Re: Tek 2230 PSU


 

On 06 Nov 2015 03:57:32 -0800, you wrote:

Hi All,

I was hoping for some advice on the power supply of a 2230 I'm working on.

I received the unit with mains fuse blown. Checked and found shorted rectifiers in the main bridge. I also found C904 cracked and with evidence of arcing. I found many of the LV electrolytics on both sides of the PSU having very poor ESR so I replaced pretty well all the electrolytics.

I then powered the unit up; no fuse blowing. However, the 43V supply to the inverter was not existent and C925 not charging up to power the preregulator. I did some more checking and found Q908 shorted, R909 open and C944 shorted. The FET Q9070 isn't shorted but I've not checked that it actually works.

Further, measuring resistance across C925 gives only 25ohms (having lifted R907, CR920). Is this normal or is it likely U930 is cooked too?
I do not see how Q908 and R909 could be bad without Q9070 and U930
also being bad.

C944 being shorted is also a bit interesting and leaves me wondering how much else of this power supply I should be suspicious of.
I would be suspicious of everything except high value resistors at
this point.

At present, replacing the components I know to be bad and powering up doesn't seem to to be the best idea given I don't know the cause of the issue.

...

Any thoughts?
These power supplies tend to go big when they fail so I would plan on
testing every part and replacing every semiconductor and aluminum
electrolytic capacitor. There are modern replacements for every part
except the transformers.

If you have a suitable power supply, the inverter can be disconnected
from the preregulator and tested separately. The preregulator can be
tested using a 42.8 volt load.

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