Lighted LCD microwave display is intermittent

[Makull]

Our Sharp built in microwave, model no. R-420DK, hasn't had a LCD
display that was easily visible (especially at night) since we bought
the house 3 months ago. The light for the display came on yesterday
and today while we were using the touch pad. The light stayed on for 5
or 6 seconds each time and went out when we opened the door or punched
another button on the touch pad.
I'd like to try to troubleshoot and repair the LCD light circuit, and
need info on safely accessing the lighting circuit.

Paul B.
Paul <[email protected]> cut Phil to respond.

 

[Ancient_Hacker]

Makull wrote:

I'd like to try to troubleshoot and repair the LCD light circuit, and
need info on safely accessing the lighting circuit.

Well, let's look at the pros and cons:

(1) You spend an hour or so tracing out the problem. You're down
however much you think your time is worth.

(1a) You find and fix the problem. You're up the worth of an old
microwave (maybe $10?) minus your hour's worth. I suspect you think
you're worth more than $10 an hour.

(1b) You dont find the problem. You're down the time you spent.
Maybe up a little enjoyment.

(2) You accidentally touch the AC line voltage terminals, or the
capacitor terminakls, or the magnetron wire (2000+ volts) and die.
You're out your time, and your life. And your survivors will probably
feel bad to keep the oven, so they're out $10 too.

(3) You give the oven to your local charity, get $15 credit towaerd
your deductions.
You go out and buy a new microwave for $80, which will have a
working light, a full warranty, more features, and not smell like
bacon. You're out $65, but you have your life and a good feeling for
donating.

 

[Art]

Order the complete control assembly from Sharp and save all the hassle.

 

[Sam Goldwasser]

Our Sharp built in microwave, model no. R-420DK, hasn't had a LCD
display that was easily visible (especially at night) since we bought
the house 3 months ago. The light for the display came on yesterday
and today while we were using the touch pad. The light stayed on for 5
or 6 seconds each time and went out when we opened the door or punched
another button on the touch pad.
I'd like to try to troubleshoot and repair the LCD light circuit, and
need info on safely accessing the lighting circuit.

Someone else basically said to buy a new oven. That's ridiculous.
This could be a simple bad connection to the backlight.

But you do need to have some electronics experience to find it and
understand that there may be very lethal voltages present once you remove
the cover of the microwave. The controller PCB and backlight are nowhere
near the microwave high voltage supply but it will be exposed. However,
there will still be line voltage on the controller PCB.

What is your level of electronics expertise?

--- sam | Sci.Electronics.Repair FAQ: http://www.repairfaq.org/
Repair | Main Table of Contents: http://www.repairfaq.org/REPAIR/
+Lasers | Sam's Laser FAQ: http://www.repairfaq.org/sam/lasersam.htm
| Mirror Sites: http://www.repairfaq.org/REPAIR/F_mirror.html

Important: Anything sent to the email address in the message header above is
ignored unless my full name AND either lasers or electronics is included in the
subject line. Or, you can contact me via the Feedback Form in the FAQs.

 

[Makull]

Someone else basically said to buy a new oven. That's ridiculous.
This could be a simple bad connection to the backlight.

But you do need to have some electronics experience to find it and
understand that there may be very lethal voltages present once you remove
the cover of the microwave. The controller PCB and backlight are nowhere
near the microwave high voltage supply but it will be exposed. However,
there will still be line voltage on the controller PCB.

What is your level of electronics expertise?

--- sam | Sci.Electronics.Repair FAQ: http://www.repairfaq.org/
Repair | Main Table of Contents: http://www.repairfaq.org/REPAIR/
+Lasers | Sam's Laser FAQ: http://www.repairfaq.org/sam/lasersam.htm
| Mirror Sites: http://www.repairfaq.org/REPAIR/F_mirror.html

Important: Anything sent to the email address in the message header above is
ignored unless my full name AND either lasers or electronics is included in the
subject line. Or, you can contact me via the Feedback Form in the FAQs.

Thanks for the direct answer. I'm a retired EE with experience in
troubleshooting tube based circuitry so I'm well aware of dangers of
high voltage circuits.
Lately, I've been troubleshooting and repairing tape decks and the
some of the Tektronix 500 series scopes. Microwave ovens are
completely foreign to me. I was hoping someone had dealt with this
specific problem on this specific model and could efficiently guide me
through the mechanical disassembly required to service the controller
PCB and backlight. I'm particularly concerned about compromising the
oven's microwave shielding.
Paul <[email protected]> cut Phil to respond.

 

[Homer J Simpson]

I'm particularly concerned about compromising the
oven's microwave shielding.

That's not a concern. It's very unlikely and easy to check.

Be more concerned about the voltages. Make a discharger and short out the
main cap while working on the unit. Remove short before testing.


--
_____ _ _
|_ _| | | | |
| | __ _ _ __ ___ | |__| | ___ _ __ ___ ___ _ __
| | / _` | '_ ` _ \ | __ |/ _ \| '_ ` _ \ / _ \ '__|
_| |_ | (_| | | | | | | | | | | (_) | | | | | | __/ |
|_____| \__,_|_| |_| |_| |_| |_|\___/|_| |_| |_|\___|_|
__ ____
/ _| | _ \
___ | |_ | |_) | ___ _ __ __ _
/ _ \| _| | _ < / _ \| '__/ _` |
| (_) | | | |_) | (_) | | | (_| |_
\___/|_| |____/ \___/|_| \__, (_)
__/ |
|___/

 

[Sam Goldwasser]

Thanks for the direct answer. I'm a retired EE with experience in
troubleshooting tube based circuitry so I'm well aware of dangers of
high voltage circuits.
Lately, I've been troubleshooting and repairing tape decks and the
some of the Tektronix 500 series scopes. Microwave ovens are
completely foreign to me. I was hoping someone had dealt with this
specific problem on this specific model and could efficiently guide me
through the mechanical disassembly required to service the controller
PCB and backlight. I'm particularly concerned about compromising the
oven's microwave shielding.
Paul <[email protected]> cut Phil to respond.

Since you've worked on electronics, you are aware that bad connections are
a very common fault, which may be the problem here.

The disassembly will be obvious once the cover is
removed and you won't be going anywhere near anything that would compromise
the microwave integrity. The controller is outside the shielded area.
But to be safe, do discharge the HV cap. This should happen automatically
once it's powered off for awhile but better safe than sorry.

See the info - especially safety - at the sites below or www.microtech.com .

WARNING: There is up to 5000 V at AMPs available from the HV circuits when
energies and a HV cap that can store a nasty charge. Experienced techs
have been killed by microwave ovens.

--- sam | Sci.Electronics.Repair FAQ: http://www.repairfaq.org/
Repair | Main Table of Contents: http://www.repairfaq.org/REPAIR/
+Lasers | Sam's Laser FAQ: http://www.repairfaq.org/sam/lasersam.htm
| Mirror Sites: http://www.repairfaq.org/REPAIR/F_mirror.html

Important: Anything sent to the email address in the message header above is
ignored unless my full name AND either lasers or electronics is included in the
subject line. Or, you can contact me via the Feedback Form in the FAQs.

 

[Art]

Main reason the recommendation regarding obtaining the complete controller
from SHARP is the fact that even tough you may be a totally experienced EE
and very capable of engineering a complete operational product, once you
determine that indeed it is not just a flippin poor connection, that you may
need a descrete device that SHARP will not provide.
Then you are again going to ask the same question, how do I fix this?/ Not
to be flippant, Sam gives you a whole lot of very good advice, and obviously
you know absolutely everything about engineering electronic devices.
So, Have at it!! Enjoy!! When done and totally frustrated, go but another
complete microwave, they are cheap especially for someone of an E/E salary,
Right?/

 

[jakdedert]

Main reason the recommendation regarding obtaining the complete controller
from SHARP is the fact that even tough you may be a totally experienced EE
and very capable of engineering a complete operational product, once you
determine that indeed it is not just a flippin poor connection, that you may
need a descrete device that SHARP will not provide.
Then you are again going to ask the same question, how do I fix this?/ Not
to be flippant, Sam gives you a whole lot of very good advice, and obviously
you know absolutely everything about engineering electronic devices.
So, Have at it!! Enjoy!! When done and totally frustrated, go but another
complete microwave, they are cheap especially for someone of an E/E salary,
Right?/

Oh for gawd's sake. What's the point in the above? The guy wants to
fix his microwave. His reasons are his own. He asked for help, not
derision. There are others here willing to give it to him. Obviously
if he's unsuccessful, he'll either live with the problem--as he has been
doing--or he'll get a new one...or perhaps he'll totally destroy it.

Or, he'll fix it and keep it out of the waste stream for a while longer.

What was your point, again? Do you have one, or are you just a troll?

jak