Tag Archives: microwave surveillance receiver

Micro-Tel MSR-902C Microwave Surveillance Receiver: a very intriguing, 60 pound briefcase

A few days a ago, a most intriguing briefcase arrived, brown color, looking like the late 70s… Samsonite. It is heavy! Really heavy!!

msr-902c briefcase

Inside – a fully equipped MSR-902C receiver, including all cables (which are rare, and extemely expensive to fabricate, because they use special military connectors). This receiver can more or less receive any signal, down to very low levels, and comes in 3 modules, the actual receiver, a 1-18 GHz tuner, and a 18-26 GHz tuner. Other tuners and harmonic mixers were also available from Micro-Tel, but most likely, not many of these have ever been sold.

msr-902c view1

A brief description of the MSR-902, which is very close to the 902C:

msr-902 description

Unfortunately, there is very little literature or even manuals on the MSR-902C, no instructions, no schematic – fortunately, is shares some circuits with the MSR-904A, and 1295 Micro-Tel receiver, and it is an all-discrete construction, with a lot of wires and circuit boards, so it is repairable, even without schematic (just taking 10x longer….). Should you have a manual, or any other related documentation for the MSR-902C,

Inside of the main receiver (the tuners have not yet been touched), a most amazing combination of wires, switches, boards, and so on. All hand-soldered in Maryland, USA.

msr-902c wires

msr-902c wires2

msr-902c wires3

It is a marvel of engineering, but, currently, not in working order. It blows the fuse, as soon as it is connected to mains power. Something wrong with the power supply. After removing a cup full of screws, here it is.

msr-902c pwr supply

Strongly shielded by a thin magnetic shield, all nicely machined and assembled. Now all has to come apart for repair.

msr-902c mag shield

The internals of the power supply, a good number of boards and parts. The power supply can either work from AC mains, or from 12 VDC. The 12 VDC section appears to be find.

msr-902c side view

msr-902c top view

After some tests, found the first suspect item, a full short on one of the MJ12002 transistor that drive the primary of the switchmode power supply converter.

msr-902c dead mj12002

msr-902c transistor short

It a quite old-fashined part, but could still find 3 pieces, USD 5 each. Not cheap, but OK.

msr-902c pwr transistor mj12002

Once the transistor had been removed, time for some checks of the drive circuit. This circuit is based on an MC3420 switchmode controller.

msr-902c pwr supply disassembled

As you can see, the switch mode regulator is working, just no drive transistors around that could actually drive the transformer. But will be only a matter of days.

msr-902c pwr supply drive signal

For those interested, here are the specifications (of the very closely related MSR-902).

msr-902 specifications

More to come – stay tuned!