dark lcd display

[legg]

LCD display is dark.
All necessary wiggles being delivered to solderable pins.
Backlight visibly ON.
Unit runs without indication.

Is it toast?

Custom unit for Sharp microwave - only replacement is
full panel at us$200. Unit retails at us$360.
'Light Commercial' duty stainless - in marketplace
since 1999 and still sold.

Also requires replacement lamp and stirring reflector
motor.

RL

[Peter W.]

If you had done your Consumer Reports back in the day, you would have found that Sharp has notoriously frequent display issues. With this in mind, you might contact Sharp for suggestions. They know their reputation, and are counting on the consumers not knowing.

Peter Wieck
Melrose Park, PA

[legg]

Peter,

I don't buy microwave ovens, I just fix them.

This model of microwave R21LV has a few variants
which have been mfred since before Y2K.

It's service manual illustrates a panel with a
completely different display on the control board,
possibly even LED, vs the LCD variety present here.

I've got nothing but respect for Sharp stuff. My
pocket calculator from the 90s has been through the
laundry twice, without permanent damage. It has an
early type of LCD display.

I've seen LCDs that have obvious damage/discoloration
and flakey elements before, but never something that
was permanently, uniformly dark.

There's no carbon press strip to degrade, just 15
solderable in-line pins.

I would suspect the controller chip, or its ceramic
resonator, but the chip seems to be performing normally.
The unit runs.

RL

[three_jeeps]

"All necessary wiggles being delivered to solderable pins" - Not sure what this means so I'll make an inference: All the LCD segment lines change state appropriately? Checked voltages on all segment pins at the same time (with perhaps a 16 line digital analyzer)? Bias voltage on the LCD correct? If all true then the LCD is dead.
Does this model have a separate LCD controller chip or does it use a micro with a number of DIO lines?

[legg]

On Sun, 24 Dec 2023 09:45:39 -0800 (PST), three_jeeps
<jjh...@gmail.com> wrote:

>On Sunday, December 24, 2023 at 11:22:45?AM UTC-5, legg wrote:
<snip

>>
>> I've seen LCDs that have obvious damage/discoloration
>> and flakey elements before, but never something that
>> was permanently, uniformly dark.
>>
>> There's no carbon press strip to degrade, just 15
>> solderable in-line pins.
>>
>> I would suspect the controller chip, or its ceramic
>> resonator, but the chip seems to be performing normally.
>> The unit runs.
>>
>
>"All necessary wiggles being delivered to solderable pins" -
> Not sure what this means so I'll make an inference:
> All the LCD segment lines change state appropriately?
> Checked voltages on all segment pins at the same time
> (with perhaps a 16 line digital analyzer)?

dream on

> Bias voltage on the LCD correct? If all true then the LCD is dead.
>Does this model have a separate LCD controller chip or does it use a micro with a number of DIO lines?

Service manual shows 4x9 connections more suited to an LED display
coming from a 64pin micro through a quad buffer and nine unbuffered
lines from paralleled ports with 100R series limiters.

The current rev board is a 56pin QFN package driving the 15 pins of
the display directly.

3 of the 15 pins generate quad-state ~ramps between 0 and 5V.
Pins 1 , 2 and 10.
The rest just clock (150Hz) between the two mid-state levels, in
sync with the ~ramping steps.

This controls segments of 4 digit clock, its middle colon and
5 symbols for mode of operation, spaced ~ equally below the digits
and mid-colon.

I've searched all over for a more accurate service manual, or
a revision that includes the change to micro and display, but
this is only reflected in purchasing spares. The old control
panel assy number is retired to be replaced by . . .

A custom LCD-only part for the control board assembly isn't a
likely after-market item. The whole panel is available for $$$.

This one is from 2012, about half way through the product's history.

RL

[legg]

This thing is in working order and programmes.

It had some gunk penetrating the stiring motor
couplig shaft area that had carbonized and would cause
visible arcing, until the polyproplylene components
were scraped completely clean.

It's just inconvenient and unsafe to run without
confirmation of an obvious countdown in the run
time.

If I brush my thumb across the display the major
' 1 ' and 'ON' segments display, regardless of
operating state or cooking time. These fade
gradually.

RL