HP8559A spectrum analyzer reference level? opt 002 - Page 1
Forum section: electronics / testgear

author: sarepairman2
author_rank: Frequent Contributor
timestamp: July 02, 2015, 04:37:10 am
content: Does anyone know what the deal is with the options on the HP8559A spectrum analyzer?I got a unit that has a busted ref level adjust knob, so I just took the broken plastic off and it works easily enough, if I push it in I can adjust the attenuation, and if I pull it out I can adjust the reference level, I put a smaller knob on the fine adjust but it seems to work fine.However, I am confused by something. The manual says it is capable from -112dBm to 60dBm. Like, it says for the basic test "set to 0dBm" or set to 50dBm (if you have the 002 option, which I do not have).The cracked plastic knob I took off has a little indicator wheel for the setting, and it spans from -100 to 70dBm.Since the fine adjust goes from 0 to -12, so I assume the -100dBm is used, since -100+-12 = -112.However, my unit only clicks 9 times. I opened it up and had a look at the switch assembly (without actually disassembling the switches), the traverse of the switch is blocked by a little metal rod embedded into a hole, clearly put there on purpose. This means that my unit is either -100 to -10 dBm or -90 to 0 dBm.Only the -90 to 0 dBm makes sense, as the manual specifies that for the "002" option 50dBm should be used, while for other units 0dBm should be used.Is this SA limited from -90 to 0, and the option 002 gives it -100 to +50? I think I can move the position of the pin to enable the knobs to traverse where ever.. but does anyone know any details on what the 002 option actually changes ? Someone speculated that they might include a beefier attenuator to support +50dB.The knob I had is completely fubar, so I have no idea what the reference levels actually are. I read that I should not take the switches apart unless I really wanna punish myself so...oh fuck, its a god damn analog computer knob. !!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!https://www.youtube.com/watch?v=56nvlgyg9-M&feature=youtu.beI got that hunch like, 2 minutes before watching this video

author: Stray Electron
author_rank: Super Contributor
timestamp: July 05, 2015, 09:19:53 pm
content: LOL! I just got a HP 8559 last week and it also has a busted Reference Level knob (and a broken fine Tune shaft and other mechanical problems) and I also can't guess at what it's set at. I posted on here one or two days ago about it. I posted to anoldHP 8559 thread instead of starting a new one. You might want to combine those threads.But to continue, I played around with the knobs and did get the Cal Output signal to display so I think the RF section is good so I'm going to try to resurrect mine. I have the PN for the knob and will call HP tomorrow to see if it is still available. FWIW the same knobs was used on the 8558 and it has an 8558 part number (08558-60167). The military also used the 8558 so the knob also has an NSN."However, my unit only clicks 9 times. I opened it up and had a look at the switch assembly (without actually disassembling the switches), the traverse of the switch is blocked by a little metal rod embedded into a hole, clearly put there on purpose. This means that my unit is either -100 to -10 dBm or -90 to 0 dBm."Since mine isn't working properly I can't help you. But the service manual (available on-line) does have a section about how to install the knobs and align them correctly. It starts at page 291.

author: sarepairman2
author_rank: Frequent Contributor
timestamp: July 07, 2015, 01:55:05 am
content: nah it seems to work right, i found a diagram of the ref level knob in the manual so I know what I can set it to, i think there is maybe some gain compresson error (possibly a bad PIN diode in the 10db amp according to the manual) but I am not sure.Right now I just put some random knob on the fine adjust and manually turn the ring with my hand, it seems to work ok.i think i will wait until you fix yours before I fiddle with mine anymore, I would rather verify against someone elses then start buying like 10$ pin diodes and shit. If you don't fix yours then I need to wait until I get a RF signal generator n some other tools to see exactly whats going on.. the fastest signal I have available currently is the 35 MHz output on the calibrator.. this started my probobly expensive venture into RF electronics.

author: ddrl46
author_rank: Regular Contributor
timestamp: July 07, 2015, 11:45:20 am
content: Option 002 seems to be for a reference level calibrated in dBmV instead of dBm, if the numbering of the options is similair from the HP 8558B and the HP 8559A.I have a HP 8558B and 8559A as well, had to go through the joy of fixing the switch assembly. The metal contacts in the switches like to come loose over time and cause all kinds of wacky issues. Frequency stability of these spectrum analyzers is also quite poor by modern standards but good enough to see whether or not something is there. Here is some information on the switch issue:http://www.orionsword.net/Electronics/TestEquipment/HP8559A/HP8559A.html.

author: Stray Electron
author_rank: Super Contributor
timestamp: July 07, 2015, 04:08:08 pm
content: I spent an hour on the phone yesterday with HP trying to get the parts that I need for my HP 8559A. I couldn't convince most of the nit-wits there that HP ever sold another other than computers and printers! After I told one clown that the part was not for a computer he asked what the part was for and I said "a piece of electronics test equipment called a spectrum analyzer". He then asked if it was a laptop!I tried to tell each of them that HP actually made test equipment BEFORE they made computers but only ONE person believed me!I started out by calling the phone number that is supposed to handle parts for things other than computers, printers etc but they couldn't find any of the parts numbers, model numbers or product numbers that I gave them. Oddly enough it's the same phone that I called 15+ years ago to get parts but now they don't seem to have any record of any test equipment or parts for the same.I have four other SAs that work so considering the low performance of this model and the difficulty in getting parts AND the time that it would require to remove and disassemble the front panel and fix it, I think I just going to take this one back where i found it and give it back to them. The price was cheap enough but it looks like it would take a LOT of time to make all of the mechanical repairs that this one needs. Also I can't do a thorough electrical check till the mechanical problems are fixed it this one could involved even MORE work.

author: mmagin
author_rank: Frequent Contributor
timestamp: July 07, 2015, 05:21:38 pm
content: I spent an hour on the phone yesterday with HP trying to get the parts that I need for my HP 8559A.You'd be better off trying Keysight. That's the former part of HP that made that kind of stuff. If you look up the part in the service manual, you can probably try searching for it athttp://www.keysight.com/my/faces/fapHomePage.jspx?cc=US&lc=eng&_afrLoop=404978781711000&_afrWindowMode=0&_afrWindowId=null#%40%3F_afrWindowId%3Dnull%26_afrLoop%3D404978781711000%26lc%3Deng%26cc%3DUS%26_afrWindowMode%3D0%26_adf.ctrl-state%3Dnsgnveib_4Of course, if they have the part, they'll probably want a ridiculous amount of money. E.g. I wanted to replace the noisy fan in my HP 8562A. They wanted something over $100, Digikey had the same fan (Papst-EBM) for $35. Had to solder the connector on, but perfect otherwise.I bought a HP 8559A previously, but sadly the triple function knob you were talking about was FUBAR also. Seems like it's a weak point. (Fortunately the seller took it back for a full refund.) My 8562A cost a lot more, but it is synthesized and thus easy to lock to a 10mhz reference.

author: Stray Electron
author_rank: Super Contributor
timestamp: July 08, 2015, 04:19:51 pm
content: I thought about that too. But when i called the published number I asked if they were handling HP parts or if Keysight was or if Agilent was and they said that they were and that I had the right number. FWIW this is the same phone number that I used to order HP instrument parts from even though it was Agilent by then.I did a lot of searching on the net and I saw a LOT of postings about people getting HP 8558s and 8559s and it seems like ALL of them complained about that knob being FUBAR! I guess that they weren't one of HP's better better ideas!FWIW I found another home for this one. Also it appears that I have all the pieces of the knob so he's going to attempt to rebuild it. His buddy has the same model so they're already familiar with their idiosyncrasies. I will ask him to photograph his repair attempts and, if successful, I'll have someone post them on the net.

author: mmagin
author_rank: Frequent Contributor
timestamp: July 10, 2015, 02:27:27 am
content: Quote from: Stray Electron on July 08, 2015, 04:19:51 pmWeird.Quote from: Stray Electron on July 08, 2015, 04:19:51 pmSounds like a perfect project for someone with a 3D printer and CAD skills. Maybe would need a metal insert between the plastic and the shaft though, I dunno.

author: Stray Electron
author_rank: Super Contributor
timestamp: July 10, 2015, 12:43:23 pm
content: There is a brass insert that goes around the shaft. But big problem is that the knob has both an inner and an outer ring with only one "spoke" the connects them so naturally it's a very weak design. The inner ring is moulded around the brass insert and the insert has large teeth on it and it also looks as is those teeth create stress points in the inner plastic ring. Mine was broken in three or four places and has cracks in several more. The single "spoke" is only about 3/8" wide and only covers about 1/8 of the interior and the rest is hollow. The knob has a disk of plastic that appears to have been glued to the front of the knob and there's a thin aluminium disk glued to it that has the legends printed on it. The plastic disk on my knob has come off also. My thoughts are (1) if you have all the plastic parts,then glue it back together and then fill the empty inner space with epoxy to help strengthen it. or (2) mill out the interior of the outer ring of the knob and discard the inner ring and the brass hub. Then turn a disk out aluminium or other metal who'd id will fit directly on the shaft and who'd od will fit the inside of the outer knob ring. The aluminium disk should be the same thickness as the other ring. Then glue the plastic and aluminium legend disks to the surface of the new knob. Or you could just discard all of the plastic knob parts and turn an entirely new knob of aluminium, but you'd probably need to knurl the outside in order to be able to grip it. The aluminium legend plate could be glued to that or you could even stamp the legends directly onto the aluminium knob.It would be nice if some company in China would set up and make the correct part! There seems to be a big demand for these knobs.