HP 8590A Wrong Frequency and Amplitude Measurements below 17MHz - Page 1
Forum section: electronics / repair

author: Johnny10
author_rank: Frequent Contributor
timestamp: August 30, 2020, 11:46:22 am
content: I just purchased a problem unit HP8590A Spectrum Analyzer it has measurement problems below 17MHz.I have read the service manual and done the software tests but before opening the unit I wondered if there was any advice from those of you who have worked on unit.No errors listed or in memoryManual says problems are most likely in the FM coil circuitry.So what I have done so far.Done a Cal Frequency and Amplitude cal and store.Run the FM Coil Drive RoutinePicturedDone the ADC routines.Seem normal switches at listed frequencies.Checked LO for Frequency0 2.050901 GHz16.92MHz 2.07947 GHz1.5 GHz. 3.548310 GHzMeasurements and AmplitudesSeems I get wrong Frequency measurements from 17MHz down.I get wrong Amplitude from 2MHz down.Drifting signal (Where peak walks across screen) from 200K down.Amplitude drops pretty consistent -60 dBmI also noticed as I worked the Amplitude on the signal generator the Amplitude measurements in 8 to 2MHz intermittently were correct.

author: Johnny10
author_rank: Frequent Contributor
timestamp: August 30, 2020, 06:11:07 pm
content: Been reading through all the forum information and watching feedbackloop's youTube videos.Will order the new diodes for the mixer and look over components in the FM Coil Driver circuitry on the Analog board.

author: Johnny10
author_rank: Frequent Contributor
timestamp: September 21, 2020, 03:32:24 pm
content: Well I had a chance this week to finish the HP8590A repair.Parts came in and I made a new work area to do the soldering.Before repair I could only get non-sensical readings below 17MHz in both Frequency and Amplitude.Sometimes readings would be off 1-3MHz, Amplitude would be accurate or drop -60dBm.I used the Avago RF Mixer/Detector Diode HSMS-2822. The original diode pair were not shorted or open.I pulled the A7 board and checked all Capacitors, checked the Voltages and the Reference voltage at the Reference IC output pin. Re-soldered any joint that looked odd, reseated connectors.The manual showed these problems could be traced to the FM Coil Drive circuitry, The First LO or the Mixer Diodes.Checked over FM Coil Driver no problems. Used example traces from the troubleshooting section of Supplementary Manual.Pic showing 1MHz signal after repair.

author: bdunham7
author_rank: Super Contributor
timestamp: September 21, 2020, 03:41:15 pm
content: Quote from: Johnny10 on September 21, 2020, 03:32:24 pmThanks for posting the repair. I wonder if you could characterize the presumably faulty diodes to see what the issue is? Capacitance, leakage, forward voltage,

author: Johnny10
author_rank: Frequent Contributor
timestamp: September 21, 2020, 03:48:20 pm
content: I do have a question for all you HP SA owners out there.In the manual there is a description of the Cal Data which shows RL-VENRranging from 255-30. I believe these are the DAC correction figures, even after my repair my last figures are still in the 116-138 range. Does this imply the DAC's are aging? And should be replaced.

author: Johnny10
author_rank: Frequent Contributor
timestamp: September 21, 2020, 05:45:55 pm
content: Checking the diodes on the curve tracer... the first diode fell apart when I connected the probes.The diode must have had cracked lead inside.

author: Johnny10
author_rank: Frequent Contributor
timestamp: September 22, 2020, 05:10:12 pm
content: I believe my unit has an early A7 Board. Wondering if any know of Schematics?08950-60001There are lots of different schematics available but haven't found more than portions of this one.

author: Johnny10
author_rank: Frequent Contributor
timestamp: September 27, 2020, 12:55:53 am
content: 10KHz Lower frequency limit, 100KHz shorter Span

author: Oberon
author_rank: Contributor
timestamp: April 28, 2025, 09:33:07 am
content: Colleagues! Good time! Unfortunately, no one answered... Now I'm asking for help with something else. I need a diagram of the parts and the schematic diagram of the 09590-60001 Analog Interface board (A-2739-53). I kindly ask for your help in finding a schematic diagram for this board. I have an old device and I want to restore it! With respect, to the whole society, Alex.

author: Oberon
author_rank: Contributor
timestamp: July 20, 2025, 04:49:32 pm
content: I am glad to welcome you! Colleagues, I fixed my HP8590a!! To do this, I had to buy a second converter. I changed the faulty one to the purchased one and everything worked! Replacing the HP 1GS1-4210 in TO72 transistor with a BFW30, as described in the link:http://f1chf.free.fr/F5DQK/2_Amplis_RF_amplifiers/432%20MHz/HP8970b%20erreur%2018.pdf, did not lead to success, as I could not set the frequency to the required value. Thank you all for your attention! Here is my screen with display cal data: