Anritsu ML2438A power meter calibration problem - Page 1
Forum section: electronics / repair

author: Aiy
author_rank: Regular Contributor
timestamp: December 12, 2020, 02:30:07 pm
content: Hello everyone,My Anritsu ML2438A with power sensor MA2474D has an offset when calibrating against the internal 50MHz source.When I enable the RF-output from the calibrator after Zero/Cal cycle (no error) the readout is -2.55 dBm. No Calfactor is set.Does anybody have experience with these meters and power sensors and their function?How should I approach the troubleshooting?Best regards

author: Aiy
author_rank: Regular Contributor
timestamp: January 12, 2021, 08:13:40 pm
content: So I ended up taking the power sensor apart.Here's my reverse engineering so far.The detector is built with three sections,1. RF sectionDirectly after the K-connector I see what I assume is a DC-blockAfter that I see what I think is dual diode detectors and 50Ohm termination, possibly positive/negative mounted.After that is a mystery chip (see attached picture) which I think is a Maxim orMacomchip. Possibly this is a crosspoint switch. One of the control signals going to the RF section is switching 0 to 5V at low power levels (less than -30dB). I believe this could be to eliminate the detector bias?2. DC amplification and signal conditioning, the signal chain is:Two stages of amplification, differential, one for each diode and a gain selection. As the attached PCB top and bottom photo shows the layout is symmetrical for the two diodes.2.1. is a TI TLC2202AI dual OPAmp (PCB Top)2.2. is a Max 393 Quad SPST switch (PCB Bottom). Single 0/5V control signal from the Power meter. Two switches are used to change the gain between Unity and an amplification ratio.2.3. is a Max 410 dual OpAmp (PCB Top)There is also a 24AA64/24LC64 64k I2C eeprom for model and calibration coefficients, neat compared to older HP models I've used.The bottom side holds a bunch of ESD protection diodes aswell.3. 12-pin interface to cablePinout coming when I find my notes, but from the top of my head there's the following:Ground+-5VTwo control signals - Gain, Crosspoint switch?I2C - SDA, SCLDifferential detection signal - makes sense for long cable lengthsIt seems something is broken in the RF section, possibly one of the diodes in my detector is dead.I see the output on the differential amplifiers chain react to RF signals, and when I inject negated DC signal with the same magnitude as the working side, the readout is very close to the correct RF amplitude.Best regards

author: Aiy
author_rank: Regular Contributor
timestamp: March 16, 2021, 06:45:16 pm
content: I replaced both diodes in the detector with Macom MSS10 beam-lead diodes from Mouser.The sensor now does the Zero-0dBm calibration correctly.I have swept the detector side-by-side with two other Anritsu detectors and the frequency response is nearly identical.I also took a photo of the mystery Maxim chip. It is a Maxim AC642-EZ 72A (C) 1993.Best regards

author: Jabi
author_rank: Newbie
timestamp: July 19, 2024, 04:21:40 am
content: Good morning:Where are the dual diode detectors in the photos? I can't quite see them to replace them in my Power meter...Regards de Jabi, ea2aru.