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Re: HP Agilent 8753ES VNA repair [Help]
VNA parameters used ?:?
- Frequency center 100 MHz
- SPAN zero mode?
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TP20 (VCO):
RF signal is at 39.100 MHz, -1.3 dBm instead of 39.840 on your board for frequency >16 MHz seems KO ?
RF signal is at 39.280 MHz, -1.3 dBm ?for frequency <16 MHz?
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TP16 (VCXO):?
RF signal is at 40.000 MHz, - 5 dBm. Seems OK
TP6:
No signal at 160 KHz but a square signal at 909 Khz. Look KO ?
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TP14 (LO2)
RF signal at 10.000 MHz, -8 dBm. Look KO ?
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VCO TUNE TP (with frequency start 15 MHz, stop 16 MHz):
Signal is flat and stay at +21V ?Look KO ?
Same result on VCXO TUNE TP (flat signal)
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Re: HP Agilent 8753ES VNA repair [Help]
开云体育There are some TP to verify on A12 board. Test for high frequency only for now.? CW FREQ >16MHz ? ? ? ? De?: [email protected] <[email protected]> De la part de MattSNE via groups.io ? I tried to apply a 10 MHz external reference 1VPP and the problem is the same.? |
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Re: HP Agilent 8753ES VNA repair [Help]
开云体育If we focus on the high band for now, 3 sources are involved: the 10 MHz reference, the 40 MHz VCXO and a VCO near 40 MHz (39.996 MHz). ? Check your 10 MHz reference. Measure the TP VCO TUNE PRESET START 15MHz STOP ?16 MHz ? I'll look for places to plug in to measure the 40 MHz VCXO output and the VCO. The cause could be a faulty divider. ? ? ? ? _._,_._,_ |
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Re: HP 3403C True RMS Voltmeter display fault
On 3/1/25 11:57, AArnaud via groups.io wrote:
Hello everyone,That solder-looking ball is metallic tantalum that melted and burst through the outer shell of the capacitor. This is a classic failure mode for a shorted tantalum capacitor, usually the "dipped" variety. I've taken both them out and although C2 is apparently healthy the C1, which is the smoothing cap of +12V, was shorted. Good thing it was regulated.An excellent recovery of an excellent instrument. Nice work! -Dave -- Dave McGuire, AK4HZ New Kensington, PA |
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Re: HP Agilent 8753ES VNA repair [Help]
PLL 2 is 977 KHz instead of 996 Khz. I have a delta of 19 KHz on PLL on high band. This explain why the IF on A10 is 23 KHz instead of 4KHz and do not pass the digital filter.?
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Problem is common on high and low band. Do you have an idea on where to look at now ?? |
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Re: HP 3403C True RMS Voltmeter display fault
Hello everyone,
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I'm glad to report the HP 3403C works again!
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I've replaced the duos of LDs A/D chips, but this was not enough to revive the unit. It kept blinking +1 although it had lost its tendency to sometime display garbage.
I turns out I lost the +12V supply rail which I previously had. On the test point of the supply had a dead short. Taking boards out I found that it was on A7 (the board between the converter and the motherboard). Looking at it I found that both C1 and C2 looked really weird has they had a ball of solder on them and you could see inside of them. I've taken both them out and although C2 is apparently healthy the C1, which is the smoothing cap of +12V, was shorted. Good thing it was regulated.
With them out the unit works again and is not too far off reality aswell. Very happy about it.
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My beginner mistake was that I made the power supply measurements with basically all of the boards out. However I think the new chips were necessary as the display was not working even when A7 was out.
I'll order new capacitor for that board, and i'll also recap the power supply aswell. ?
Here it is reading the probe test of my oscilloscope together with its friend the Racal Dana.
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Thanks everyone! |
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Re: HP Agilent 8753ES VNA repair [Help]
开云体育Hi, ? This means that one of the PLLs does not have the right frequency. The frequency near 22.5kHz will not pass through the filters which are for 4kHz at the DIGITAL IF. ? You should check the second LO, it arrives through the motherboard, not easy to access. Connect a test wire as in the picture to measure the output of the second LO on A12 PCB. ? For a frequency below 16MHz, the frequency will be CW FREQ+4kHz, for example, for 100kHz output Port#1, you will have 104kHz. For frequencies of 16MHz and above, you will have 996kHz. ? Yves ? ? De?: [email protected] <[email protected]> De la part de MattSNE via groups.io ? Hello Yves, ? Thank you for your screenshoot. Here is what I got on my board. ? TP20 B (with look cable between port 1 and port 2):? ? ? TP18 A (OPEN loop between port 1 and port 2): ? ? TP16 R: ? ? I check the TP1 5V and the voltage is OK here.? ? Two points here : - I had to put the probe level in x2 mode in my scope to measure the same voltage than you in peak to peak mode. The voltage I measure initially was divided by two. I don't think this is important.? ? ? |
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Re: Service manual scan post processing
On 3/1/25 01:20, Martin via groups.io wrote:
Don't know where I read this, but it said: better use high resolution with JPEG compression than low resolution without. For the same file size, that is.Don't believe everything you read. There's a vast amount of misunderstanding and bad information about JPEG floating around; it has been that way for a very long time. This is a result of people thinking it's just fine to use technology without first learning even the most basic things about it, while at the same time cheerfully ignoring the advice of people who do know something about it. My experience: 300dpi is largely sufficient even for schematics, with compression. If the original is bad, has exceptionally small lettering or such, I take 600dpi as a precautionary measure.At the museum we use 600DPI as a minimum for most things. Data storage is cheap, compression works great, and cheap paper is aging quickly. Of course JPEG does the artefacts around sharp contrasts, but as long as its perfectly readable I prefer that to humongous files that take minutes to open...That depends on the goal, but I personally believe that when any document is scanned, it should be treated as if it is the only known copy (which it may be), and that getting it scanned may be a matter of life and death for someone in the future (which it may be). Either may be true; we have no way to know. The artifacts introduced in JPEG compression, in particular those which result in 8x8 blocking (JPEG's DCT and other steps operate on 8x8 pixel blocks) make subsequent OCR very difficult. This can never be undone, as JPEG is a lossy compression algorithm. JPEG *discards data* in changing the nature of an image file to exploit weaknesses in the human vision system. This is detrimental to most any sort of subsequent processing that may need to be performed. So having researched this exhaustively many years ago, and having been "all up in there" with the JPEG algorithm, I stand by my assertion that JPEG should never, ever be used for something like this. There are plenty of other compression algorithms which will result in the same, if not better image size reductions. -Dave -- Dave McGuire, AK4HZ New Kensington, PA |
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Re: Manual for HP 466A amplifier
I have a paper copy of the HP-466A manual, serial prefix 226, and could copy the schematic for you.? Jeremy? N6WFO? On Fri, Feb 28, 2025 at 8:12?PM WB2UAQ via <pschuch=[email protected]> wrote:
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MattSNE
factory
Dave McGuire
Jeremy Nichols