LC-15SH7U Button Question
 

I have a Sharp LC-15SH7U that took a power surge & went dead. After
fixing a shorted zener diode in the 33V power supply & a shorted dual
fet in the backlight inverter the tv powers up just fine & has a
normal picture but now the top six buttons don't work properly.
Power works properly
Menu, Input, & Volume Down don't work at all.
Volume Up works as Volume Down.
Channel Down works as Volume Up.
Channel Up works as Channel Down.
Button order is Menu, Vol down, Vol up, Chn down, Chn up, Input,
Power.

It has a four wire interface to the main board. I haven't traced the
circuit out yet, but a quick glance shows all switches are connected
to pin 1. I imagine the other three pins work a set of buttons each,
but I'm not sure. Is this a common configuration for Sharp TV's? I
haven't been able to find any service info for this TV, so I'm sure
I'll have to start tracing.

Thanks for any help,
Steve

LC-15SH7U Button Question
 

On Thu, 26 Feb 2009 21:27:58 -0600, Steve put finger to
keyboard and composed:

I have a Sharp LC-15SH7U that took a power surge & went dead. After
fixing a shorted zener diode in the 33V power supply & a shorted dual
fet in the backlight inverter the tv powers up just fine & has a
normal picture but now the top six buttons don't work properly.
Power works properly
Menu, Input, & Volume Down don't work at all.
Volume Up works as Volume Down.
Channel Down works as Volume Up.
Channel Up works as Channel Down.
Button order is Menu, Vol down, Vol up, Chn down, Chn up, Input,
Power.

It has a four wire interface to the main board. I haven't traced the
circuit out yet, but a quick glance shows all switches are connected
to pin 1. I imagine the other three pins work a set of buttons each,
but I'm not sure. Is this a common configuration for Sharp TV's? I
haven't been able to find any service info for this TV, so I'm sure
I'll have to start tracing.

Thanks for any help,
Steve

I have seen the following technique used in corded VCR remote
controls:

SW1 SW2 SW3 SW4
_|_ _|_ _|_ _|_
| | | | | | | |
GND o-- R1 --o-- R2 --o-- R3 ---o-- R4 ---|
|
SW o-------------------------------------|

The resistors could be binary weighted, ie R, 2R, 4R, 8R.

I can't see how this scheme fits in with your setup, though.

- Franc Zabkar
--
Please remove one 'i' from my address when replying by email.

LC-15SH7U Button Question
 

It's a pretty clever little circuit. It's a four pin connection. Pin
4 is ground, 3 is 3.3V. Pin 1 goes to the menu button with a basic
pull up resistor, switched ground configuration. Pin 2 goes to all
the other buttons in a voltage divider configuration. Power button
pulls pin 2 to ground, the other buttons switch in different legs of
the divider. The voltages measured are
CH+ .50V
CH- .88V
V+ 1.30V
V- 1.68V
Input 2.51V
Power 0V
This corresponds to the circuit tracing. By that, I mean the CH+
button swtiches in 1.5k, CH- switches in another 1.5k for 1.5k + 1.5k,
V+ switches in 1.5 + 1.5 + 2.2k, V- 1.5 + 1.5 + 2.2 + 2.7k, and input
1.5k + 1.5k + 2.2k + 2.7k + 10.5k. All are divided into themselves
plus the pullup of 10k (for V- it would be (1.5 + 1.5 + 2.2 +
2.7)/(1.5 + 1.5 + 2.2 + 2.7 + 10). I'm awful w/ ascii schematics, I
can give it a shot if anyone wants. It looks like the circuit's fine,
so it's somewhere else downstream that either isn't measuring
properly, or is doing the wrong function for the wrong voltage. Not
suprising for a lightning strike.

Steve

LC-15SH7U Button Question
 

Looks like I'm SOL. The traces each go through a 33 ohm resistor into
pins 3 & 4 of the uC. I imagine the prom got corrupted in the surge.
It has an EEPROM port, I bet if someone could flash it it'd work fine.
Oh well, I haven't tried the remote yet. This one was kind of fun,
the board was a PITA though, not meant for rework.

Steve

LC-15SH7U Button Question
 

On Fri, 27 Feb 2009 18:46:54 -0600, Steve wrote:

Looks like I'm SOL. The traces each go through a 33 ohm resistor into
pins 3 & 4 of the uC. I imagine the prom got corrupted in the surge.
It has an EEPROM port, I bet if someone could flash it it'd work fine.
Oh well, I haven't tried the remote yet. This one was kind of fun,
the board was a PITA though, not meant for rework.

Steve

Well, after some probing, it looks like it might not be wiped out
program. The divider input is 3.3V, but the output is 3.5V when open
circuit. The only thing else connected to the circuit is the uC. It
looks like the uC pin may be pulling the divider a little high causing
all the buttons to shift up, causing the higher ones to not work, and
the lower ones to be shifted one over. What is curious, though, is
that the menu button has its own pin, and it doesn't seem to work.
The menu button is only high or low, no divider output. When high, it
is pulled up to 3.5v as well, instead of 3.3v.

LC-15SH7U Button Question
 

On Fri, 27 Feb 2009 21:30:06 -0600, Steve put finger to
keyboard and composed:

On Fri, 27 Feb 2009 18:46:54 -0600, Steve wrote:

Looks like I'm SOL. The traces each go through a 33 ohm resistor into
pins 3 & 4 of the uC. I imagine the prom got corrupted in the surge.
It has an EEPROM port, I bet if someone could flash it it'd work fine.
Oh well, I haven't tried the remote yet. This one was kind of fun,
the board was a PITA though, not meant for rework.

Steve

Well, after some probing, it looks like it might not be wiped out
program. The divider input is 3.3V, but the output is 3.5V when open
circuit. The only thing else connected to the circuit is the uC. It
looks like the uC pin may be pulling the divider a little high causing
all the buttons to shift up, causing the higher ones to not work, and
the lower ones to be shifted one over. What is curious, though, is
that the menu button has its own pin, and it doesn't seem to work.
The menu button is only high or low, no divider output. When high, it
is pulled up to 3.5v as well, instead of 3.3v.

Why not install a buffer between pin 2 and the switch commons? You
could use a 3.3V rail-to-rail op-amp wired as a voltage follower. I've
"repaired" faulty I/O pins on uCs using similar methods. It appears
that the Menu button is unrecoverable, though.

- Franc Zabkar
--
Please remove one 'i' from my address when replying by email.

LC-15SH7U Button Question
 

On Sun, 01 Mar 2009 06:46:41 +1100, Franc Zabkar
wrote:

On Fri, 27 Feb 2009 21:30:06 -0600, Steve put finger to
keyboard and composed:

On Fri, 27 Feb 2009 18:46:54 -0600, Steve wrote:

Looks like I'm SOL. The traces each go through a 33 ohm resistor into
pins 3 & 4 of the uC. I imagine the prom got corrupted in the surge.
It has an EEPROM port, I bet if someone could flash it it'd work fine.
Oh well, I haven't tried the remote yet. This one was kind of fun,
the board was a PITA though, not meant for rework.

Steve

Well, after some probing, it looks like it might not be wiped out
program. The divider input is 3.3V, but the output is 3.5V when open
circuit. The only thing else connected to the circuit is the uC. It
looks like the uC pin may be pulling the divider a little high causing
all the buttons to shift up, causing the higher ones to not work, and
the lower ones to be shifted one over. What is curious, though, is
that the menu button has its own pin, and it doesn't seem to work.
The menu button is only high or low, no divider output. When high, it
is pulled up to 3.5v as well, instead of 3.3v.

Why not install a buffer between pin 2 and the switch commons? You
could use a 3.3V rail-to-rail op-amp wired as a voltage follower. I've
"repaired" faulty I/O pins on uCs using similar methods. It appears
that the Menu button is unrecoverable, though.

- Franc Zabkar

Good solution, shouldn't take more than a few parts & I could probably
just glue them to an unpopulated section of the board. This was kind
of a botched repair anyway, I had to guess at equivalent parts and the
board was damaged during the rework. Oh well, can't win them all.

Thanks,
Steve