HP54503A dont work - Page 1
Forum section: electronics / testgear

author: venuscube
author_rank: Newbie
timestamp: August 02, 2013, 01:23:21 am
content: I bought a HP 54503A last year, it worked perfect at the beginning. It haven't been used for a few month. Yesterday I tried to turn on it but it didn't work at allThe fan is running and I can hear a click sound when turn on the power. But the screen has nothing on. Tested with meter I saw the VCC voltage on the TTL chips is OK. What is the possible problem according to you experts? Can the failure of the NVRAM cause such problem? many thanks

author: free_electron
author_rank: Super Contributor
timestamp: August 02, 2013, 02:27:54 am
content: does it smell like cat-wee ? ( no seriously . does it smell like cat-wee .. ) these machines suffer from bad caps in the power supply...

author: venuscube
author_rank: Newbie
timestamp: August 02, 2013, 02:35:32 am
content: oppps.. really, my colleague asked my why the room has a strange smell, like burning paper.Quote from: free_electron on August 02, 2013, 02:27:54 am

author: free_electron
author_rank: Super Contributor
timestamp: August 02, 2013, 03:05:04 am
content: bingo.easy to fix. pop cover off machine. the power cartridge has a large ribbon cable. unplug that , slide cartridge out. take cover off cartridge. use facial proboscis ( nose) to locate the stinkers and swap em. clean the goop off the board as it is corrosive.

author: venuscube
author_rank: Newbie
timestamp: August 02, 2013, 03:10:29 am
content: openned..but haven't found any cap looks bad. Metering now

author: MetraCollector
author_rank: Regular Contributor
timestamp: August 02, 2013, 08:51:51 am
content: Gentlemen, I have bought 54503A too, month ago at Friedrichshafen HAM. I saw 500MHz label and 4 channels and higher number, so I thought I'd replace my 54502A. Then I discovered it has much more worse parameters than 502A.Anyway, the scope worked for a while. One next time I switched on and nothing happened. I intuitively swapped PSU and it worked.So, could you please tell me, WHICH of caps are usual to go wrong ? Every of them looks alright, no smell and no visible damage.Thank you

author: free_electron
author_rank: Super Contributor
timestamp: August 02, 2013, 01:36:20 pm
content: Typically the ones in the low voltage section. They are either blue or orange if i remebe correctly.

author: ddavidebor
author_rank: Super Contributor
timestamp: August 02, 2013, 01:43:26 pm
content: Check the iec filter.

author: venuscube
author_rank: Newbie
timestamp: August 06, 2013, 12:51:55 am
content: Quote from: ddavidebor on August 02, 2013, 01:43:26 pmCan IEC filter cause such problem? the PSU is working and the voltages seems to be right. Now the screen looks like this.What will cause such problem?

author: venuscube
author_rank: Newbie
timestamp: August 06, 2013, 01:19:16 am
content: Quote from: MetraCollector on August 02, 2013, 08:51:51 amCan you pls tell me where to get a PSU?

author: Stonent
author_rank: Super Contributor
timestamp: August 06, 2013, 02:32:22 am
content: A screen like that could be no signal or too much.

author: free_electron
author_rank: Super Contributor
timestamp: August 06, 2013, 03:35:05 am
content: monitor is on but the scope mainboard is not running

author: Jwalling
author_rank: Unknown
timestamp: August 06, 2013, 01:20:12 pm
content: Quote from: venuscube on August 02, 2013, 01:23:21 amYes, those series of scopes won't complete boot if the NVRAM battery dies. I forget if that particular model has a Dallas type part or a lithium battery. All the 545XX scopes right up to the 54542A/C will fail to boot when the battery dies.Jay

author: ddavidebor
author_rank: Super Contributor
timestamp: August 06, 2013, 06:40:20 pm
content: that's wrong they boot and show "cal error"you should check the various power rail on the power supply, they're accessible without any throuble on an extra connector in the middle.if you need nvram or main filter i've one

author: MetraCollector
author_rank: Regular Contributor
timestamp: October 13, 2013, 12:21:29 pm
content: Greetings, I finally put this machine on my bench yesterday and took leads in hand.When I turn on the PSU, I hear some click and then I hear periodic very weak click (that small relay ?). When I turn it off, I hear two clicks, very similar to locust sound.Voltages are shown in the picture. +12V and -12V branches act very similar, voltage is varrying from 8V to 11V in about 2Hz.Voltages in brackets are the ones written in service manual.Could you please tell me what it is supposed to be wrong ? Is it definitely electrolytics fault ? The reason I am asking this is that I don't have the values of elyts available in my home stock.(especially lowESR).Thank you

author: willb
author_rank: Regular Contributor
timestamp: October 13, 2013, 12:59:50 pm
content: I'd check those organge Sprague caps first (that's what they look like anyway). Pretty much every HP machine I bought broken off eBay which had these orange Sprague caps were bad.My 6034L has +15V and -12V rails, which both had bad orange Sprague's, and the rails behaved in a very similar fashion as yours...

author: Shock
author_rank: Super Contributor
timestamp: October 13, 2013, 01:57:33 pm
content: There has been more oscilloscopes fixed by replacing the input filter caps on this forum than Daves rooftop solar panels.

author: MetraCollector
author_rank: Regular Contributor
timestamp: January 17, 2014, 07:22:48 pm
content: Hello again.I put it on the workbench again with my colleague and checked EVERY electrolytic cap (desoldered) on LCR and every of them is in perfect condition. Even changing caps doesn't make a difference.Any hint what else I should look for ?Thank you.

author: KJDS
author_rank: Super Contributor
timestamp: January 17, 2014, 07:33:53 pm
content: When you tested the supply, did you have a load on each rail?

author: MetraCollector
author_rank: Regular Contributor
timestamp: January 17, 2014, 08:43:52 pm
content: Yes, I had. No difference too.

author: MetraCollector
author_rank: Regular Contributor
timestamp: January 18, 2014, 05:13:36 pm
content: And another problem is one of the four attenuators. Sometimes it switches, sometimes not.Any hint about repairing that relay ? Is it safe to desolder it from ceramics ?