[time-nuts] Best Rubidium Frequency Standard

cdelect at juno.com cdelect at juno.com
Sat Mar 12 12:14:25 EST 2016


Mike,

If you are planning to buy "suspect units" with the intent to repair I
would steer clear of the PRS10.

It is true you can pay for a factory repair but having the schematics and
theory of operation only helps for particular repairs.

This is because a lot of the alignment parameters are stored in memory
and there are no instructions on these alignments and how to store them.

An example: I had a unit come in for repair. It had no output. The
customer, a professor, said a student applied a large DC to the output.
The output is direct from an RF transformer. It burnt open the winding.

I thought, how hard can it be?

I popped off a good output board from a junker and installed it. I now
had an output but the unit would not operate properly. Part of the output
go to other circuitry that would need to be aligned to match. No way to
do that or store the alignment! Bummer.

Luckily the transformer was a metal can type. I opened it up and rewound
the tiny wire output coil and that restored the unit to operation.

After that I sold my pile of defunct PRS10 units and don't plan to
purchase any more.

For ease of repair the HP 5065A is first, then the FRKL and H, these have
bog standard thru hole circuitry and the manuals are excellent. Another
of the worst is the M100 as its cards are conformal coated and the lamp
oven assy. is potted! As you mentioned most of the later telecomm units
are surface mount and most have some sort of microprocessor involved.

Cheers,

Corby



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