[time-nuts] HP 8566B repair

Jeff Mock jeff at mock.com
Thu Dec 6 22:54:56 EST 2007

Thanks so much, that's just the encouragement I need to crack open the 
RF section.  I'll take a look at the electrolytic caps you suggest. 
Assuming that I find something, do you think it's worth replacing other 
caps in the area figuring that they will also go bad soon enough?


John Miles wrote:
> Never fear.  I have seen this a few times, in a couple of 8566Bs that I have
> owned as well as in some others.  The YTO UNLOCK error always seems to come
> down to an open electrolytic on the YTO driver or pretune DAC boards, under
> the hinged plastic cover toward the rear of the RF section.
> Check power supply voltages first, then check ESR of all of the axial-lead
> electrolytics on all boards under that cover.  Then, if those areas are both
> OK, go through the YTO calibration procedure in the manual until you either
> successfully recalibrate the pretune/driver system, or reach a particular
> step that you can't complete.
> -- john, KE5FX
>> -----Original Message-----
>> From: time-nuts-bounces at febo.com [mailto:time-nuts-bounces at febo.com]On
>> Behalf Of Jeff Mock
>> Sent: Thursday, December 06, 2007 7:38 PM
>> To: Discussion of precise time and frequency measurement
>> Subject: [time-nuts] HP 8566B repair
>> Does anyone have any suggestions or advice about 8566B repair?
>> I've had an 8566B for 7-8 years, it's been a faithful tool, never had a
>> problem with it.  It's reasonably clean unit that's never seen a tough
>> life.  It sits in the storeroom 90% of the time and is on my bench maybe
>> 10% of the time.
>> So, this week, after a 4 month hiatus, I've been using it on the bench
>> and it starting producing a "YTO UNLOCK" message, the trace seems to
>> basically work properly but is clearly unlocked and the trace will
>> randomly slide to the left or right.  The Yttrium oscillator is clearly
>> unlocked.  I'm hopeful that the problem is in one the control loops
>> outside the oscillator module.
>> I read the repair guide that Agilent kindly keeps on their website, they
>> have some good instructions and narrow the problem to 3-4 modules, but
>> I've never opened up the instrument and am a little apprehensive about
>> making things worse.  My hunch is that the problem is an electrolytic
>> cap that has dried out over the years and has failed.
>> Any suggestions for either self repair or outside repair and
>> re-calibration is appreciated...
>> In full disclosure, I also have a 70908A based spectrum analyser that
>> that has much better specs, especially in microwave. It can completely
>> replace the 8566B, but I'm quite fond of the 8566B, I can operate it
>> blind folded, it's like an old friend and I would really like to fix it.
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