Concern with my HP 1662as oscilloscope - Page 1
Forum section: electronics / testgear

author: hp fan
author_rank: Contributor
timestamp: February 02, 2013, 10:43:39 pm
content: Hi I am a newby to this group so please dont be too hard on me. I just purchased my third oscilloscope it worked twice then while working the second time it turned off the screen (went black) it will not turn back onbut it does smell. Any hope of self-repair? I have been a automotive technician for years specializing in electronics. Anyone here have experience with these scopes? I removed the cover and used some compressed air but it was clean inside I am not sure where to next I see no fuse.

author: free_electron
author_rank: Super Contributor
timestamp: February 02, 2013, 11:05:28 pm
content: The power supplies in these machines die when they get old.Remove cover , find the large metal box with the big wide flatcable coming out of it. That's the power unit.unplug the cable. on the side of the scope you will find two pieces of plastic , round. like a kind of big knitting needle. pull those out. you will see they have a little 'flag' at the top. You can now slide the power module out of the chassis.Open up and look for exploded capacitors. the thing should smell like cat-wee...i've seen this happen before.

author: hp fan
author_rank: Contributor
timestamp: February 02, 2013, 11:18:22 pm
content: Thank you very much. I will take it back apart after supper do you happen to know the pico farad rating of said capacitorsis that the thing that goes bad the most?

author: c4757p
author_rank: Super Contributor
timestamp: February 03, 2013, 06:31:08 am
content: Er.... isn't the 1662AS a logic analyzer, not an oscilloscope?Quote from: hp fan on February 02, 2013, 11:18:22 pmWell, much more than picofarads. They will be microfarads, and they will be marked. Pay attention to both the capacitance and the voltage rating, and if you must use a capacitor with a different value, only go up, not down, on both numbers, and only a little bit. Some of them need to be low ESR types. (In general, it's the ones that should be low ESR that will fail, so I would just assume low ESR if unsure. They fail because the high ripple current through them causes internal heating, and the low ESR ones do not heat as much (power dissipated as heat is the ESR multiplied by the square of the ripple current).A suggestion - in general, you only need to replace failed capacitors, but I would also replace any capacitors of the same type as a failed one, as they likely came from the same batch.QuoteUsually.

author: free_electron
author_rank: Super Contributor
timestamp: February 03, 2013, 07:38:03 am
content: 1662 is a logic analyzer with scope module installedThese machines die of old age.Especially when they have not been used for a long time. You power them up and poof. The caps go.Replace with same value/voltage/temp rating.

author: hp fan
author_rank: Contributor
timestamp: February 03, 2013, 06:04:13 pm
content: Thank you very much is there a "best place" to obtain the capacitors from. I belive I see the concern wont know till I test with my new capacitance meterthe capacitors of this type of which there are six they are wrapped with wire and a type of tape/tube three have red paint on the end three have white I dont know for sure they are capacitors I would guess to test I need to unsolder from board?

author: SeanB
author_rank: Super Contributor
timestamp: February 03, 2013, 06:13:55 pm
content: Photos will help identify them. Nice clear ones.

author: Unknown
author_rank: Unknown
timestamp: February 03, 2013, 06:36:19 pm
content: Specifying location is also helpful if you're asking about where to source stuff. People are volunteering their time to help you, try to make their job as easy as possible.

author: hp fan
author_rank: Contributor
timestamp: February 03, 2013, 07:03:34 pm
content: I want to thank everyone who has taken the time to try to help methe possible capacitors are the ones with the tape around them two with white ends, one with red, this is where it smells the most. I hope this picture is semi clear. I had to delete the drivers twice and reload the software

author: hp fan
author_rank: Contributor
timestamp: February 04, 2013, 02:04:10 am
content: What I thought were capacitors are in-fact inductorsThat"s what you get when someone is doing something new! I will start by replacing the capacitors one at a time. I just ran out of old electronics that I was de-soldering capacitors from now I have to order some other ones. Thank You

author: Harvey
author_rank: Newbie
timestamp: February 21, 2013, 04:33:23 pm
content: The problem with old capacitors is that you don't always know where they've been, and what they've been doing. You may end up replacing a marginal part with another marginal part.Considering the amount of work you need to do to fix this supply, I'd recommend new parts. Any good supplier such as Mouser, Digikey or Avnet will be a good choice. If you find surplus parts, make sure they are unused.Of course, if you have to have it up and running now, and all you have is a used part, then that's what gets put in.All this assumes you can get new parts, though.Harvey

author: hp fan
author_rank: Contributor
timestamp: February 22, 2013, 12:12:42 pm
content: Thank you Harvey: I replaced all the old capacitors. It ran for five minutes then stopped. I found one of the capacitors was burning the board under the cap could not be seen till removed. The new/old concern is a different type of capacitor I "believe" it is bad it has 165V to it .025 out of it it would have to be ordered and I still have the possible concerns of items going bad on the power supply so I bought a computer power supply and changed the voltage outputs 3.3 to 3.5v, -5.2 instead of -5.0v I need to wire it in now to see if it will work. Hope it does. I know I cant afford the 650.00 cost of a aligent supply. Rich

author: nctnico
author_rank: Super Contributor
timestamp: February 22, 2013, 12:41:28 pm
content: A computer supply is not going to work. The -5.2V probably draws several amps because of the ECL logic. A computer power supply can only deliver a couple of hundred mA from the -5V. Fixing the original power supply is still your best bet.

author: hp fan
author_rank: Contributor
timestamp: February 22, 2013, 02:46:24 pm
content: Darn just when I have high hopesIs the ECL part of the power supply. If so what aspect of the o/scope would it run?Thank you so much Rich

author: hp fan
author_rank: Contributor
timestamp: February 22, 2013, 02:51:32 pm
content: I researched the neg voltage to small extent and asked one of my friends about it. I came up with this picture for building a circuit for it

author: hp fan
author_rank: Contributor
timestamp: February 22, 2013, 03:16:56 pm
content: I will order the part I need for the original power supply in the mean time though I would like to try with the computer power supply just to see what might happen i.e. If it will power up and length of life span am I putting the rest of the scope at risk for attempting this? Thank you Rich

author: PedroDaGr8
author_rank: Super Contributor
timestamp: February 22, 2013, 05:46:20 pm
content: Quote from: hp fan on February 22, 2013, 03:16:56 pmComputer PSU might be too noisy if the oscilloscope is expecting a cleaner linear type power supply. Additionally, you may risk damage as the negative voltage drifts out of spec as switching PSU's, like computer PSUs, tend to go nuts when their current capabilities are exceeded (basically the bottom drops out on the ripple and you get massive voltage spikes). Mind you this assumes OCP doesn't kick in and shut the supply down (which it SHOULD but its not guaranteed).

author: free_electron
author_rank: Super Contributor
timestamp: February 22, 2013, 06:59:49 pm
content: don;t go messing around with building your own supply the scope needs access to the line frequency for triggering.just fix the scopes supply.

author: hp fan
author_rank: Contributor
timestamp: March 16, 2013, 01:12:53 am
content: I just wanted to thank everyone for their informationThe scope is fixedI tried the computer power supply. It did not work. It did nothing 25.00 down the drain. I tried a capacitor that was a special one in the original power supply did nothing. Then I found a power supply on eBay for a older HP scope it had the part# 0950-1879 after looking up the information about that power supply. I thought I would give it a try only cost 51.00 with shipping. It looks like it was pre-aligent thus it looks better made then the original one mine was supposed to take. It was a 0950-2261 The only difference I can tell is the ability to adjust the +5volt. Hopefully this can help some one in the future looking to fix their scope. Rich

author: Wuerstchenhund
author_rank: Super Contributor
timestamp: March 17, 2013, 12:10:02 pm
content: Quote from: hp fan on March 16, 2013, 01:12:53 amThey are all Pre-Agilent. And all the PSUs for these scopes and Logic Analyzers were standard embedded PSUs made by Computer Products (which has subsequently been bought by Artesyn and then Emerson later on) and not by HP. That's why they are (within limits!) interchangeable between scope/LA models.Since they are not made by HP finding schematics for them is nearly impossible. Emerson of course has them but due to 'IP protection' only gives them out to companies, not individuals, and also requires to sign an NDA beforehand which for an approx. 20 year old PSU is just ridiculous.I'm currently in a similar position with a Computer Products XL130-3630E PSU from a HP 54542A scope, but unfortunately this scope uses the most powerful model of these PSUs and thus doesn't work with a PSU from a different scope. And finding a spare is very difficult, especially if it should be affordable. And since they are out of production for more than 15 years any replacement is very likely to fail due to age sooner or later anyways, so the best solution is probably to fix the broken PSU

author: 1kostik1976
author_rank: Contributor
timestamp: July 13, 2015, 05:04:19 pm
content: Hi everyone. someone has the power supply circuit on the HP 54524A.