestions. Here are some notes from your recommendations:

1.clean lens with diluted isopropyl alcohol or glasses napkins and blow quality (no residue) canned compressed air below it (from some distance);
I did this already, one of the first things I tried after getting the spindle spinning.
2.clean and re-lube with siliconic grease the guide for the laser head (the little stainless steel rod);
I did this as well, it is perfectly clean and smooth.
2'.clean the linear potentiometer inside the mechanism;
I'm not sure exactly what this is referring to - could you explain? Are you referring to the magnetic slide that moves the laser back and forth? If so, I did carefully clean that as well. It has tiny metal "fingers" that remind me of the clock switch in a VCR. Or is there another potentiometer somewhere inside the actual laser mechanism? And if so, just mark it, and clean it with DeoxitD5?
2''.one drop of light oil for the turntable motor will not hurt;
I replaced the turntable motor when it didn't spin initially, but replacing caps C15,C16,C17,C18,C19,C20 got the spindle moving well again.
3.replace electrolytics in the servo stage (mostly top right in your photo);
Are you referring to the capacitors to the right of the CD mech? (Not on the main board, correct?)
4.replace electrolytics in power supply stage of the servo stage (middle/middle right);
I did replace these, C15,C16,C17,C18,C19,C20. This is what got the spindle moving.
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;
If you have the schematic of the servo gain adjuster, PLEASE SHARE. I have not found any information about it anywhere and there are other threads where people are asking to find one of these to really dial in some of those Technics CD players.
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.
I have not been able to find a replacement for the SOAD60A/S0AD60A laser diode.

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.
I have been testing with good 1990s-era big record house CDs. So far, I've not been able to get anything to read.
If your player can do the revers search (using that dial) flawlessly than you can consider that you did a great job.
I have not been able to read a ToC yet, so if I can just get it to play at all, I'll consider that a great job.

Thanks again for your help!!