Hi there,
I got this Dantax cable TV digibox for free some time ago...I think it had suffered a mains voltage spike due to a lightning strike. Now trying to get it back working.
Initial inspection revealed that the chopper controller / mosfet chip TNY265PN had exploded. What was left of the mosfet drain pin was still attached to PCB but not to the chip anymore.
HV side of the circuit is constructed pretty much according to TNY datasheet recommended layout on page 12. All components in HV branches measured fine offline.
I had a TNY267PN I had salvaged from somewhere lying around. Replaced, turned the digibox on, something emitted an audible snap and the chip was dead. I figured either the chip was already somehow damaged or then there must be something else wrong with the circuit.
I got a good deal on a 5-pack of TNY266s on eBay. They arrived just today. Replaced, turned on....nothing goes off instantly, front panel leds are alive, chopper transformer secondary voltages seem ok. I went a few steps away to get the remote to see if it worked. Came back and the system was dead again.
Drain voltage is fine, steady ~ 325VDC (230V * sqrt(2)), so I suppose the culprit must lie somewhere in the feedback system. Other than FB exceeding the absolute maximum ratings (haven't had a chance to measure if it does), I don't see what could keep destroying the chip. I mean, TNYs have short circuit and over temperature protection so they should be immune to those, right? Right after the most recent failure the chip was quite warm, though. The print on the top had partially faded away, apparently due to heat.
Attached are the datasheet and pictures of the PCB. I've swapped and aligned the back side pic for easy comparison in image editors.
I got this Dantax cable TV digibox for free some time ago...I think it had suffered a mains voltage spike due to a lightning strike. Now trying to get it back working.
Initial inspection revealed that the chopper controller / mosfet chip TNY265PN had exploded. What was left of the mosfet drain pin was still attached to PCB but not to the chip anymore.
HV side of the circuit is constructed pretty much according to TNY datasheet recommended layout on page 12. All components in HV branches measured fine offline.
I had a TNY267PN I had salvaged from somewhere lying around. Replaced, turned the digibox on, something emitted an audible snap and the chip was dead. I figured either the chip was already somehow damaged or then there must be something else wrong with the circuit.
I got a good deal on a 5-pack of TNY266s on eBay. They arrived just today. Replaced, turned on....nothing goes off instantly, front panel leds are alive, chopper transformer secondary voltages seem ok. I went a few steps away to get the remote to see if it worked. Came back and the system was dead again.
Drain voltage is fine, steady ~ 325VDC (230V * sqrt(2)), so I suppose the culprit must lie somewhere in the feedback system. Other than FB exceeding the absolute maximum ratings (haven't had a chance to measure if it does), I don't see what could keep destroying the chip. I mean, TNYs have short circuit and over temperature protection so they should be immune to those, right? Right after the most recent failure the chip was quite warm, though. The print on the top had partially faded away, apparently due to heat.
Attached are the datasheet and pictures of the PCB. I've swapped and aligned the back side pic for easy comparison in image editors.
Attached Files
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