I had almost given up. It seemed that a full manual of a MSR-904A would be perfectly unobtainium. Well, most secrets of the MSR-904A were reverse engineered anyway, but there are some subtle details and adjustments – just a bit arbitrary to do without proper documentation and at a least a bit of insight into the thoughts of the designers of this marvelous apparatus.
One reason might be that these units were long banned from export and mostly governmentally owned. Eventually, the units reached the secondary market, but the manuals, they rest in some archives, or have long been disposed off by the agencies.

Now, to my greatest surprise – a copy of the manual has been located – in Germany. The paper copy, it seems to belong (or have belonged) to a certain H. S. in Webenheim, a place, a mere 72 miles form my German home.
Another fellow German must have scanned this, and again, another fellow, send it to me, electronically. Albeit, not for free, but, fair enough.

It is complete with all adjustments instructions, explanation of how it works, parts list, and SCHEMATICs.

Here, a block diagram of the IF chain – without the 160 MHz 2nd IF output option (by conversion of the 250 MHz 1st IF using a 410 MHz LO) installed in the unit I have for repair.

Screening through the manual, the complexity of the thing is pretty much amazing. All without any controllers or processors – but there is at least one programmable part, a PROM that has the filter switching matrix. Come on, this could have been done with a diode matrix!