Servo 140 Power Feed Pilot Light - Lamp, Bulb, Light - Whatever It's Called

ptsmith · Jun 4, 2019

I picked up a couple of used Servo 140 power feed units. The pilot light on one is very dim and needs replacing. Below is a photo of a replacement board. It's the bulb on the upper right hand corner. The glass on mine is red but a clear one would be fine. Anyone know what type of bulb this is?

BoxcarPete · Jun 4, 2019

Can you get your meter on it when it's energized? After that, all you'd need to do is find an LED that's the right size and voltage rating.

jwhartley · Jun 4, 2019

Take some care to check the supply voltage. That looks a bit like a neon bulb. (picture is small.) It could be a high voltage?

ptsmith · Jun 4, 2019

Thanks.

I'm not knowledgeable about electronics, but I do know a tiny bit.

The power feed uses 120V AC. I don't see anything that looks like a rectifier so I assume that the bulb is AC.

I googled small neon bulb and that does look like that's what it is. And they appear to be AC.

https://www.amazon.com/slp/neon-bulb/yrjms7pcbhmored

So I guess you answered my question. Thanks!

jwhartley · Jun 4, 2019

The neons would need around 100+v to light. Usually this would be AC. There is also a current-limiting resistor. The board is fairly simple. You could trace out the circuit and post the schematic. (Or maybe someone has one?).

If you can, check the voltage across the lamp under-power and you can rule out the use of a modern LED. If the voltage across the lamp is greater than 2-3v, or if it is AC, then is is a neon bulb. If you put an LED in, it will be destroyed and the magic smoke will escape.

-Jess

Yan Wo · Jun 4, 2019

It's a neon lamp, as in these at Digi-Key.

HWElecRepair · Jun 10, 2019

Ive got a box of them, but I am on my last day of vacation and dont know how much we charge for them. PM and I can let you know tomorrow.

Jon
H&W Machine Repair

Gordon Heaton · Jun 10, 2019

It is common for those neon bulbs to go dim over time. At some point they will flicker erratically. Sometimes, exposing them to light/dark will cause them to light steady, then go out or flicker when the opposite is done (can't remember if light makes them work, or dark). They are easily found, even at Ace Hardware, etc., last one I got there was under $1. Digikey's prices are mostly sub $1 too.

ptsmith · Jun 10, 2019

I found one and have already replaced it. A model NE-2E/A9A. Nice and bright now. Thanks for all the help!

PS: These neon lamps require a resistor. Everything I found suggested 100K. The servo circuit board has a 33K resistor. At least it does if I'm deciphering the color code correctly.

Yan Wo · Jun 10, 2019

ptsmith said:
I found one and have already replaced it. A model NE-2E/A9A. Nice and bright now. Thanks for all the help!

PS: These neon lamps require a resistor. Everything I found suggested 100K. The servo circuit board has a 33K resistor. At least it does if I'm deciphering the color code correctly.

What are the colors?

ptsmith · Jun 11, 2019

4 band, one gold and three orange. I used this site to get the value: Internal Error

I just looked at a resistor color code chart. Maybe it was faded brown instead of orange?

Yan Wo · Jun 11, 2019

ptsmith said:
4 band, one gold and three orange. I used this site to get the value: Internal Error

I just looked at a resistor color code chart. Maybe it was faded brown instead of orange?

33K 5% is correct, I believe. Read it with the gold band on the right: 3 3 and 3 zeros. You can put a meter across it to verify.

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Servo 140 Power Feed Pilot Light - Lamp, Bulb, Light - Whatever It's Called

ptsmith

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BoxcarPete

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Yan Wo

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HWElecRepair

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Gordon Heaton

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