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Speed Issue - Sansui SR-838; Help?

Looks like the speed is still slipping every so often with quartz lock. It seems to happen towards the end of one side of a record. Just a bit, maybe 1 or 2 times per side. It's much better after I did the recap, but it still seems like there's something off.

(Side note, I decided to plug it directly into my amplifier, in the "unswitched" section, and the speed was jumping more often, with and without quartz lock. After I plugged it back into the wall, it fixed this issue. Now it only slightly jumps in quartz lock. So I should never plug this turntable into the back of an amplifier.)

I'm thinking this is my order of operations:
1) clean the VRs used with oscilliscope calibration with deoxit (I skipped this step during the recap)

2) while it's open, check the the soldering job on the PLL again to see if I messed anything up.

3) recalibrate using oscilliscope

4)once it's closed back up, clean the chopper wheel one more time to make sure dust or something didn't get on it while I was working on it.

What do you think about this plan? Right now it's just trial and error, but let me know if you think I should try something else.
 
kbuch8586 said:
Looks like the speed is still slipping every so often with quartz lock.
Click to expand...
Does the speed hold steady when you turn OFF the Quartz lock or is it unstable just like when Quartz Servo is ON?

1783605767679.png

Also, when you remove the feet, make sure you mark which one goes on each corner because they are three types and not all not the same.
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Hey, thanks for the reply. I basically did everything I outlined in the post above (after the recap). Checked 3 capacitors on PLL, cleaned VRs with deoxit, recalibrated with scope, then cleaned chopper wheel.

Looks like the speed still jumps and then stabilizes. It recovers very quickly, maybe 1 seconds. It happens a handful of times now when playing through a record.

This is happening with quartz lock AND without.

I'm out of ideas.

-Are there other electronic components that I need to check?

-Should I disconnect the switches and thoroughly clean? (This sounds like a lot of work!)
 
kbuch8586 said:
Hey, thanks for the reply. I basically did everything I outlined in the post above (after the recap). Checked 3 capacitors on PLL, cleaned VRs with deoxit, recalibrated with scope, then cleaned chopper wheel.

Looks like the speed still jumps and then stabilizes. It recovers very quickly, maybe 1 seconds. It happens a handful of times now when playing through a record.

This is happening with quartz lock AND without.

I'm out of ideas.

-Are there other electronic components that I need to check?

-Should I disconnect the switches and thoroughly clean? (This sounds like a lot of work!)
Click to expand...
Did you replace the trimmers? If not, that's your next step. Use Bourns.
 
I had some speed issues with my Yamaha YP-D71, and the culprit was a 2SC945 on the motor control board. I see there are several used in the SR-838, according to the service manual. Those are known for failing, so I would suggest to replace all, just in case.
 
Ok, I'll replace the trim pots first. Please let me know the model and how many I need to replace.

Affinity for Artefacts is where I got the capacitor kit. He suggests spraying cold spray on the transistors first to see if they act up...then I'll see where to go from there
 
That's how I found the faulty transistor on my Yamaha, alternating cold spray and a hair dryer, as the quartz lock was only acting up when warm. ;)
 
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Interesting. Did you pull the transistors out individually and test on multimeter or did you set up the turntable to run on a stand while you were spraying components on the boards from underneath?
 
I went out of town last weekend and when I came back, the turntable seemed fine....no speed issues for days! I thought the issue just resolved somehow...maybe some corrosion coming off one of the switches after I sprayed it?? But then yesterday it started jumping speeds again every few minutes. I just ordered some freeze spray. I really hope I can locate a faulty transistor by spraying on the motor control board. I'll report back with what I find. Thanks everyone for the help!
 
I'm done with my first round of freeze spray and I'm cautiously optimistic. By spraying, I was able to locate a capacitor that made the speed jump like crazy when I sprayed it. Touching the capacitor with a plastic screwdriver also made it jump like crazy. I removed solder and tested the capacitance and it seemed fine. I cleaned up the old solder and installed again. I did not get the same kind of speed jump when I retested with freeze spray and touching it. So I think it must have been a cold solder joint that was my fault when I was recapping....
 
Ooof, I spoke too soon! Too optimistic! I think what I found was a bad solder joint, glad I found it, but it didn't fix the problem. I'll try again with the freeze spray.
 
I didn't find anything after messing around with it this time. Sprayed everything...tapped everywhere. During testing, I'd say I can see/hear one speed fluctuation every 10-15 minutes of use.

So i think I'd like to replace the trim pots to see if that does anything. Can someone help me out and tell me which ones I should replace (all?) and a link to exactly what I need to replace them with?

I think Vintagear previously said to use Bourns. Which model is it?

-Also, at this point, when I add new trim pots, should I reflow all the connections???

Thanks!
 
kbuch8586 said:
I didn't find anything after messing around with it this time. Sprayed everything...tapped everywhere. During testing, I'd say I can see/hear one speed fluctuation every 10-15 minutes of use.

So i think I'd like to replace the trim pots to see if that does anything. Can someone help me out and tell me which ones I should replace (all?) and a link to exactly what I need to replace them with?

I think Vintagear previously said to use Bourns. Which model is it?

-Also, at this point, when I add new trim pots, should I reflow all the connections???

Thanks!
Click to expand...

Lucky I found my old spreadsheet. Below are the ones I used several years ago. Please confirm for yourself before ordering:

LocValueBourns Part#Digi-Key Part#
VR33 100k652-3296Y-1-104LF490-2914-ND
VR44 100k 652-3296Y-1-104LF490-2914-ND
VR71 330k 1/2w652-3296Y-1-504LF3296Y-504LF-ND
VR72 330k 1/2w652-3296Y-1-504LF3296Y-504LF-ND
VR73 22k 1/2w652-3296Y-1-223LF3362P-1-223LF-ND
 
Awesome! Thank you! The only difference I see is that the new variable resistors for vr71 and VR72 are 500kOhm instead of the original 330kOhm
 
kbuch8586 said:
Awesome! Thank you! The only difference I see is that the new variable resistors for vr71 and VR72 are 500kOhm instead of the original 330kOhm
Click to expand...

Yeah, that series does not have a 330K. 500K is the next best choice. It's a multi-turn so you'll have no trouble adjusting. You can try just replacing the speed adjustment trimmers (VR33 & VR45) first to see if that solves your issue.
 
Ok....5 new trim pots are installed and calibrated. Everything is up and running...but I think I caught the speed jumping every once in a while like it did before. (Just to reiterate the problem: turntable looses speed for half a second then recovers, but it seems random, 1 to 3 times per side of record...sometime not at all.) I will test it some more to confirm, but I'm going to assume replacing the trim pots did not fix the problem.

So now, what are my options? Please chime in if you have any ideas. I could reflow all the boards, starting with the motor control board? Or before that, should I go around and try to check the resistors and/or diodes? How about the ceramic capacitors?
 
kbuch8586 said:
Ok....5 new trim pots are installed and calibrated. Everything is up and running...but I think I caught the speed jumping every once in a while like it did before. (Just to reiterate the problem: turntable looses speed for half a second then recovers, but it seems random, 1 to 3 times per side of record...sometime not at all.) I will test it some more to confirm, but I'm going to assume replacing the trim pots did not fix the problem.

So now, what are my options? Please chime in if you have any ideas. I could reflow all the boards, starting with the motor control board? Or before that, should I go around and try to check the resistors and/or diodes? How about the ceramic capacitors?
Click to expand...
If you have replaced all capacitors and trimmers and the issue remains the same, I would carefully examine every solder joint you have not touched starting with the PLL board S-00014 and work from there.
 
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