2465b problems after replacing caps. - Page 1
Forum section: electronics / testgear

author: ZBIQ
author_rank: Contributor
timestamp: January 03, 2015, 07:12:15 pm
content: Hi!There is the story:Oscilloscope was working pretty well but there was disturbing smell coming out while powering up.After taking it apart, I saw four electrolytic caps leaking (on A5 board). Ive replaced them and repaired few etched copper traces. There was a lot of oxidation in caps surrounding, so Ive cleaned it with flux removal and distilled water (only where needed - not whole board).After powering up my tek, I realized there are some issues:1. One of the markers is constantly shaking. You can see this on video below. I can live with this, but all four channels (inputs grounded) are also not very stable (verticaly shaking). It drives me crazy (but it is hardly visible in video).https://www.youtube.com/watch?v=tk_9U6uKQtQ&feature=youtu.be2. First channel is always visible (even when its off). The best explanation is on the vid below:https://www.youtube.com/watch?v=2hgtawLPF7s&feature=youtu.beIts my third day of fighting with the A5 board.There are no errors (all tests passed).Power supplies are good (there is some excess ripple - need to check this again).But it was all ok before repairing A5 board...Does anyone know what may cause this problems ?Can you help me?

author: tautech
author_rank: Super Contributor
timestamp: January 03, 2015, 07:37:53 pm
content: Quote from: ZBIQ on January 03, 2015, 07:12:15 pmFix the PSU first.The whole scope's stability and accuracy depends on a perfect PSU.Ensure it is to Tek's spec or better.

author: ZBIQ
author_rank: Contributor
timestamp: January 03, 2015, 08:25:44 pm
content: Ok.But what means "Ripple at two times line frequency"? How to set my other scope?My English is not very good so I dont really understand that.Okgot it. In my case at 100Hz

author: ZBIQ
author_rank: Contributor
timestamp: January 03, 2015, 08:41:26 pm
content: Ok. There is definitely something going on.On +10V (reference J119-4) there is about 30mVpp ripple with period about 1.12s. Hmmm interesting.

author: malch
author_rank: Regular Contributor
timestamp: January 04, 2015, 01:12:49 am
content: I read somewhere that the caps leaked under a nearby chip and caused a partial short under the chip. ?Got it. "further research I discovered a short circuit under an IC. (also a result of the leaking capacitor) When this was solved the Readout is functioning as it should be."From Yahoo TekScopes

author: ZBIQ
author_rank: Contributor
timestamp: January 12, 2015, 07:19:31 pm
content: Hello again !I did a full recap of my scope. Not an easy job at all...Stability of markers and traces has improved.But I have the second problem unsolved. 1st channel is always on (as on video). I need to sniff around processor ...By the way, I copied all calibration data form Exerciesr 2 menu in scope. I would kill myself if RAM fails and all cal data lost.

author: mij59
author_rank: Frequent Contributor
timestamp: January 13, 2015, 06:51:48 am
content: Quote from: ZBIQ on January 12, 2015, 07:19:31 pmI don't think that's a problem.

author: avvidclif
author_rank: Regular Contributor
timestamp: January 13, 2015, 03:49:07 pm
content: Quote from: ZBIQ on January 12, 2015, 07:19:31 pmMine works exactly the same way. With no channel selected CH1 is on. If I select CH2,3,4 then CH1 goes off unless selected.Leave it alone, mine has been thru a refurb and is working correctly, so is yours.

author: c4757p
author_rank: Super Contributor
timestamp: January 13, 2015, 04:10:45 pm
content: This is correct behavior; all the scopes in this series refuse to shut off all four channels simultaneously. Ch 1 comes on whenever all the other three are off.

author: ZBIQ
author_rank: Contributor
timestamp: January 14, 2015, 09:00:49 am
content: Ok, so my scope works just fine, thats great.Thanks for your help !