Re: [time-nuts] HP 8566B repair
Jeff Mock wrote: 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. jeff ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there. This document is very helpful in dealing with YIG oscillators. http://www.vhfcomm.co.uk/pdf/A%20Simple%20Approach%20tyo%20YIG%20Oscil.pdf YIG oscillators should be quite reliable, and I would expect that it is just an electrolytic cap or similar as you mentioned. The oscillator portion clearly works, so the only thing that could be wrong with the oscillator itself is a burned out FM coil which is unlikely. The oscillator would not oscillate at all without main coil current assuming it is not a PMYTO, which is extremely unlikely in an older unit. I would expect that the FM coil (fine tune, driven by the PLL) current is pegged to either side or the FM coil is not being driven. It could be as simple as adjusting a pot on the main coil (course tune) driver. The PLL and FM coil may have as small of a tuning range as 10 MHz. Darrell Harmon ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] HP 8566B repair
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? jeff 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: [EMAIL PROTECTED] [mailto:[EMAIL PROTECTED] 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. ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there. ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] HP 8566B repair
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: [EMAIL PROTECTED] [mailto:[EMAIL PROTECTED] 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. ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] HP 8566B repair
I don't think much of the idea of shotgun-replacing these particular caps. There are a great many of them, they're not *that* unreliable, and unlike the notorious radial-lead tantalums, they tend to fail open, not shorted, so they're unlikely to damage other parts when they fail. On the other hand there are definite risks, from ESD to human error, associated with unsoldering and resoldering a bunch of parts unnecessarily. Just be prepared to open it up once every couple of years to track down the next one. Nothing to be afraid of inside the 8566s. You could rebuild the whole thing from scratch with HP's docs, if you had to. -- john, KE5FX -Original Message- From: [EMAIL PROTECTED] [mailto:[EMAIL PROTECTED] Behalf Of Jeff Mock Sent: Thursday, December 06, 2007 7:55 PM To: Discussion of precise time and frequency measurement Subject: Re: [time-nuts] HP 8566B repair 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? jeff ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
