Polyester Film Capacitor

Thread Starter

spike1947

Joined Feb 4, 2016
405
Hi Guys

Can anyone id the Cap in the picture, I took it that it was Polyester Film Capacitor 333uf, but I don't seem to be able to find a cap of that type in that value ! .

Spike
 

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MisterBill2

Joined Jan 23, 2018
12,704
AC rated capacitors are less common, but they should be available from the larger distributors. That triangular figure is a brand trademark of a fairly common brand, but I do not recall which.
 

Thread Starter

spike1947

Joined Feb 4, 2016
405
Is there another type of Cap I can use instead of this one , difficult to get that value and type and pitch ?.
 

MisterBill2

Joined Jan 23, 2018
12,704
First, the voltage rating is MAX working, so a 400 or 600 volt cap will be just fine, a bit bigger and cost more but that is OK most of the tie. The AC voltage part is a bit bothersome, so I ask what part of the circuit is it in? And now for the question not asked yet: Are you planning on replacing that part? Or duplicating the circuit? Do you think that it has failed? Or what?? The best choice for a cpacitor type depends quite a bit on the application.
 

Thread Starter

spike1947

Joined Feb 4, 2016
405
First, the voltage rating is MAX working, so a 400 or 600 volt cap will be just fine, a bit bigger and cost more but that is OK most of the tie. The AC voltage part is a bit bothersome, so I ask what part of the circuit is it in? And now for the question not asked yet: Are you planning on replacing that part? Or duplicating the circuit? Do you think that it has failed? Or what?? The best choice for a cpacitor type depends quite a bit on the application.
Hi
Thanks for your reply, it is off a Sony PS11 Turntable, the platter would not self start , just give it a nudge and it will run ok , so I thought it might be a Cap problem , so I took out the 3 large Caps on the board, 2x Electrolyte and 1x Polyester !( as in the picture posted) the 2xElectrolyte tested ok, but the 1x Polyester did not !,( tested the same as a Electrolyte Cap ! ).

Cheers
Spike
 

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MisterBill2

Joined Jan 23, 2018
12,704
A low value capacitor would not be tested the same as electrolytic capacitors, it it were, the results would be totally different. The value is far different and the type is totally different.
What I think I see is that the label on the board calls that capacitor "CP1", an encapsulated component, and elsewhere as a mylar capacitor. And it is connected across the power switch, explaining the AC rating.
No matter if a capacitor in that position was open or shorted or leaky, the running would not be affected by it. So probably that capacitor is OK, and the problem is elsewhere. So since the motor runs when given a push start, check the power supply voltages, since the symptom is not quite enough torque. It may also be that the power switch has failed. The manual gives a lot of assistance and so reading it is a good start.
Randomly checking components is a terribly inefficient way to do trouble shooting and seldom produces results in the first few hundred checks.
Since the turn table drive motor runs it is reasonable that most of the parts are OK, and that ALL of the critical parts are at least close to OK. So then you need to consider what it does not do, which is start by itself. That points towards either a weak starting circuit or else just not quite enough torque. It might even be from poor lubrication in a bearing causing excessive drag.
 
Last edited:

Thread Starter

spike1947

Joined Feb 4, 2016
405
A low value capacitor would not be tested the same as electrolytic capacitors, it it were, the results would be totally different. The value is far different and the type is totally different.
What I think I see is that the label on the board calls that capacitor "CP1", an encapsulated component, and elsewhere as a mylar capacitor. And it is connected across the power switch, explaining the AC rating.
No matter if a capacitor in that position was open or shorted or leaky, the running would not be affected by it. So probably that capacitor is OK, and the problem is elsewhere. So since the motor runs when given a push start, check the power supply voltages, since the symptom is not quite enough torque. It may also be that the power switch has failed. The manual gives a lot of assistance and so reading it is a good start.
Randomly checking components is a terribly inefficient way to do trouble shooting and seldom produces results in the first few hundred checks.
Since the turn table drive motor runs it is reasonable that most of the parts are OK, and that ALL of the critical parts are at least close to OK. So then you need to consider what it does not do, which is start by itself. That points towards either a weak starting circuit or else just not quite enough torque. It might even be from poor lubrication in a bearing causing excessive drag.
Hi
Thanks for your reply, that explains a lot , not very good at reading this particular drawing , can you tell me where on the drawing is the starting circuit located ! .
cheers
Spike
 

Ian0

Joined Aug 7, 2020
5,889
Does it connect to a 230V AC motor?
If so, it's the "motor run" cap for a small synchronous or induction motor.
Use a Class-X capacitor - they are all rated at either 275V AC or 305V AC and are designed to connect to the mains.
Available in most values from 1nF up to 1uF.
 

MisterBill2

Joined Jan 23, 2018
12,704
If you read the specifications it is an AC tachometer feedback speed servo motor. That is also clear from the circuit drawing.
Pages 3 and 4 describe the operation. What I see is a set of four adjustments, two gain setting and two offset setting. There is only one setting for each of the four that will provide proper operation, I think adjusting them is covered in the calibration section of the service manual.
 

Ian0

Joined Aug 7, 2020
5,889
Yes - found it - that part of the circuit is on page 13, but the cap is labelled as 1nF not 33nF. It's across the mains, so a class-X cap is the right one for the job. Presumably, they decided it needed to be bigger!
 

MisterBill2

Joined Jan 23, 2018
12,704
There are at least 2 versions of the player, but becuse it is across a switch it is really not a critical part. Either value could be fine, but I doubt that there is anything wrong with it, since it's test results will be vastly different from electrolytic capacitor results.
And the turntable running as you can see on that earlier block diagram, depends on the four adjustments. And now I am thinking that it may also depend on the speed pickup gain setting. That may be what changed. But you really should check the various supply voltages.
 

Ian0

Joined Aug 7, 2020
5,889
Agreed about the capacitor. It will still work without it.
Is there power to BOTH windings on the motor? It's a synchronous motor, so it will run on one winding once it has started.
 

MisterBill2

Joined Jan 23, 2018
12,704
Agreed about the capacitor. It will still work without it.
Is there power to BOTH windings on the motor? It's a synchronous motor, so it will run on one winding once it has started.
NO, it is not just a synchronous motor, it is an AC servomotor driven by the electronics portion of the system. LOOK AT THE CIRCUIT!! The motor is driven by the transistors fed by the DC power supply. AND read the description in that service manual. Reading is important, without reading it is very hard to know very much!!
 

Ian0

Joined Aug 7, 2020
5,889
It's an AC motor. It has no brushgear. That means it is either a synchronous motor or an induction motor. Its rotor is a permanent magnet. That means that it a SYNCHRONOUS motor. (One wouldn't use an induction motor in a speed-critical application because of the slip.
The AC signal comes from an oscillator controlled by a hall-effect position sensor - exactly the circuit used when driving a SYNCHRONOUS motor from a DC supply.
The speed is proportional to the frequency of the AC supply - so it's a SYNCHRONOUS motor.
It needs two windings with 90 degrees phase shift between the driving signals to be able to control both speed and direction, but once it has started rotating its inertia will keep it going if there is only power to one of the windings.
 
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