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I'm officially lost now with this 8753ES
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Last I left off I had an intermittent contact on one of the modules in the hybrid assembly in the source module.
The good news is I found the root cause, it was one of those elastomeric pieces which got too squished and over time lost its resilient properties. The bad news is that the unit now has a fault which I cannot isolate. I was able to acquire another source module, albeit of a slightly different part number, untested, from a UPS damaged instrument.? I figured it would at least be good for spares. Anyhow, before I found the specific bad connection, I went through the following steps: I tried the new source assembly, went through the required initializations, and it didn't work.? No output at all.? Upon opening the new hybrid module I found that a lot of screws were missing.? I borrowed them from my unit and now it is putting out power, but the output frequency is all over the spectrum even with the PLL turned off.? The Keysight website says this model number is compatible with my unit, but perhaps it isn't afterall. I placed the last hybrid module from the new unit in my unit. Success!? although the (divided) output was about -7 dBm, it was remarkably uniform from 300 kHz through 3 GHz.? So I decided I would run through the necessary adjustments spelled out in the manual. One of them is hooking up a power meter.? I will add that the instrument had been on for some time by then and stable.? During theroutine, I saw a few flashes of phase lock errors.? uh-oh.? And then at the end the cal failed.? Right after that everything was just awful.? The manual says if you get that failure message you start at square one, source troubleshooting.? So I did, right from the top. One of the first tasks is to run test 48, pretune correction constants.? It fails this.? I rechecked the sampler/mixer check, the problem isn't there (I didn't think so but I want to be thorough). The next is to check a few frequencies in SRC tune mode.? This is done with the PLL open.? This fails miserably, the 300 kHz is around 263 MHz and 30/40 MHz are similarly high.? The next test is "YO coil drive check with analog bus".? The 1 V/GHz signal looks substantially like in the manual, and more importantly completely identical to what I had seen before (I took a photo) when I didn't have this problem.? All the manual now says is to replace the source assembly. So I am lost.? I tried checking the 3.8 GHz oscillator, it's fine. I checked the frequency of the YTO and it is very high at the lower frequencies but is exactly where it's supposed to be at 1 GHz instrument output and above (4.8 GHz YTO and above). The weird thing is that this specific problem seems to have occurred when I was running the power level cal routine.? That may just be coincidence. I'm lost.? It seems the YTO is way too high at the lower frequencies for the PLL to lock, but the drive signal (at least on the analog bus) is correct.? Do I check the voltages at the coil of the YTO next?? Has the YTO gone bad?? (I do have a potential spare).? What do I do now?? I didn't give all the steps and there were many cases where I went in circles. Peter |
So I am lost.? I tried checking the 3.8 GHz oscillator, it's fine. I checked the frequency of the YTO and it is very high at the lower frequencies but is exactly where it's supposed to be at 1 GHz instrument output and above (4.8 GHz YTO and above).Peter, is this a typo? The cavity oscillator should be just below 3 GHz. Vladan |
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Thanks.? I've been working off of the 8753B CLIP, not too much has seemed to have changed.? What is the part number for A11 in the 8753D?? In my ES it is 08753-60162.
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What I'm seeing is that the YTO is over 200 MHz too high on the lower frequencies (under say 1-1.5 GHz) so the test 48, generate proper pretune voltages, fails.? The output at P1-1 to P1-2 is somewhat higher at the low end than the manual shows, being 4.0 volts in mine vs. 3.5 volts stated in the manual.? U18-6 voltages (not shown on the schematic shown below), out of the DAC, look good.? The drive signal from A11 is current rather than voltage so a slight difference could be attributed to tolerance of my YTO coil resistance (45.2 vs. 44.4 ohms?? Not enough for that difference).? I also tried swapping the YTO for another and the replacement behaved exactly the same. The instrument PLL locks nicely when using an external source. Where did you find the CLIP you sent?? I'd like to see the rest of the A11 board, and maybe more, as it may be closer than the A/B CLIP I have.? And I'd *love* to see a CLIP for the A3 source PCB! Peter On 3/16/2019 8:42 PM, pianovt via Groups.Io wrote:
Maybe this will be helpful. It's from the 8753D, but should be the same for the ES. |
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It's available on eBay listed as 8753D CLIP. I bought mine that way. Artek doesn't seem to have it. Not sure if the eBay seller is licensed to sell it or not, but it's been years since I bought, and it's still listed by the same seller. On Sat, Mar 16, 2019, 6:07 PM Peter Gottlieb <hpnpilot@...> wrote: Thanks.? I've been working off of the 8753B CLIP, not too much has seemed to |
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Thanks, just ordered one.
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On 3/16/2019 9:41 PM, Colby Burkett wrote:
It's available on eBay listed as 8753D CLIP. I bought mine that way. Artek doesn't seem to have it. |
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The schematic is for 08753-60162, so it matches what you have. I would monitor the voltage across R43 (the 40 Ohm power resistor) as you tune the YTO. It should be a fairly linear function of frequency with some d.c. offset.
As far as I know, the A3 source board schematic has never been published in a CLIP. I once saw it, and to my eye it didn't look nice enough for official publication. It was probably just good enough to extract the netlist and lay out the board. I suspect they never intended to publish it, so they didn't spend the money on making it look nice. Vladan |
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I ordered the CLIPs from the ebay seller who likely got them from Manuals Plus which is now gone.
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Nothing is obviously wrong with the VCO drive to the YTO.? I say "obviously" because the waveform has the same shape as it shows in the manual, but yet the voltages are off, most especially at the low frequency end where the manual says the drive should be 3.5 volts it is actually 4.0.? But is this a normal difference or has the PLL card drifted out of spec? If I get a hold of another A11 card I will know that answer. So here's the thing:? is it possible something I did in the hybrid module could have caused this?? I would not have thought so as it is operating at high RF frequencies only and not directly controlling the YTO frequency, especially when the PLL loop is opened. I am thinking I will try and draw out a diagram of the PCB on the source module. Peter On 3/16/2019 10:28 PM, pianovt via Groups.Io wrote:
The schematic is for 08753-60162, so it matches what you have. I would monitor the voltage across R43 (the 40 Ohm power resistor) as you tune the YTO. It should be a fairly linear function of frequency with some d.c. offset. |
开云体育Hi I have the original CLIP manual for 8753D and I have done a PDF and uploaded at ? To download ? ? Regards Yves De?: [email protected] <[email protected]> De la part de Colby Burkett ? It's available on eBay listed as 8753D CLIP. I bought mine that way. Artek doesn't seem to have it. ? Not sure if the eBay seller is licensed to sell it or not, but it's been years since I bought, and it's still listed by the same seller. ? On Sat, Mar 16, 2019, 6:07 PM Peter Gottlieb <hpnpilot@...> wrote:
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Thank you Yves, that's fantastic!
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Peter On 3/17/2019 1:49 AM, Yves Tardif wrote:
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Thank you soooo much. Really appreciate it.?
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On Sun, Mar 17, 2019 at 01:49 AM, Yves Tardif wrote:
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To help me in my fault isolation efforts, Pete Manfre has offered to mail me a new, never used 08753-60162 A11 PLL board.? (Thank You Pete!)
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This will help immensely.? The trouble with the HP troubleshooting guide is that problems can be subtle and fall between the cracks where their only suggestion is to try replacing subassemblies with known good ones.? One example is the 1 V/GHz waveform; if the shape matches the image shown but is slightly offset is that a pass or a fail?? Another is the output level; if it's supposed to be 0 dBm and it's actually -7 dBm is something wrong?? It can be adjusted to spec and still be set to beyond instrument max output, so is that a problem or is it ok? If you work on a certain type of instrument all the time your experience fills in these questions the service guide leaves unanswered. Regarding the A3 source PCB, I see that it has two 12 bit DACs and a quad 8 bit DAC.? It also has OC drivers for the switchable attenuator that is an option in the 8753ET.? Does anyone know what all those DACs are used for?? The coild drive for the YTO comes from the A11 board, so all that's left are the FM coil on the YTO and the tune input for the 3.8 GHz cavity oscillator.? What am I missing? Peter On 3/16/2019 10:28 PM, pianovt via Groups.Io wrote:
The schematic is for 08753-60162, so it matches what you have. I would monitor the voltage across R43 (the 40 Ohm power resistor) as you tune the YTO. It should be a fairly linear function of frequency with some d.c. offset. |
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On Sun, Mar 17, 2019 at 10:08 AM, Peter Gottlieb wrote:
Regarding the A3 source PCB, I see that it has two 12 bit DACs and a quad 8 bit DAC.? It also has OC drivers for the switchable attenuator that is an option in the 8753ET.? Does anyone know what all those DACs are used for?? The coild drive for the YTO comes from the A11 board, so all that's left are the FM coil on the YTO and the tune input for the 3.8 GHz cavity oscillator.? What am I missing?The DACs are part of the leveling loop. In addition to setting the power level, there are various breakpoints and offset adjustments for the level detector and logamp, a slope adjustment, etc. On the ES (and maybe also D), the ALC range was expanded which made this loop very difficult to control. Also on this board is the bias and temperature compensated varactor drive circuit for the 3.8GHz oscillator. Then, there are also power supply filters for those microcircuits underneath. As far as I remember, the main coil drive merely passes through this board. For Opt. 006 analyzers, there is all the drive circuitry for switching bands. The 8753D/ES analyzers with internal test sets all have step attenuators, so those are also driven from this board. This board has given me problems more than once. It's a multi-layer board, so tracing it out could take a life time. I have had open vias on it, one board had a cracked pad where that huge power resistor solders in. The design is mecahnically fragile there, but production instructions required bending the resistor after it's soldered into place. I think that may have caused problems on my unit. I also had a leveling loop which oscillated. But, I don't think any of this is related to your YTO tuning problem. Keep in mind that the reference channel is derived from the last thick film microcircuit. If you have a bad elastomer contact between the microcircuit and the SMA connector, it can cause problems. I can't however explain why the tuning is off only below 1 GHz RF out. Vladan |
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Thank you for all that info, it will be helpful.
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Regarding my problem, I am still not sure where it is located.? It could either be in the phase lock board or the source assembly.? I will know for sure when I get the replacement phase lock board.? The YTO tuning voltages are enough off from what the service guide says that it could go either way. With a signal generator as external source, at 1 MHz the unit locks from roughly 500 kHz to 4 MHz so this means the pretune must get to that range (there's the 3.8 MHz osc to work with too).? 200 MHz high is way off. It might be interesting to feed the YTO with a power supply and see what currents are required at different target frequencies and compare to what the default pretune is in my unit. To be continued... Peter On 3/17/2019 8:25 PM, pianovt via Groups.Io wrote:
On Sun, Mar 17, 2019 at 10:08 AM, Peter Gottlieb wrote: |
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On Mar 18, 2019, at 1:35 PM, pianovt via Groups.Io <pianovt@...> wrote:
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开云体育Hi PeterIt's an image file.? I was able to open it with Irfanview.?? I just saved it as a JPG for you. Daun On 3/18/2019 1:41 PM, Peter Gottlieb
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What is the file you sent? ?Neither my iphone nor Win10 machine knows what to do with it.? --
Daun E. Yeagley II, N8ASB |
开云体育I was able to see Daun’s image, thank you.?The interesting thing is that my waveform starts somewhat higher. This may be very significant. I did verify that the analog bus is reading correct as the voltages shown match up within tight tolerance to my calibrated scope. I will know quickly when I receive that replacement phase lock board from Pete whether this is the root cause or not.? Peter On Mar 18, 2019, at 2:05 PM, pianovt via Groups.Io <pianovt@...> wrote:
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