[sdiy] Siel OR400 Transformer needed

[ASSI]

Hi Nicholas,

On Friday 26 July 2013, 15:29:49, Nicholas Keller wrote:
> I'm trying to help Maeghan out with this, but am only slightly more
> confident than her.  When you offer suggestions, can you be more
> specific?  Assume we need to know exactly where to place the probes,
> because we actually might. For instance, how do we test "across the load
> caps" and between the secondaries?  And what values should we hope to
> find?

Well, if we need to tell you that, then I'd suggest this is too close to 
mains input to be safe, especially if there's potentially some damage from 
an earlier short/spark with live mains involved.  It sounds like you're on 
110VAC, is that right?  That would have a much higher chance of not having 
done too much damage giving the description of the accident.  I haven't seen 
the board, I can only go from the schematics, so if I say "check Ra3", then 
I have to trust you you'll find this on the board and not the primary fuse.
 
> I told her that I thought the transformer was bad because she told me that
> she measured 17V (but I'm not sure how).

If she measured with an AC meter, then 17V is about right, unloaded.

> I figured if that is off, then
> the outputs of the regulators would be off too, even if the regulators
> are still good.  Does this make sense?

>From the measurements she just sent, the transformer, rectifier and load 
caps seem to not suffer any catastrophic damage.  You 'd have to load the 
transformer before / after the rectifier to rated power to really see if 
things are still working, two 24V/6W auto brake lights in series should be 
about right.  From the things I know so far I don't think it's the 
transformer.

The apparent asymmetry between positive / negative is a bit disconcerting 
and may hint at a single blown rectifier, but it could be a leaky cap as 
well.

Once you've checked that and are reasonably certain that things are OK until 
this point,  go over all the measurement points marked with blue circles in 
the schematic (PNG).  If they're off, then that would explain why the 12V 
outputs don't regulate correctly and the most likely reason is that one or 
all of the resistors Ra3 to Ra6 is damaged.  If any of those are discolored 
or have charring, then replace them right away.  They aren't marked in the 
schematics, but I think these should be 1/4 or 1/2W types.  With some luck, 
when the resistor values are correct so should the output or the regulators.  
If so, try it again with a load on the output of the regulator, this time a 
12V/2W motorcycle brake light or something like that.


Regards,
Achim.
-- 
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