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On 25 Apr 2009 08:37:36 -0400, (Scott Dorsey) wrote:

wrote:
Hi, I have an IO-4555 Heathkit O-Scope that started spewing out smoke
15 seconds after turning it on.

One of two things happened. Either an electrolytic cap failed, or the
power transformer failed. The power transformers on these were very
cheaply made, and the high voltage winding had a bad tendency to short
to the case. If it made a loud snapping sound, it was probably the
transformer. If it made a smell that was more sharp and chemical than
ordinary burning, it was probably a cap.

Would like to find someone that can shoot me a PDF of the assembly
manual with schematics. The operations manual would be nice also.

I've checked Google and Dogpile for variations and can only find a
schematic for the dual trace version. (IO-4550)

That'll probably be sufficient since the supply is more or less the same
and it's a power supply problem you've encountered. You may also look on
BAMA.

You should not need the manual. Find the high voltage winding that
generates the anode voltage for the CRT.... measure resistance to ground
and you should see at least hundreds of ohms across the winding. Then
look at the supply caps.

You can also try powering it up with the case off and seeing what smokes.

If the transformer is good, it's worth it to replace the caps. If the
transformer has failed, scrap it for parts and get another scope.
--scott

Thanks for the trouble shooting tips. The smell and color reminded me
more of frying resistors :-) I haven't opened her up yet to peek at
the damage.

Tim...

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