[sdiy] M5320L voltage regulator incorrect outputs

Mike profpep at hotmail.com
Sat Mar 1 19:19:30 CET 2008


> I've just refurbished my JX8P's power supply unit,
> replacing all caps. I check the voltages and see
> +14.40v and -14.40v instead of -15v and +15v.
>
> The schematics shows a M5230L dual tracking regulator
> which is probably responsible for the +15v and -15v
> output voltages ?
>
> I'm trying to figure out whether the non-accurate
> voltages are caused by a bad (or old) M5230L, or other
> component at the area ... any help ?
>

The design is striaght out of the application note. R4 and R5 being equal
make it symmetrical, and the voltage is set by the ratio of R3 (24K) and R7
(3.3K). Check the values of R3 and R7 first, then check if C4 (1uF 50V) is
in the right way round, or leaky. If the apparent resistance of  R3 is low,
the output will drop. The fact that you are getting an identical (14.40)
rail voltage leads me to suspect a problem at the regulator, rather than a
bad load in circuit, though I can't remember if dropping one rail would pull
the other down with it. Do you get the same results with CN1 and CN2
pulled? - a check there would elimate any bad load problems, (sorry for
stating the obvious here). If C$ is an old Tantalum, then I would replace it
on spec, just in case.

HTH

Mike




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