Apple II power light won't come on; computer works fine otherwise

4 replies [Last post]
Joined: Feb 17 2008
Posts: 195

The power bulb under the power key on my Apple II (original 1978 with raised power key) will not glow on. The computer powers on and operates fine otherwise, loads a game from Disk ][ etc. Light bulbs on a language card glow fine. Beeps from speaker fine.

I removed the bulb, but as it is very small cannot tell for sure if it is fused. I have a replacement bulb (slightly larger size but I am told a genuine Apple II replacement part) which when I mechanically connected it to the power key copper output contacts (no soldering) also would not glow.

Before I bring out the multimeter, what output voltage should I expect from the power key terminals? Assuming its OK to test the "original" bulb using a household battery, what voltage should I work with?

Anything else that could be causing this besides a faulty bulb?

Thanks for the suggestions.

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Joined: Dec 20 2003
Posts: 211
Test the bulb using a 1.5 vol

Test the bulb using a 1.5 volt battery. If it lights up, however dimly, it works.

Joined: Feb 17 2008
Posts: 195
Replacement bulb lights fine

Replacement bulb lights fine when test fitted to the power key.
Power key is delivering a healthy 5V measured on multimeter.

My issue is now a mechanical one. The replacement bulb is double the size of the original and the power key will not fit over it.

Could anyone here point me to the specs I need in a replacement bulb (non-LED)?

Joined: Feb 17 2008
Posts: 195
A 5v grain of wheat wire ende

A 5v grain of wheat wire ended sub-miniature bulb did the trick.
Perfect glow, easy to install and no heat issues.

Rapid Online ( in the UK were very helpful and shipped me one free of charge.

Sherlock's picture
Joined: Dec 20 2014
Posts: 135
Re: Apple II power light won't come on; computer works fine ...

So I know this is an old thread, but it's an issue I ran into recently - where the power light on my Apple II with raised power key light went out.

I couldn't find much with "grain of wheat" size bulb, so after a bit of online researching, I found a suitable part. The bulb measures about 0.125" in diameter, and 0.25" long.

Some more details for the part I found from a USA seller is as follows:

Digikey part # CM683-ND
Description: LAMP T1 WIRE TERM 5V .06A

It cost about $1.50 USD, and I just got it.

Another detail about this light is that when you take the raised key light cap off (it just slides up with just small pressure), it's not clear if it's soldered in. It's actually easily removable just by pulling up on the leads of the lamp. Just use a pair of tweezers, and it comes right out. The replacement part had leads that were a bit longer, so I trimmed them to the same size as the original lamp. The replacement lamp is a tiny bit longer, but otherwise looks the same. I slid the new leads into the tiny "tubes" where the old lamp leads went, and it went in just fine. Replaced the key cap (had to bend the bulb down a bit because it's a tiny bit longer), turned the machine on, and it worked great!

Again, not a lot of info out there about this situation, so here is my take. Anyway, hope this helps someone.