Maybe of absolute zero value to you, but here is some docs I collected on the M-500. Might be too different for it to be useful, but just in case.

https://w2hx.com/?prefix=x/InfoTech/Info-Tech%20M500/

73 Eugene W2HX

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From: [email protected] <[email protected]> On Behalf Of w1aea
Sent: Sunday, October 3, 2021 5:37 PM
To: [email protected]
Subject: [MRCA] Info needed

Hi all

Looking for a operating manual for the  Info Tech M-600 or M-800 Multimode Data Demodulator or link to a Download site

Thanks   Jeff W1AEA

Sent from my Galaxy Tab® A