Sharp Model R1810 Carousel II microwave starts and cooks(heats) but
shutsdown after about 40 seconds. Electronic control board display
stays lit, countdown stops and displays remaining time--magnetron
cooling fan works during the first 40 seconds but then shutsoff--just
before shutdown, fan speed increases(doubling or tripling in speed)
These items seemed to check out good with VOM--
power fuse
interlock switches (2)
monitor switch
capacitor
diode
thermal cutout switch(only found one)
fan motor
power tranformer

Additional trouble shooting note--a power surge protector I had plugged
the microwave into was discovered fried--suspect a near by lightning
strike?

Read an informative article by Sam Goldwasser-- "NOTES ON MICROWAVE
OVEN FAILURE DIAGNOSIS AND REPAIR v1.01" but need more help. Thanks

"electroninja" writes:

Sharp Model R1810 Carousel II microwave starts and cooks(heats) but
shutsdown after about 40 seconds. Electronic control board display
stays lit, countdown stops and displays remaining time--magnetron
cooling fan works during the first 40 seconds but then shutsoff--just
before shutdown, fan speed increases(doubling or tripling in speed)
These items seemed to check out good with VOM--
power fuse
interlock switches (2)
monitor switch
capacitor
diode
thermal cutout switch(only found one)
fan motor
power tranformer

Does it do the same thing if set to defrost so that the magnetron only
runs for a few seconds/30 seconds?

Can it be restarted immediately?

How is the behavior different than if the STOP button was presssed
(maybe aside from the fan speed)?

Isn't the fan simply on the AC line so how would its speed change?
Or, is it a multispeed fan?

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Additional trouble shooting note--a power surge protector I had plugged
the microwave into was discovered fried--suspect a near by lightning
strike?

Read an informative article by Sam Goldwasser-- "NOTES ON MICROWAVE
OVEN FAILURE DIAGNOSIS AND REPAIR v1.01" but need more help. Thanks

Ref your questions Sam:
Q. Does it do the same thing if set to defrost..
A. Yes, will run longer in the cycle but eventually shutsdown
Q. Can it be restarted immediately?
A. Yes, I can hit the start button and the cycle replicates as many
times as I restart-ie runs 40 seconds and shutsdown
Q. How is the behavior different than if the STOP button was pressed
A. No difference
Q. Isn't the fan simply on the AC line so how would its speed change?
A. Looks like an AC fan--speeds up only on first cycle--otherwise runs
at top speed. Blade turns freely--no obstructions--low ohms on the
coil--can sub another fan from a different brand if appropiate--your
thoughts

Sam--appreciate your help--thanks

"electroninja" wrote in message
ups.com...
| Ref your questions Sam:
| Q. Does it do the same thing if set to defrost..
| A. Yes, will run longer in the cycle but eventually shutsdown
| Q. Can it be restarted immediately?
| A. Yes, I can hit the start button and the cycle replicates as many
| times as I restart-ie runs 40 seconds and shutsdown
| Q. How is the behavior different than if the STOP button was pressed
| A. No difference
| Q. Isn't the fan simply on the AC line so how would its speed change?
| A. Looks like an AC fan--speeds up only on first cycle--otherwise runs
| at top speed. Blade turns freely--no obstructions--low ohms on the
| coil--can sub another fan from a different brand if appropiate--your
| thoughts

Sounds a bit like an overheat situation. If the fan really is 120V and not
speed controlled then I'd be looking for burnt wiring in the AC input
system.

However, I have a Panasonic doing much the same things. Pulled it apart and
found the main MOV across the AC line was shooting flames out of the top!
Then I noticed that the main power transistor (this is a inverter machine)
has a big crack through the body. Only uWave I ever bought that failed on
me.

N

NSM wrote:
"electroninja" wrote in message
ups.com...
| Ref your questions Sam:
| Q. Does it do the same thing if set to defrost..
| A. Yes, will run longer in the cycle but eventually shutsdown
| Q. Can it be restarted immediately?
| A. Yes, I can hit the start button and the cycle replicates as many
| times as I restart-ie runs 40 seconds and shutsdown
| Q. How is the behavior different than if the STOP button was
pressed
| A. No difference
| Q. Isn't the fan simply on the AC line so how would its speed
change?
| A. Looks like an AC fan--speeds up only on first cycle--otherwise
runs
| at top speed. Blade turns freely--no obstructions--low ohms on the
| coil--can sub another fan from a different brand if
appropiate--your
| thoughts

Sounds a bit like an overheat situation. If the fan really is 120V
and not
speed controlled then I'd be looking for burnt wiring in the AC input
system.

However, I have a Panasonic doing much the same things. Pulled it
apart and
found the main MOV across the AC line was shooting flames out of the
top!
Then I noticed that the main power transistor (this is a inverter
machine)
has a big crack through the body. Only uWave I ever bought that
failed on
me.

N

-- No visual evidence of burnt wiring in the system
-- Will monitor fan motor voltage vs speed thru shutdown cycle
tomorrow--leaning toward possible fan replacement
Thankyou for your input

"electroninja" writes:

Ref your questions Sam:
Q. Does it do the same thing if set to defrost..
A. Yes, will run longer in the cycle but eventually shutsdown
Q. Can it be restarted immediately?
A. Yes, I can hit the start button and the cycle replicates as many
times as I restart-ie runs 40 seconds and shutsdown
Q. How is the behavior different than if the STOP button was pressed
A. No difference
Q. Isn't the fan simply on the AC line so how would its speed change?
A. Looks like an AC fan--speeds up only on first cycle--otherwise runs
at top speed. Blade turns freely--no obstructions--low ohms on the
coil--can sub another fan from a different brand if appropiate--your
thoughts

Not sure what you're saying here about the fan. If it runs at top (normal)
speed, it's not the problem.

The fact that you can restart immediately and get the same exact behavior
suggests that it may not be a cooling problem but also check across the
thermal protector if possible, or is there a thermistor to monitor
magnetron temp? Could be a problem in that area. Is there a schematic
with it?

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Ref your questions Sam:
Q. Not sure what your saying here about the fan?
A. Fan looks like an AC vs DC fan--one open air coil around
core--armature alum--motor has appearance of bathroom vent fan. Fan
runs on low speed only on first cycle but speeds up prior to shutdown.
Todays test shows 115 volts across motor's coil at both low and high
speed. Shaft rotates freely, but will try a drop or two of oil.

Q. Is there a thermistor to monitor magnetron temp?
Is there a schematic?
A. Limited schematic (unit door closed/cook cycle off)
One thermal switch on magnetron in series with power fuse--activation
shutsdown all power (not our case.)

- One oven thermistor shown as input to control unit circuit. No
details given (including wire color coding). Had thought this might be
convection oven temperature control.

- Control unit connected to a "relay unit" --Triac, small transformer,
relays etc. Schematic shows one relay that if activated would shutdown
magnetron and fan while leaving power to rest of unit (our case
possibly.)

--Action plan:
- Oil fan motor monitor affect
- Locate thermistor and test--assume a two wire device whose resistance
rises with temp. Uncertain what I should expect for ohm delta--comments
appreciated

"electroninja" writes:

Ref your questions Sam:
Q. Not sure what your saying here about the fan?
A. Fan looks like an AC vs DC fan--one open air coil around
core--armature alum--motor has appearance of bathroom vent fan. Fan
runs on low speed only on first cycle but speeds up prior to shutdown.
Todays test shows 115 volts across motor's coil at both low and high
speed. Shaft rotates freely, but will try a drop or two of oil.

Q. Is there a thermistor to monitor magnetron temp?
Is there a schematic?
A. Limited schematic (unit door closed/cook cycle off)
One thermal switch on magnetron in series with power fuse--activation
shutsdown all power (not our case.)

- One oven thermistor shown as input to control unit circuit. No
details given (including wire color coding). Had thought this might be
convection oven temperature control.

- Control unit connected to a "relay unit" --Triac, small transformer,
relays etc. Schematic shows one relay that if activated would shutdown
magnetron and fan while leaving power to rest of unit (our case
possibly.)

--Action plan:
- Oil fan motor monitor affect
- Locate thermistor and test--assume a two wire device whose resistance
rises with temp. Uncertain what I should expect for ohm delta--comments
appreciated

There have been cases where for whatever reason, RFI from the magnetron,
triac, who knows, gets into the controller and does strange things.
Unfortunately, hard to track down those sorts of problems.

But you said it happens on Defrost but takes longer. Defrost is 10 or 20
percent duty cycle (I'm assuming this is your basic HV transformer/cap/diode
design) so any heating would be minimal.

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Oiled motor--unit runs now for 2 additional seconds before shutdown on
first cycle--11 additional seconds on subsequent restarts

Unit is HV, cap, diode system.

Will attemp to track down thermistor--any input on how to test with VOM
when found?

Additional info--after fan motor was oiled it runs at high speed
continually now.

"electroninja" writes:

Additional info--after fan motor was oiled it runs at high speed
continually now.

So, at least that mystery is solved. From your other post, so something
may be overheating but I don't know that there would be anythinb beside
the thermal cutout, and that isn't activating.

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"electroninja" wrote in message
oups.com...
| Additional info--after fan motor was oiled it runs at high speed
| continually now.

Makes sense. A small rise in voltage when the magnetron cuts out was
affecting it. Now you have to look for what is cutting the thing out. Maybe
the uProcessor got zapped?

N

I tried shielding the control board with aluminum foil to isolate any
stray RF--no change in unit response.

A spare microwave I recently purchased for parts to fix the Sharp has
two thermal cutout switches--the R1810 doesn't according to the
schematic we discussed. Still looking for the thermistor. Contacted the
company repair reps--no response yet.

This unit fits as a built-in wall unit in our Foretravel RV--if not for
that, it would be in the trash can.

Sam what's the downside of this idea--

Substitute a dummy load for the magnetron (1500w low ohm external
load-maybe a heating coil) and run unit to see if controller shutsdown
the unit. Test could rule out overheating issue.

"electroninja" wrote in message
ups.com...
| Sam what's the downside of this idea--
|
| Substitute a dummy load for the magnetron (1500w low ohm external
| load-maybe a heating coil) and run unit to see if controller shutsdown
| the unit. Test could rule out overheating issue.

You could use a small electric heater/fan heater as a load for a test.

N

"electroninja" writes:

Sam what's the downside of this idea--

Substitute a dummy load for the magnetron (1500w low ohm external
load-maybe a heating coil) and run unit to see if controller shutsdown
the unit. Test could rule out overheating issue.

Should work. Of course, what you really mean is substitute a dummy load
for the high voltage transformer so that there is no power to any of the
high voltage components.

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Like your idea better i.e. substitute for transformer loading--nice
gentle caution

Will try a 1500W toaster--power circuit fused for 15A--a little
inductive load should balance well.

Test results with 1500W toaster--

Load worked well--toaster heated normally

Microwave unit functioned as in the past--it shutdown the transformer
load (toaster in this case vice magnetron and cooling fan) after a
period of time with the exception that the run cycle continued for an
additional 10 sec over actual magnetron and fan loading tests.
(Additional ten seconds may have resulted from no magnetron heating at
all.)

Suspect: 1. Faulty temperature sensor--perhaps opened thermistor or 2.
bad relay/control unit

Any thoughts Sam?

I often use my wife's electric iron as a high-power capabilty load.
Just be sure to use the highest possible heat to keep the iron on
continuously. It works better than a toaster becuse it will stay "on"
much longer than a toaster stays down.

H. R.(Bob) Hofmann

Sounds a bit like an overheat situation. If the fan really is 120V and not
speed controlled then I'd be looking for burnt wiring in the AC input
system.

However, I have a Panasonic doing much the same things. Pulled it apart
and
found the main MOV across the AC line was shooting flames out of the top!
Then I noticed that the main power transistor (this is a inverter machine)
has a big crack through the body. Only uWave I ever bought that failed on
me.

N



First thing I'd check is the fan motor itself, some hair or gunked up grease
in the bearings could be making it run slow which overheats the magnetron.

On 6 Jan 2005 20:04:23 -0800, "electroninja" wrote:

Sharp Model R1810 Carousel II microwave starts and cooks(heats) but
shutsdown after about 40 seconds. Electronic control board display
stays lit, countdown stops and displays remaining time--magnetron
cooling fan works during the first 40 seconds but then shutsoff--just
before shutdown, fan speed increases(doubling or tripling in speed)
These items seemed to check out good with VOM--
power fuse
interlock switches (2)
monitor switch
capacitor
diode
thermal cutout switch(only found one)
fan motor
power tranformer

Additional trouble shooting note--a power surge protector I had plugged
the microwave into was discovered fried--suspect a near by lightning
strike?

Read an informative article by Sam Goldwasser-- "NOTES ON MICROWAVE
OVEN FAILURE DIAGNOSIS AND REPAIR v1.01" but need more help. Thanks

Clear the mag first so::Go to the Mag filament wires{ be sure the HV secondary
wire is removed} then test for between 2.9vac and 3.9vac depending on model
when powered up.Replace Filament wires and re-coneect clipping test leads to mag
terminals and check again at switch on for the same a.c. voltage.A lower voltage
can be the result of the mag lowering the filament transformer voltage.Move on
from there if correct but get the MAG out of the loop first.



"Texas Hold'em Poker"

"The bigger you bet,the less you win when you lose!"

(Harry Hotspur) writes:

On 6 Jan 2005 20:04:23 -0800, "electroninja" wrote:

Sharp Model R1810 Carousel II microwave starts and cooks(heats) but
shutsdown after about 40 seconds. Electronic control board display
stays lit, countdown stops and displays remaining time--magnetron
cooling fan works during the first 40 seconds but then shutsoff--just
before shutdown, fan speed increases(doubling or tripling in speed)
These items seemed to check out good with VOM--
power fuse
interlock switches (2)
monitor switch
capacitor
diode
thermal cutout switch(only found one)
fan motor
power tranformer

Additional trouble shooting note--a power surge protector I had plugged
the microwave into was discovered fried--suspect a near by lightning
strike?

Read an informative article by Sam Goldwasser-- "NOTES ON MICROWAVE
OVEN FAILURE DIAGNOSIS AND REPAIR v1.01" but need more help. Thanks

Clear the mag first so::Go to the Mag filament wires{ be sure the HV secondary
wire is removed} then test for between 2.9vac and 3.9vac depending on model

Can't overemphasize this. There may be up to 5,000 V at very lethal current
availability present on the magnetron filament wires while operating with
the high voltage capacitor holding a dangerous charge after shutdown.

ANY testing in the microwave oven high voltage circuits is extremely dangerous.
Very knowledgeable and experienced professionals have been killed doing this.
It's too easy to be careless and you don't get a second shot.

If you insist, while unplugged, make sure the HV cap is discharged, then
hook up meter, stand clear and turn it on. Take reading without touching
meter including its test leads, power down and remove plug from wall socket,
discharge HV cap. Etc.

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when powered up.Replace Filament wires and re-coneect clipping test leads to mag
terminals and check again at switch on for the same a.c. voltage.A lower voltage
can be the result of the mag lowering the filament transformer voltage.Move on
from there if correct but get the MAG out of the loop first.

Located thermistor--results follow:
- Thermistor resistance reading was 275K ohms
- Substituted variable resistor in circuit for thermistor and ran
system operational testing for multiple values from 16K-2.2Meg ohms

--Result: Microwave ran for approximately the same length of time
before shutdown (40-60 sec) except for extreme resistance tests ie
extreme highs and lows then shutdown was 10-38 seconds.

Conclusions: Suspect control board problem--haven't located one from
suppliers yet--have have only found a control board varistor
replacement part for this unit. Assume a varistor is a variable
resistor--part photo from supplier looks like a small capacitor.

Comments appreciated regarding possible function of varistor in
circuit--are they possibly used in timing control circuits?

"electroninja" wrote in message
ups.com...
| Located thermistor--results follow:
| - Thermistor resistance reading was 275K ohms
| - Substituted variable resistor in circuit for thermistor and ran
| system operational testing for multiple values from 16K-2.2Meg ohms
|
| --Result: Microwave ran for approximately the same length of time
| before shutdown (40-60 sec) except for extreme resistance tests ie
| extreme highs and lows then shutdown was 10-38 seconds.
|
| Conclusions: Suspect control board problem--haven't located one from
| suppliers yet--have have only found a control board varistor
| replacement part for this unit. Assume a varistor is a variable
| resistor--part photo from supplier looks like a small capacitor.
|
| Comments appreciated regarding possible function of varistor in
| circuit--are they possibly used in timing control circuits?

No. They may be voltage variable (varistor) or temperature variable
(thermistor, PTC or NTC). Very unlikely that they are used for timing. Is
this a sensor model?

N

This is a Sharp R1810 convection oven and microwave--it has a sensor
probe if that is what you mean by "sensor model." Trying to figure out
what on the control unit might be causing the magnetron to shutdown
prior to end of cooking cycle.

"electroninja" wrote in message
oups.com...
| This is a Sharp R1810 convection oven and microwave--it has a sensor
| probe if that is what you mean by "sensor model." Trying to figure out
| what on the control unit might be causing the magnetron to shutdown
| prior to end of cooking cycle.
|

Common fault?

http://www.euras.com/repair_tips_1/S...1810_Sharp.htm

Try the 30 day Free Trial?

Is the probe a temperature probe that you poke in the meat? If so, maybe it
is 'sensing' end of cycle?

N

The probe is disconnected--are you saying perhaps the probe socket has
shorted. Thanks for the www.... site--will check it out.

"electroninja" wrote in message
oups.com...
| The probe is disconnected--are you saying perhaps the probe socket has
| shorted. Thanks for the www.... site--will check it out.

I'd check that circuit area for sure. That's the sort of thing that would
cause those symptoms.

N

Tested the probe socket by inserting two small pins into the wires
running to the socket. (Getting to the socket would require disassembly
of a great deal of panels) Ohm meter shows and open circuit condition
meaning the socket checks out good. Any other suggestions I might try?
Thanks

"electroninja" wrote in message
oups.com...
| Tested the probe socket by inserting two small pins into the wires
| running to the socket. (Getting to the socket would require disassembly
| of a great deal of panels) Ohm meter shows and open circuit condition
| meaning the socket checks out good. Any other suggestions I might try?

Connect an ohmmeter to the probe and then put it in hot water. What are the
ohm readings before and after?

Is the oven rated to work OK with the probe disconnected? Is there a manual
or automatic switch to detect that?

N

Have never used the probe since I've owned it and not sure where it is.
The probe socket wiring routes directly to the control board. Any
suggestions for trouble shooting the board--part suppliers don't seem
to carry control boards for the Sharp R1800.

If it's a convection oven, there is a thermistor for controlling the
temperature but only of the convection heater. On the ones I've seen, it
is screwed in above the oven chamber. This does not affect microwave
behavior.

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"electroninja" writes:

Have never used the probe since I've owned it and not sure where it is.
The probe socket wiring routes directly to the control board. Any
suggestions for trouble shooting the board--part suppliers don't seem
to carry control boards for the Sharp R1800.

Did you run the test disconnecting the HV transformer? Don't even bother
with a load at first, just see what happens.

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Lets review where I'm at--testing done with a digital VOM when required

--HV loads check out good (capacitor, diode, magetron, HV transformer)
--Fan runs at high speed during cook cycle
--Switches good (monitor, thermal cutout, interlock)
--Power fuse good
--Thermistor good
--Temperature probe socket good


Symtoms review:
--Microwave system cooks/heats for about 40 seconds then shutsdown HV
load circuitry only (fan, magnetron, timer coundown)--everything else
appears normal (lights on, control panel displays timer countdown
seconds remaining in cycle)
--Cook cycle can be restarted immediately by pushing start
button--system will cook for another 40-50 seconds and then shutdown
again
--Microwave was tested with dummy HV load (magnetron, cap, and diode
disconnected) with same results--ie system ran for 40 seconds then
shutdown HV load circuitry indicating no overheating problem due to
magnetron.

Possible cause: Conrol or relay board.

Proposed action: (1) Replace board(s)--problem-none available
(2) Repair current board(s)

Suggestions anyone?

"electroninja" wrote in message
ups.com...
| Have never used the probe since I've owned it and not sure where it is.
| The probe socket wiring routes directly to the control board. Any
| suggestions for trouble shooting the board--part suppliers don't seem
| to carry control boards for the Sharp R1800.

Like so many things now, they probably figure the cost of the board plus
labor to diagnose and install it plus the cost of any warranty afterwards
makes for a non-economic repair.

N

"electroninja" writes:

Lets review where I'm at--testing done with a digital VOM when required

--HV loads check out good (capacitor, diode, magetron, HV transformer)
--Fan runs at high speed during cook cycle
--Switches good (monitor, thermal cutout, interlock)
--Power fuse good
--Thermistor good
--Temperature probe socket good


Symtoms review:
--Microwave system cooks/heats for about 40 seconds then shutsdown HV
load circuitry only (fan, magnetron, timer coundown)--everything else
appears normal (lights on, control panel displays timer countdown
seconds remaining in cycle)
--Cook cycle can be restarted immediately by pushing start
button--system will cook for another 40-50 seconds and then shutdown
again
--Microwave was tested with dummy HV load (magnetron, cap, and diode
disconnected) with same results--ie system ran for 40 seconds then
shutdown HV load circuitry indicating no overheating problem due to
magnetron.

Possible cause: Conrol or relay board.

Proposed action: (1) Replace board(s)--problem-none available
(2) Repair current board(s)

Suggestions anyone?

I assume by no HV, you mean HV transformer disconnected. If not, do that -
just disconnect the primary entirely with no dummy load.

But it sure sounds like the controller at this point. If a relay was
dropping out, pushing START again wouldn't do anything becaseu the
controller would think it's still running.

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-- An earlier test subtituted 1500W toaster at transformer
primary--unit ran normally (toaster elements heated) but then shutdown
at the same point in the cycle as it had been doing with normal
transformer, magnetron, capacitor load.

--Disconnected transformers primary for test you suggested. Units
shutdown pattern was unchanged--ie shutdown about 40 seconds into the
cook cycle.

--The schemetic shows one relay located on the relay board that
controls power to the primary side of the transformer. I can hear it
tripping, interrupting the cook cycle--prior to it tripping though
there are one or two noises in that general area that may be other
relays activating.

--Both control and relay circuit boards appear normal from the top--no
discolored parts, no odors, loose wires etc.

Sam

Took another look at the schematic--it shows a TRIAC in parallel with
relay boards power transformer. If the TRIAC were to fail that could
possibly lower the voltage to the relays on the relay board causing
them to open.

I'm unsure whether the control board is telling the relay board to
shutdown the magnetron--or if the relay controlling the power to the
magnetron is tripping off line (for example because of TRIAC failure)
causing the control board to think a manual stop has been issued from
the front panel.

Any thoughts?

"electroninja" wrote in message
oups.com...
Sam

Took another look at the schematic--it shows a TRIAC in parallel with
relay boards power transformer. If the TRIAC were to fail that could
possibly lower the voltage to the relays on the relay board causing
them to open.

I'm unsure whether the control board is telling the relay board to
shutdown the magnetron--or if the relay controlling the power to the
magnetron is tripping off line (for example because of TRIAC failure)
causing the control board to think a manual stop has been issued from
the front panel.

Any thoughts?


Every time I've seen a triac fail, it's shorted out, causing whatever device
it controls to be stuck on.