Re: HP 8567A YTO Unlock message!

In article <a6ece70a.0506080214.200ada8d@xxxxxxxxxxxxxxxxxx>,
pdmtr@xxxxxxxxx says...
> > It'll be in the RF section.
>
> Yes it should be there!!! Only thing is I cannot find it! :))

Sounds like there's a TCXO module buried somewhere, instead of the
standard 10811-60111 oven. I wouldn't worry about it any further.

> > > If you find something related (anything really) it would be a great
> > > help, as the basic working philosophy behind the 8568 (8567) & 8566
> > > Spectrum Analyzers should be the same!!! :))

In the case of my broken 8566B, the problem turned out to be A20C7, a 10
uF electrolytic that was open. The YTO main-coil driver circuit was
oscillating at about 1 MHz, which kept the outer YTO control loop from
locking up.

I started troubleshooting by verifying that the M/N and 20/30 MHz
synthesizers were both working properly, using a frequency counter.
That meant the problem had to be the YIG or its driver circuitry,
including the pretuning DAC. I went through the YTO loop adjustments
section in the tests/adjustments manual (which should be freely
downloadable from Agilent), and found that while the pretune DAC
adjustments were OK, I couldn't bring the actual YTO output frequencies
into range. There was a 1 MHz oscillation in the voltage-to-current
driver circuit that clearly didn't belong there, so I poked around with
an ESR meter and found an open electrolytic (A20C7). Replacing it and
recalibrating A20 took care of the issue.

> My major problem is that here in Greece we don't have a lot of HP
> support and to find something (used or not) we must take our chances
> with the "SLR" (shipping lose risk) parameter as I call it :( Have
> allready lost 3 manuals for test equipments ordered from US and
> another one delivered to me after 5 months from shipment!!! And mostly
> here, there is a total lack of (second hand) spare parts sources for
> things like test instruments...
> I have seen in the past, your tracking generator for the 8566. Nice
> mod you've done there on the 86222A plug-in. Will something similar
> work with 8567A/8568?

Thanks! Spare parts are a problem everywhere, unfortunately. I was
glad that I didn't actually have a bad YTO, or I would have been in
trouble. The 1.5-GHz analyzers are pretty different with regard to
their tuning/conversion schemes, so no, the 86222A mod won't work with
the 8567/8 directly. Check out the article linked from the DKD
Instruments page at http://www.dkdinst.com/products/TGdescrip.html for a
good discussion of what it takes to track an 8567/8.

-- jm

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