Help Identify Tiny Lamp - Page 1
Forum section: electronics / repair

author: vidarr
author_rank: Frequent Contributor
timestamp: December 30, 2018, 12:24:12 pm
content: I need to replace this tiny light that goes inside a coffee/espresso machine. I tried a couple local stores and they don't know, or have, anything. It is a 120v appliance. There is also a resistor before the bulb, but it looks like someone did a repair near the light and had to MacGyver it back together with a candle and some clay. The resistor is covered and I could not clean it off without removing the bands. I need help to identify the bulb and resistor so I can replace it. Thanks.

author: Armadillo
author_rank: Super Contributor
timestamp: December 30, 2018, 12:27:24 pm
content: https://www.ebay.com/itm/20pcs-Neon-Bulb-Indicator-5mm-Lampada-Lamp-Red-Neon-Light-5-mm-Neon-Light/222950531484?hash=item33e8e3219c:g:kywAAOSw43Ba4tyr:rk:7:pf:0

author: ciccio
author_rank: Frequent Contributor
timestamp: December 30, 2018, 12:54:34 pm
content: It is a standard Neon bulb, they are everywhere.https://en.wikipedia.org/wiki/Neon_lampIf you cannot find locally, they are inside any illuminated AC switch, so you can cannibalize one.The series resistor is in the order of 100 K (for 230 V ac).This is an axample:https://uk.rs-online.com/web/p/neon-indicator-lamps/0105017/Best regards

author: vidarr
author_rank: Frequent Contributor
timestamp: December 30, 2018, 02:06:18 pm
content: Thanks guys. They don't sell these here. I will have to pull one from a switch -- thanks for that tip.

author: Ian.M
author_rank: Super Contributor
timestamp: December 30, 2018, 02:20:11 pm
content: Unless the glass has cracked/broken that neon bulb is probably OK. Remove the solder blob, replace the resistor and try it . . .

author: vidarr
author_rank: Frequent Contributor
timestamp: December 30, 2018, 06:59:00 pm
content: How do I calculate the resistance for 120V mains power? I don't know the current. I don't have a datasheet for the lamp. There should be a "standard" size resistor most people use right?

author: Armadillo
author_rank: Super Contributor
timestamp: December 30, 2018, 07:34:41 pm
content: The current is about 1.5mA and the minimum voltage across is 60V; hence the resistor should be;= (120 - 60) / 1.5mA = 40Kohm;Size of resistor = 90mW; Select 1/4W is OK.Quote from: vidarr on December 30, 2018, 06:59:00 pm

author: Armadillo
author_rank: Super Contributor
timestamp: December 30, 2018, 07:40:26 pm
content: If you want it slightly brighter then select 36Kohm @1/4W.

author: soldar
author_rank: Super Contributor
timestamp: December 30, 2018, 07:45:29 pm
content: You can start with 100K and adjust down according to brightness wanted. Ambient light makes quite a difference.

author: Nusa
author_rank: Super Contributor
timestamp: December 30, 2018, 08:04:20 pm
content: First off, have you tried measuring the old resistor with your meter? If you get a reasonable reading, that may not have been the failure point.At 120V, I'd pick 33Kohm for an NE-2H lamp, or 120Kohm for NE-2. They look the same, of course.You don't know what you have, so I'd try 120K first. If it works, do NOT try 33K.Pick a higher value if you think it's too bright...you presumably remember what it looked like before.Your other option is to replace it with an LED indicator circuit. You'll lose the neon flicker, but otherwise quite adequate.

author: vidarr
author_rank: Frequent Contributor
timestamp: December 31, 2018, 01:44:34 pm
content: I had an 89k resistor handy and it worked well. Thanks guys.The little light looks so much better without the red plastic cover. It looks kind of cool. I have to put the cover back on though.