Power Circuit Board and Diodes
 

This weekend my wife and I were watching a DVD and suddently we heard
a pop and the TV went blank. I replaced the 1.6A fuse and immediately
blew another one. I tested all the diodes on the power board by
reversing ohmeter leads and found 5 or 6 good ones and 7 bad ones. Of
the bad ones, 4 are small and near the fuse so I assume they are a
rectifier bridge. Two others are up off the PCB and near a
transformer; one of these is larger and the other MUCH larger. The
7th one is small (like the first 4) and right next to a tiny chip.

1) Will a good diode ever test bad by this method as a result of still
being in the circuit? (I did not lift one leg for any of these
tests.)

2) If I remove the 7 diodes that tested bad, will a parts house be
able to identify the appropriate replacement from markings on the
diode itself?

3) If I successfully replace these without damaging any other
components, what is the likelyhood that all the other components are
ok? High? 50/50? Low?

PS, I know that DVD players are cheap these days but I like DIY
projects, plus I hate to throw stuff in the landfill if it can be
fixed without too much trouble or expense.

--
Bob Simon
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May acutally want to purchase a service manual for your set, generically we
can only guess at this point. You state that your tele took a dump and you
are trying to fix it yourself. No information regarding make or model, or
even chassis number.
"Bob Simon" wrote in message
...
This weekend my wife and I were watching a DVD and suddently we heard
a pop and the TV went blank. I replaced the 1.6A fuse and immediately
blew another one. I tested all the diodes on the power board by
reversing ohmeter leads and found 5 or 6 good ones and 7 bad ones. Of
the bad ones, 4 are small and near the fuse so I assume they are a
rectifier bridge. Two others are up off the PCB and near a
transformer; one of these is larger and the other MUCH larger. The
7th one is small (like the first 4) and right next to a tiny chip.

1) Will a good diode ever test bad by this method as a result of still
being in the circuit? (I did not lift one leg for any of these
tests.)

2) If I remove the 7 diodes that tested bad, will a parts house be
able to identify the appropriate replacement from markings on the
diode itself?

3) If I successfully replace these without damaging any other
components, what is the likelyhood that all the other components are
ok? High? 50/50? Low?

PS, I know that DVD players are cheap these days but I like DIY
projects, plus I hate to throw stuff in the landfill if it can be
fixed without too much trouble or expense.

--
Bob Simon
remove both "x"s from domain for private replies

On Mon, 4 Apr 2005 15:27:21 -0400, "Art"
wrote:

May acutally want to purchase a service manual for your set, generically we
can only guess at this point. You state that your tele took a dump and you
are trying to fix it yourself. No information regarding make or model, or
even chassis number.

Thanks.

No it was the DVD that died. Toshiba SD-2900KU. PCB: PM0004503010;
PC-POWER-K510.



"Bob Simon" wrote in message
.. .
This weekend my wife and I were watching a DVD and suddently we heard
a pop and the TV went blank. I replaced the 1.6A fuse and immediately
blew another one. I tested all the diodes on the power board by
reversing ohmeter leads and found 5 or 6 good ones and 7 bad ones. Of
the bad ones, 4 are small and near the fuse so I assume they are a
rectifier bridge. Two others are up off the PCB and near a
transformer; one of these is larger and the other MUCH larger. The
7th one is small (like the first 4) and right next to a tiny chip.

1) Will a good diode ever test bad by this method as a result of still
being in the circuit? (I did not lift one leg for any of these
tests.)

2) If I remove the 7 diodes that tested bad, will a parts house be
able to identify the appropriate replacement from markings on the
diode itself?

3) If I successfully replace these without damaging any other
components, what is the likelyhood that all the other components are
ok? High? 50/50? Low?

PS, I know that DVD players are cheap these days but I like DIY
projects, plus I hate to throw stuff in the landfill if it can be
fixed without too much trouble or expense.

--
Bob Simon
remove both "x"s from domain for private replies



--
Bob Simon
remove both "x"s from domain for private replies

1, yes a good diode can test bad in circuit due to other shorts, you
can clip one side of the diode and test it out of circuit with one leg
still attached (power off of course)

2 is this a switching power supply? you can probably use generic
diodes or bay another bad unit off ebay for parts

3 probably something bad in the power supply, maybe more than just the
diodes though

Mark