HP 8569B - How to engage or fix Resolution Bandwidth control - Page 1
Forum section: electronics / testgear

author: pfm
author_rank: Regular Contributor
timestamp: December 22, 2017, 11:35:10 pm
content: I have a HP 8569B in otherwise pretty good condition. If you are familiar with the unit you know that the Frequency Span/DIV and Resolution Bandwidth are two coaxial knobs. (Center knob in the pic). The outer knob is Freq Span/DIV and works good. But the inner Resolution Bandwidth control does not have any effect on the actual resolution bandwidth, it always shows 10Khz on the screen. It does turn and 'click' fine all through the positions but no change whatsoever on the screen.This happens regardless of the "optimum" coupling (push outer knob in), the bandwidth always reads 10Khz on the screen whether the knobs are coupled for 'optimum' or decoupled.Any advise or help in troubleshooting and fixing this would be highly appreciated. Except for this the unit works great so I really want to get this function working properly.If you think there might be a user error and I may not be operating these controls properly please advise on that as well.Thanks!

author: AF6LJ
author_rank: Unknown
timestamp: December 24, 2017, 12:38:04 am
content: What usually happens with these is the contacts fall off the switch rotor.See below...The switch contacts are held on by posts molded into the plastic. They are hot staked in place by heating the post and pressing it down to form a clamp for the contacts.First if you opened up the analyzer be very observant and find the loose contact.You will have to glue it back on in the proper antiabortion.In one respect you are lucky. the resolution bandwidth switch rotor is the rear most one and is affixed to the inner shaft.Get a copy of the manual; therein you will find disassembly instructions for those controls.You will need some special tools...Spline wrenches to remove the collets holding the plastic rotors in place.You will need a good camera to take pictures of the switch assembly as you take it apart.The reason for this has to do with the positioning of the collets, they don't explain that in the manual......You will need allen wrenches (hex wrenches) to fit the knob set screws.Take lots of pictures and don't overlook the position of the collets. As I said above THEY HAVE TO BE INDEXED PROPERLY otherwise the switch will not rotate through its complete range.Be warned. The knob set screws are mild steel in a brass hub, pressing against a stainless steel shaft. They can become seized. Pennitrating oil can help...In stubern cases you will have to purchse a left hand drill (actually two one small enough to fit in the hex head set screw, and one ether just at or just under the drill tap size for that set screw. (they are #4 set screws. ) ) I had the sweep time knob o the second 8569 that needed to have the set screw removed with a left hand drill. I had to chase the threads with a 4-40 tap... Don't use a starting or thread forming tap...I'll be starting on the second 8569 front panel this January... There has been a number of delays in getting that project started. I will repost links to my pictures from my Google photos account. in the HP-8569 thread.This is not a project for the faint at heart, good mechanical skills are a must, along with attention to detail. I had to rebuild the Reference Level / Input Atten knob assembly three times before getting it right on the first 8569, so be patient.In the end it is worth it, that is a damned good analyzer.

author: AF6LJ
author_rank: Unknown
timestamp: December 24, 2017, 01:03:32 am
content: A few other useful notes...I bought my manuals from here...http://artekmanuals.com/They produce some really fine manuals, good scans, at a reasonable price.If you haven't taken the analyzer apart yet here is a picture of the back of the front panel module.This is not hard to remove, and all the RF plumbing stays put.I did take a marker and draw index lines to make sure the connectors went in the right direction.Once again make sure you find that small contact...Inspect the other contacts while you are at it.

author: pfm
author_rank: Regular Contributor
timestamp: December 24, 2017, 04:29:13 am
content: Thank You for your response!I will open the analyzer and take a look inside, seems like a tricky job.I wish I had taken pictures when I took out the Ref Level and Attn knob! I have the manual but it does not show an assembly diagram that tells the sequence of the parts and so I couldn't figure out how the retainer ring and metal disc with the window and plastic washers go so had to leave those out. Luckily it functions fine though.

author: AF6LJ
author_rank: Unknown
timestamp: December 24, 2017, 12:20:35 pm
content: For this analyzer the manual comes in three volumes.The HP archive has the service manual, and it does describe the assembly / disassembly of the controls.

author: KrudyZ
author_rank: Frequent Contributor
timestamp: January 13, 2018, 10:24:59 pm
content: Quote from: pfm on December 24, 2017, 04:29:13 amI have the same spectrum analyzer and it also suffers from losing the wiper contacts.I fixed some of the them after finding them inside the unit, but then was left short as some must have fallen out through the vent holes sometime over the last 50 years...

author: AF6LJ
author_rank: Unknown
timestamp: January 14, 2018, 10:55:36 am
content: I have been on the lookout for those contacts. If anybody ever finds a source of those wiper contacts please post it here.

author: pfm
author_rank: Regular Contributor
timestamp: January 14, 2018, 04:30:52 pm
content: One would think considering that this problem is so common and widespread that by now someone would have come up with pre-built rotors and contacts to just swap them out with the broken ones.

author: pfm
author_rank: Regular Contributor
timestamp: January 14, 2018, 04:36:29 pm
content: Quote from: KrudyZ on January 13, 2018, 10:24:59 pmyou might have looked at this thread but here it is anyway -https://www.eevblog.com/forum/repair/hp-8569-spectrum-analyzer-repairs/100/

author: AF6LJ
author_rank: Unknown
timestamp: January 14, 2018, 07:22:24 pm
content: One quick note...When I reassemble my front panel module, I will include the sequence for tear down of the reference level control group.This one is hard because snap ring pliers are needed for the removal of the retaining ring holding the reference level knob baffle in place.

author: pfm
author_rank: Regular Contributor
timestamp: January 19, 2018, 12:58:59 am
content: I found this in the Service manual parts list. Could this be the RBW rotor ? Has anyone tried sourcing it ? From Agilent Keysight or any surplus contractor ?

author: AF6LJ
author_rank: Unknown
timestamp: January 19, 2018, 01:29:48 pm
content: That is it and you can go to the Keysight website and see if they have any in stock.There is a search page there you can plug in the part number.

author: pfm
author_rank: Regular Contributor
timestamp: March 30, 2018, 03:26:25 pm
content: ! I FIXED IT !I tried hard but I could not find the spare anywhere. However, by just sheer stroke of luck I found someone selling this stash of rotors on ebay!Not all were in usable condition but I did manage to salvage a few.The one thing different about my repair story is that I didnotdisassemble so extensively. I just unscrewed the small pcb and flipped it on its side and I had full access to the rotor. It was all over in a matter of 2-3 hours.One interesting thing I did not realize until later is that the resolution bandwidth rotor has only one of those metal hand/fingers while other switch rotors have a set of two.And yes I did find the missing one lying on the bottom cover.Its working great now! Anyone want this unit let me know I am going to sell it to make room for something else.P.S: If anyone wants the rotors let me know I can spare some for your personal use.

author: AF6LJ
author_rank: Unknown
timestamp: March 30, 2018, 08:00:04 pm
content: Good Deal!

author: NateOcean
author_rank: Newbie
timestamp: July 31, 2018, 03:36:03 pm
content: Quote from: pfm on March 30, 2018, 03:26:25 pmI coulddefinitelyuse a single one of the 4-finger metal contact tabs!(I haven't heard back from the poster (pfm); anyone have an alternate way to message him? The email icon doesn't seem to work.)

author: AF6LJ
author_rank: Unknown
timestamp: July 31, 2018, 04:34:45 pm
content: Quote from: NateOcean on July 31, 2018, 03:36:03 pmHaven't tried...On another subject;What you have going there I wanted to do, however I couldn't come up with a setup I was happy with considering my limited resources....Nicely Done

author: pfm
author_rank: Regular Contributor
timestamp: July 31, 2018, 10:29:11 pm
content: Quote from: NateOcean on July 31, 2018, 03:36:03 pmHi there,just wanted to confirm I have seen your post and PM also. I will pull out the stash from storage and check. I am sure I will find something that you can use but I just need a couple of days time to get back to you.

author: pfm
author_rank: Regular Contributor
timestamp: August 03, 2018, 05:35:08 am
content: Quote from: NateOcean on July 31, 2018, 03:36:03 pmSent you PM but it does not support attachments so adding here the picture I wanted to send. Perhaps it might be helpful to anyone who might come looking for these. These are what I have.

author: REveret
author_rank: Newbie
timestamp: November 05, 2019, 10:49:10 pm
content: I am looking for these two rotors, one is the Freq Span and the other if the Freq Bandwidth.

author: pfm
author_rank: Regular Contributor
timestamp: November 11, 2019, 12:20:27 am
content: Do you need one rotor with one contact and another with two contacts, just like they are in your picture ? Here's what I found see pic. Please note within each set there is one with a raised bevel in the center hole and another that does not have it, its just a plain hole.Also, in the double contact one where I have marked with a red arrow is slightly loose in one out of the two mounting stubs, nothing that a little glue cant fix.PM me which ones you want and we can take it from there.

author: pfm
author_rank: Regular Contributor
timestamp: November 11, 2019, 04:38:12 pm
content: Quote from: REveret on November 05, 2019, 10:49:10 pmunable to reply to your pm, your inbox is full.

author: REveret
author_rank: Newbie
timestamp: November 19, 2019, 12:51:19 pm
content: Not sure what is up with inbox, there are only a couple messages in the box. Sending you a PM.

author: TubeAlloy
author_rank: Newbie
timestamp: February 03, 2023, 05:07:27 pm
content: Hi,This is a very old thread. I wonder if the old timers are still on this board.I have recently got an HP 8569B with quite a few of these fingers missing. I would like to buy 3 if someone still have them.Also, are these fingers all of the same shape? The ones on the "Sweep Time/Div" switch disappeared. I wonder if they are the same as those shown in the thread, which appear to be the same.

author: Ea4CMV
author_rank: Newbie
timestamp: June 22, 2023, 02:43:14 am
content: Hi Sir, do you still have fingers contac rotor?Please if do you still have the item let me know.Thank you very much.73s EA4CMV.Javier

author: Ea4CMV
author_rank: Newbie
timestamp: June 22, 2023, 03:03:41 am
content: Quote from: pfm on August 03, 2018, 05:35:08 am

author: Ea4CMV
author_rank: Newbie
timestamp: June 22, 2023, 03:24:26 am
content: Hi again!I would need the fingers contact for the sweep rotor control.Thank you very much!!Javier.

author: pfm
author_rank: Regular Contributor
timestamp: June 22, 2023, 03:48:18 am
content: Hi Javier,sorry no I dont have any left. Hope someone reads your post and has any to spare.

author: Ea4CMV
author_rank: Newbie
timestamp: June 22, 2023, 09:57:53 am
content: Quote from: pfm on March 30, 2018, 03:26:25 pmHi again!Olease, please!!I need one of this rotor!!Thank you very, very much!!Javier.

author: pfm
author_rank: Regular Contributor
timestamp: June 22, 2023, 02:55:16 pm
content: Looks like you completey skipped my reply. I replied, see above your last post.

author: Ea4CMV
author_rank: Newbie
timestamp: June 22, 2023, 11:55:59 pm
content: Oh, thank you very much again.I apreciate your answer.73s.Javier.EA4CMV.

author: Ea4CMV
author_rank: Newbie
timestamp: June 23, 2023, 08:55:19 am
content: I have been on the lookout for those contacts. If anybody ever finds a source of those wiper contacts please post it here.