[Test-Equipment] Tek 7904 o-scope, power supply(tantalum caps) ?

Thu, 15 May 2003 13:00:53 -0400

Shorted tantalum caps is a "classic" problem with switching supplies. I 
would replace it with a low ESR cap that is designed for high frequency 
operation. While I had the power supply out of the scope, I would check all 
of the electrolytics for leakage, value and ESR. Any that are bad should be 
replaced with newer low ESR high frequency electrolytics. What I consider 
bad is an electrolytic that reads marked value or less. All electrolytics 
that I have seen, when good, read above marked value.

The clicking is an indication that the switcher is not starting.

73
Glenn
WB4UIV

At 12:28 PM 05/15/03 -0400, Cmos wrote:
>Hi all,
>
>I have a few tek 7904 o-scopes that I am
>working on, 3 of them have a power supply
>problem, and just click.
>
>I have started on one and found a shorted
>big 47uf dipped tantalum cap, on the +17v
>supply.
>Any one know if this is a common problem ?
>
>I am wondering if the other 2 may have the
>same shorted cap.
>Also, I see these cost 4 to 5$, not so cheap if
>I am replaceing 2 of them, in and 3 scopes.
>Was wondering about useing a low esr alumunum
>cap instead, the esr figures for these are even
>lower then tantalum. And they only cosr about
>0.30$, much cheaper.
>Dose any one have any experence with this ?
>
>Thanks for any help,
>Jim Martz
>
>-------------------------------------------
>Jim Martz,
>Home: [email protected]
>work: [email protected]
>web: http://www.shol.com/cmos
>Wifes page: http://www.shol.com/cmos/amparo
>
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