EEVblog Electronics Community Forum

Electronics => Repair => Topic started by: codex0 on February 16, 2021, 10:59:37 pm

Title: Breadcrumb for Agilent E4418B repair / Power button not working
Post by: codex0 on February 16, 2021, 10:59:37 pm
There are a number of threads detailing issues with the front membranes on these, many people end up ordering replacements from China because the real deal from Agilent is so expensive.

My unit would not turn on or off via the power button - always in standby.

A few users mentioned here and on the Agilent group that checking the battery is important on these - mine was dead.

Behavior with a dead (or missing) battery is the unit will turn on, but once you turn it off it will not turn on again (until unplugged/drained). These batteries are really difficult to remove because they are siliconed on, so I pried off the solder tabs before removing the battery then desoldering each tab. I bought a replacement with installed wires and used a zip tie to fasten it so it would be easy to replace in the future (the manual suggests every 3 years).

Replacing my battery did nothing to fix this issue - removing it made things slightly better. - when I plugged it in with the battery detached via the battery jumper it would immediately turn on, then it would turn off happily once with the power button then not turn back on again.

I measured resistance across the power button pins (If you are facing the front of the instrument from the top, they are pins 5 and 6 counting FROM THE RIGHT to the left). 2MOhms open and about 70 ohms closed.

Based on other threads I was afraid I had a bad front membrane and would need to replace it. On a whim, I removed the keyboard flex cable where it plugged into the mainboard and cleaned the contact areas with alcohol (gently). A noticeable amount of carbon came off. Everything now works as it should.

I'm leaving this as a breadcrumb / thing to try before ordering a replacement membrane.
Title: Re: Breadcrumb for Agilent E4418B repair / Power button not working
Post by: nfmax on February 07, 2022, 10:44:29 am
Thanks for this post, it gave me some vital clues to fixing my instrument:

https://www.eevblog.com/forum/repair/(mended)-ep4418b-power-meter-doesnt-turn-on/new/#new (https://www.eevblog.com/forum/repair/(mended)-ep4418b-power-meter-doesnt-turn-on/new/#new)