Kenmore Microwave Oven - 2 failures in 2 years

[Jamie]

Jim Yanik wrote:

Jeff Liebermann <jeffl@cruzio.com> wrote in
news:rbjmd59f73uatcpkj25m1nrqpm624jab0b@4ax.com:


On Sun, 18 Oct 2009 10:37:57 -0400, Meat Plow <meat@petitmorte.net
wrote:


I did factory repair for cheap brands like but not limited to Goldstar
and Tatung (basically Korean) back when the Amana Radar Range models
started to be taken over by those who didn't have a grand to spend on
the cheapest Amana. Also have worked on a ton of commercial Amanas
(every Burger King seemed to have at least one back then.)

Ok, you're an experienced expert, assuming you didn't just juggle
sub-assemblies and modules. However, I still think that increasing
the diode rating 25% is a good idea and doesn't have an effect on
safety, unless the diode is somehow used as a crowbar to blow the
fuse.


I note he didn't answer my question about HOW increasing the rating on the
HV diode would affect safety". Instead,he made an attack.
IOW,he doesn't know,thus not so "expert".

I don't believe the HV diode is "used as a crowbar" to blow the fuse,nor is
the diode intended to blow as a "safety" device.

You can put in a higher rated Diode/rectifier, it just cost more..

Most likely the original one is border line.

 

[Baron]

RF wrote:

whit3rd wrote:
On Oct 15, 6:13 pm, RF <R...@NoDen.con> wrote:
Hi Experts,

This model 721.63252 301 has gone belly up for the 2nd time in 2
years. Both times it blew there was a pop, then a smell of
overheated plastic and then a loud hum. I took it to Sears the first
time and they replaced the
diode. It then worked fine though it had very small usage.

Now is the second time and it is off the warranty. I opened up the
oven case and
quickly found the diode. It has the marker T3512 and H6N below it.
One end of the
diode has two silver bands around it. It doesn't look overheated.

Do a test on the diode, then; it's unlikely that it is dead, but
possible.
A 'pop' can mean any kind of spark, a smell can be left over from
the first failure, and 'loud hum' might mean you hear the
fan motor loudly when you listen (but would ignore it in normal
circumstances).

Most microwave oven failures are traced to the interlock switches
and fuses, so check those too.

All tests will be with the power disconnected, and the capacitor
discharged
(i.e. crowbar it with an insulated handle tool), of course.


My thanks to everyone for their interest and efforts and my
condolences for the strains.

To answer a question from just above, there is no doubt that the hum
that appeared just before I shut the oven off was FAR louder than the
normal operating level.

The situation now is that the replacement diode I ordered has arrived
and is now
installed. Question now is, should I start up the oven or getter a
stronger diode?
Thanks Jeff for the suggestion.

I looked through the Sears website (Thanks Jeff) and found the model
but the transformer,
magnetron and diode are missing. Even a search for the word diode
gives nothing.

BTW, has anyone seen the wierd screws that are used to keep the cover
on the oven? They are Torx but with a difference. There is a tiny but
very strong spike right in the middle of the hole in the screw where
the key fits. SO in essence, to remove the screws the right way, a
Torx key with a hole in it is the way to go.

They are security Torx screws. There are also some that have one less
notch than standard Torx screw heads.

That should keep
most users away but not engineers, mechanics and other knowledgeable
folks

--
Best Regards:
Baron.

 

[bw]

"RF" <RF@NoDen.con> wrote in message
news:7k18u4F3769uuU1@mid.individual.net...

whit3rd wrote:

BTW, has anyone seen the wierd screws that are used to keep the cover on
the oven?
They are Torx but with a difference. There is a tiny but very strong spike
right
in the middle of the hole in the screw where the key fits. SO in essence,
to remove the
screws the right way, a Torx key with a hole in it is the way to go.

Security Torx

 

[Jeff Liebermann]

On Sun, 18 Oct 2009 12:36:00 -0700, RF <RF@NoDen.con> wrote:

My thanks to everyone for their interest and efforts and my condolences for
the strains.

Some of us do fencing for recreation. At other times, we answer
questions on the internet. The skills required and entertainment
value are fairly similar.

To answer a question from just above, there is no doubt that the hum
that appeared just before I shut the oven off was FAR louder than the
normal operating level.

When the diode shorts, the transformer starts to suck LOTS of power.
The eventual result is a blown fuse or breaker, but meanwhile, the
high 60Hz current causes plenty of buzz.

The situation now is that the replacement diode I ordered has arrived
and is now
installed. Question now is, should I start up the oven or getter a
stronger diode?

Hold it. You haven't done any of the other suggestions. I'm still
worried if the waveguide to magnetron connection is correct, if the
window is properly attached, and if there's any evidence of arcing
inside the waveguide. Something caused the diode to blow twice and
you'll need to find the cause before blundering onward. Replacing the
diode is just damage control. Since it has happened twice, it could
also be a metal fabrication error. Look for the problem BEFORE you
fire it up.

I would use the diode you just installed. They're cheap enough that
you could blow it up without much worry. However, if it does blow up,
then you'll have to find the cause, or the replacement, which is only
25% "better" will probably also blow up.

They are Torx but with a difference. There is a tiny but very strong
spike right
in the middle of the hole in the screw where the key fits.

Those are 6 point Torx security screws. Bits can be found at the
local hardware store or on eBay:
<http://cgi.ebay.com/ws/eBayISAPI.dll?ViewItem&item=230385409827>
While you're at it, you should also get the 5 point variety. I had to
do that to tear apart a Seagate USB disk drive enclosure:
<http://cgi.ebay.com/ws/eBayISAPI.dll?ViewItem&item=360198377299>

That should keep
most users away but not engineers, mechanics and other knowledgeable
folks

If I'm in a rush, I grab the Dremel tool, insert an abrasive disk, and
cut a slot across the head. Then, I just use an ordinary flat blade
screwdriver to extract the screw. I recently had a situation where I
couldn't do that, so I just used a die grinder and destroyed most of
the screw head. I consider tamper proof screws an attractive
nuisance.

--
Jeff Liebermann jeffl@cruzio.com
150 Felker St #D http://www.LearnByDestroying.com
Santa Cruz CA 95060 http://802.11junk.com
Skype: JeffLiebermann AE6KS 831-336-2558

 

[Michael A. Terrell]

Jeff Liebermann wrote:

RF wrote:

They are Torx but with a difference. There is a tiny but very strong
spike right
in the middle of the hole in the screw where the key fits.

Those are 6 point Torx security screws. Bits can be found at the
local hardware store or on eBay:
http://cgi.ebay.com/ws/eBayISAPI.dll?ViewItem&item=230385409827
While you're at it, you should also get the 5 point variety. I had to
do that to tear apart a Seagate USB disk drive enclosure:
http://cgi.ebay.com/ws/eBayISAPI.dll?ViewItem&item=360198377299

That should keep
most users away but not engineers, mechanics and other knowledgeable
folks

If I'm in a rush, I grab the Dremel tool, insert an abrasive disk, and
cut a slot across the head. Then, I just use an ordinary flat blade
screwdriver to extract the screw. I recently had a situation where I
couldn't do that, so I just used a die grinder and destroyed most of
the screw head. I consider tamper proof screws an attractive
nuisance.

Harbor Freight has several different sets of security bits:
<http://search.harborfreight.com/cpisearch/web/search.do?keyword=security+bit&Submit=Go>


--
The movie 'Deliverance' isn't a documentary!

 

[Bob Larter]

Jeff Liebermann wrote:

If I'm in a rush, I grab the Dremel tool, insert an abrasive disk, and
cut a slot across the head. Then, I just use an ordinary flat blade
screwdriver to extract the screw. I recently had a situation where I
couldn't do that, so I just used a die grinder and destroyed most of
the screw head. I consider tamper proof screws an attractive
nuisance.

Agreed. But I have a (Chinese, of course) set of Torx security
screwdriver bits, so I use them. I save the Dremel + cutting disk
technique for the /seriously weird/ screws.

--
W
. | ,. w , "Some people are alive only because
\|/ \|/ it is illegal to kill them." Perna condita delenda est
---^----^---------------------------------------------------------------

 

[Jeff Liebermann]

On Mon, 19 Oct 2009 03:21:08 -0400, "Michael A. Terrell"
<mike.terrell@earthlink.net> wrote:

Harbor Freight has several different sets of security bits:
http://search.harborfreight.com/cpisearch/web/search.do?keyword=security+bit&Submit=Go

Thanks.

I have the 100 piece set, which I bought at the local hardware store
for about 3 times the price. It does NOT have 5 point Torx style
bits, but does include some other weird bits. About 2/3 of the set
are NOT security bits, but just common Torx, Allen, Phillips, straight
blade, etc bits. There are also some duplicate bits that seem to have
been added so that they total 100 bits. The quality of the supplied
bits are kinda marginal.

I also have several of the 33 piece sets, which are all security bits.
This is a good selection, but also do not include 5 point Torx style.
The quality of the bits are much better than the 100 piece set.

--
Jeff Liebermann jeffl@cruzio.com
150 Felker St #D http://www.LearnByDestroying.com
Santa Cruz CA 95060 http://802.11junk.com
Skype: JeffLiebermann AE6KS 831-336-2558

 

[Baron]

Jeff Liebermann wrote:

On Mon, 19 Oct 2009 03:21:08 -0400, "Michael A. Terrell"
mike.terrell@earthlink.net> wrote:

Harbor Freight has several different sets of security bits:
http://search.harborfreight.com/cpisearch/web/search.do?keyword=security+bit&Submit=Go

Thanks.

I have the 100 piece set, which I bought at the local hardware store
for about 3 times the price. It does NOT have 5 point Torx style
bits, but does include some other weird bits. About 2/3 of the set
are NOT security bits, but just common Torx, Allen, Phillips, straight
blade, etc bits. There are also some duplicate bits that seem to have
been added so that they total 100 bits. The quality of the supplied
bits are kinda marginal.

I also have several of the 33 piece sets, which are all security bits.
This is a good selection, but also do not include 5 point Torx style.
The quality of the bits are much better than the 100 piece set.

The five point ones are often found in automotive applications and
domestic electrical goods where there is an electrocution hazard.
Though I have seen some with a triangular recess with a centre pin.

--
Best Regards:
Baron.

 

[Jim Yanik]

"bw" <bwegher@hotmail.com> wrote in
news:hbg4b6$g6m$1@news.eternal-september.org:

"RF" <RF@NoDen.con> wrote in message
news:7k18u4F3769uuU1@mid.individual.net...
whit3rd wrote:

BTW, has anyone seen the wierd screws that are used to keep the cover
on the oven?
They are Torx but with a difference. There is a tiny but very strong
spike right
in the middle of the hole in the screw where the key fits. SO in
essence, to remove the
screws the right way, a Torx key with a hole in it is the way to go.

Security Torx

Harbor Freight sells those bits.

On my Nissan sentra,I encountered two 5-lobed security screws,at first I
thought it was the usual 6-lobed Torx.Fortunately,the screws had an
integral washer that was thick enough for my mini-channellock pliers.
the screws were on the Mass airflow sensor/housing.

--
Jim Yanik
jyanik
at
localnet
dot com

 

[Jim Yanik]

Jeff Liebermann <jeffl@cruzio.com> wrote in
news:jr9nd51qdiv9l11811p61rut5g8j8t832f@4ax.com:

While you're at it, you should also get the 5 point variety. I had to
do that to tear apart a Seagate USB disk drive enclosure:
http://cgi.ebay.com/ws/eBayISAPI.dll?ViewItem&item=360198377299

Thanks for the link,Jeff!
I could have used these a few weeks ago,on my Nissan Sentra SpecV MAF
sensor.

--
Jim Yanik
jyanik
at
localnet
dot com

 

[Meat Plow]

On Sun, 18 Oct 2009 10:41:29 -0700, Jeff Liebermann
<jeffl@cruzio.com>wrote:

On Sun, 18 Oct 2009 10:37:57 -0400, Meat Plow <meat@petitmorte.net
wrote:

I did factory repair for cheap brands like but not limited to Goldstar
and Tatung (basically Korean) back when the Amana Radar Range models
started to be taken over by those who didn't have a grand to spend on
the cheapest Amana. Also have worked on a ton of commercial Amanas
(every Burger King seemed to have at least one back then.)

Ok, you're an experienced expert, assuming you didn't just juggle
sub-assemblies and modules. However, I still think that increasing
the diode rating 25% is a good idea and doesn't have an effect on
safety, unless the diode is somehow used as a crowbar to blow the
fuse.

Well what would you rather have, a magnetron gone wild, stuff being
heated to the point of fire or a shorted diode blowing a fuse? I was
taught in seminars by factory representatives never to exceed the
ratings of parts if we had to use subs. And to always use factory
supplied parts first. Do I feel this practical every time? No. But I
tend to trust those that designed the equipment first. Does that
mean your microwave is going to blow sky high or melt down if you
replace the diode with one that has a 25% increased rating? I doubt
it. Would I suggest you exceed the factory ratings on any part? Not
where public safety including children are concerned.

On another note, stop with the cheap shot innuendoes. It's hard to
respect those even with the vast knowledge you have when they fuck
with you in a non humorous manner.

I'm not sure I know how to do that without being abusive, abrasive,
irritating, obnoxious, humiliating, etc. I've been answering usenet
questions for so long, that it's become almost an institution. It's
also fun. Of course, when customers pay for my advice, I can be
diplomatic. On rare occasions, I even use a spelling chequer.

It might be helpful if I point out that few of my assorted usenet
rants are intended to be insulting. They're intended to inspire the
intended target to think. I never offer an opinion without
substantiation, usually in detail, and with plenty of examples, URL's,
analogies, and detail. I've experimented with various styles of
answering questions and engaging in discussions. Humor, mixed with
satire, and a dash of "you're not meeting my expectations" is what
seems to work best for me. Motivation through humiliation is not very
popular or politically correct, but it works well. For example,
getting people with questions to supply enough information to answer
their question is often a difficult process. If you are on the
receiving end of one of my detailed rants, you might ask yourself why
I would spend the time on you.

Re-reading my previous rants in this thread, I don't see where I have
"fuck(ed) with you in a non-humorous manner". If I did, it was not
intentional, so please accept my apologies. However, if you're
complaining about my style or method of argumentation, as I indicated,
I'm not sure I can change that even if I wanted to do so.

However, I'll offer you a deal. I'll try to control my verbal fencing
with you, if you will ease up on the profanity (even when I screwup).
I don't have a problem with profanity, except that it creates a
generally unprofessional impression. I just hate to see someone do
that to themselves.

Agreed. Sorry about the profanity, worked on too many CB radios back
when the boom was on and truckers would drive hundreds of miles to our
shop. We liked to make them feel at home if you know what I mean.

 

[Michael A. Terrell]

Meat Plow wrote:

On Sun, 18 Oct 2009 10:41:29 -0700, Jeff Liebermann
jeffl@cruzio.com>wrote:

On Sun, 18 Oct 2009 10:37:57 -0400, Meat Plow <meat@petitmorte.net
wrote:

I did factory repair for cheap brands like but not limited to Goldstar
and Tatung (basically Korean) back when the Amana Radar Range models
started to be taken over by those who didn't have a grand to spend on
the cheapest Amana. Also have worked on a ton of commercial Amanas
(every Burger King seemed to have at least one back then.)

Ok, you're an experienced expert, assuming you didn't just juggle
sub-assemblies and modules. However, I still think that increasing
the diode rating 25% is a good idea and doesn't have an effect on
safety, unless the diode is somehow used as a crowbar to blow the
fuse.

Well what would you rather have, a magnetron gone wild, stuff being
heated to the point of fire or a shorted diode blowing a fuse? I was
taught in seminars by factory representatives never to exceed the
ratings of parts if we had to use subs. And to always use factory
supplied parts first. Do I feel this practical every time? No. But I
tend to trust those that designed the equipment first. Does that
mean your microwave is going to blow sky high or melt down if you
replace the diode with one that has a 25% increased rating? I doubt
it. Would I suggest you exceed the factory ratings on any part? Not
where public safety including children are concerned.

Do you really think that the OEM for the HV rectifer only ships units
that break down exactly at the rated voltage? It is the minimum rating,
and often the rectifier will handle the 25% you're complaining about.
The original rectifier may have been able to stand 100% more PIV than
the guarantteed voltage

The transformer will saturate if the line voltage is too high.
Anything that increases the load current will blow the line fuse.

What 'I' would rather have is a technician that actually understands
the circuit they are working on instead of one who makes mindless rants.


--
The movie 'Deliverance' isn't a documentary!

 

[Michael A. Terrell]

Jeff Liebermann wrote:

On Mon, 19 Oct 2009 03:21:08 -0400, "Michael A. Terrell"
mike.terrell@earthlink.net> wrote:

Harbor Freight has several different sets of security bits:
http://search.harborfreight.com/cpisearch/web/search.do?keyword=security+bit&Submit=Go

Thanks.

I have the 100 piece set, which I bought at the local hardware store
for about 3 times the price. It does NOT have 5 point Torx style
bits, but does include some other weird bits.

That is a nice set. It is on sale for $5.99 right now.

About 2/3 of the set are NOT security bits, but just common Torx,
Allen, Phillips, straight blade, etc bits. There are also some
duplicate bits that seem to have been added so that they total 100
bits. The quality of the supplied bits are kinda marginal.

I haven't found any low grade bits in the HF set I bought a couple
years ago. At one time Torx was considered a security bit, but they
became mainsteam and ruined that. I like that there are duplicates.
That way if you lose on on a jobsite you should have a spare.

I also have several of the 33 piece sets, which are all security bits.
This is a good selection, but also do not include 5 point Torx style.
The quality of the bits are much better than the 100 piece set.

http://www.harborfreight.com/cpi/ctaf/displayitem.taf?Itemnumber=91796
is another nice set. Especially when it's on sale for half price.

Also, HF calls Torx either tourqe or star.

Did you know that HF had an assortment of 1/2W 5% carbon film
resistors at one time? It was a nice starter kit for newbies.


--
The movie 'Deliverance' isn't a documentary!

 

[JD]

Michael A. Terrell wrote:

Jeff Liebermann wrote:
RF wrote:

They are Torx but with a difference. There is a tiny but very strong
spike right
in the middle of the hole in the screw where the key fits.
Those are 6 point Torx security screws. Bits can be found at the
local hardware store or on eBay:
http://cgi.ebay.com/ws/eBayISAPI.dll?ViewItem&item=230385409827
While you're at it, you should also get the 5 point variety. I had to
do that to tear apart a Seagate USB disk drive enclosure:
http://cgi.ebay.com/ws/eBayISAPI.dll?ViewItem&item=360198377299

That should keep
most users away but not engineers, mechanics and other knowledgeable
folks
If I'm in a rush, I grab the Dremel tool, insert an abrasive disk, and
cut a slot across the head. Then, I just use an ordinary flat blade
screwdriver to extract the screw. I recently had a situation where I
couldn't do that, so I just used a die grinder and destroyed most of
the screw head. I consider tamper proof screws an attractive
nuisance.


Harbor Freight has several different sets of security bits:
http://search.harborfreight.com/cpisearch/web/search.do?keyword=security+bit&Submit=Go

Believe it or not I went to a branch last week and they had no knowledge
of these bits!

 

[JD]

Jim Yanik wrote:

Jeff Liebermann <jeffl@cruzio.com> wrote in
news:jr9nd51qdiv9l11811p61rut5g8j8t832f@4ax.com:


While you're at it, you should also get the 5 point variety. I had to
do that to tear apart a Seagate USB disk drive enclosure:
http://cgi.ebay.com/ws/eBayISAPI.dll?ViewItem&item=360198377299

Thanks for the link,Jeff!
I could have used these a few weeks ago,on my Nissan Sentra SpecV MAF
sensor.

I was able to get the screws out by bending the center pins just enough
to allow
the hole-less Torx key to catch the 6 faces in the screw. Then I brought
them to a
strong vice and I flattened said little pins with a few whacks. Now I
can do some
real screwin'

OK guys, I have installed the diode but I was unable to ḟind a wave
guide. I have seen
pictures of guides - a small channel to direct the waves. but I have no
such channel, unless
it is the short duct between the magnetron and the oven wall. On the
inside of the wall there
is a plastic plate about 5" x 3". The oven has a curved back inside.
Presumably the waves
get scattered all around inside. The inside is in pristine shape - I
could see nothing like
small burn holes.

My situation now is whether to try to start it up or start taking
measurements. There is a
small pamphlet with some measurement guidelines.

 

[Jeff Liebermann]

On Mon, 19 Oct 2009 11:01:39 -0400, Meat Plow <meat@petitmorte.net>
wrote:

We're now digging up my septic tank, so I'm in the correct frame of
mind to discuss such issues. Both my arms ache from shoveling (I'm
otto shape). Typing hurts, so I'll be brief.

Well what would you rather have, a magnetron gone wild, stuff being
heated to the point of fire or a shorted diode blowing a fuse?

That's a rather limited selection of options. I don't think any of
those apply to a change of diode rating. What might apply is if a
diode failure is used as a crowbar to blow the breaker or fuse. It
might also be used to protect the maggot-tron by sacrificing itself
before something else blows up. I doubt either of these are true.

Please note my previous comment that "such safety is for those that
don't understand how things work". If the OP were a clueless idiot,
with no electronics experience, no test equipment, and no
understanding of the hazards involved, my advice would be to replace
everything with manufacturer approved stock components. If the OP had
some idea of what he was doing, has some electronics repair
experience, and maybe owns a DVM, I would suggest that some
substitution might be tolerated, but to check with the experts first.
If the OP were able to design a microwave oven, understands exactly
how it works, knows what a damper diode does, and is safety conscious,
then I would suggest making all manner of radical circuit
modifications. After reading how he extracted the Torx security
screws, I consider the OP in the first category and somewhat regret
suggesting a substitute part.

I was
taught in seminars by factory representatives never to exceed the
ratings of parts if we had to use subs. And to always use factory
supplied parts first.

I got the same lecture when I was fixing consumer audio/radio/tv from
the various manufacturers. However, it wasn't a safety issue. It was
to avoid litigation based upon "unsafe" substitutions. The company
will honor the warranty after repairs only if the repairs were done
with approved parts. Substitute or modify, and the warranty is lost.
It's bad enough when customers attempt to fix their own equipment, and
then return it under warranty. It would be really bad if that were
done by a factory authorized warranty station. More simply, customers
can substitutes, while factory repair stations cannot.

Do I feel this practical every time? No. But I
tend to trust those that designed the equipment first.

I've never designed a microwave oven, but I can tell you how it works
in consumer electronics and marine radio. At some point, early along
the design cycle, the design is frozen. A major modification to one
radio turned into a 12 week design cycle, but my initial design was
frozen after only 2 weeks from start. I was finding errors all along
the way, but was not allowed to make any changes for fear of
introducing delays. Near the end, production required some changes,
which was where I snuck in some changes. There were also some changes
inspired by the dealers, as inspired by customers, and delivered
through marketing. On occasion, there have been cost cutting
exercises, which is another opportunity to fix things. Something like
"We can cut $0.0001 off the cost if we switch to a diode rating that
closer to the failure point. The savings, over millions of units,
will offset any increase in dealing with failures".

Today, things are done quite differently. There's usually no
breadboarding and the design cycle is MUCH shorter. The design is
simulated on a computah, there's no breadboard, and it goes directly
into production. If there are any problems, the standard answer is
that the replacement model is already in the pipe and to wait for the
replacement, and not fix the defect.

About the only thing that prevents total disaster is that most new
products are evolutionary, not revolutionary. Changes tend to be
small and earlier mistakes tend to eventually get fixed. However, my
adage of "features and functions get added faster than bugs get fixed"
also applies, thus keeping quality just above adequate.

So, you may trust the designer, but I wouldn't exactly trust the
design.

Does that
mean your microwave is going to blow sky high or melt down if you
replace the diode with one that has a 25% increased rating? I doubt
it.

Could that mean you agree with me?

Would I suggest you exceed the factory ratings on any part? Not
where public safety including children are concerned.

Not public safety or children. Think certifications, litigation,
liability, and tort law. For example, it's not UL or FCC certified if
ANY component changes were made (without applying for minor change
recertification).

Agreed. Sorry about the profanity, worked on too many CB radios back
when the boom was on and truckers would drive hundreds of miles to our
shop. We liked to make them feel at home if you know what I mean.

I got my start in RF doing CB radios. I designed two CB radios, a CB
pager, a mess of accessories, and worked for radio shops that did
mostly commercial, but also some CB. Yeah, profanity is part of the
culture. I managed to pickup a few choice words and phrases in high
skool that have been difficult to eradicate. At least I've purged
them from my writing. If I want to be abusive, there are other and
better ways.

--
Jeff Liebermann jeffl@cruzio.com
150 Felker St #D http://www.LearnByDestroying.com
Santa Cruz CA 95060 http://802.11junk.com
Skype: JeffLiebermann AE6KS 831-336-2558

 

[Michael A. Terrell]

JD wrote:

Michael A. Terrell wrote:
Jeff Liebermann wrote:
RF wrote:

They are Torx but with a difference. There is a tiny but very strong
spike right
in the middle of the hole in the screw where the key fits.
Those are 6 point Torx security screws. Bits can be found at the
local hardware store or on eBay:
http://cgi.ebay.com/ws/eBayISAPI.dll?ViewItem&item=230385409827
While you're at it, you should also get the 5 point variety. I had to
do that to tear apart a Seagate USB disk drive enclosure:
http://cgi.ebay.com/ws/eBayISAPI.dll?ViewItem&item=360198377299

That should keep
most users away but not engineers, mechanics and other knowledgeable
folks
If I'm in a rush, I grab the Dremel tool, insert an abrasive disk, and
cut a slot across the head. Then, I just use an ordinary flat blade
screwdriver to extract the screw. I recently had a situation where I
couldn't do that, so I just used a die grinder and destroyed most of
the screw head. I consider tamper proof screws an attractive
nuisance.


Harbor Freight has several different sets of security bits:
http://search.harborfreight.com/cpisearch/web/search.do?keyword=security+bit&Submit=Go

Believe it or not I went to a branch last week and they had no knowledge
of these bits!

Read the disclaimer on their website: Not available at all
locations. If they don't sell well at a particular store, they are
discontinued at that location.


--
The movie 'Deliverance' isn't a documentary!

 

[Michael A. Terrell]

JD wrote:

Jim Yanik wrote:
Jeff Liebermann <jeffl@cruzio.com> wrote in
news:jr9nd51qdiv9l11811p61rut5g8j8t832f@4ax.com:


While you're at it, you should also get the 5 point variety. I had to
do that to tear apart a Seagate USB disk drive enclosure:
http://cgi.ebay.com/ws/eBayISAPI.dll?ViewItem&item=360198377299

Thanks for the link,Jeff!
I could have used these a few weeks ago,on my Nissan Sentra SpecV MAF
sensor.

I was able to get the screws out by bending the center pins just enough
to allow the hole-less Torx key to catch the 6 faces in the screw. Then
I brought them to a strong vice and I flattened said little pins with a
few whacks. Now I can do some real screwin'

OK guys, I have installed the diode but I was unable to find a wave
guide. I have seen pictures of guides - a small channel to direct the
waves. but I have no such channel, unless it is the short duct between
the magnetron and the oven wall.

That is the waveguide, AKA a duct to carry the RF into the oven
cavity.

On the inside of the wall there is a plastic plate about 5" x 3". The
oven has a curved back inside.

Take a look under the plastic plate for bugs or grease.

Presumably the waves get scattered all around inside. The inside is in
pristine shape - I could see nothing like small burn holes.

My situation now is whether to try to start it up or start taking
measurements. There is a small pamphlet with some measurement
guidelines.

--
The movie 'Deliverance' isn't a documentary!

 

[Meat Plow]

On Tue, 20 Oct 2009 10:54:32 -0700, Jeff Liebermann
<jeffl@cruzio.com>wrote:

On Mon, 19 Oct 2009 11:01:39 -0400, Meat Plow <meat@petitmorte.net
wrote:

We're now digging up my septic tank, so I'm in the correct frame of
mind to discuss such issues. Both my arms ache from shoveling (I'm
otto shape). Typing hurts, so I'll be brief.

Well what would you rather have, a magnetron gone wild, stuff being
heated to the point of fire or a shorted diode blowing a fuse?

That's a rather limited selection of options. I don't think any of
those apply to a change of diode rating. What might apply is if a
diode failure is used as a crowbar to blow the breaker or fuse. It
might also be used to protect the maggot-tron by sacrificing itself
before something else blows up. I doubt either of these are true.

Please note my previous comment that "such safety is for those that
don't understand how things work". If the OP were a clueless idiot,
with no electronics experience, no test equipment, and no
understanding of the hazards involved, my advice would be to replace
everything with manufacturer approved stock components. If the OP had
some idea of what he was doing, has some electronics repair
experience, and maybe owns a DVM, I would suggest that some
substitution might be tolerated, but to check with the experts first.
If the OP were able to design a microwave oven, understands exactly
how it works, knows what a damper diode does, and is safety conscious,
then I would suggest making all manner of radical circuit
modifications. After reading how he extracted the Torx security
screws, I consider the OP in the first category and somewhat regret
suggesting a substitute part.

I was
taught in seminars by factory representatives never to exceed the
ratings of parts if we had to use subs. And to always use factory
supplied parts first.

I got the same lecture when I was fixing consumer audio/radio/tv from
the various manufacturers. However, it wasn't a safety issue. It was
to avoid litigation based upon "unsafe" substitutions. The company
will honor the warranty after repairs only if the repairs were done
with approved parts. Substitute or modify, and the warranty is lost.
It's bad enough when customers attempt to fix their own equipment, and
then return it under warranty. It would be really bad if that were
done by a factory authorized warranty station. More simply, customers
can substitutes, while factory repair stations cannot.

Do I feel this practical every time? No. But I
tend to trust those that designed the equipment first.

I've never designed a microwave oven, but I can tell you how it works
in consumer electronics and marine radio. At some point, early along
the design cycle, the design is frozen. A major modification to one
radio turned into a 12 week design cycle, but my initial design was
frozen after only 2 weeks from start. I was finding errors all along
the way, but was not allowed to make any changes for fear of
introducing delays. Near the end, production required some changes,
which was where I snuck in some changes. There were also some changes
inspired by the dealers, as inspired by customers, and delivered
through marketing. On occasion, there have been cost cutting
exercises, which is another opportunity to fix things. Something like
"We can cut $0.0001 off the cost if we switch to a diode rating that
closer to the failure point. The savings, over millions of units,
will offset any increase in dealing with failures".

Today, things are done quite differently. There's usually no
breadboarding and the design cycle is MUCH shorter. The design is
simulated on a computah, there's no breadboard, and it goes directly
into production. If there are any problems, the standard answer is
that the replacement model is already in the pipe and to wait for the
replacement, and not fix the defect.

About the only thing that prevents total disaster is that most new
products are evolutionary, not revolutionary. Changes tend to be
small and earlier mistakes tend to eventually get fixed. However, my
adage of "features and functions get added faster than bugs get fixed"
also applies, thus keeping quality just above adequate.

So, you may trust the designer, but I wouldn't exactly trust the
design.

Does that
mean your microwave is going to blow sky high or melt down if you
replace the diode with one that has a 25% increased rating? I doubt
it.

Could that mean you agree with me?

Would I suggest you exceed the factory ratings on any part? Not
where public safety including children are concerned.

Not public safety or children. Think certifications, litigation,
liability, and tort law. For example, it's not UL or FCC certified if
ANY component changes were made (without applying for minor change
recertification).

Agreed. Sorry about the profanity, worked on too many CB radios back
when the boom was on and truckers would drive hundreds of miles to our
shop. We liked to make them feel at home if you know what I mean.

I got my start in RF doing CB radios. I designed two CB radios, a CB
pager, a mess of accessories, and worked for radio shops that did
mostly commercial, but also some CB. Yeah, profanity is part of the
culture. I managed to pickup a few choice words and phrases in high
skool that have been difficult to eradicate. At least I've purged
them from my writing. If I want to be abusive, there are other and
better ways.

Some times the best way to blow off some steam is with words.

I worked for a commercial radio shop back in the 80s and designed a
paging system for Timken Roller Bearing's two lines of equipment and
the journeymen responsible for their continuous operation. I've helped
design one of the best amateur radio repeaters in the Cleveland/Akron
area now being used for the backbone of NOAA - W8CLE and SKYWARN.

 

[Jeff Liebermann]

On Wed, 21 Oct 2009 09:04:11 -0400, Meat Plow <meat@petitmorte.net>
wrote:

Some times the best way to blow off some steam is with words.

Yep. I've learned more about effuent terminology and profanity while
working on the septic system than all the CB lingo in my chequered
past.

I've helped
design one of the best amateur radio repeaters in the Cleveland/Akron
area now being used for the backbone of NOAA - W8CLE and SKYWARN.

Well, working backwards, I either built or helped build:
W6JWS-2m Bonny Doon. (no photos)
K6BJ Santa Cruz. <http://www.LearnByDestroying.com/k6bj/>
KI6EH Watsonville. (no photos)
A bunch of junk in Smog Angeles I would like to forget.
WB6EEP West L.A.
<http://802.11junk.com/jeffl/pics/Old%20Repeaters/slides/wb6eep-01.html>
and a bunch of commercial stuff.
<http://802.11junk.com/jeffl/pics/Old%20Repeaters/index.html>
My favorite was a repeater built into a hollowed out 4x4 fence post
and installed in a prominent location. Sorry, but no photos.

The problem with ham repeaters is that they seem to run forever,
usually with zero maintenance. When something finally breaks, I get
to fix it. When someone builds it wrong, I get to fix it. When
something blows, I get to repair it.

Design is usually done on the back of an envelope. Documentation? We
don't do no stinkin documentation:
<http://members.cruzio.com/~jeffl/k6bj/K6BJ%20Repeater/slides/Documentation.html>

One of the few smart things I've done is to NOT build my own repeater.

--
Jeff Liebermann jeffl@cruzio.com
150 Felker St #D http://www.LearnByDestroying.com
Santa Cruz CA 95060 http://802.11junk.com
Skype: JeffLiebermann AE6KS 831-336-2558