NEW to me HP8566B - Page 1
Forum section: electronics / repair

author: davidwenrich
author_rank: Contributor
timestamp: January 25, 2023, 09:34:47 pm
content: Hello to everyone. First and foremost, I am new to all things RF. I am not new to electronics (AC/DC circuitry). I have just acquired a HP8566B Spectrum analyzer, in hopes of repairing it to specification. I have access to all repair manuals related to this instrument, and have read much of them. (Not all). I purchased this analyzer in pieces and stages Display from one seller, RF section from another, and interconnect cables from yet another source. Initially I had a bus connection issue, easily resolved. Then I did a scratch and sniff, all appeared viable, so I powered up, current limited and monitored. All ok. Display however shows what I interpret as noise in the low frequency band. Upon investigation of the front end, so far, is no signal throughput. I have only a tinySA spectrum analyzer at the moment to produce signal to ~6GHz, but also no signal through in the .100Hz-2.5GHz using my arb gen at any amplitude. Low signal is no connection through the low/high range switch. (replacement on the way)This leads me to believe possible over voltage applied to front end. What I need to figure out however, is whether the linear noise slope I see on the display can somehow have something to do with it, and where I may need to investigate. I have no way to characterize response from any components at frequencies >80MHz as I can only produce, or measure at once, not both. Hoping someone more experienced than I can see what I see and go,"I've seen that before, it's the (insert obvious answer here)" Again I am new to RF equipment, but not totally clueless.

author: davidwenrich
author_rank: Contributor
timestamp: January 25, 2023, 09:38:32 pm
content: Also, I can get the YTO unlock error to clear if I tune the analyzer to frequencies under 2-3GHz

author: Runco990
author_rank: Frequent Contributor
timestamp: January 26, 2023, 12:50:58 am
content: Make sure the little hard jumper coax is installed on the front.As to the YTO unlock error, did ya google that? Many posts and videos on it. On my own unit it was the bad capacitor, but I don't recall the board number right now. Give it a quick look up.These are magnificent analyzers! Once you fix it, just make sure you NEVER put DC into the front end.

author: davidwenrich
author_rank: Contributor
timestamp: January 26, 2023, 04:15:23 am
content: Yes I've googled the YTO unlock. I plan to tackle that after the switch repair, but the strange ramped display has me puzzled. Almost like a filter of some sort is not functioning correctly, lower frequency noise at higher amplitudes getting through, and noise decrease with frequency increase, in a linear fashion... AND, a DC block is on my order list. Just in case I do something dumb.

author: davidwenrich
author_rank: Contributor
timestamp: January 26, 2023, 02:41:33 pm
content: Capacitor C7 A20 YTO Main Coil Driver. 10uF 60V. Mine measures 6 puffs lol and 1.97megohm ESR at 1khz out of circuit. 24$ for one cap at digikey....noise still a mystery.

author: Runco990
author_rank: Frequent Contributor
timestamp: January 26, 2023, 05:03:38 pm
content: Well, did you run it's calibration routine just to eliminate anything simple first?Which reminds me... I think these have a battery also... have to peek in the manual. I just backed up the calibration constants on my 8593E. If you loose them, the analyzer will be way out of whack.I'm no expert on spec-A's, but I always make sure to go through all the obvious dumb things before delving into the hardware itself. Also.... Re-seating cards on old HP gear seems to be a good idea these days. Dirty connections, etc.Amazing this stuff still runs as good as it does!

author: davidwenrich
author_rank: Contributor
timestamp: January 27, 2023, 10:32:10 pm
content: Thanks for reply. All cards were removed , contacts checked cleaned and reinstalled. This SA has no error for battery. (monitor built it) Can't run self cal routine until I correct the YTO unlock error. Will post update as soon as my over-priced capacitors arrive.

author: Runco990
author_rank: Frequent Contributor
timestamp: January 28, 2023, 06:33:19 pm
content: Capacitors have gone through the roof since covid....I was going to order a bunch of Vishay axial caps to restore one of my HP meters "Properly" but I'll put that project aside for now.The electronics hobby has definitely gotten a lot more expensive.

author: davidwenrich
author_rank: Contributor
timestamp: February 01, 2023, 05:32:42 am
content: Update... After replacing C7 on A20 board, unfortunately YTO unlock condition persisted. Put my thinking cap on. Decided the easiest adjustment of which I possess enough instruments to carry out which could affect the unlock condition was the sweep, DAC, and main coil driver procedure. Carried out the procedure and viola! YTO unlock problem solved. Pots were pretty far off from the now correct settings, leading me to believe someone may have been poking about willy nilly turning pots? hard to believe things would have drifted so far, or that my one cap replacement would have altered much from previous settings. Still have the strange sloping noise floor however, and notice when instrument is cold, the noise floor is much more flat....I have concluded the I'm going to have to carry out a complete alignment, which will take a lifetime, gathering all necessary instruments... at least I have a retirement project.