Misterious DEC-Module M7071

Hi, I got a strange board in recentley. Made by DEC, Quad-heigh, Dual-width, only one double sided 2x18 pin edge-connector that is snmaller as usual, aperantley carrying only power-supply connections. Has some 80 SSI/MSI TTL-chips, one prom 19-10818-02, and 10pcs 93l422 256kx4 ram's. Chips have 1979 date codes. The strange thing about this board is, that there is hardley any external connections, there is 1 (one) split-lug terminal, and one 16 pole IC-socket, as normalley used for automated testing signal connection. On the solderside there is the wording: "Waveform Generator" and 5012514F-P1 Who knows what this board is, and what it does? In what equipment was it used? How and for what purpose are the 10 Mbit of RAM filled with what kind of data? Fieldguide says: M7071 U Video Display Sys: image memory, RAMs & buffer logic. I don't understand this, because ther is no unibus-connection on this module at all. Is it a part of something bigger? Thanks, Frank