"electroninja" writes:

-- 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.

Pointing more to the controller.

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On 08 Jan 2005 12:14:31 -0500, Sam Goldwasser wrote:

(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.

Figured after all the tests he had done he would know enough not to test without
cap.discharged as he had read your article.Anyway I did say to switch on whilst
testing fil.voltage when connected and not connected.
I agree with the danger,this is the first road I would go down coupled with
mag.filament/case continuity test.Last repair on Sharp I did close to this was
the thermal cut out but he said he'd discounted this.
Maybe worth another look ranges are 127C to 88C approx for open and reset.



"Texas Hold'em Poker"

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

Sam--the contoller board has a hardwired LC6041 chip. My spare parts
microwave has the same chip and it works. Ever tried to unsolder a 48
pin LC without damaging it thru overheating?

Harry--this unit has only one thermal cutoff switch physically mounted
on the casing surrounding the magnetron--electrically it is upstream of
all loads and were it to activate it would shutdown everything (lights,
fans, control display.. etc)--which is not the case here. Thoughts?
Thanks for all comments--

Update:

--Removed the panel unit (selector buttons, control and relay boards)

--Visual inspection shows a zener diode (panel marking Z02) that has
overheating signs (black outline around diode.) The zener is 3/16 long,
with a diameter of a round toothpick and is much larger than other
zeners on the board.

Question: Does anyone know a way to determine proper zener replacement
visually?(markings, color codes etc.) Plan to replace this diode.

Recommendations: Manufacturer no help to this point--authorized
factory rep in local area has no listing for the Sharp R1810.
Thanks!

"electroninja" wrote in message
oups.com...
| Update:
|
| --Removed the panel unit (selector buttons, control and relay boards)
|
| --Visual inspection shows a zener diode (panel marking Z02) that has
| overheating signs (black outline around diode.) The zener is 3/16 long,
| with a diameter of a round toothpick and is much larger than other
| zeners on the board.
|
| Question: Does anyone know a way to determine proper zener replacement
| visually?(markings, color codes etc.) Plan to replace this diode.

WITH GREAT CAUTION (Avoid Death) measure the voltage present on the diode
and select a lower voltage.

N

NSM:

Not exactly sure what you mean by "select a lower voltage." According
to:
www.americianmicrosemi.com/tutorials/zener.htm

the "zener diode voltage must be specified" for circuit operation. They
go on to say "...the breakdown voltage is the zener voltage for
operation and is intended to operate at that voltage..." I like your
idea to check the operational voltage at the diode connections (suspect
diode heating breakdown at 40 sec however) but can you tell me what
watt diode this might be given the size or other physical markings?

NSM
Sorry, I'm new to the web game--the www address is good but try this:
http://www.americanmicrosemi.com/tutorials/zener.htm

"electroninja" wrote in message
oups.com...
| NSM:
|
| Not exactly sure what you mean by "select a lower voltage." According
| to:
| www.americianmicrosemi.com/tutorials/zener.htm
|
| the "zener diode voltage must be specified" for circuit operation. They
| go on to say "...the breakdown voltage is the zener voltage for
| operation and is intended to operate at that voltage..." I like your
| idea to check the operational voltage at the diode connections (suspect
| diode heating breakdown at 40 sec however) but can you tell me what
| watt diode this might be given the size or other physical markings?

If you find. say, 12.3 VDC across the terminals (assuming the old diode is
open circuit) then I'd try 10 VDC. As for power I would eyeball it.

Or, you could get a selection of diodes and slowly substitute them, going
from the lowest voltage to the highest. It's a crap shoot situation. Of
course, if you can trace the diode directly to a chip that needs 5 VDC then
problem solved. But the diode may be the supply for the temp probe bridge
circuit.

N

NSM--

Help me out here--you/ve mentioned the temp probe twice now and you've
sent me in previous correspendence to
http://www.euras.com/repair_tip_/sha...1810-sharp.htm, an
overseas repair service.

I don't want to offend anyone trying to help me, but I've got to ask
you--Do you have a repair manual--and is it pointing to the temp probe
bridge?

"electroninja" wrote in message
oups.com...
| NSM--
|
| Help me out here--you/ve mentioned the temp probe twice now and you've
| sent me in previous correspendence to
| http://www.euras.com/repair_tip_/sha...1810-sharp.htm, an
| overseas repair service.
|
| I don't want to offend anyone trying to help me, but I've got to ask
| you

: Do you have a repair manual?

No. Is there one?

Apart from the aforementioned site which in fact has only this fault: "LIST
OF FAULT SYMPTOMS: Operates for 2 minutes and shuts down. Cooling fan motor
runs continuously or operates intermittently" which seems to be almost
exactly your fault, it seems there is no service support. I'm giving you the
best advice I can under the circumstances.

FWIW, it's easy to become too hung up on the 'right way' as if it was god
given. Example: If the zener diode is open, a new diode cannot make the
problem worse so try it and see. That's what the pros do - believe it or
not. Servicing isn't about some sort of magic finding of the right answer -
it's about not wasting time on things which cannot be the problem - as
Sherlock Holmes was wont to say, "When you have eliminated all which is
impossible, then whatever remains, however improbable, must be the truth".

N

NSM

I appolize for offending you but I do apprieciate your input--in
review:

--System operates for 40 seconds then shutsdown (fan included but not
monitor lights)

--Only system fault detected thus far is an over heating zener diode on
the control circuit board

Not sure what FWIW means because I'm truly new to all of this--however
I do appreciate your input and help. I will sub the zener--however I
perfer "not to wastetime on time on things which cannot be the problem"
as you suggest. I'm sure you can't be saying replacing the zener is a
waste of time? Still waiting for some best guess on watt rating for
replacement.

Can't quote Holmes but I remind you of an old Sgt Friday phrase "just
the facts mam."

"NSM" writes:

"electroninja" wrote in message
oups.com...
| Update:
|
| --Removed the panel unit (selector buttons, control and relay boards)
|
| --Visual inspection shows a zener diode (panel marking Z02) that has
| overheating signs (black outline around diode.) The zener is 3/16 long,
| with a diameter of a round toothpick and is much larger than other
| zeners on the board.
|
| Question: Does anyone know a way to determine proper zener replacement
| visually?(markings, color codes etc.) Plan to replace this diode.

WITH GREAT CAUTION (Avoid Death) measure the voltage present on the diode
and select a lower voltage.

Huh (about the safety warning)? It's probably a 5 V or 12 V diode.

Indeed, simply measure the voltage across the diode. The microwave
doesn't need to be running as long as the control board is alive.

What are the markings on it?

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"NSM" writes:

"electroninja" wrote in message
oups.com...
| NSM:
|
| Not exactly sure what you mean by "select a lower voltage." According
| to:
| www.americianmicrosemi.com/tutorials/zener.htm
|
| the "zener diode voltage must be specified" for circuit operation. They
| go on to say "...the breakdown voltage is the zener voltage for
| operation and is intended to operate at that voltage..." I like your
| idea to check the operational voltage at the diode connections (suspect
| diode heating breakdown at 40 sec however) but can you tell me what
| watt diode this might be given the size or other physical markings?

If you find. say, 12.3 VDC across the terminals (assuming the old diode is
open circuit) then I'd try 10 VDC. As for power I would eyeball it.

Why?

If I find 12.3 VDC across a zener, I expect it to be approximatley a
12 V zener.

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Repeat of Update:


--Removed the panel unit (selector buttons, control and relay boards)


--Visual inspection shows a zener diode (panel marking Z02) that has
overheating signs (black outline around diode.) The zener is 3/16 long,
with a diameter of a round toothpick and is much larger than other
zeners on the board.


Question: Does anyone know a way to determine proper zener replacement
visually?(markings, color codes etc.) Plan to replace this diode.


Recommendations: Manufacturer no help to this point--authorized
factory rep in local area has no listing for the Sharp R1810.

Thanks!

If it's fatter, I'd suggest 1 W is probably the correct power rating.

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Sam

I don't see any markings on the diode yet--perhaps when its removed
from the circuit--will advise at that point.

Thank you for your recommendations--I've reviewed the list of your
work--I must say that for a person of your stature to spend time
helping people like me hunt down microwave problems is commendable--god
bless.

"Sam Goldwasser" wrote in message
...
| "NSM" writes:

| If you find. say, 12.3 VDC across the terminals (assuming the old diode
is
| open circuit) then I'd try 10 VDC. As for power I would eyeball it.
|
| Why?
|
| If I find 12.3 VDC across a zener, I expect it to be approximatley a
| 12 V zener.

I'm assuming the zener is open (OP says burned out). I'd also look for other
clues to voltage - cap rating, chip rating etc. This would be easier to fix
if he had another working unit!

N

"electroninja" wrote in message
ups.com...
| Sam
|
| I don't see any markings on the diode yet--perhaps when its removed
| from the circuit--will advise at that point.
|
| Thank you for your recommendations--I've reviewed the list of your
| work--I must say that for a person of your stature to spend time
| helping people like me hunt down microwave problems is commendable--god
| bless.

How tall are you Sam?

N

"Sam Goldwasser" wrote in message
...
| "NSM" writes:

| WITH GREAT CAUTION (Avoid Death) measure the voltage present on the
diode
| and select a lower voltage.
|
| Huh (about the safety warning)? It's probably a 5 V or 12 V diode.

I'm not sure of the skill level of the OP. Digging into the 'guts' like this
carries more hazard of accident IME unless you know how to remove the HV
danger. Too easy to get distracted.

N

Sam

I'm ready to test the diode voltage--DC voltage setting correct?

Test results:

Tested the zener diode during operation cycle:

Voltage at inital unit plug-in to AC line was 2.24 volts DC
Voltage during run runcycle and at shutdown was 2.23 volt
Conclusion: Would not appear diode was fault solution

Comments?

Test results:

Tested the zener diode during operation cycle:

Voltage at inital unit plug-in to AC line was 2.24 volts DC
Voltage during run runcycle and at shutdown was 2.23 volt
Conclusion: Would not appear diode was fault solution

Comments?

"electroninja" wrote in message
oups.com...
| Sam
|
| I'm ready to test the diode voltage--DC voltage setting correct?

Yes.

N

"electroninja" wrote in message
oups.com...
| Test results:
|
| Tested the zener diode during operation cycle:
|
| Voltage at inital unit plug-in to AC line was 2.24 volts DC
| Voltage during run runcycle and at shutdown was 2.23 volt
| Conclusion: Would not appear diode was fault solution

That's VERY low for a zener. Not impossible, but I wonder if it is a zener?
Also, you can't deduce from your test that the zener is good or bad. At this
point I would try to test it out of circuit.

N

NSM--Ich versuche Ihre Antwort.

"NSM" writes:

"Sam Goldwasser" wrote in message
...
| "NSM" writes:

| If you find. say, 12.3 VDC across the terminals (assuming the old diode
is
| open circuit) then I'd try 10 VDC. As for power I would eyeball it.
|
| Why?
|
| If I find 12.3 VDC across a zener, I expect it to be approximatley a
| 12 V zener.

I'm assuming the zener is open (OP says burned out). I'd also look for other
clues to voltage - cap rating, chip rating etc. This would be easier to fix
if he had another working unit!

I usually expect a zener to fail shorted.

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"NSM" writes:

"electroninja" wrote in message
ups.com...
| Sam
|
| I don't see any markings on the diode yet--perhaps when its removed
| from the circuit--will advise at that point.
|
| Thank you for your recommendations--I've reviewed the list of your
| work--I must say that for a person of your stature to spend time
| helping people like me hunt down microwave problems is commendable--god
| bless.

How tall are you Sam?

It varies.

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"NSM" writes:

"electroninja" wrote in message
oups.com...
| Test results:
|
| Tested the zener diode during operation cycle:
|
| Voltage at inital unit plug-in to AC line was 2.24 volts DC
| Voltage during run runcycle and at shutdown was 2.23 volt
| Conclusion: Would not appear diode was fault solution

That's VERY low for a zener. Not impossible, but I wonder if it is a zener?
Also, you can't deduce from your test that the zener is good or bad. At this
point I would try to test it out of circuit.

Any hint of what it connects to?

There are 2.3 V zeners but that would be unusual.

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I'm assuming the zener is open (OP says burned out). I'd also look for
other
clues to voltage - cap rating, chip rating etc. This would be easier to
fix
if he had another working unit!

I usually expect a zener to fail shorted.


Me too, though I have seen them go open before, as well as change value or
become leaky.

Gents: My computer wiz is standing by me and tells me that because of
the way your messages are input to the system that many are imbeded not
sequential as I had thought. I had missed the discussion about zener
not zener, and OP says short, etc. I will try to keep up.

I don't know if the zener is shorted or not--only that 2.3 volts was
the reading across it--and it is a diode--and the circuit board lists
it as Z02 vs Dxx as for other diodes on that same board. During my
research on zeners today, the lowest voltage value I found was 3.3
volts. So at what value do you recommed I start? Seems odd to me that a
control board would use 3.3 volts to drive a relay circuit. Thoughts
please?

Do zener diodes have any markings on there cases to give any indication
of their voltage rating or wattage?

"electroninja" wrote in message
oups.com...
| Gents: My computer wiz is standing by me and tells me that because of
| the way your messages are input to the system that many are imbeded not
| sequential as I had thought. I had missed the discussion about zener
| not zener, and OP says short, etc. I will try to keep up.
|
| I don't know if the zener is shorted or not--only that 2.3 volts was
| the reading across it--and it is a diode--and the circuit board lists
| it as Z02 vs Dxx as for other diodes on that same board.

That sure sounds like a zener. Can you measure the resistance forward and
backwards with power off?

| During my
| research on zeners today, the lowest voltage value I found was 3.3
| volts. So at what value do you recommed I start? Seems odd to me that a
| control board would use 3.3 volts to drive a relay circuit. Thoughts
| please?
|
| Do zener diodes have any markings on there cases to give any indication
| of their voltage rating or wattage?

Yes, but there's no simple standard IME. 3.3 volts is typical for power to a
computer chip, though low for a controller like this.

N

What voltage would you recommend I start at--3.3, 4.3, 5.1, 5.6 or
higher? Also, Je ne sais pas ce que signifie IME?

Thanks

"electroninja" wrote in message
oups.com...
| What voltage would you recommend I start at--3.3, 4.3, 5.1, 5.6 or
| higher? Also, Je ne sais pas ce que signifie IME?

http://40single.com/acronyms.html

....
IIRC If I recall correctly
IMCO In my considered opinion
IME In my experience
IMHO In My Humble Opinion
IMNSHO In my not so humble opinion
IMO In My Opinion
....

Sorry, at this point I can't suggest a voltage. It's really a matter of
experience and looking at what clues there are.

N

Thanks, I'll remove the diode and give the circuit a quick voltage
test.
Any chance I could damage the LC4061 by pulling the diode and putting a
VOM in the circuit? Ever heard of Queens University in Kingston, ahe?

"electroninja" wrote in message
ups.com...
| Thanks, I'll remove the diode and give the circuit a quick voltage
| test.
| Any chance I could damage the LC4061 by pulling the diode and putting a
| VOM in the circuit?

I would not do that.

| Ever heard of Queens University in Kingston, ahe?

Kingston ON?

N

"electroninja" writes:

Thanks, I'll remove the diode and give the circuit a quick voltage
test.

Any chance I could damage the LC4061 by pulling the diode and putting a
VOM in the circuit? Ever heard of Queens University in Kingston, ahe?

DON'T do that. It could end up with much much greater voltage on the
circuit and blow something out.

What does the top of the zener connect to?

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Sam, your question was:

Q. What does the top of the zener connect to?
A. One end traces to a 25V electrolytic cap--other end traces to a 4
pronged rectangular chip (S1VB ?) and eventually to the 32 pin on a
38870L25 processor.

In-circuit diode test:

1. VOM attached diode leads--ohm meter reading started low and rose to
1.6 meg ohms

2. Leads were reversed and test repeated--initial reading neg number
but rose to 1.38 meg ohms

Diode is made of clear glass, black painted line around the circum at
on end, has markings 180 or 18D on its casing--will have to remove to
get clear image of # markings--

Diodes glass body is cloudy--not shiny like others on the board
Proposed Action: Remove diode and head to electronics supply store

Update:

Zener removed and resistance check done with VOM on 2000K
setting--zener measured 1.94 meg ohms in one direction and above 2 meg
ohms in the other

Diode case marking is 20B1--can someone interpret before I talk the
Radio Shack sales rep

Thanks

"electroninja" writes:

Sam, your question was:

Q. What does the top of the zener connect to?
A. One end traces to a 25V electrolytic cap--other end traces to a 4
pronged rectangular chip (S1VB ?) and eventually to the 32 pin on a
38870L25 processor.

In-circuit diode test:

1. VOM attached diode leads--ohm meter reading started low and rose to
1.6 meg ohms

2. Leads were reversed and test repeated--initial reading neg number
but rose to 1.38 meg ohms

Inconclusive.

Diode is made of clear glass, black painted line around the circum at
on end, has markings 180 or 18D on its casing--will have to remove to
get clear image of # markings--

Might be 18 V but only a guess at this point.

Diodes glass body is cloudy--not shiny like others on the board
Proposed Action: Remove diode and head to electronics supply store

Forget Radio Shack. They will be worse than useless.

Need more details on circuit. If the end with the bar (cathode) comes
from + on a 25 V cap, that could be a clue that it might be something
like 18 V but not yet time to risk one like that.

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Sam,

Just reviewed your paper on "Basic Testing of Semiconductor Devices..."
and as a result retested diode. Analog readings were 4.7K and 2.7K
ohms--still bad I assume.

Will attempt to better trace circuit--also I've noticed Radio Shack has
really changed from the old days--where is Allied Radio when I need them