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TDS684A freezing during boot (erratic behaviour)


Rogerio O
 

Dear all,
I bought this scope from Ebay some time ago and it has been working very well.
However, since one month ago, it started to "freeze" during boot.
It does not happens all the time, but once every two or three power on attempts.
When it happens, I manage to make it run by powering on/off a couple of times, but that made me think I will run into trouble soon.
I suspected that I could have a capacitor leakage problem but I inspected the boards for corrosion but I could not find it.
Maybe the caps are just starting to fail so here comes the one million dollar question: Should I recap this scope?
Is this a common failure in this model?
Any other suggestions?
Thank you very much in advance for the help.


amirb
 

psu is a good starting point but it could be your NVRAM about to give up
at what stage during boot does it freeze?
I would suggest you build the debug port and see the debug console first. That will give you a better clue as to what the problem is


Stephen Hanselman
 

If you have not done it already open it up and blow all the dust out of the unit. The fan sucks air through the PS andHV card. We have found virtually all of the units we’ve worked on had a serious reduction in air flow through the PS area

Regards,

Stephen Hanselman
Datagate Systems, LLC

On Aug 23, 2020, at 07:18, Rogerio O <@rodd414> wrote:

Dear all,
I bought this scope from Ebay some time ago and it has been working very well.
However, since one month ago, it started to "freeze" during boot.
It does not happens all the time, but once every two or three power on attempts.
When it happens, I manage to make it run by powering on/off a couple of times, but that made me think I will run into trouble soon.
I suspected that I could have a capacitor leakage problem but I inspected the boards for corrosion but I could not find it.
Maybe the caps are just starting to fail so here comes the one million dollar question: Should I recap this scope?
Is this a common failure in this model?
Any other suggestions?
Thank you very much in advance for the help.



Rogerio O
 

That you all for the replies.
I tried to turn it on just to make sure I would provide a correct answer to reply to amirb and I had two different issues now.
First I had SPC fail ( which not happened when I rebboted).
The second is a "shaky display".
What is the "usual cause" for a shaky display? PSU?
Thanks,
Roger


amirb
 

Now, this very much looks like a power supply problem or (less likely for the time being) the CRT driver board.

the PSU (and also acquisition board) on these units run very very hot generally and need a lot of air flow
and the caps are more likely to give up under these conditions

psu can be run without connecting to the other parts, so it is easy to work on it


Stephen Hanselman
 

I would look in the HVPS. This PS is fed 24V only and makes all of its internal use voltages it self. Usual suspects caps and such. Shoot me on you have and I’ll see if I have a spare.

If you get it working otherwise and don’t’ try mind spending some money look at SimmCon Labs for the lcd replacement. I have one in my TDS-540C and also my 8593 both work fantastic, lower the heat output and are sharper imaged. Downside they do range in cost from 399 to 899(8566’s). Our customers love them also.

Regards,

Stephen Hanselman
Datagate Systems, LLC

On Aug 23, 2020, at 14:44, Rogerio O <@rodd414> wrote:

That you all for the replies.
I tried to turn it on just to make sure I would provide a correct answer to reply to amirb and I had two different issues now.
First I had SPC fail ( which not happened when I rebboted).
The second is a "shaky display".
What is the "usual cause" for a shaky display? PSU?
Thanks,
Roger