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53132A TB CAL FAIL

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dadler:
Anyone know what in particular causes this error? Is it the timebase itself, the incoming signal, or something else? "Fail" doesn't mean a whole lot to me. Per the manual:

"TB CAL FAIL You have invoked the TIMEBAS? choice from the Calibration menu item CAL:, and the calibration failed."

The manual claims it should not fail if the 53132A has been heated up/on for 24 hours. I've had it plugged in for over a month now (the PS+oscillator heater are always on if the unit is plugged in). I tried leaving the counter actually on (display on) for several hours, and yield the same issue (don't think this helps, as the counter is already hot from being powered all the time).

Some background:

A few months ago I bought a new-old-stock 53132A, and then upgraded it with a clone high-stability timebase and 3ghz prescaler from eBay (shipped from Poland, same as the one reviewed by Shahriar).

I'm feeding in the 10Mhz sine output from my BG7TBL (2014) unit. The BG7TBL is locked but has only been running for about 12 hours. The output "looks" stable on my other counter.

The cal runs for a while, and then results in "TB CAL FAILED".

I was able to successfully calibrate the unit a month or so ago with FEI rubidium oscillator, but now I get the same error with that. Also tried feeding the OCXO output from my Philips counter, get the same error.

I'm wondering if maybe the used OCXO that came with the high-stability timebase from Poland has failed in some fashion?

dadler:
I should add that the clone high-stability OCXO seems to have drifted about 12Hz in the past two months. This makes me think that the OCXO is dead/dying and can't be trimmed back into spec.

The Morion OCXO I received did look quite torn up/old. I contacted the eBay seller, but would still like to know if anyone has had a similar experience.

Thanks in advance.

motocoder:

--- Quote from: dadler on August 26, 2015, 08:40:41 pm ---I should add that the clone high-stability OCXO seems to have drifted about 12Hz in the past two months. This makes me think that the OCXO is dead/dying and can't be trimmed back into spec.

The Morion OCXO I received did look quite torn up/old. I contacted the eBay seller, but would still like to know if anyone has had a similar experience.

Thanks in advance.

--- End quote ---

Check for a missing shorting jumper on your OCXO. The one commonly sold on eBay comes in two configurations. One just has a trimpot and does not have the D/A circuitry populated. The other has the D/A circuitry for auto-cal, but does not have the trimpot. There's a jumper that needs to be installed to enable the D/A functionality, and for some reason putting that jumper on there seems to be beyond the technical capabilities or care of the eBay seller.

I bought one of these OCXO for my 53131A off of eBay. I had the same problem. I hooked up the frequency reference to channel 1/trigger on my scope, and the counter 10 MHz out to channel 2, and ran a timebase calibration cycle. It was immediately apparent that the oscillator was not having its frequency adjusted at all. I checked, saw the missing jumper, put one on and re-ran the cal - problem solved.

dadler:
Ah thanks so much for the response!

Here's what my board looked like before I put it in:

dadler:
Now that I actually look at the circuit, seems that trace in the center of pic #4 is going off into the ether... Guess that's the trim pot and buffer? I'm not familiar with the pinouts on these oscillators. Can't tell what's under the OCXO/DAC exactly although I can sort of make it out.

Is the jumper your referring to the one in pic #6?

I was able to calibrate this OCXO once, just after I received it. Don't know if it was actually adjusting anything, but on first try I got TB CAL PASS and it was nearly in-spec compared to my other counter.

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