Re: New member and owner of a dead 2225


 

On 14 Nov 2017 10:11:05 +0000, you wrote:

On higher voltage caps, it's it the case the higher V often means higher ESR?
With higher voltage ratings up to about 100 volts, dissipation factor
and ESR drop and ripple current rating increases. Ripple current
rating depends on ESR and surface area for dissipating heat. There is
a jump at about 160 volts and higher where the dissipation factor and
ESR increase because the electrolyte is different (at least I think it
is due to a different electrolyte) to support higher voltage
operation.

I am planning on pulling all the switcher electrolytic caps out and am hoping to find what went bad to help with the general diagnosis. Right now, my bet is on either C915 or C971. Hopefully the series regulator and inverter are ok as I don't have a scope to debug my scope with...
It might just be a case of Q913 failing for whatever reason including
CR912 shorting, R920 failing open or high, base drive being
insufficient, or contamination through the package. But I would still
change the aluminum electrolytic capacitors in the power supply except
maybe for C900 if it and the bridge rectifier diodes CR901 through
CR904 test good. If diode shorted and then failed open, it might
have damaged C900 without it being apparent.

Another thing which could have caused failure of Q913 is a low input
voltage. With low input voltage, the duty cycle to maintain the
output voltage is higher so Q913 conducts longer and runs hotter.

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