I appreciate products that possess exquisite quality. One of my first was a synthesized RF generator. I have never seen a manual for this piece, but I managed to get it working anyway. How? By utilizing the writing on the backplane of the unit.
I acquired this pup, sans covers, in bad shape. The previous owner had piped the 10 MHz oven oscillator out to a dangling cable to be used elsewhere. I bought it for $35, and it had dirt clods from being left out in the cold.
Inspection revealed that the underside of the backplane was a treasure trove of information. What a great idea, two square feet of PCB with backplane connectors and lots of room. The wizards at GenRad labeled almost every pin with what the signal should be on it. Things like: 1 MHz CLK, 15 volts, BCD 2, etc.
By checking a bunch of pins I narrowed down the fault to a single plug-in card. I somehow motivated myself to make a pictorial drawing and then schematic close to reality. Standard signal tracing got me to a TO-5 transistor that looked shorted. The signal went there, but no farther.
The part number on the can was very weird -- No 2NXXXX or 2SXXXXX -- plus the pins were somehow not quite right. I decided to saw the TO-5 case open, and to my surprise, inside was a tiny ferrite transformer or coil. One of the coil form's pins was shorting out to the metal can.
I bent it a bit and the 150 MHz synthesized generator works. There’s no power switch. The oven wants to be on all the time. Come to think of it, that oven is twice the size of the usual crystal oven. I think I might measure its Allan variance with my new HP 5370B.
This entry was submitted by Steve Lindberg and edited by Rob Spiegel.
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