Dear all,
Recently acquired a Sansui Sr525. It was spinning very fast and with high wow and flutter as measured by an Android app.
Did these and managed to bring the speed down to 43rpm on the 33rpm setting:
1. Replaced the fine pitch controls and VR1 and VR2 on the motor board.
2. Opened the microswitch and cleaned it as much as possible.
3. Replaced all electrolytics caps on the power and motor control boards.
It is the slowest speed I could get by putting the fine pitch control and the trim pots to the slowest setting.
I have since replaced the zener 5.1v and 2 ceramic caps near the dual transistor at the motor circuit, to no avail as well.
Any suggestions? Thank you very much!
Recently acquired a Sansui Sr525. It was spinning very fast and with high wow and flutter as measured by an Android app.
Did these and managed to bring the speed down to 43rpm on the 33rpm setting:
1. Replaced the fine pitch controls and VR1 and VR2 on the motor board.
2. Opened the microswitch and cleaned it as much as possible.
3. Replaced all electrolytics caps on the power and motor control boards.
It is the slowest speed I could get by putting the fine pitch control and the trim pots to the slowest setting.
I have since replaced the zener 5.1v and 2 ceramic caps near the dual transistor at the motor circuit, to no avail as well.
Any suggestions? Thank you very much!
Update :
I have checked the power supply output, they are outputting 17.5V and -4.7V (spec sheet shows 18V and -5V). I have also replaced Q008 and Q007, to no avail. The sensing coils NS 201 - 203 show continuity too.
I am thinking of replacing Q001 - 003 next.
I am thinking of replacing Q001 - 003 next.
You´re going about this the wrong way.
Read the adjustment part of the manual, and follow it precisely point for point.
Set the two fine adjustmet pots to center. On the bottom of the motor, you have two basic settings for 33/45.
Adjust the 45 setting first. Then the 33. Then check 45 again, and readjust if needed.
After that, check that you can adjust the 33/45 speeds to both a bit faster and a bit slower than the exact speed.
Replacing transistors out of the blue, is just a waste of money 😉
Read the adjustment part of the manual, and follow it precisely point for point.
Set the two fine adjustmet pots to center. On the bottom of the motor, you have two basic settings for 33/45.
Adjust the 45 setting first. Then the 33. Then check 45 again, and readjust if needed.
After that, check that you can adjust the 33/45 speeds to both a bit faster and a bit slower than the exact speed.
Replacing transistors out of the blue, is just a waste of money 😉
Hi, thanks for the reply.
Unfortunately this was the first thing I had tried. I had turned the 33 rpm VR all the way to the slowest, and with the fine control at the center, and it is 44rpm at the 33rpm setting. Similarly, I had turned the 45 rpm VR all the way to the slowest too, and getting 55 rpm at the 45 rpm setting.
Unfortunately this was the first thing I had tried. I had turned the 33 rpm VR all the way to the slowest, and with the fine control at the center, and it is 44rpm at the 33rpm setting. Similarly, I had turned the 45 rpm VR all the way to the slowest too, and getting 55 rpm at the 45 rpm setting.
OK....... Then you have eliminated faults in Q001 - Q006. Since the error is the same for both speeds, you need to look at and measure, what
lies before these.
Check the small electrolytics C018 - C017 - C016 etc. Check resistors going to "ground" in voltage dividers and feedback like R019 -
R023 - R021/C012 etc. How about zener diode ZD001?? Is the voltage correct across it??
Hope, I´ve given you some hints to NOT just replace trasistors, because it appears to be the easiest way. It very seldom is.
Also..... the right approach is measure, find the defect component and then replace it 😉
lies before these.
Check the small electrolytics C018 - C017 - C016 etc. Check resistors going to "ground" in voltage dividers and feedback like R019 -
R023 - R021/C012 etc. How about zener diode ZD001?? Is the voltage correct across it??
Hope, I´ve given you some hints to NOT just replace trasistors, because it appears to be the easiest way. It very seldom is.
Also..... the right approach is measure, find the defect component and then replace it 😉
Thanks boydk!
"Check resistors going to "ground" in voltage dividers and feedback like R019 -
R023 - R021/C012 etc."
So I should lift one leg, and check the resistance?
I have replaced ZD001 and replaced all electrolytic caps , but I shall check V on the zener again.
"Check resistors going to "ground" in voltage dividers and feedback like R019 -
R023 - R021/C012 etc."
So I should lift one leg, and check the resistance?
I have replaced ZD001 and replaced all electrolytic caps , but I shall check V on the zener again.
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Coming to think of it............
Maybe time to take the motor apart and check??
Let´s imagine, if the "lower end" of adjustment is common for both potentiometers and has a bad connection??
That could also be the reason, that you´re not able to adjust to low enough speed.
Just a thought.
Maybe time to take the motor apart and check??
Let´s imagine, if the "lower end" of adjustment is common for both potentiometers and has a bad connection??
That could also be the reason, that you´re not able to adjust to low enough speed.
Just a thought.
Thanks for the suggestion.
I did a quick check for the V across the zener, it is reading -4.95V. Is that the expected reading? The zener is speced at 5.1V. I connected the red probe to the anode and the black to the cathode.
Thank you!
I did a quick check for the V across the zener, it is reading -4.95V. Is that the expected reading? The zener is speced at 5.1V. I connected the red probe to the anode and the black to the cathode.
Thank you!
Update: R019 to R023 all showed correct values. R019 and R023 also confirmed connected to ground as per spec sheet.
I suppose so. If you read the datasheet for the specific diode (zener), you´ll probably realize, that the tolerances are bigger
than you would expect.
Example: I ordered a batch of 7815/7915 IC´s, and the 7915 were spot on around 15volt +/- very little, all the positive 7815
gave 14,36volt average........ all of them.
Which brings me back to my last suggestion..... The error could be around the 2 potentiometers inside the motor itself 😉
Hmm, I have changed the 2 pots in the motor. I have checked them again , as far as normal operation goes, they are operating normally. On 33rpm, the leftmost extreme is 42rpm, while the rightmost extreme is 60rpm.
I have sinking feeling that it might be the dual transistor at fault.. 🙁
I have sinking feeling that it might be the dual transistor at fault.. 🙁
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Then replace it....... You should be able to find one on the big WWW for around $10-15.
It´s "only" a 50volt transistor, so you should also be able to replace it with 2 easily available common transistors
like 2SC/KSC-945 or similar.
https://www.diystompboxes.com/smfforum/index.php?topic=103921.0
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BTW....... Those red digits on the 2SC1583-picture is wrong.
2SC1583 seen from the front, the pins are (from left....house up/pins down) 1-2-3-4-5
1 = base on TR1
2 = collector on TR1
3 = common emitter
4 = collector on TR2
5 = base on TR2
😉
2SC1583 seen from the front, the pins are (from left....house up/pins down) 1-2-3-4-5
1 = base on TR1
2 = collector on TR1
3 = common emitter
4 = collector on TR2
5 = base on TR2
😉
Another suggestion, as I did in post #7.
Changing potmeters doesn´t mean, that there still couldn´t be a problem. I made a small drawing (drawings are surely NOT my strong side) 🤣
to better explain, what I meant,
Hi Boydk, I am afraid I don't understand what you suggested here. So I should trace the path from VR33 and VR45 (rough tuning) on the motor circuit board, to the actual coil themselves? Or do you mean the path from the fine tuning VR101 and VR102 pots, to the VR33 and vr45 on the motor board?
Thank you for your time and suggestions!
It seems to me that the circuit works okay (adjustment), but it is off a bit in "one direction". So, what would set the reference voltage? The prime suspect is the Zener ZD001 XZ051. Now, if we expand that a bit, there are (many) other components that set the reference voltages at the bases of Q009, and the base of Q008.
The switch S 701a... you can temporarily bypass it with a piece of wire while testing. The switch can get dirty/oxidised contacts... and the only way to clean it is to pull it apart and polish the contacts.
In addition to that switch above, there are those two trimpots that you already replaced and the associated wiring (+, - 45, GY, COM, 33, GND)
Then if all looks good, I'd move to the parts I highlighted below:
You could take another suspect out of the equation (internal power supply), if you use a lab power supply adjusted for +18V DC, and -5V DC.
Thanks a lot @Extreme_Boky !
I checked the switch when it's closed, it reads 0.2ohm, that means the switch is alright, doesn't it?
GY and the anodes of the 3 diodes shows continuity, although I admit I have no idea how to check if the diodes are actually connected to the coils.
I checked the switch when it's closed, it reads 0.2ohm, that means the switch is alright, doesn't it?
GY and the anodes of the 3 diodes shows continuity, although I admit I have no idea how to check if the diodes are actually connected to the coils.
That would be a good idea....... and please disregard my last comments. I confused myself on the vr33 & vr45, sorry.
@Extreme_Boky has good suggestions, although I think, you have already tried most of it.
Stupid me, that I forgot about the 33/45 switch (having recently dealt with a defective switch on a Technics DD) 🤣 .
You write: "I checked the switch when it's closed, it reads 0.2ohm, that means the switch is alright, doesn't it?"
Maybe, maybe not. Depends on the accuracy of your DVM and the current draw in the circuit.. Before you bother to take
it apart, you could play piano on the switch (S701A) like 50-100 times. If the speed results changes just a little bit, the switch
is probably failing. If the rotation is exactly exactly the same, no matter how many times you massage the switch, the fault
probably lies elsewhere. The 3 x R018 and R031 might be worth checking also.
This seems to have been a difficult "bugger" to localize..... Will be really interrested in hearing, when you finally get it solved 👍
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