HELP! Capacitor identification needed

[Eric R Snow]

Thanks for looking at my post. I am clumsy and broke a capacitor off a
circuit board in an encoder. This encoder is probably 30 years old.
The capacitor is made, I think, by NEC, because it has marked +NEC at
the bottom. The device has the following markings: 6.8-M

20VE

+NEC
The letter "E" after the "20V" is twice as big as all the other
letters and numbers. I have contacted NEC and they said they cannot
help me, the device is too old. I think it might be a tantalum
capacitor. The reason I think it's a capacitor is because the circuit
board has printed on it "C1" and the symbol of two parallel, vertical
lines with each line having a line perpendicular and bisecting the
vertical line. These markings are right next to where the capacitor is
soldered to the circuit board. This capacitor is soldered across the
positive and negative where the 5 volt power comes in to the encoder.
Thanks for any help.
Eric R Snow,
E T Precision Machine

 

[Bob Eldred]

Thanks for looking at my post. I am clumsy and broke a capacitor off a
circuit board in an encoder. This encoder is probably 30 years old.
The capacitor is made, I think, by NEC, because it has marked +NEC at
the bottom. The device has the following markings: 6.8-M

20VE

+NEC
The letter "E" after the "20V" is twice as big as all the other
letters and numbers. I have contacted NEC and they said they cannot
help me, the device is too old. I think it might be a tantalum
capacitor. The reason I think it's a capacitor is because the circuit
board has printed on it "C1" and the symbol of two parallel, vertical
lines with each line having a line perpendicular and bisecting the
vertical line. These markings are right next to where the capacitor is
soldered to the circuit board. This capacitor is soldered across the
positive and negative where the 5 volt power comes in to the encoder.
Thanks for any help.
Eric R Snow,
E T Precision Machine

This could be a 6.8 Microfarad 20 Volt tantalum cap if it is across a power
supply connection as you have indicated. Fortunately this is a non-critical
application and it may not even need a cap there depending on how much
by-passing is done elsewhere in the circuit, assuming your description is
correct. The purpose of the cap is probably to reduce noise on the 5 Volt
line and has little to do with the operation of the encoder, per-se. Remove
the cap and see if the circuit works without it. A new 6.8 uF 10V or more
aluminum or tant electrolytic cap should work fine in that application if
you feel it needs replacing or if there is any noise or erratic behavior
without a cap. Be sure to observe the polarity of the cap when replacing it.
Bob

 

[Eric R Snow]

This could be a 6.8 Microfarad 20 Volt tantalum cap if it is across a power
supply connection as you have indicated. Fortunately this is a non-critical
application and it may not even need a cap there depending on how much
by-passing is done elsewhere in the circuit, assuming your description is
correct. The purpose of the cap is probably to reduce noise on the 5 Volt
line and has little to do with the operation of the encoder, per-se. Remove
the cap and see if the circuit works without it. A new 6.8 uF 10V or more
aluminum or tant electrolytic cap should work fine in that application if
you feel it needs replacing or if there is any noise or erratic behavior
without a cap. Be sure to observe the polarity of the cap when replacing it.
Bob

Thank You Bob,
It seemed to me that the cap was there for some kind of filtering. I'm
glad that my guess was probably correct. I'll try the thing without
the cap to see what happens but I'm going to buy and install a new cap
anyway. This encoder is used in a machine shop with other cnc machines
nearby and a TIG welder in the same building. I don't know much about
how noise is picked by wires but I can hear the servo amps on one
machine through an AM radio.
Cheers,
Eric

 

[Rich Grise]

Thank You Bob,
It seemed to me that the cap was there for some kind of filtering. I'm
glad that my guess was probably correct. I'll try the thing without
the cap to see what happens but I'm going to buy and install a new cap
anyway. This encoder is used in a machine shop with other cnc machines
nearby and a TIG welder in the same building. I don't know much about
how noise is picked by wires but I can hear the servo amps on one
machine through an AM radio.

Then replace the cap before you try to run it - it helps filter out
that noise so that your encoder will operate reliably.

Cheers!
Rich