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| Roberto Salerno |
Brand: Inno-Hit 21”
Model: RF ST TX Silver chassis 11AK30
Schematic: download from www.electronica-pt.com
Fault: completely dead
Once opened, the first thing I do is measure the voltage presence on the electolytic terminals C809 (150uF-400V), but no voltage results here. The main fuse is not burnt black and gives me a good measurment.
I notice however that the resistor R828 (2,2 ohm-5W) is interrupted.
For sure there is a short circuit somewhere, this reflecting on the fuse and which damaged the limit resistance.
The rectifier bridge, composed of four separate diodes is Ok, so also for various other components.
I finally find that it is the MosFet Q801 to be in short-circuit between Source and Drain.
On the schematic I see that it should be a 2SK2750, I instead find a P6NK60ZFP assembled.
I decide to fit a 2SK1118 which normally adapts well on these circuits.
Beforehand I try to understand the real cause of the MosFet fault in question.
I check a few things, in particular the weldings. There is no evident sign of dry joints however some-thing happens when I stimulate the blue capacitor C811. The rheophore (warm side) found on the welding seems to slightly move. I resolder this welding and others nearby; the new MosFet is already inserted and I replace the R828 resistor (2,2 ohm).
I notice however that the resistor R828 (2,2 ohm-5W) is interrupted.
For sure there is a short circuit somewhere, this reflecting on the fuse and which damaged the limit resistance.
The rectifier bridge, composed of four separate diodes is Ok, so also for various other components.
I finally find that it is the MosFet Q801 to be in short-circuit between Source and Drain.
On the schematic I see that it should be a 2SK2750, I instead find a P6NK60ZFP assembled.
I decide to fit a 2SK1118 which normally adapts well on these circuits.
Beforehand I try to understand the real cause of the MosFet fault in question.
I check a few things, in particular the weldings. There is no evident sign of dry joints however some-thing happens when I stimulate the blue capacitor C811. The rheophore (warm side) found on the welding seems to slightly move. I resolder this welding and others nearby; the new MosFet is already inserted and I replace the R828 resistor (2,2 ohm).
I give power on and the unit remains in standby mode with the red led on. With the remote control I switch on the TV and obtain positive results.
The welding at fault was practically invisible, there were no evident "cold" cracks.
It's important in a case like this to find the real cause of the MosFet shorted.
After a normal test period my repair is complete.
How much you charge normally?
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