HP 8903A - Clean up and moving the BNC jacks to the front - Page 1
Forum section: electronics / repair

author: gdnichols31
author_rank: Regular Contributor
timestamp: November 21, 2020, 11:39:27 pm
content: This topic is a continuation of repairing an HP8903A I have. The oscillator board was repaired. See the link below for that topic if your interested.https://www.eevblog.com/forum/repair/hp-8903a-a5-oscillator-board-distortion/msg3327922/#msg3327922

author: gdnichols31
author_rank: Regular Contributor
timestamp: November 22, 2020, 01:00:42 am
content: I started taking it apart to clean it.First PicThe over all shot so I can remember how to put it back together.Second PicAll the cards out, stacked in the order they came out.Third PicEverything (almost everything anyway) disassembled and clean!I was going to stop cleaning here and start putting it back together, but I thought It would be a good time to move the BNC connectors to the front panel. I was thinking it wouldn't take much more time.The only problem was the input and output coaxes were run behind the plotter and monitor BNC connector board. The only way to to get the cables out was to remove the motherboard from the chasis. So much for not taking too much time! I didn't get a pic of the cables running behind the connector board, sorry.

author: gdnichols31
author_rank: Regular Contributor
timestamp: November 22, 2020, 01:04:16 am
content: I was wrong I did take pic of the cables behind the board.

author: gdnichols31
author_rank: Regular Contributor
timestamp: November 22, 2020, 01:11:38 am
content: Heat sink and voltage regulators removedMotherboard removed

author: gdnichols31
author_rank: Regular Contributor
timestamp: November 22, 2020, 01:18:44 am
content: Everything out except the front panel

author: gdnichols31
author_rank: Regular Contributor
timestamp: November 22, 2020, 01:25:30 am
content: I got the connectors out and started re-assembly. I wanted to get it back together to make sure it still worked before I took the front panel out.Installing the motherboard

author: gdnichols31
author_rank: Regular Contributor
timestamp: November 22, 2020, 01:34:26 am
content: BNCs are gone and the motherboard is back in.

author: gdnichols31
author_rank: Regular Contributor
timestamp: November 22, 2020, 01:36:18 am
content: Everything back together and it still WORKS!Now we take the front panel out

author: gdnichols31
author_rank: Regular Contributor
timestamp: November 22, 2020, 01:42:20 am
content: 2 output connectors inThe input connectors in.Ready for the circuit board

author: gdnichols31
author_rank: Regular Contributor
timestamp: November 22, 2020, 01:47:24 am
content: All reassembled and on the bench ready to use!I left out repairing the springs in the keyboard buttons. This has been covered in several other places. I do have some springs missing, but it won't affect the use of the instrument. I'll watch for a keyboard on EBay to show up.Overall it wasn't very difficult to move them and it makes it a lot easier to use.

author: wn1fju
author_rank: Frequent Contributor
timestamp: November 22, 2020, 02:20:14 pm
content: For the front panel leaf switches, you might also be on the lookout for a cheap (possibly broken) HP 3437A System Voltmeter. These things often go real cheap on eBay. Not only can you pull out the leaf springs, but at least on the 3437A's I have seen, the red plastic switch housings are not heat staked to the board. That means you not only get a dozen or so springs, but a dozen or so switch housings should you ever need to replace one on another HP piece.

author: gdnichols31
author_rank: Regular Contributor
timestamp: November 22, 2020, 10:12:40 pm
content: Quote from: wn1fju on November 22, 2020, 02:20:14 pmThanks, I'll set an alert for one.

author: james_s
author_rank: Super Contributor
timestamp: November 23, 2020, 12:50:23 am
content: Why not just run cables off the outputs under the bottom of the housing instead of butchering the front panel? I cringe whenever I see people drilling holes in gear.

author: gdnichols31
author_rank: Regular Contributor
timestamp: November 23, 2020, 01:48:24 am
content: Quote from: james_s on November 23, 2020, 12:50:23 amI considered something like that, but I don't have room for a BNC patch panel. I also didn't want an additional set of cables to add noise to the system.Gary

author: Tony_G
author_rank: Super Contributor
timestamp: November 23, 2020, 03:49:02 pm
content: Congrats again on getting this up and running. Were the original cables long enough for the swap?As for the keyboard springs, I've heard that people have used cut down feeler gauges to replace missing springs - I think this was discussed over on the HP Groups.io forum.TonyG

author: gdnichols31
author_rank: Regular Contributor
timestamp: November 24, 2020, 12:41:55 am
content: Quote from: Tony_G on November 23, 2020, 03:49:02 pmThanks,Cables are plenty long enough no problems there. The biggest head ache was having to remove the motherboad to remove the cables at the back. Another minor irritation was the threads on the BNC connector weren't long enough for the nuts and the washers. I had to leave the washers off.wn1fju, had a good idea above. I've got an EBay alert setup for them. Not only do you get the key parts, but you get all the other parts too!Gary

author: Rico75
author_rank: Newbie
timestamp: April 10, 2025, 04:32:00 am
content: Hello everyone,My name is Rico, and I recently purchased an HP 8903A. The unit is working well, and I’m very pleased with it. However, I believe it would be beneficial to have the service manual to better understand how to maintain and care for it—this is my first unit of this kind.I’ve spent the last two days searching online but haven’t found a complete version with schematics and maintenance procedures. If anyone has a copy of the service manual or schematics they’d be willing to share, I’d be extremely grateful!Thank you in advance for your help.

author: squadchannel
author_rank: Frequent Contributor
timestamp: April 10, 2025, 06:42:26 am
content: https://www.ko4bb.com/getsimple/index.php?id=download&file=HP_Agilent_Keysight/HP_8903A_Audio_Analyzer-Service.pdfhttps://www.ko4bb.com/getsimple/index.php?id=manuals&dir=HP_Agilent_Keysight#:~:text=HP%208903A%20Audio%20Analyzer%2DService