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Speed Issue - Sansui SR-838; Help?

plresults

plresults

Active Member
My trusty & beloved SR-838 appears to have developed a speed issue. It seems to slow down about every three seconds before recovering. I have tried moving the fine pitch control to address, but the problem persists. Has someone here encountered this and the protocols & triage for fixing for it? Thanks for any & all help!
 
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Others will recommend deoxit on the pots, and maybe on trim-pots on the circuit board. That may fix it — but requires disassembly, some skill, and the issue of getting the pots back to the right spot.

Others may suggest renewing all the electrolytic caps... and there're lots of them and lots of work.

But this fixed my 838 fast and easy. 5 minutes. Speed was all over the place, speeding up/slowing down, worse than yours. It had been in storage in a garage, and I found two dead bugs on the chopper wheel. I removed them, gave them a decent burial — and speed was perfect.

__57_28429.JPG

Pic shows motor in center, with 3 big screws holding it to the plinth. There are two very small screws at 3 and 9 o'clock — they release the motor cover, and reveal the "chopper wheel" inside. I can't find a pic of it — it's a thin metal disc with 100s of very fine slits. An optical sensor passing through the slits as they spin, determines correct speed.

Use a fine fiber brush, or compressed air, to clean dust (or bugs) off. The slits are fragile. There's no need to remove the motor.

I'd try it first. It's very quick,and easy — 5 minutes — if it's your problem. The linked AK thread gives more info. Study it.

It's a great table, and the tonearm is too. It's hard to better with a new one, without spending serious money. And if the black lacquer paint and dustcover are in good shape, it's stylish and beautiful.

https://audiokarma.org/forums/index.php?threads/sr-929-and-sr-838-turntable-speed-problem.362903/
 
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Thank you bimasta! I will try this approach. This table has been my 50% daily driver (along with an XR-Q7) for the past 11-12 years. It is in great cosmetic shape, as is the dust cover - though I don't use it at all (for either table). I'll report back here in a day or three. Again, thanks!
 
SR-838 tone wheel.jpg

That crap on the tone ring is enough to give the 838 a serious hitch in its giddy-up. Different from the speed problem you mention but you gotta check this, too.

See the ring of slots? See the crap at 11:00 that is going to be interfering with the pulse generation? That stuff has to go.
 
Blue Shadow said:
View attachment 1781513

That crap on the tone ring is enough to give the 838 a serious hitch in its giddy-up. Different from the speed problem you mention but you gotta check this, too.

See the ring of slots? See the crap at 11:00 that is going to be interfering with the pulse generation? That stuff has to go.
Click to expand...
plresults said:
Thank you bimasta! I will try this approach. This table has been my 50% daily driver (along with an XR-Q7) for the past 11-12 years. It is in great cosmetic shape, as is the dust cover - though I don't use it at all (for either table). I'll report back here in a day or three. Again, thanks!
Click to expand...
Bimasts and Blue Shadow: I opened her up per Bimasta approach, and she was as clean as factory new. Not even dust, which surprised me, as our house is a bit dusty. Further, I don't use the cover for this or my other turntable. I did the air clean approach for the slotted wheel, then cleaned and lubed the fine speed control pot, twisting it between applications of spray. I am listening to The London Philharmonic + The Who do 'Tommy', and she sounds like a champ. So weird. I didn't see any dust, dirt, bugs or demons in there. Thank you again for your help!
 
The smallest piece of interference to an electrical signal, dirt, dust, smoke or whatever is one million times larger than an electron so just cause we can't see it doesn't mean it isn't there causing trouble. Might have been dust by the sensor which we wouldn't see either. Bottom line glad this table is back on service. Don't forget to run all you controls full range a few times and reconnect everything to keep those parts clean and sounding their best.

Enjoy that table.
 
Blue Shadow said:
The smallest piece of interference to an electrical signal, dirt, dust, smoke or whatever is one million times larger than an electron so just cause we can't see it doesn't mean it isn't there causing trouble. Might have been dust by the sensor which we wouldn't see either. Bottom line glad this table is back on service. Don't forget to run all you controls full range a few times and reconnect everything to keep those parts clean and sounding their best.

Enjoy that table.
Click to expand...
Interesting 'new' problem - or one I never noticed before: I'm getting a hum via the speakers for the turntable that increases with increasing the volume pot. Seems like it must be the ground wire, as the hum disappears for the other input modes ie tuner, aux (CD) etc...How does one resolve a ground issue on a (Sansui) turntable? Thanks!
 
If this hum is when playing a record but not when the tonearm is not playing the record and both times you have phono selected that is feedback. If the hum is even when the nail is not in the groove, you have a bad ground. Verify that the outer ring connection on both RCA plugs reach the cartridge (Green for right and Blue for left channel) and that the ground wire goes from the table to the amp ground.
 
Blue Shadow: Thank you, I will try these fixes this evening. I believe my TT ground goes to the preamp, not the amp. Fairly sure I would have to cut, extend and patch the ground wire from the TT to make it reach amp. Hum varies with volume pot irrespective of needle in groove
 
bimasta said:
Others will recommend deoxit on the pots, and maybe on trim-pots on the circuit board. That may fix it — but requires disassembly, some skill, and the issue of getting the pots back to the right spot.

Others may suggest renewing all the electrolytic caps... and there're lots of them and lots of work.

But this fixed my 838 fast and easy. 5 minutes. Speed was all over the place, speeding up/slowing down, worse than yours. It had been in storage in a garage, and I found two dead bugs on the chopper wheel. I removed them, gave them a decent burial — and speed was perfect.

View attachment 1781266

Pic shows motor in center, with 3 big screws holding it to the plinth. There are two very small screws at 3 and 9 o'clock — they release the motor cover, and reveal the "chopper wheel" inside. I can't find a pic of it — it's a thin metal disc with 100s of very fine slits. An optical sensor passing through the slits as they spin, determines correct speed.

Use a fine fiber brush, or compressed air, to clean dust (or bugs) off. The slits are fragile. There's no need to remove the motor.

I'd try it first. It's very quick,and easy — 5 minutes — if it's your problem. The linked AK thread gives more info. Study it.

It's a great table, and the tonearm is too. It's hard to better with a new one, without spending serious money. And if the black lacquer paint and dustcover are in good shape, it's stylish and beautiful.

https://audiokarma.org/forums/index.php?threads/sr-929-and-sr-838-turntable-speed-problem.362903/
Click to expand...
I just recently bought an 838 for $100 with the speed issue. The owner was upfront about it and I couldn't resist the cheap price ( it would also look great with my AU 999 ). I've been reading the thread and figured it's probably just dirt on the "chopper wheel". I open her up and discover that the disc with the million slits is partially raised in one spot- I guess someone tried to unsuccessfully remove it :( Could this be the cause of the problem? Any ideas how to flatten this thing without adding more damage? Any constructive input is appreciated. Thanks!
 
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Such an AWESOME community. Followed the suggested plate removal and delicate cleaning of the optical wheel (which did, in fact, have some debris on it) and now the speed is solid and smooth as ever. THANKS SO MUCH!

Peace
 
Blue Shadow said:
View attachment 1781513

That crap on the tone ring is enough to give the 838 a serious hitch in its giddy-up. Different from the speed problem you mention but you gotta check this, too.

See the ring of slots? See the crap at 11:00 that is going to be interfering with the pulse generation? That stuff has to go.
Click to expand...
This is great advice!!! Fixed my SR 838 in minutes. I just bought it, with the servo lock issue. It was pulsing to a faster speed every couple seconds. No issue now. Thank you!!
 
This thread mentions cleaning the chopper wheel, which I've done. What about the optical sensor itself? Should I just hit it with compressed air or is there a better way to clean it? (Still getting speed problems after cleaning....eventually it will lock it, but I usually have to keep hitting switches back and forth until it does.)
 
kbuch8586 said:
This thread mentions cleaning the chopper wheel, which I've done. What about the optical sensor itself? Should I just hit it with compressed air or is there a better way to clean it? (Still getting speed problems after cleaning....eventually it will lock it, but I usually have to keep hitting switches back and forth until it does.)
Click to expand...

IME the symptom you describe points to the PLL Servo. I would replace the 3 electrolytic capacitors on PLL Servo board S-0014. See post #4 in the below thread where I suggested same to @petesui who was having similar issues and he tracked the issue to a loose connection on one of those caps.
Vintagear

Post in thread 'Sansui SR-838 - An Atypical Speed Issue'

petesui said:
Thank you, @Vintagear. You and this table have taught me a lot. Fully adjusted and spinning perfectly, whether Quartz-Servo or Pitch-Control, for the first time since it arrived eight months ago, and sounding really good.
View attachment 3642350View attachment 3642351
Click to expand...

That's fantastic!! Wow eight months, I'm glad I saw your post and was able to help you finally resolve the issues. Good thing you didn't give up on the 838, it's an excellent deck. I've benefited a lot from the collective technical knowledge base here on AK and am happy to give back.

Enjoy your 838.
  • Like
 
I posted this question in another post, but the last response was from a few years ago, so will try this one

I'm planning to recap very soon due to speed issues with quartz lock. Can you tell me how to go about removing the boards during the recap? After unscrewing them is there enough slack in the lines to just flip them over and work on them with everything connected?

Also, for the motor control board. Can those white plastic connectors with the gold pins just be unplugged? (Sorry, I've done a few recaps before but just not familiar with the terminology) Thanks!
 
Ok. New update. Received the parts yesterday and spent some time very carefully putting them in. It was about 1:30am when I finished, but I was able to plug it in and test and it already looks like it's better...the speed is steady and not jumping. 45 rpm looks steady but too fast ..I'll need to hook the oscilloscope up to calibrate. Thanks everyone!

Side question, and maybe I'll try a different thread on this one...all the plastic feet are good, but the upper rubber part inside the spring is brittle and crumbling everywhere. I'm thinking I should remove the upper cracked part and shove magic eraser material in the springs to dampen. What do you think?
 
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