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On Sun, Mar 6, 2022 at 06:16 AM, Jinxie wrote:
Ozan said about checking the PPL2 unlock indicator on A10A6 naming HUL2 as the test point which should be at zero volts for normal operation. However, the service manual only refers to TP1 in this context as far as I can see. I have checked HUL2 and the voltage is just jumping around all over the place so can't be measured I'm afraid. And TP1 looks like it will require an extender board. :(
The Service Manual says:
Unlock Indicator
When the phase lock loop is in a steady state condition, the voltage at TPl is zero. If
unlocked, the voltage will be non-zero except for transients passing through zero. When
the voltage TPl exceeds 0.7 V, either Ql or Q2 is turned on, discharging Cl5 or Cl4
respectively and tripping comparator Ul. When TPl voltage settles to less than 0.7 V, Cl4
and Cl5 must recharge before the comparator is reset. This takes 5 ms. The comparator
output is TTL high for an unlock condition and remains there for 5 ms after a lock condition
is established.
---------------- HUL2 is the output of comparator mentioned in above paragraph. If HUL2 is going jumping high/low PLL2 is unlocked. I recommend starting the check with 500kHz reference coming in and the divided feedback clock. The are generated at A10A7 (TP5 and TP1) . Ozan
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Thanks, Ozan. Well I couldn't get a meaningful reading with a DVM on HUL2 so I scoped it and clearly the voltage levels at that point are randomly jumping all over the place, so it looks like you've identified the problem here. Well done! I'm just not at all sure how to proceed next as I don't quite understand what you're suggesting as a follow-up test.
I really need to familiarize myself with the relevant schematic(s) and will do that next; seems the obvious thing to do before delving in any further.
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I just needed a bit of a refresher on PLLs from my notes of 40 years ago; I'd forgotten quite a lot.
Anyway, there's no access to any test points on A10A7 from the top side but I note on the opposite side where the PCB traces are visible there were a couple of tiny holes in the perspex sheet which I assume are there to permit one to stick the point of a probe through (with difficulty) and they were marked something like 500khz ref and 500khz divided so I assume on my model that's where one is supposed to measure the signals. However, on probing, both were intermittent and grossly distorted square waves so something's obviously not right there.
I was really struggling with the PDF schematic on my computer so printed out the A10 20/30 block diagram from the manual which makes things a lot clearer not having to flip from one page to another and lose where all the connections are going to and from!
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So here is a thought. I would attack the REF UNLOCK first. Note that all the other PLLs depend on an output from the 100 MHz REF oscillator. It that has problems, anything associated with it (virtually everything) should be considered in doubt. You really should get a set of extenders. There used to be a guy on e-bay that would custom make them - don't see him advertizing now, but if you search past auctions you can probably find him. Another possibility would be to purchase an extender card that matched the height requirement but had more contacts and cut it down - the best choice would be one with more than 2x times the contacts needed and you could make two extenders from one card - the required connectors are available from Digiket, e-bay, and other sources. Extender cards are a MUST. Cheers! Bruce Quoting Jinxie <paul666@...>:
I just needed a bit of a refresher on PLLs from my notes of 40 years ago; I'd forgotten quite a lot.
Anyway, there's no access to any test points on A10A7 from the top side but I note on the opposite side where the PCB traces are visible there were a couple of tiny holes in the perspex sheet which I assume are there to permit one to stick the point of a probe through (with difficulty) and they were marked something like 500khz ref and 500khz divided so I assume on my model that's where one is supposed to measure the signals. However, on probing, both were intermittent and grossly distorted square waves so something's obviously not right there.
I was really struggling with the PDF schematic on my computer so printed out the A10 20/30 block diagram from the manual which makes things a lot clearer not having to flip from one page to another and lose where all the connections are going to and from!
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@Bruce,
I'll check out the 100Mhz REF osc next, then.
I did make up an extender board myself for an earlier model of analyzer and that might work, but it's not very elegant, using loose wires for the extension part which is not optimum, but better than nothing hopefully. Certainly worth a try. And there is always the chance of pulling a board out and finding a glaringly obvious blown component on it with no further testing necessary.
Is there any particular care needed in pulling the A10 section boards out? They're not just pushed-in like the ones I've pulled before. They're well-fitted with screws!
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On Mon, Mar 7, 2022 at 08:58 AM, Jinxie wrote:
..
marked something like 500khz ref and 500khz divided so I assume on my model that's where one is supposed to measure the signals. However, on probing, both were intermittent and grossly distorted square waves so something's obviously not right there.
----- Without a stable 500kHz coming from the reference block PLL2 won't be able to lock. "HULR" test point accessible through the hole in the plexiglass shows if the reference PLL is locked.?This is the same block Bruce suggested looking at. If it is not locked then the focus should be on A7A1 and related blocks.? Seeing distorted square waves at all points needs more thought. How are they distorted, are they just jittery or is the shape distorted. If it is the latter, and supply voltages are stable, there may be an issue with the probe you are using. Ozan
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I haven't been following this thread closely, but since you are now looking at the 100 MHz reference, I vaguely recall long ago having to fix it in a 8566B. The main reason it's kind of memorable, is that it was an unusual failure - a regular old ceramic cap in the PLL loop filter had gone leaky or maybe even shorted. I've seen very few ceramic cap failures over all my years, especially where they were not stressed as in HV or bypassing applications. In this one, it was just part of the filtering of the oscillator control voltage - a very low stress occupation.
Ed
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I believe Bruce is referring to the 100Mhz oscillator on A7A2 which is probably a good call to check next.
WRT Ozan's remarks, I would simply confirm it's not a probing issue in this case. The waveforms are only barely recognizable as a square wave when intermittently present if at all. In fact the randomness of the duty cycle looks very similar indeed to that I saw on HUL2 on A10A6; so much so I'd say they must surely be related. Checking the power rail in the area of this fault also looks like a good idea to me in case it's a reg playing up.
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@Ed Breya
? I've never come across a failed ceramic in a low voltage role, either. But now you've mentioned that, I'll be paying particular attention!
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he important thing is FIRST to get rid of the REF UNLOCK error - that could be the root cause of the others. Read the manual and look at the control voltage and frequency out of the REF module - available via SMB on top of the module Cheers! Bruce Quoting Jinxie <paul666@...>:
I believe Bruce is referring to the 100Mhz oscillator on A7A2 which is probably a good call to check next.
WRT Ozan's remarks, I would simply confirm it's not a probing issue in this case. The waveforms are only barely recognizable as a square wave when intermittently present if at all. In fact the randomness of the duty cycle looks very similar indeed to that I saw on HUL2 on A10A6; so much so I'd say they must surely be related. Checking the power rail in the area of this fault also looks like a good idea to me in case it's a reg playing up.
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I seem to remember, when playing with oscillators, that there was
a condition that allowed (or perhaps permitted) the oscillator to
run at the wrong frequency.? It may be the drive to the crystal,
and I wonder if the actual VCC to the oscillator is somehow
wrong.? It was a long time ago, relatively, but I seem to remember
something that was stable suddenly running at twice the
frequency.? Since (as I remember the waveform here, zero counting
would ignore the peaks and simply say that it's twice the
frequency).? Might be a bypass cap, a feedback cap wrong, not
sure.? If it were a crystal problem, it almost seems as if it's in
overtone mode.
Harvey
On 3/7/2022 3:06 PM, Jinxie wrote:
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I believe Bruce is referring to the 100Mhz oscillator on A7A2
which is probably a good call to check next.
WRT Ozan's remarks, I would simply confirm it's not a probing
issue in this case. The waveforms are only barely recognizable as
a square wave when intermittently present if at all. In fact the
randomness of the duty cycle looks very similar indeed to that I
saw on HUL2 on A10A6; so much so I'd say they must surely be
related. Checking the power rail in the area of this fault also
looks like a good idea to me in case it's a reg playing up.
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If you make a "hard" extender, be sure to insulate it where it can hit the edge of the EMI cage. I usually glue a narrow strip of PC board horizontally across the extender very close to the top of the cage. I think that a wire extension may well contribute to the problem - I would try to make a "hard" extender ASAP - you surely will need them in the future and it makes diagnostics soo much easier. Also, it is not a bid idea to have some spare cards. Many of the cards available on e-bay are functional, the main cards to be nervous about are the xtal filter cards - almost all of those will be bad. Cheers! Bruce Cheers! Bruce Quoting Jinxie <paul666@...>:
@Bruce,
I'll check out the 100Mhz REF osc next, then.
I did make up an extender board myself for an earlier model of analyzer and that might work, but it's not very elegant, using loose wires for the extension part which is not optimum, but better than nothing hopefully. Certainly worth a try. And there is always the chance of pulling a board out and finding a glaringly obvious blown component on it with no further testing necessary.
Is there any particular care needed in pulling the A10 section boards out? They're not just pushed-in like the ones I've pulled before. They're well-fitted with screws!
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We may be commenting at cross purposes here. Most of what I'm talking about involves the 100MHz REF OSC A7A2 and it sounds like you may be talking about the internal 10MHz ref. If he is using an external 10MHz ref, then the internal 10MHz is not involved. If he has not either qualified the internal 10MHz ref or eliminated it, there could be a lot of tail chasing going on.
Cheers!
Bruce
Quoting Harvey White <madyn@...>:
toggle quoted message
Show quoted text
I seem to remember, when playing with oscillators, that there was a condition that allowed (or perhaps permitted) the oscillator to run at the wrong frequency.? It may be the drive to the crystal, and I wonder if the actual VCC to the oscillator is somehow wrong.? It was a long time ago, relatively, but I seem to remember something that was stable suddenly running at twice the frequency.? Since (as I remember the waveform here, zero counting would ignore the peaks and simply say that it's twice the frequency).? Might be a bypass cap, a feedback cap wrong, not sure.? If it were a crystal problem, it almost seems as if it's in overtone mode.
Harvey
On 3/7/2022 3:06 PM, Jinxie wrote:
I believe Bruce is referring to the 100Mhz oscillator on A7A2 which is probably a good call to check next.
WRT Ozan's remarks, I would simply confirm it's not a probing issue in this case. The waveforms are only barely recognizable as a square wave when intermittently present if at all. In fact the randomness of the duty cycle looks very similar indeed to that I saw on HUL2 on A10A6; so much so I'd say they must surely be related. Checking the power rail in the area of this fault also looks like a good idea to me in case it's a reg playing up.
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The 10Mhz doubling issue was down to measurement error. It turned out to be fine and dead-on 10Mhz.
We've now moved on to the issue flagged up by the severely twitching voltage on HUL2 on A10A6. We then checked the 500kHz reference and 500khz division test points and they are likewise twitching all over the place.
Bruce has suggested taking a closer look at A10A7, the 100MHz reference oscillator and I plan to do that when time permits tomorrow.
This is where we are currently at.
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What errors are CURRENTLY reported by the SA ? What was the frequency reference used by the counter that verified te 10MHz internal osc? Cheers! Bruce Quoting Jinxie <paul666@...>:
The 10Mhz doubling issue was down to measurement error. It turned out to be fine and dead-on 10Mhz.
We've now moved on to the issue flagged up by the severely twitching voltage on HUL2 on A10A6. We then checked the 500kHz reference and 500khz division test points and they are likewise twitching all over the place.
Bruce has suggested taking a closer look at A10A7, the 100MHz reference oscillator and I plan to do that when time permits tomorrow.
This is where we are currently at.
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@Bruce
When you say "reported by the SA" do you mean the on-screen messages which are there during normal operation or some kind of internal diagnostics procedure I'm unfamiliar with?
The persistent one is "YTO Unlock" - that's just on all the time.
The frequency reference is just the internal one in my Philips 10Ghz counter which I admit hasn't been calibrated for years - but I'm just a hobbyist and can't justify the expense of periodic calibration.
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Periodic calibration is a ridiculous expense. I am a hobbyist - for about 30 years :-) Regarding the 10MHz calibration, it is a good idea to have a 10MHz GPS based standard - they are not overly expensive and give you at least one source you can depend on for comparison. Your frequency counter (at least) should be driven by that reference. Ideally ALL instruments should be driven from a common 10MHz reference (that is GPS synched). SA stands for spectrum analyzer What I was asking is what diagnostic message appear on the screen. There is a procedure in the adjustments section of the manual for the 100MHz reference oscillator - you should try following it WITHOUT performing any adjustments - If you find the PLL voltage excessively far off,you should probably do the oscillator centering adjustment, but probably best to let us know the results B4 making the adjustment. Are you seeing REF UNLOCK or just YTO unlock or what ? Quoting Jinxie <paul666@...>:
@Bruce
When you say "reported by the SA" do you mean the on-screen messages which are there during normal operation or some kind of internal diagnostics procedure I'm unfamiliar with?
The persistent one is "YTO Unlock" - that's just on all the time.
The frequency reference is just the internal one in my Philips 10Ghz counter which I admit hasn't been calibrated for years - but I'm just a hobbyist and can't justify the expense of periodic calibration.
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I agree about the GPSDO lab frequency reference.? These days it's about $150 for the Leo Bodnar GPSDO, and maybe $100 for a distribution amplifier.? ?Probably you could build your own DA for even less.? Pretty darn cheap!
Jim Ford
Sent from my T-Mobile 4G LTE Device
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-------- Original message -------- From: Bruce <bruce@...> Date: 3/7/22 3:13 PM (GMT-08:00) Subject: Re: [HP-Agilent-Keysight-equipment] Scoping the Power Rails [8566B]
Periodic calibration is a ridiculous expense.? I am a hobbyist - for? about 30 years :-) Regarding the 10MHz calibration, it is a good idea to have a 10MHz GPS? based standard - they are not overly expensive and give you at least? one source you can depend on for comparison. Your frequency counter? (at least) should be driven by that reference.? Ideally ALL? instruments should be driven from a common 10MHz reference (that is? GPS synched). SA stands for spectrum analyzer What I was asking is what diagnostic message appear on the screen. There is a procedure in the adjustments section of the manual for the? 100MHz reference oscillator - you should try following it WITHOUT? performing any adjustments - If you find the PLL voltage excessively? far off,you should probably do the oscillator centering adjustment,? but probably best to let us know the results B4 making the adjustment. Are you seeing REF UNLOCK or just YTO unlock or what ? Quoting Jinxie <paul666@...>: > @Bruce > When you say "reported by the SA" do you mean the on-screen messages? > which are there during normal operation or some kind of internal? > diagnostics procedure I'm unfamiliar with? > The persistent one is "YTO Unlock" - that's just on all the time. > The frequency reference is just the internal one in my Philips 10Ghz? > counter which I admit hasn't been calibrated for years - but I'm? > just a hobbyist and can't justify the expense of periodic calibration. > > >
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It's getting really late here again now so this will be my final comment of the day. I was seeing YTO unlock AND REF Unlock after switch-on. However, I believe (and I'll have to double-check because I'm working on this thing with its screen facing away from me so very hard to see) last time I checked, REF Unlock message went away after a few minutes of warming up but the YTO warning is permanent. I'll double check this in the morning and report back here on it then, but that's how I remember it from the end of last week's T/S sessions anyway.
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Bruce ,
In regards to calibration I care to argue that periodic calibration in a hobby/home lab environment is not a necessity , I do however see a benefit in having a initial calibration performed when a piece of equipment has been acquired or if a repair has been performed , first of it gives you the certainty that the equipment does not have any faults and in the case of power sensors for example the updated calibration factors ensure that you are reading correct power levels
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-----Original Message----- From: [email protected] < [email protected]> On Behalf Of Bruce via groups.io Sent: Monday, March 7, 2022 5:14 PM To: [email protected]Subject: Re: [HP-Agilent-Keysight-equipment] Scoping the Power Rails [8566B] Periodic calibration is a ridiculous expense. I am a hobbyist - for about 30 years :-) Regarding the 10MHz calibration, it is a good idea to have a 10MHz GPS based standard - they are not overly expensive and give you at least one source you can depend on for comparison. Your frequency counter (at least) should be driven by that reference. Ideally ALL instruments should be driven from a common 10MHz reference (that is GPS synched). SA stands for spectrum analyzer What I was asking is what diagnostic message appear on the screen. There is a procedure in the adjustments section of the manual for the 100MHz reference oscillator - you should try following it WITHOUT performing any adjustments - If you find the PLL voltage excessively far off,you should probably do the oscillator centering adjustment, but probably best to let us know the results B4 making the adjustment. Are you seeing REF UNLOCK or just YTO unlock or what ? Quoting Jinxie <paul666@...>: @Bruce
When you say "reported by the SA" do you mean the on-screen messages
which are there during normal operation or some kind of internal
diagnostics procedure I'm unfamiliar with?
The persistent one is "YTO Unlock" - that's just on all the time.
The frequency reference is just the internal one in my Philips 10Ghz
counter which I admit hasn't been calibrated for years - but I'm just
a hobbyist and can't justify the expense of periodic calibration.
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Jinxie