There were two companies in Massachusetts doing Datamarine repairs: Datamarine Instruments, and DMI Marine. Both had roots in the company which made your depth sounder, Datamarine International, later Sea-Datamarine, which is now inactive.
I have had several experiences with each repair facility. I would highly recommend DMI Marine; they are a real company, know what they are doing, and also manufacture a limited range of instruments, including a depth indicator and a knotmeter which are updated replacements for the old Datamarine instruments. I have used them for repairs several times in my business, and also have one of their new knotmeters on my boat. DMI's website is DMI Marine, Inc.
. They are not quick to respond by either email or telephone, but they do good work.
Datamarine Instruments, on the other hand, appears to be out of business now, and it sounds like that is where you sent your depthsounder. Their website is down & they had a garage sale of their inventory and test equipment. I also have had experience with them, and let's just say it wasn't as good as with DMI.
More on this confusing subject here: Panbo: The Marine Electronics Weblog: Old instruments #1, Datamarine doubled