Had a customer with this system that was installed around mid 1980's. Found programming guide on internet.

Problem, 1 or 2 phones have a MIC button that works when using speakerphone. (Button beeps when pressing it, but doesn't lite up. Also does not work while holding it down).

Checked all the programming options. Switched phones and found the problem to be in the Phone, not in system programming. Customer thinks it was intentionally disabled at one time by previous business owners.

So are the phones (all but 1 or 2) broken or is there a way to enable/disable the MIC in the phone, or is it not even functional in those phones.

are the phone part numbers ending in a h or s
also if you get a manual look at program 5xx
sta class of service there are options to enable speakerphone/and mic on at start of call/and handsfree answer back

I'll have to ask the cutomer about the model number. Didn't look at them.

I made sure that all options in 5XX re mic were enable on all phones, speakerphone enable, mic lock, and mic at start of call. Also changed settings to see what happens, which was nothing changed. And if all phones were programmed the same, it didn't make sense that only a couple worked.

Didn't check if handsfree answerback worked. Another tech at my co said that older systems sometimes worked with answerback, but speakerphone was an extra option, sometimes added to the phone. They all had a MIC button with light.

I Didn't open the working phone to see if anything was different then the non-working phone (I was on the clock and didn't want to kill him with a bill when nothing got fixed).

I told him I'd ask around and email him if I got an answer.

that system takes phones going back to about 1982 and ends with the 6000 series that discontinued manufacture in 2000

Make sure that the phones are "S" or "SD" models. It sounds to me like you have some "H" models. They still have the button and the light, but they do not have an internal mic. They will only function handsfree on intercom and the transmit quality will be terrible as it uses the handset mic to transmit in handsfree mode. An "H" phone is not a speakerphone and will not function handsfree on outside calls.

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Avaya Telephone Repair
Toshiba Telephone Repair

I found a site that sells phone for that sysem and proved what you said. a EKT6025S and EKT6025H look identical, but one is speakerphone and one is handsfree answerback.

Although I opened one of the phones when I was there and saw what looked like a Mic connected.

I emailed the customer to let him know.

Thanks