Author Topic: 2465b problems after replacing caps.  (Read 3511 times)

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Offline ZBIQ

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2465b problems after replacing caps.
« on: January 03, 2015, 07:12:15 pm »
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.be

2. 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.be

Its 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?
 

Offline tautech

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Re: 2465b problems after replacing caps.
« Reply #1 on: January 03, 2015, 07:37:53 pm »
Power supplies are good (there is some excess ripple - need to check this again).
Fix the PSU first.
The whole scope's stability and accuracy depends on a perfect PSU.
Ensure it is to Tek's spec or better.
Avid Rabid Hobbyist
 

Offline ZBIQ

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Re: 2465b problems after replacing caps.
« Reply #2 on: January 03, 2015, 08:25:44 pm »
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.

Ok :) got it. In my case at 100Hz
« Last Edit: January 03, 2015, 08:33:41 pm by ZBIQ »
 

Offline ZBIQ

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Re: 2465b problems after replacing caps.
« Reply #3 on: January 03, 2015, 08:41:26 pm »
Ok. There is definitely something going on.
On +10V (reference J119-4) there is about 30mVpp ripple with period about 1.12s. Hmmm interesting.
 

Offline malch

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Re: 2465b problems after replacing caps.
« Reply #4 on: January 04, 2015, 01:12:49 am »
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
« Last Edit: January 04, 2015, 11:22:53 pm by malch »
 

Offline ZBIQ

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Re: 2465b problems after replacing caps.
« Reply #5 on: January 12, 2015, 07:19:31 pm »
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.
 

Offline mij59

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Re: 2465b problems after replacing caps.
« Reply #6 on: January 13, 2015, 06:51:48 am »

But I have the second problem unsolved. 1st channel is always on (as on video).  I need to sniff around processor ...


I don't think that's a problem.
 

Offline avvidclif

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Re: 2465b problems after replacing caps.
« Reply #7 on: January 13, 2015, 03:49:07 pm »
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.

Mine 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.
Clif Holland KA5IPF
www.avvid.com
 

Offline c4757p

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Re: 2465b problems after replacing caps.
« Reply #8 on: January 13, 2015, 04:10:45 pm »
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.
No longer active here - try the IRC channel if you just can't be without me :)
 

Offline ZBIQ

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Re: 2465b problems after replacing caps.
« Reply #9 on: January 14, 2015, 09:00:49 am »
Ok, so my scope works just fine, thats great :).

Thanks for your help !
 


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