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Identify the capacitor type

Thread starter #1
Hi. Need some help here. Can someone give me the full/exact description of the 2 blue capacitor above the 10W 0.1 ohms resistor ? I believe I need to replace both of them and I need the exact description to tell the electronic store. I am quite a newbie in electronics. Thanks



Well-Known Member
An Older Type of Capacitor. "OIL FILLED".
Might be Quite Difficult to find these types now.
Rated: .05uF, 1200 VDC.

What makes you think they need replacing?
Thread starter #3
One of them has a bulging end. The 1Hp DC motor runs erratically. the speed rpm goes up and down and sometimes it run to its maximum of 1800 rpm and you cannot control the speed . Attached is a close up of the capacitor in question. If these oil filled capacitors are hard to find, what is the best solution in replacing them. maybe you can help me out. Thank you


Thread starter #6
Thanks for the advice, Mr.Goodwin. In case it is faulty, I've learned that these type of capacitors are quite rare. what can i use to replace it with? Do you think I can replace it with this " Mouser #:
5989-MMWA10S47K-F .
Thread starter #8
could anyone suggest me a DC controller sold in aliexpress or any other site that has these features. The important feature is it can be used on a 4 wire DC motor(AHJK wiring) with controllable volt of 0-160 volts. can be attache to a RPM meter and an "on/off switch that can be connected to a magnetic contactor. I cant attach a picture of my controller because the file is too big.
Thank you in advance
those caps are in series with low value resistors which are connected to the motor, looks more like a snubber circuit. caps being bad there wouldn't cause the problem you are describing. however, you have electrolytics in the speed control circuit that could be dried out. date codes on components suggest a manufacture date of around 1984, so the five electrolytic caps around the IC would be the first thing i would replace. LA6324 is a standard quad op amp (Sanyo's copy of the LM324). another possible cause of erratic motor operation is the brushes and commutator in the motor. the brushes are usually spring loaded graphite blocks that make contact with the commutator. if the brushes have worn down to where the spring tension is slack, then the motor can run erratically. bad contact pads on the commutator can also cause problems. if the commutator has rough spots in the copper from arcing, you can clean the commutator, but you should also replace the brushes, because loose contact between the brush and commutator will cause that. the brushes are contained under plastic covers that can be opened with a screwdriver. if you open those covers, and the spring tension isn't pushing back with much pressure, the brushes need to be replaced... also keep track of the way the faces of the brushes are oriented, the new brushes will need to be installed the same way. you will notice the brush face is curved, and there is one edge of the face that's more pointed than the other. the pointed side kind of points in the direction of rotation.

the oil caps are most likely ok. the main failure mode of an oil cap is short circuit or current leakage, and open circuit would be the next likely failure. they do not fail the same way electrolytics do.
Thread starter #11
Hi uncleJed613,
Thanks for the input. I've checked the carbon brushes of the DC motor, they're still good. And we used a DC Voltmeter to check the output of the controller and it shows high voltage(175 volts ) and sometimes erratic voltage and voltage can hardly be controlled by the potentiometer(which we tested to be ok too). You suggested that I replace the 5 electrolytic caps, attached are some photos. are those the one you suggested to replace. pls take note of the left .05uf capacitor, the top part seems to be bulging that is why we suspect this is the problem but that part is now obsolete and very hard to find if ever.


You can get ceramic capacitors with similar voltage ratings, also polypropylene ones which may be a better substitute. But you really can't tell by looking and the original ones are probably perfectly ok. It is electrolytic capacitors which bulge when there is a problem with them. Oil filled caps are probably one of the most reliable types, working fine after many decades.

However in addition to what Unclejed says, there are a few other possibilities for the fault you describe.
First I would re-work all the soldered joints on the board, because you say the motor behaviour is erratic, it may be caused by a dry (aka "cold") joint, especially since the unit is quite old.
Check all the resistors. It's quicker than trying to do proper fault finding if one of them should be the culprit. On the other hand even if they all check out ok it doesn't guarantee there isn't an intermittent fault with one of them.
I'd check all those screw terminal connections too for dirt, corrosion, whatever.
You can get weird faults with old transistors and diodes. I would check to see if any respond to heat/cold whilst the circuit is running - well they'll all respond a bit but you are looking for a response that relates to the fault.
Preset potentiometers are another weak point as the wiper contact can develop a bad connection to the track. If you haven't already adjusted them, I would mark the positions and give them all a good tweak and maybe even a squirt of switch cleaner. You can use your marks to put them back in their original positions.
Other kinds of electro-mechanical fault include switches and relays. Again contacts can become corroded and cause an erratic connection. Switch cleaner is your friend. Check for corroded wires too.
With the unit powered on, check the voltages across the zener diodes, make sure they agree with the body marking, check if they vary whilst the fault is occurring.
Check the DC supply voltages to the circuit - are they stable?
Unfortunately you can't test the IC's without powering up the device and doing voltage checks on the pins. Find the data sheets for them so you know what pin does what, so you can make some sense of the readings.
If none of that helps, it's down to good old fashioned fault finding. Good luck!
Thread starter #13
Thanks for the all those great tips throbscottle. I will do what you suggested just for curiosity and additional knowledge. In the mean time , I've found some inexpensive dc motor controller in aliexpress and most probably would just buy a new one and replace my old motor controller( 29 years old) . attached is the model I have researched to be the closest to my old controller . any opinion is highly welcomed.


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