Mustek DVD, logic is dead

[Stefan Toftevall]

Hi all,
I got a Mustek DVD player into my repair shop some days ago. The
customer told me the unit was all dead. TRUE!
A fast examination of the smps revealed a shorted zener diode in the
primary part of the supply (a 15V zener used as transient surpression
on the switching FET's gate to ground).
Ok, I replaced the zener and the smps now operates perfect generating
all its secondary voltages.
BUT, the player is STILL DEAD! The mainboard gets all the power it
should and so does the display board, but there is absolutely NO
response from the logic.
This tells me, either some sort of Power on reset pulse is missing, or
otherwise the microcontroller is blown. Though, I still believe I
should have at least something light up or the standby/power on led
light up.
Maybe some of you have faced the same problem somewhere,
Any advice is appreciated!
Regards
Stefan

 

[James Sweet]

"Stefan Toftevall" <stefan.toftevall@bredband.net> wrote in message
news:c4f805eb.0312231141.2f40efd1@posting.google.com...

Hi all,
I got a Mustek DVD player into my repair shop some days ago. The
customer told me the unit was all dead. TRUE!
A fast examination of the smps revealed a shorted zener diode in the
primary part of the supply (a 15V zener used as transient surpression
on the switching FET's gate to ground).
Ok, I replaced the zener and the smps now operates perfect generating
all its secondary voltages.
BUT, the player is STILL DEAD! The mainboard gets all the power it
should and so does the display board, but there is absolutely NO
response from the logic.
This tells me, either some sort of Power on reset pulse is missing, or
otherwise the microcontroller is blown. Though, I still believe I
should have at least something light up or the standby/power on led
light up.
Maybe some of you have faced the same problem somewhere,
Any advice is appreciated!
Regards
Stefan

Is there a surface mount fuse anywhere on the logic board? Perhaps the power
supply's voltage shot way up and blew it. The micro could also easily be
dead if the voltage went up.

 

[Stefan Toftevall]

"James Sweet" <jamessweet@hotmail.com> wrote in message news:<hd2Gb.640400$Fm2.571690@attbi_s04>...

"Stefan Toftevall" <stefan.toftevall@bredband.net> wrote in message
news:c4f805eb.0312231141.2f40efd1@posting.google.com...
Hi all,
I got a Mustek DVD player into my repair shop some days ago. The
customer told me the unit was all dead. TRUE!
A fast examination of the smps revealed a shorted zener diode in the
primary part of the supply (a 15V zener used as transient surpression
on the switching FET's gate to ground).
Ok, I replaced the zener and the smps now operates perfect generating
all its secondary voltages.
BUT, the player is STILL DEAD! The mainboard gets all the power it
should and so does the display board, but there is absolutely NO
response from the logic.
This tells me, either some sort of Power on reset pulse is missing, or
otherwise the microcontroller is blown. Though, I still believe I
should have at least something light up or the standby/power on led
light up.
Maybe some of you have faced the same problem somewhere,
Any advice is appreciated!
Regards
Stefan

Is there a surface mount fuse anywhere on the logic board? Perhaps the power
supply's voltage shot way up and blew it. The micro could also easily be
dead if the voltage went up.

Hi James,
I don't really think the smps got out of regulation and output
excessive voltages, maybe some nearby thunder light storm caused nasty
spikes on the mains and caused the 15v clamp zener to short. Its mains
fuse were also open though it didn't "looked blown", more like it
opened softly.
I'll go check the board for surface mount fuses and protectors.
Thanks for the tip.

MERRY X MAS TO ALL OF YOU!

Regards
Stefan