- Network analyzer theory
- Internal design
Many of our readers may got impression that only DC-level signals are discussed here, but actually it’s not all the truth. DC and low frequency is just a one area of electronics engineering. While it’s applications are wast and wide, people who work in communications, high-speed digital and radio fields cannot do their job without set of RF-equipment. Here we will do an little extreme case experiment, getting old and abused HP 8753A-010 vector network analyzer for repair. Today HP/Agilent 8753 series network analyzers are replaced by Keysight ENA series with starting price US$ 15756.
I don’t have proper set of RF test equipment, suitable for full diagnostics and performance testing of complex gear like network analyzer, but it will be fun to see how much can be done without dedicated RF workshop, using what is available.
The 8753C was discontinued on 01 Nov 1995 and went out of support on 24 Jan 2001.
The 8753D was discontinued on 01 Jan 2000 and went out of support on 30 Jun 2003.
The 8752C and 8753E were discontinued on 01 Sep 1999 and went out of support on 01 Sep 2004.
The 8753ES/ET were discontinued on 01 Nov 2006 and went out of support on 01 Dec 2011.
Since these products are no longer supported, their associated kits and accessories are not listed on Keysight site anymore.
For complete reference, documentation and manuals are provided for all generations of 8753-series instruments, not just first-generation A
Network analyzer theory
Network analyzer sources known RF signal to DUT and measures response, unlike spectrum analyzers which measure unknown signal amplitude. Having calibrated and known source allow to measure both phase and amplitude and provide much more information about DUT RF device. Similar results, but at worse accuarcy can be achieved with tracking generator and spectrum analyzer. There also different types of network analyzers, as well as multi-port systems to evaluate complex DUTs.
Modern NA’s also have integrated “test sets”, which route signal generator output to the device under test, and also routes the signal for measurement to the NA’s receivers. It often splits off a reference R channel for the incident wave. Often directional coupler or two resistor power dividers are used for signal separation, instead of dedicated test set. Some microwave test sets include the front end mixers for the receivers. 8753A in this article does not have internal test set, so external tools are required to do measurements and DUT tests. Good introduction is available on National Instruments white paper covering some network analysis basics.
Unit was just tossed into cardboard box on top of 4262A LCR meter, and suffered screen protector damage.
Pure luck that CRT display is not damaged and still intact.
First attempt to power instrument on revealed sticky buttons, but it’s actually did power on.
A1 Front Panel
N-type RF ports, made by Amphenol, part number 131-445 are heavily damaged and two of them sustained impact hard enough to get support frame bend.
Inner contacts are damaged and heavily corroded as well, so these are going to be replaced.
A2 Front Panel Interface
A4/A5/A6 Sampler IF
Lot of dust and dirt particles grow everywhere.
A7 Pulse Generator
There is some severe aluminum corrosion plague on the gold plated can.
Close up on triple RF output circuitry:
Angled photograph revealing leveled construction for tunnel diode?
This module assembly had HP P/N 08753-60008 A-2533-45 and manufactured in 1985. Newer 8753C using other part number board (08753-60208 A-2849-45).
This module assembly had HP P/N 08753-60009 A-2529-45 and manufactured in 1985. Newer 8753C using other part number board (08753-60138).
Motorola 68000-series process is known chip used in many different instruments used here as well. There are six ROM chips to store instrument’s firmware.
This board using 16.000 MHz oscillator as main digital clock source. Newer 60138 board found in 8753C is using different oscillator clock, 19.6608 MHz.
New board using only four firmware ROMs.
A10 Digital IF
This module assembly had HP P/N 08753-60010 B-2539-45 and manufactured in 1985. Newer 8753C using other part number board (08753-60095 B-3126-45).
Burr-Brown (today part of Texas Instruments) ADC, P/N ADC76KG is SAR 16-bit hermetic hybrid with laser trimmed thin-film resistors. It’s complete solution with internal ±15ppm/K reference and digital interface. KG version provides ±0.003% maximum linearity error in temperature range 0…+70°C.
A11 Phase Lock
This module assembly had HP P/N 08753-60012 and manufactured in 1985. Same assembly using in newer 8753C as well.
A13 Fractional-N Analog
This module assembly had HP P/N 08753-60013 B-2538-45 and manufactured in 1985. Almost same assembly using in newer 8753C (C-2814-45) as well.
A14 Fractional-N Digital
This module assembly had HP P/N 08753-60014 and manufactured in 1985.
A16 Rear panel board
Power supply module
Power supply have two boards, enclosed in own shield cage.
Power supply have own HP part number:
A16 Rear Panel
8753A analyzer is designed to be paired with HP 85046A test set, HP 85031B calibration kit and HP 11857D return cables for test ports.
Cooling fan is very dirty and have gunk all over it’s body, so it’s just easier to swap it with same specification and size brand new DC 24V one.
Color LCD upgrade with Simmconnlabs NewScope-9 LCD kit
The Simmconnlabs NewScope-9 Color LCD replacement kit is a turn-key solution designed to replace the HP® 1349A and 1349D monochrome CRT display modules used in HP 8753A/B, 8757A, 8702A, 8720A and other test equipments. The Kit supports 8.0” or 8.4” TFT color LCD with SVGA (800 × 600) or XGA (1024 × 768) resolutions. The LCD display is powered from the regulated +5V and +15V in VNA, already present and dedicated for the 1349A/D display in the system. It’s bit pricey at 400 $USD, but that’s mostly due an included top-tier Sharp LCD panel.
On positive side, everything comes ready for installation, screws, frames and hardware all included, so no more hassle shopping is required to get kit going.
CRT could have up to 20 kV potential on the anode, even right after power off. Use proper precautions when handling CRT Assembly. Make sure unit turned off with good delay before doing service and removing CRT module.
Kit arrived from USA in large box with plenty of thick foam, very well packed, no problems there.
Make sure you careful and remove only protective film. There is polarization film right under it, which is required for proper LCD operation. Make sure not to remove it by accident, as replacing it would never make LCD as good as new.
Very happy with Simmcon Labs.
First test. It is working and giving color! :)
Input ports conversion N to 3.5mm
4pcs for total 60$ + 34$ shipping
Well, the HP 85044A test set still has N-type ports. :) And that pesky APC7…
Promised photos of connectors. I’d appreciate if someone knows their original HP/Agilent part-number.
I bought 4pcs. N-SMA on the right is original from 8753A.
Two connectors are decent shape, two other bit worse. But nothing too bad.
Close-up of inner collet:
“Air” isolator, clearly visible by backlit photo on the right. Of course it’s not air in full meaning of the word, but most of gap space is empty, hold just by the transparent plastic spacer.
To actually install them into 8753A’s frame, some metal work would be required, as new connectors have only one notch on threaded mount, while old N-SMA had two notches on both sides.
I’ll just mill excessive metal on the frame with Proxxon :)
And everything would look somehow like this:
Why all this trouble? Here are macro of original N-type ports:
Probably not so bad as most VNA-nuts would say to me, but I don’t like that crud and rust on collets and housings. And you can see dents on the front outer shell, likely due to physical drop impact.
This 8753A VNA have next calibration kits listed in manuals for verification and test:
- HP 85033C 3.5 mm calibration kit
- HP 85031B 7 mm calibration kit
- HP 85032B N 50 Ohm calibration kit
- HP 85036B N 75 Ohm calibration kit
- HP 85033A SMA calibration kit
- HP 85029A 7 mm verification kit
https://groups.yahoo.com/neo/groups/hp_agilent_equipment/conversations/messages/61196 – focus issues
http://artekmanuals.com/manuals/hp-manuals/ – HP 1349A – display unit in 8753A
|Bad HP 8753A VNA from local refub||333$||20$|
|HP 85044A T/R 50Ω Test set, eBay||75$||92$|
|Color LCD NewScope-9 kit for 8753A||450$||50$|
|4pcs HP/Agilent Bulkhead Connector 3.5mm 26.5 GHz||63$||36$|
Total spent 1119$ USD
Modified: Feb. 10, 2017, 12:48 p.m.
- EEVBlog : Newscope LCD kit discussion for 8753A
- Artek Manuals : HP section
- EB5AGV's Workbench: HP-8753C repair
- HPAK Firmware history log for 8753 series
- KE5FX CRT restoration methods page
- Color LCD kit manufacturer page for 8753A
- KIRKBY MICROWAVE page on HP 8753
- EEVBlog : Repair of HP 8753A forum thread