Sansui SR-929 strobe light constant

[dksp]

Hi all.

I had my Sansui SR-929 turntable in storage for almost 3 years, and when I set it up again, about a month ago, everything was working fine. No problem at all. Great.

Not this morning… today I noticed that the strobe was not working correctly anymore. I still lit up, but the blocks were not showing anymore. The speed of the platter was spot on though, no problem there. I tried all the buttons (33, 45, quartz lock, power on/off), but no change.

After a while, at the end of side B, when turning the turntable off, I noticed that the strobe was working again, perfectly stable.
But this noon, it was defective again (the turntable was off all morning).

I assume the light is not "strobing" anymore, but putting out constant light due to a fault in the control circuit, a faulty transistor (TR13 or TR19) or an IC maybe.

Do you know where to look?

 

[Vintagear]

Hi all.

I had my Sansui SR-929 turntable in storage for almost 3 years, and when I set it up again, about a month ago, everything was working fine. No problem at all. Great.

Not this morning… today I noticed that the strobe was not working correctly anymore. I still lit up, but the blocks were not showing anymore. The speed of the platter was spot on though, no problem there. I tried all the buttons (33, 45, quartz lock, power on/off), but no change.

After a while, at the end of side B, when turning the turntable off, I noticed that the strobe was working again, perfectly stable.
But this noon, it was defective again (the turntable was off all morning).

I assume the light is not "strobing" anymore, but putting out constant light due to a fault in the control circuit, a faulty transistor (TR13 or TR19) or an IC maybe.

Do you know where to look?


View attachment 3692693

I had one with the same issue. I would first check the two electrolytic capacitors on the S-0008 PLL circuit board. I suspect one of those small capacitors is out of spec. That solved my issue.

 

[dksp]

I have a test record with a 3150 Hz tone that I use with an app on my phone.

Test record used: https://en.elipson.com/product-page/vinyle-de-reglage
App used: Spectroid - Apps on Google Play

And to my ears, it sounded completely normal too.

 

[Vintagear]

I have a test record with a 3150 Hz tone that I use with an app on my phone.

Test record used: https://en.elipson.com/product-page/vinyle-de-reglage
App used: Spectroid - Apps on Google Play

And to my ears, it sounded completely normal too.

OK, replace the two electrolytics on S-0008 and you should be fine. Below is an image of mine before the fix. You can see the speed on the KAB SpeedStrobe is perfect but blurry in the platter block window like yours. I did this a few years ago and it's been perfect since then. Of course, it may be another component in that path but the small electrolytic caps on that board are the primary suspects.

Let me know if you have any questions on taking it apart. I've worked on a few of these.

 

[dksp]

Great thank you!

I will try that, but it wiIl take some time though. I want to get all the needed caps before opening the turntable. It seems a bit difficult to get to the boards, as you need to take the tonearm off.


EDIT:
I think I will get both the TR13 and TR19 transistors too. You never know.
TR19 is on the S-0009 board.

 

[Vintagear]

Great thank you!

I will try that, but it wiIl take some time though. I want to get all the needed caps before opening the turntable. It seems a bit difficult to get to the boards, as you need to take the tonearm off.


EDIT:
I think I will get both the TR13 and TR19 transistors too. You never know.
TR19 is on the S-0009 board.

View attachment 3692821

View attachment 3692822

Yes, the tonearm must be removed. Care must be taken when desoldering and resoldering the fine tonearm leads to the RCA plate but otherwise not that hard to do. Then remove the three large bolts that connect to the bezel. There are also several screws that secure the resin base to the plinth (feet must be removed because there are some under the feet). Take note where they are pulled from because some are short and some are long. You don't want to use the long ones where the short belong when putting it back together otherwise you may screw into the top of the plinth and damage the finish.

You can go ahead and order the transistors to be safe but I would not replace them unless necessary. I'm fairly confident the issue will be one of the electrolytics on that board. Replace them and check to see if it solved the issue before proceeding. If you are planning on recapping all the boards while you're in there, I would suggest to first repair the issue before replacing any additional parts.

Good luck.

 

[Vintagear]

@dksp one more point, if I recall correctly the values of the electrolytic capacitors for S-0008 in the service manual may not be correct. Both are listed as 4.7uF but I believe one of them was 47uF (you should order one or two just in case). Replace the caps with the same value that is in there, not what the SM says, sometimes there are errors.

 

[dksp]

Thank you!