HP 8559A+853A Repair - Page 1
Forum section: electronics / repair

author: idpromnut
author_rank: Unknown
timestamp: April 08, 2014, 05:18:33 pm
content: Hi! I am now the proud owner of a 0.01-21GHz HP spectrum analyzer paper weight… repair project!I have a trace, but it seems to be only the internal system noise, i.e. no calibration signal when connected and nothing on the 21.4MHz IF out. At least it limits the possible problem areas to the entire RF down-mixing front-endDoes anyone have any contacts where I could find the following servicing extension cable: 5060-0303Also, if anyone has any words of wisdom in tracking down problems with this model of SA, I am all earsCheers!id

author: Stray Electron
author_rank: Super Contributor
timestamp: July 04, 2015, 02:46:28 pm
content: Any update on this?I just picked one of these up yesterday and when i opened the case one set of those tiny switch contacts fell out.Also several knobs on the front panel are smashed so it looks like I have my work cut out for me! But the display looks GOOD and I think I can see a signal when I connect the Cal Output but it's hard to be sure what's going on since the Tuning and Reference Level controls are messed up.Turn your's off and hold down the Grad key and then turn it back on. The display should say #0 on the LH side. That's the test number. Press and release the Grad key several more times until you get to test 4. That will be a box that should match the outside gradicale on the CRT, use the Focus and Grad X and Y position adjustmentson the 853to adjust as necessary. I think most of those tests are generated within the 853 so they're a good way to check it without possible problems in the 8559 from interferring.FWIW my 8559 showed noise but I couldn't see any signals when I added an antenna to the input so I thought the front end was probably burnt out. However when I connected the Cal Out to the Input and switched to Band 1 (.1 to 6MHz) and rotated the Reference Level and Frequency Span around until I found the strong signal at 0 Hz. Then I was able to also see the Cal signal (35 Mhz) on each side of it. The Reference Level and Frequency Span knobs are both messed up on mine so I just had experiment until I found the correct settings.

author: idpromnut
author_rank: Unknown
timestamp: July 04, 2015, 04:50:11 pm
content: Hi!Actually there quite a few updates regarding this. First, the primary issue was the video filter was turned all the way to the detent (i.e. MAX) which I think was squashing any signal I was trying to apply to the 8559A. The second issue is a gremlin in the display power supply section (of the 853A) which was causing the display to not power up intermittently. Then a fuse popped in this same section.After that, everything seems to be working reasonably well. The calibration is in question now, and there is an odd behavior that I have noticed which is signal < 3GHz (so from Band 1) appearing when the 8559A is switched to the higher bands (2-6). I believe this is because there is no YIG tuned filter in this unit, and so the lower frequencies are not filtered out. It makes picking out the correct signal a bit more challenging, but nothing terribly difficult at the level that I am using the unit.I have also calibrated the display using the method you described, as well as I did an adjustment to the reference level and frequency display. I am able to measure a signal's power to a reasonably decent accuracy (at least for my needs) as a result of this. The manual mentions a 250MHz cal signal, which surely is not generated (that I could find) by the 8559A. I ended up using a HP 8642B and checking the output level with a power meter to verify that I was feeding a -10dBm signal to the 8559A. I am assuming that it is a -10dBm signal, as the service manual makes no mention of anything other than it is 250MHz.As for the fingers falling out of the switches, I have not had this problem (thankfully!) but I had come across a link where a fellow re-built his switches using pieces of brass:http://www.orionsword.net/Electronics/TestEquipment/HP8559A/HP8559A.htmlIf you look in the service manual (which I can send to you if you don't have it; it should be about 440 pages), there is a functional description of the switch positions and which lines are shorted for each position for the reference/attenuator knob, and I would imagine the same exists for the frequency/div knob.Good luck and post pictures/comments if you get stuck and I'll see if I can help

author: Stray Electron
author_rank: Super Contributor
timestamp: July 04, 2015, 06:08:54 pm
content: Hi,Thanks for the reply. I'm glad that you've mostly sorted your's out. I NEED to get the parts and fix the switches in mine before I can really tell what's going on. I downloaded the service manual and I found all of the parts so I have their PNs. I will call HP Monday and see if the parts are still available. I'm afraid that the most difficult one is going to be the outside Reference Level knob. The one that you press down to adjust the attenuation. I have to have it so that I know what the attenuation and ref level is but AFIK it was only used on the 8558 and the 8559 so it might be hard to find. The other stuff isn't as critical and I can jury rig something to make it work.I have no idea which switch the fingers came out of! All of them seemed at least do something. I saw the web page about fixing the switches that you mentioned. It looks like a PITA!BTW do you know anyone that has parts for one of these or has a parts unit?I'll probably check back here in a week or two after I have a chance to find the parts and install them and find out what's going on in it.

author: avellanet
author_rank: Newbie
timestamp: August 24, 2018, 06:11:52 pm
content: I know this is an old thread but you never posted what you fixed for the intermittent power up display. I just acquired a decent looking 853a and all of the sudden the display went blank and haven't been able to bring it back. All the power supply voltages and fuses seem to be OK. I have no idea where to start having never worked a CRT circuit.