[SOLVED] Agilent 54502A CRT display broken - Page 1
Forum section: electronics / repair

author: brych34
author_rank: Contributor
timestamp: September 26, 2019, 05:05:58 pm
content: Hello everyoneI'm a newcomer to electronics and by luck I recently acquired an old 54502A 400MHz digitizing oscilloscope that was being thrown away:https://ibb.co/M9bfnMpUnfortunately the cathode ray tube display is broken. When I use the 'self-test' function the entire display is supposed to light up, yet only part of it down the centre does:https://ibb.co/hKXV2F2If it's just a case of replacing a component I'll try and repair it but if you think the display itself is busted I'll take it apart for parts.Thanks for the help

author: SoundTech-LG
author_rank: Frequent Contributor
timestamp: September 27, 2019, 01:38:36 pm
content: That CRT display looks great. Your problem is likely in the horizontal deflection. Likely the vertical mounted board to the left of the CRT. Unfortunately I don't think there is a schematic for it.

author: brych34
author_rank: Contributor
timestamp: September 27, 2019, 04:16:21 pm
content: Thanks - I'll have a look at it tonight after I discharge the display.

author: TurboTom
author_rank: Super Contributor
timestamp: September 27, 2019, 08:00:09 pm
content: These monochrome CRT displays usually run their horizontal deflection through a quite substantial bipolar electrolytic capacitor of a few microfarads. Over the decades, these caps will dry and ESR will increase until the horizontal deflection fails (almost) completely. You may want to search for such a capacitor on the CRT PCB and check its capacitance / ESR. Other components in its vicinity may fail as a consequence.

author: brych34
author_rank: Contributor
timestamp: September 28, 2019, 12:02:00 pm
content: I'll see if I can get my hands on an LCR meter. Thanks

author: brych34
author_rank: Contributor
timestamp: February 23, 2020, 09:11:38 pm
content: It works now! I replaced the 3.3uF bipolar capacitor on the board to the left of the CRT with one from AliExpress:As far as I can tell it works perfectly now:Thank you!

author: fcb
author_rank: Super Contributor
timestamp: February 24, 2020, 02:19:38 pm
content: Excellent repair. These are great scopes - especially for free.Remember they are equivalent time sampling at 400MHz. Realtime to 100MHz. But still excellent!

author: SoundTech-LG
author_rank: Frequent Contributor
timestamp: February 24, 2020, 09:21:09 pm
content: Great Job! I'll try to remember that fix. Lots of 54xxx scopes, logic analyzers, and the 53310A Modulation Domain Analyzer use that same CRT/board combo. How did you happen to find the cap???

author: TK
author_rank: Super Contributor
timestamp: February 24, 2020, 09:38:53 pm
content: I had the same issue with an HP8714B and replaced the bipolar capacitor. They come in a much smaller footprint now and it worked when I replaced it... but then later another magic smoke and the new capacitor was gone. I asked the forum and I remember somebody recommended using a non electrolytic capacitor and that is what I did and it has been working for 3-4 years now.

author: brych34
author_rank: Contributor
timestamp: April 09, 2020, 04:14:05 pm
content: Quote from: SoundTech-LG on February 24, 2020, 09:21:09 pmSorry for the late reply. I just searched for "3.3uF bipolar capacitor" on AliExpress and it led me to here:https://www.aliexpress.com/item/32594169451.htmlSo far it seems to be working well!