HP 54520A Oscilloscope does not start - Page 1
Forum section: electronics / testgear

author: dwight_talley
author_rank: Contributor
timestamp: December 29, 2021, 04:37:48 am
content: I picked up a used 54520A and it worked about a week. Tonight I tried to start it and all it does is flash the LED status lights on the front of the scope. No sounds or smells, just flashing LED lights. I have unplugged it and tried again but no joy. Before I open it up what should I look for and test?I am also looking for any schematics of the scope and the power supply. None of the links that were posted on this form now work.Thanks for any info you may have.Dwight

author: Martin Miranda
author_rank: Regular Contributor
timestamp: December 29, 2021, 04:59:23 am
content: there is no schematics in the service manual but there is instructions how to test.start with chapter 5, page 5 - 10

author: dwight_talley
author_rank: Contributor
timestamp: December 29, 2021, 01:23:54 pm
content: I was able to get the scope to start by holding down a button and turning it on. No error messages on the screen. I will run a self test today but it has passed the test before.ThanksDwight

author: wn1fju
author_rank: Frequent Contributor
timestamp: December 29, 2021, 01:47:01 pm
content: Check the lithium battery inside on the motherboard. It's known that the machine can hang on startup if the battery dies.

author: dwight_talley
author_rank: Contributor
timestamp: December 30, 2021, 05:26:44 am
content: The battery checks out ok. Had 3 volts on it. However the connections on the board are very small and I will need to get a large magnifying glass just to see where the trace is going. I am not sure it the tract is broken and needs to be fixed. I really need a schematic to see how this battery is connected to other chips on the board. I did a quick reflow of the battery connection to make sure it was ok. I did find a video that shows what my scope was doing.It is a good video on how to fix the battery and calibrate the scope.Anyone have a schematic?Dwight

author: wn1fju
author_rank: Frequent Contributor
timestamp: December 30, 2021, 01:07:22 pm
content: I would like to see the schematics also. But it looks like they are nowhere to be found. Sometimes HP issued Component Level Information Packages (CLIPa), but maybe not for the 545xx series. If anyone would have one, it would be Dave at Artek Manuals. But he says he has been searching for years without success.I suppose you could try to identify which chip(s) on the motherboard are SRAMs. One (or more) ought to have 3V on its power rail when the scope is powered off. That would at least verify the battery voltage is making it there. If not, look for broken or corroded traces.

author: dwight_talley
author_rank: Contributor
timestamp: December 30, 2021, 05:34:57 pm
content: My thoughts are moving in the direction of a broken trace that is temperature sensitive. I don't heat my shack when I am not there. Last night the scope would not power up at all while I was working on it in a warm environment. Today, the shack was at 45 degrees F. The scope powered up every time I started it. No problem at all. So I am sure the board suffered a crack somewhere that connects when cold.Dwight

author: dwight_talley
author_rank: Contributor
timestamp: January 07, 2022, 04:36:08 am
content: While I was waiting for a time to locate the broken trace, I purchased a HP 54522A that was for sale at less than half the price that I paid for the 54520A. It was for sale because it would not start and the photo that was posted showed the LEDs lit up just like mine did. Well I jumped on it and tonight I was able to open it up and put a new battery into the board. Scope started up without issue, just asked me to calibrate it. I guess a little knowledge and experience goes a long way. There were three HP scopes for sale with the same problem, just the sellers did not recognize the issue. One seller has really cranked the brightness up on his scope so that it is very bright, clearly shorting the life of the tube. I guess he expects to see something on the screen but the scope has not started yet. One simple battery would have fixed them all. I guess now having two scope is better than one. I was able to trace the battery connection on the 22A and figured out where the break is on the 20A, so that was a big help.Dwight