Kenmore microwave acting intermittently

[Beanie]

Okay, so I've tried everything possible to get a microwave that was
picked up off the street to work. It's a Kenmore 565.8925590, 1300W,
serial 1V7C01490, manufactured September 1991. The magnetron and
controller IC are made by Sanyo, so I imagine that the entire oven
was, too. So, here's the symptoms the microwave exhibits:
The microwave will happily begin to microwave a cup of water. After
about a minute or so, the fan and the turntable will stop. The light
stays on, and the counter keeps going. If I stop the microwave cycle
and let the oven cool down, I can start it up again, for about another
minute. So, I opened it up, and checked the usual suspects (fuse,
interlock switches, etc.) The primary interlock switch was always
open, so I replaced it. That didn't fix anything. All of the
switches appear to be making good contact with the actuators on the
door. There are two thermal protectors. Both offer a resistance of
zero, and according to the schematic (and the actual wire routing) if
either opened, it would kill power to the entire oven--so I know that
they are not at fault here. The magnetron does become hot to the
touch, but it's not _that_ (135 degrees centigrade) hot.
As far as I can tell, the only thing left to be at fault is the
relays, that are located on the controller board. I'm a little leery
of testing the relays on it with the oven live--especially because the
warning labels clearly state that the step-down transformer will give
me a jolt. There is a burn mark on the PCB in the center, but the
resistors, diodes, and caps in that area all test fine.

Any suggestions?

Thanks!

--Chris

 

[Sam Goldwasser]

You didn't say whether the oven keeps heating after the fan and turntable
stop?

How do the fan and turntable get their power? Could be a bad connection.

--- sam | Sci.Electronics.Repair FAQ Home Page: 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 Site Info: http://www.repairfaq.org/REPAIR/F_mirror.html

Important: The email address in this message header may no longer work. To
contact me, please use the Feedback Form at repairfaq.org. Thanks.


beanie_bari@yahoo.com (Beanie) writes:

Okay, so I've tried everything possible to get a microwave that was
picked up off the street to work. It's a Kenmore 565.8925590, 1300W,
serial 1V7C01490, manufactured September 1991. The magnetron and
controller IC are made by Sanyo, so I imagine that the entire oven
was, too. So, here's the symptoms the microwave exhibits:
The microwave will happily begin to microwave a cup of water. After
about a minute or so, the fan and the turntable will stop. The light
stays on, and the counter keeps going. If I stop the microwave cycle
and let the oven cool down, I can start it up again, for about another
minute. So, I opened it up, and checked the usual suspects (fuse,
interlock switches, etc.) The primary interlock switch was always
open, so I replaced it. That didn't fix anything. All of the
switches appear to be making good contact with the actuators on the
door. There are two thermal protectors. Both offer a resistance of
zero, and according to the schematic (and the actual wire routing) if
either opened, it would kill power to the entire oven--so I know that
they are not at fault here. The magnetron does become hot to the
touch, but it's not _that_ (135 degrees centigrade) hot.
As far as I can tell, the only thing left to be at fault is the
relays, that are located on the controller board. I'm a little leery
of testing the relays on it with the oven live--especially because the
warning labels clearly state that the step-down transformer will give
me a jolt. There is a burn mark on the PCB in the center, but the
resistors, diodes, and caps in that area all test fine.

Any suggestions?

Thanks!

--Chris

 

[Sam Goldwasser]

It's just a generic 12 V coil SPST? relay. So, just find a substitute that
doesn't have a 100 minimum buy and wire it in. I'm sure any number of us
could provide one from our junk boxes.

However, as I think you mention, test it first! Still may not be the
problem.

--- sam | Sci.Electronics.Repair FAQ Home Page: 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 Site Info: http://www.repairfaq.org/REPAIR/F_mirror.html

Important: The email address in this message header may no longer work. To
contact me, please use the Feedback Form at repairfaq.org. Thanks.



beanie_bari@yahoo.com (Beanie) writes:

Well, I've checked over the schematic, and I think I've narrowed it
down to one part. Relay 2, an Omron G5J-1-TP-M-12 12V coil PCB relay
("ideal for Microwave Oven Magnetrons", according to the
datasheet--see http://www.omroncomponents.co.uk/pdfs/relays/PCB%20POWER/G5J.pdf)
is more than likely at fault. Current for the blower and gear flow
from the wall, through Relay 2, through the interlock monitor switch,
and into the motors. Also, current flows from Relay 2 and the
interlock monitor switch to the HV transformer, explaining why the
oven doesn't heat food when the motors stop. This definately narrows
it down to either Relay 2 or the HV transformer; and because the
blower motor and the gear motor probably run on 120VAC (though I
haven't found a label that says otherwise), it has to be Relay 2. I
didn't bring a 12VDC power source or a heat gun with me to work today,
so I wasn't able to confirm that it's the problem. (I'll have those
handy when I come in to mess with it again on Friday.) When the oven
dies, I can still hear the "click" of a relay when I hit the Start
button, but there are two relays in the microwave, and it's probably
Relay 1 that's working.
The main problem I'm having now is locating this part. Sears repair
center doesn't have it (due to "unavailability", according to the web
site); and the only electronics company I've found that will sell it
to me is Digi-Key, and they expect me to buy 100 (at $2.82USD apeice).
Anyone have any suggestions as to where I can find this part, or an
equivalent I can hack into the oven to make it work? (It looks like
an Aromat ALE12B12 might work, see
http://dkc3.digikey.com/PDF/T032/0897.pdf.) Or does anyone want to
buy 99 relays off of me?

And at the very least, working on this oven has kept me awake during a
rainy August at a boat rental business


Sam Goldwasser <sam@saul.cis.upenn.edu> wrote in message news:<6w8yqc5kw5.fsf@saul.cis.upenn.edu>...
You didn't say whether the oven keeps heating after the fan and turntable
stop?

How do the fan and turntable get their power? Could be a bad connection.

--- sam | Sci.Electronics.Repair FAQ Home Page: 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 Site Info: http://www.repairfaq.org/REPAIR/F_mirror.html

Important: The email address in this message header may no longer work. To
contact me, please use the Feedback Form at repairfaq.org. Thanks.


beanie_bari@yahoo.com (Beanie) writes:

Okay, so I've tried everything possible to get a microwave that was
picked up off the street to work. It's a Kenmore 565.8925590, 1300W,
serial 1V7C01490, manufactured September 1991. The magnetron and
controller IC are made by Sanyo, so I imagine that the entire oven
was, too. So, here's the symptoms the microwave exhibits:
The microwave will happily begin to microwave a cup of water. After
about a minute or so, the fan and the turntable will stop. The light
stays on, and the counter keeps going. If I stop the microwave cycle
and let the oven cool down, I can start it up again, for about another
minute. So, I opened it up, and checked the usual suspects (fuse,
interlock switches, etc.) The primary interlock switch was always
open, so I replaced it. That didn't fix anything. All of the
switches appear to be making good contact with the actuators on the
door. There are two thermal protectors. Both offer a resistance of
zero, and according to the schematic (and the actual wire routing) if
either opened, it would kill power to the entire oven--so I know that
they are not at fault here. The magnetron does become hot to the
touch, but it's not _that_ (135 degrees centigrade) hot.
As far as I can tell, the only thing left to be at fault is the
relays, that are located on the controller board. I'm a little leery
of testing the relays on it with the oven live--especially because the
warning labels clearly state that the step-down transformer will give
me a jolt. There is a burn mark on the PCB in the center, but the
resistors, diodes, and caps in that area all test fine.

Any suggestions?

Thanks!

--Chris