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Tektronix model 2220 power supply problem ...
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Peter Andersen
electronics forum beginner


Joined: 21 Oct 2005
Posts: 26

PostPosted: Thu Jul 20, 2006 11:40 pm    Post subject: Tektronix model 2220 power supply problem ... Reply with quote

Hi
I have recently purchased a Tektronix 2220 digital storage scope in a very
good condition. Except the power supply!

The power supply is clicking normally due to some kind of overload. I have
repaired a lot of more "normal" smps's and I have lifted the diodes on the
secondary side and located the fault on that way.

But in this case I have unmounted everything on the secondary side, and the
problem persist! I found a service manual for a Tektronix 2230 and the PSU
seems to be the same. I have extracted a jpeg of the PSU here:

http://www.mespilus.dk/Tex_2230_smps.jpg

Can anyone please help me? I have never seen this kind of PSU design before.
It must be some king of capacitor problem or....?? can I be sure the problem
is on the primary side?

--
Vh. Peter Andersen
www.mespilus.dk
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Robert Obermayer
electronics forum beginner


Joined: 24 Nov 2005
Posts: 13

PostPosted: Fri Jul 21, 2006 11:24 am    Post subject: Re: Tektronix model 2220 power supply problem ... Reply with quote

Peter Andersen wrote:
Quote:
The power supply is clicking normally due to some kind of overload. I have
repaired a lot of more "normal" smps's and I have lifted the diodes on the
secondary side and located the fault on that way.

Check R926, C925 first.
Its common that the R increases in resistance and the C dires up.
If this fails, it could result in such trouble.
Check CR920 too.
Measure voltage across C925, should be close to the indicated value and
free of ripple, if not see above.
Also check all other electrolytics, as usual (quite common to have them
dry up by now).

If not, check the "inverter" section.
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Peter Andersen
electronics forum beginner


Joined: 21 Oct 2005
Posts: 26

PostPosted: Fri Jul 21, 2006 12:41 pm    Post subject: Re: Tektronix model 2220 power supply problem ... Reply with quote

"Robert Obermayer" <robert_ng@hobbyelektronik.org> skrev i en meddelelse
news:4ibrr9F33la8U1@individual.net...

Quote:
Peter Andersen wrote:
The power supply is clicking normally due to some kind of overload. I
have
repaired a lot of more "normal" smps's and I have lifted the diodes on
the
secondary side and located the fault on that way.

Check R926, C925 first.
Its common that the R increases in resistance and the C dires up.
If this fails, it could result in such trouble.
Check CR920 too.
Measure voltage across C925, should be close to the indicated value and
free of ripple, if not see above.
Also check all other electrolytics, as usual (quite common to have them
dry up by now).



Thanx. I read a few older postings here on the same subject and tried the
trick with an external 43V directly on C940 I disconnected Q9070 when I
tried. Current limited to just 500mA.

R934 got VERY warm (the 51V zener is not shorted). I tried to lift R934
witch resulted in a burned 33ohm resister in series with CR948. Q946 or 947
died and have to be replaced.



Can I replace all the diodes on the secondary side with 1N5059 or 1N5062?

What substitute can I use for Q946+Q947?

Is it very important to use 840uF/12V caps or could I use a standard 640uf
or 1000uf 16V?



Peter
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