Help needed on HP 54601A oscilloscope display problem.(SOLVED) - Page 1
Forum section: electronics / repair

author: JacquesBBB
author_rank: Frequent Contributor
timestamp: March 07, 2015, 09:01:58 am
content: Dear All,I have scavenged an HP 54601A scope which I will be trying to restore to full working order.As you see, there is a display problem.I will be looking to the power supply soon, butDoes any one have a hint on where the vertical problem of the display comes from ?Lettes are also inverted.Thanks !

author: KJDS
author_rank: Super Contributor
timestamp: March 07, 2015, 12:28:07 pm
content: It's one of two caps on the display driver board. From memory one is 1000uF and the other is either a 22 or 16uF cap.Either can cause the issue, it's easiest just to change both. From memory I don't think the schematic was available, but if you find it and post it up then I should be able to highlight the caps. If not then a photo of the board may jog my memory.

author: JacquesBBB
author_rank: Frequent Contributor
timestamp: March 07, 2015, 01:26:20 pm
content: Thanks KJDS,Meanwhile, I found also this post on the keysight sitewhere the problem is discussed.http://www.keysight.com/owc_discussions/thread.jspa?threadID=17356&start=15&tstart=-1All the schematics are also available on the site athttp://www.keysight.com/main/editorial.jspx?cc=FR&lc=fre&ckey=1517718&nid=-536900196.536898053.00&id=1517718I attach here the Display schematics. I will try now to change these caps.

author: KJDS
author_rank: Super Contributor
timestamp: March 07, 2015, 02:07:15 pm
content: That's close to what I remember, but I suspect I did a different scope in the series. I suspect that changing all the electrolytics round IC 601 will cure the problem. If you've not got an ESR meter then that's the easy way forwards.

author: JacquesBBB
author_rank: Frequent Contributor
timestamp: March 07, 2015, 04:33:26 pm
content: All the voltages of the power supply were right inside the spec intervall.A rubber pad had decomposed, and this is something I already saw on anotherHP 54601A that I fixed not so long ago.I look for the bad caps which were supposed to be C608 and C609.I desoldered both. C609 (1000 uF) was OK : 876 uF , 0.68 ohm ESR.While C608 (10uF , 16V) was damaged (not even readable on the ESR meter).See the picture.I inspected the other caps, but they looked OK, so I left them on place.Of course, I could have changed everything, but the other caps were 100V , andI suspect that C608 was too low voltage for its task. I replaced it with a 100V, 10 uF cap.C608 and C609 are the two caps that are under the date on the attached picture.After that, and a little bit of calibration, everything is working fine, like magic(sorry for the fuzzy pic).I spend more time then changing the fan, as the original one made a terrible sound,but I had to adapt the new fan to fit in place.Thanks again KJDS

author: JacquesBBB
author_rank: Frequent Contributor
timestamp: March 07, 2015, 04:36:49 pm
content: And the global picture

author: GreyWoolfe
author_rank: Unknown
timestamp: March 07, 2015, 04:59:15 pm
content: Glad the repair turned out to be simple. Now it is time to enjoy the scope. Take care of it so you don't

author: R Lamparter
author_rank: Contributor
timestamp: April 23, 2017, 07:17:40 pm
content: Another successful repair using this information. Only the small 10 uf capacitor, C608 on the video board tested bad (abt 7 uf and v high ESR). Replacing that fixed the problem. Before and after photos attached.

author: Bushougoma
author_rank: Regular Contributor
timestamp: April 24, 2017, 12:09:27 pm
content: This is a common issue on CRT TVs based on the symptoms and value of the cap I would say that was the vertical pump up capacitor.It's often the repair for compressed vertical deflection. I try not to think about how many CRTs were disposed of because of a single bad capacitor.