Capacitor marking, can someone explain it?

[roydm]

Hi, I have a number of 120 VAC output circuit boards
Near the output thyristor is a small surface mount device, it looks to me like a capacitor, several of these are damaged

the device is marked as below

----R+----
475
50k
906

If someone could tell me what all this means I would be most grateful

Thanks

Roy

 

[MacGyverS2000]

If it is a cap, 'k' would likely be the temp rating. '475' might be the capacitance, as in 4700000pF (or 4.7uF).

Dan - Owner

http://www.Hi-TecDesigns.com

 

[Comcokid]

Is the SMT device round or rectangular? Round SMT electrolytic capacitors will have markings. Rectangular SMT tantalum capacitors will have markings. It is very rare for other SMT capacitors (ceramic) to have markings. Are you sure it's a capacitor and can you post a picture?

 

[roydm]

They are an oblong device about 1/2" long, yellow with a foil lead out each end folded down and tucked under.
A couple have popped the top off and you can see what looks like aluminium foil inside

 

[MacGyverS2000]

Correction... I think the 50K may be the voltage (5.0V) and 'K' for Kemet (manufacturer). I stand by my description of the capacitance value. The '906' is likely the manufacture date... sixth week of year 'x9'.

Dan - Owner

http://www.Hi-TecDesigns.com

 

[Comcokid]

MacGyverS2000 may have it mostly right. It definately sounds like a tantalum capacitor (rectangular with yellow case) 4.7uF but I think it is 50V since you mention thyristors (high voltage-type circuits). 5V is more like you would find with processors or low-voltage logic circuits.

There are three sizes listed for 4.7uF 50V at a distributors site. 2312 (6032 metric), 2915 (7338 metric), 2917 (7343 metric). The sizes work like this - "2312 (6032 metric)" means: 0.23 inches long (end lead-to-end lead) x 0.12 inches wide, or 6.0mm x 3.2mm

If the "K" has a line above and a line below, then it is a Kemet part with 10% tolerance (for the 4.7uf value).

Tantalums are used for low-leakage, long life, and sometimes for low ESR. Tantalums are polarized - they only go in the circuit one direction. Tantalums have little ability to handle over-voltage, and no ability to handle reverse voltage. Reverse voltage or over voltage usually results in the part blowing apart.

Since you don't know if ESR was a factor in the original part selection, I would just go with a medium ESR rating. Low ESR devices are generally used in switch-mode power supplies for better filtering. ESR in this value range from 250m Ohm to 1.5 Ohm. A Kemet T494D475K050AT with 600m Ohm (assuming your size is 2917) is $2.58 each at Digikey (

http://www.digikey.com/product-detail/en/T494D475K050AT/399-3859-1-ND/819184).

A lower ESR part will cost double.

 

[roydm]

Thanks guys, you are a lifesaver
I was wondering about the Voltage range since the only ones I could find are low Voltage

Yes several are blown apart, but I'm not about to re-design the circuit I will just replace with an equivalent and hope for the best