Re: New member and owner of a dead 2225


Tom Jobe <tomjobe@...>
 

Hi Phillip.
I see you are getting some very good help on this problem, and when you
combine that with the fact that your voltages are only down by half, I'd
say the 2225 is only lightly wounded and that you will have it working
perfectly very soon. In order for the low voltages to be half there,
most of the power supply must be fundamentally sound.
The 2225 needs all of the aluminum electrolytic capacitors 10 uF and
larger changed anyway to regain that sharp trace you once had, and the
new ones might possibly help with your current problem as well. Get
brand new high quality 105 degree caps from a major electronics parts
supplier if you can.
There are several variations of the architecture of the small 22xx power
supplies but there are not many problems with the 2225 type of power
supply that ever show up on the Tekscopes Group .
When I read your original post about your 2225 problem, I looked on
YouTube to see what kinds of videos were available about the 2225.
Take a look at these two when you have time. This 2225 Dave Jones bought
worked just as it was received, and he gives you quite a nice lesson on
its use and claibration, as well as a tour of much of it's inner
workings (less the power supply unfortunately). He also gives you some
good common sense tips about working around the high voltages present in
the oscilloscope.

EEVBlog #196 operational review of the 2225
https://www.youtube.com/watch?v=8GR_6QH3uZk

EEVBlog #208 teardown and calibration of the 2225
https://www.youtube.com/watch?v=mHODWDBcQDg

Best of luck!
tom jobe...




On 11/12/2017 3:29 PM, phillip.lyne.barrett@gmail.com [TekScopes] wrote:

Long term electronics hobbyist. I've had a Tek 2225 for about 15 years
and used it a lot. The other day I turned it on to test a circuit I'm
prototyping and nothing. Dead. Check outlet, fuse, power cord. Nope.
The only sign of life is a little blip on the power and leds - maybe
half a second. I'm guessing it's the power supply. This scope has been
an old friend.


I got the service manual and pulled the chassis out of the case. Found
a loose torx screw inside though It didn't appear to be shorting
anything and after removing it the symptoms persist. The scope had
been sitting on the bench in the same spot for a couple of years so I
doubt the screw was the problem. Inspection didn't show anything
obvious - burnt components, bulging caps, blue smoke. In fact, it was
surprisingly clean for 30 year old scope.


Anyway, I took some test point measurements on the bottom of the main
baord and all the voltage levels were around half what they were
supposed to be. More confident it's the PS. Looked at the mains input
board. rectifiers (CR901-CR904) are ok. Pulled the board and pulled
the big @ss 2200 uF cap (C900). It tested out ok (2270 uF).


Next step is to look at the preregulator section after I put the mains
input board back.


I'm just following a fairly logical path here but thought there might
be smarter people than me here that could help short cut the process.
Any suggestions of where to look would be greatly appreciated.


Phil

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