Engenius phones, again, Jeff L...

Yeah, that's what they all say.

Have you considered using two-way (licensed) radios with a phone patch? My guess(tm) is that most of the communications is between handsets, which makes commercial radio a viable option.

Any ham radio repeater controller with a phone patch interface should also work.

Hmmm.... this is starting to sound familiar.

Yep. Welcome to the throw away economy.

Yep. Sounds like the same run-around I got.

It's really hard to fix things without a schematic. However, a fairly simple failure, like a loss of microphone audio can be troubleshot or traced. If you have one handset that still works, it should be fairly easy to identify the applicable parts and walk down the signal path with an oscilloscope. In effect, you're generating your own schematic using reverse engineering.

Incidentally, one vendor (who shall remain anonymous) refused to supply me with a schematic for troubleshooting an obsolete product. I was a bit lazy, and announced to the support droid that if I had to go through the effort of reverse engineering the product, I would either post or sell the results on the internet. Faced with the prospects of hanving literally everyone have a copy of the schematic, they faxed sent me a barely readable schematic. I swear it had been reduced and run through a fax machine several times before sending it, as it was a really bad print. However, it was good enough to repair the piece of junk. I later tried the same ploy with other vendors, all of whom refused to even acknowledge that they had possession of a schematic. That's what happens with an outsourced support service, that literally doesn't care.

I have a customer that blows up cell phones at an alarming rate. He goes in and out of refridgerated meat lockers all day long. The phone can't handle the thermal cycling. I reduced, but not eliminated, the problem with an insulated phone holster. Have these phones been going in and out of the sun or cold?

It may not be the board or the components. It could be the electret microphone. I've had problems with those losing their charge in commercial radios. If the headset works, but not the internal mic, then the mic should be suspected. However, if both fail, then it might be some common circuitry:

What did they do to fix them? I'll bet they replaced the mic element.

Jeff Liebermann fired this volley in news: snipped-for-privacy@4ax.com:

Did you ask?

Your decision. I have the same problem but tend to do it anyway, just to satisfy my own curiosity. Such reverse engineering doens't make me any money, but I find it interesting.

Bingo. The humidity also causes some circuit boards to expand and contract. It also gets inside the mic elements. Ask around about cell phone failures.

The first step to solving a problem is to assign the blame. In this case, that's a fair guess, but lacking in one respect. You have no direct evidence.

Yech. Also look for cracked components and surface mount solder joints. Why do you need to juggle batteries?

That's commonly used on cordless phones and cell phones. The concentric rings are the contacts. The ones with external DC bias have 3 rings. The ones without an internal amplifier have two rings. The mic fits in a molded hole in the plastic front panel. There's usually a foam or rubber ring to provide tension. The assembly is compressed by the board mounting system. The problem with this method is that condensation from the speakers voice tends to make the contacts rot. Gold plating is common. Mounting the mic element directly on the board isn't very useful as the mic element will not survive reflow soldering.

The electret mic elements aren't totally hermetically sealed and will also condense water inside, causing the capacitor to discharge. If you have any old Motorola flip phones floating around, each phone will have TWO electret elements you can borrow.

Jeff Liebermann fired this volley in news: snipped-for-privacy@4ax.com:

Pretty fair indirect evidence, though: torquing the case (board) temporarily fixes the problem. Even on a "hard-bad" unit, I can sometimes get the mic to come back on for a second with some brutal handling.

I'm pretty certain if the electret element had lost its charge, fiddling wouldn't make the problem come and go.

We work multiple shifts with common phones, and have a lot of talk time and general broadcasts on most of them. They also run at high power a lot of the time because of how spread out our facility is.

You've given me a lot of good tips, Jeff; thanks.

Maybe I will take a spare evening I'd have 'wasted' reading, and try to fix this pile of junk on my desk.

LLoyd