Maytag stove just displays OFF.

[David Farber]

I was repairing a Magic Chef (aka Maytag CGS3760ADW) oven because it
took too long for the burner to come on. Before I removed the old
igniter, I checked the owner's manual for any tips or technical
information. What I did find was that if you hold the "Stop Time" button
and the "Cancel" button together for 3 seconds, the bake function will
be disabled. I gave it a try and after several attempts, I was
successful. The bake function was disabled and the displayed showed,
"OFF," for 15 seconds next to the clock when you pressed the Bake
button. I removed the old igniter and tested it. It was intermittently
showing continuity so I ordered a new one. Today I received the new
igniter and installed it. I pressed the "Bake," button but the display
just showed "OFF" next to the clock. Then I held the "Stop Time" and
"Cancel" buttons together for 3 seconds (this is what the owner's manual
says to do) thinking this would re-enable the bake function but the
"OFF" display kept showing every time you pressed bake. I figured the
CPU must have locked up so I turned off the breaker to the stove, waited
a few minutes, then turned it back on. Now, not only does the "OFF"
still display, the clock will not display. I removed the control panel
and checked for anything obvious. I did not find anything unusual about
the display board. The soldering was good and nothing looked like it had
failed. I reassembled the control panel and powered on the stove. No
change. It would seem to me even if the bake function is disabled, the
clock should still display properly as it did before I turn off the
power to the stove. Has anyone seen this type of failure before?

Thanks for your reply.

--
David Farber
Los Osos, CA

[Rheilly Phoull]

What type of interconnect (If any) is used to connect the clock?
Is that self contained or run from the cpu? Sounds like a connection
problem for the clock mebbe?

[David Farber]

Here is photo of the control board:
https://www.partsimple.com/whirlpool-5760m185-60-wp5760m185-60-range-electronic-control-board.html
If you click on the photo, you can see a very clear and enlarged picture
of it.

The display tube is soldered onto the backside of the pc board. The
ribbon cable connector on the left side of the board connects to the keypad.

I did discover that the big 1K 3W(?) resistor in the middle of the board
is reading 1.4K. Can you determine from the picture what wattage it is?
The DC voltage drop across it is about 20V but that's without any of the
external cables hooked to it. I just have input going to L1 and Neutral
on my test bench. I'm going to trace the foil on the board and see if I
can figure out where the main DC supply is. All voltages on the
secondary side of the transformer are measuring negative with respect to
the chassis ground (the screw near the x'former) so that's probably not
really ground.

Now for some really strange observations:

With the control board removed from the oven and hooked up to AC from my
bench, the display did exactly the same thing. There were no other
external connections to the board. I just wanted to see if the clock
would work. It didn't. That's when I started checking voltages. The very
first thing I checked was the voltage drop across the 1K resistor I
previously mentioned. After removing my test leads from the resistor,
about 5 seconds later, the circuit board's speaker started beeping
loudly. I quickly looked at the display and it displayed, F1. That's the
generic code for controller or keypad failure. At least it was able to
display something other than "OFF." I powered it off and back on again
only this time the time appeared and it was keeping accurate time.
However, I was not able to actually set the time. It displayed 2:13 for
whatever reason. I read the owner's manual trying to see if any of the
other buttons might work and I found that if the display is showing some
other function, for example cooking temperature, pressing "Clock" will
restore the time display. So I pressed "Bake" and the display switched
to oven temperature which read "000" which is normal because it's
waiting for your to press the arrow up button to set the oven
temperature. Instead I pressed the "Clock" button and then and only then
was I able to set the time of day. Now I figured that whatever glitch
that locked up the CPU, was now cleared. I powered it off and back on
again and the result was... back to the "OFF" display. Again I measured
the voltage across the resistor and again the alarm went off. Powered it
off and back on again and then the time appeared. To make an already too
long story shorter, I am still not able to get the control board to
display the time when it's first powered up. I want to replace that
resistor but I have a feeling that even though it's reading 40% too
high, it might not make any difference. I'm off to my shop now to
parallel that out of tolerance resistor to bring it back down to 1K and
see if that helps at all.

[Rheilly Phoull]

I'd say it's 1 or 2 watt, if it gets really hot there looks enough room
for a larger one, but while you are at the shop why not replace it and
also the electrolytic as well ?

[John Robertson]

Hmm, single-sided PCB, eh? Resolder all connectors and larger item
attached to this PCB - look for cracked solder traces. I expect that
because this is single-sided PCB that cracked traces will be found.

I fixed my KitchenAid stove recently by simply resoldering the ribbon
connector to the underside of the PCB.

Don't get to involved in troubleshooting before you do an inspection of
the solder connections please!

Good luck!

John :-#)#
Vancouver, Canada

>
> If you click on the photo, you can see a very clear and enlarged picture
> of it.

...

[Rheilly Phoull]

Yup, thats a given !!

[David Farber]

> Yup, thats a given !!

The soldering looks fine but I'll touch up the connections again.

Do you think without the igniters, oven fan, and temperature probe being
connected to the control board, that that would affect the clock?

I noticed there's an EPROM on the pc board and I'm wondering if that
might have been corrupted.

[John Robertson]

EPROMs are pretty robust, so I'd be more suspicious of the electrical
connections, then electrolytic capacitors in the power supply, and work
outwards from there.

There may be a repository of EPROM images for your appliance - try
hunting for the make, model and EPROM and see what turns up! Assuming
you can read yours that is!

John :-#)#

--
(Please post followups or tech inquiries to the USENET newsgroup)
John's Jukes Ltd.
MOVED to #7 - 3979 Marine Way, Burnaby, BC, Canada V5J 5E3
(604)872-5757 (Pinballs, Jukes, Video Games)
www.flippers.com
"Old pinballers never die, they just flip out."

[David Farber]

Hi John,

I don't have an EPROM reader/programmer and therefore I've come to the
end of the troubleshooting road with this board. I've looked over every
connection with magnifying glasses, checked the ESR of the two
electrolytic caps, and have exhausted all my tricks.

By the way, the chassis ground with respect to Vcc is -5V. Therefore,
anything that reads 0 volts is Vcc.

I'm going to order a used control board because you can only go so long
without being able to use your stove!

[Mike S]

Is there any chance the controls are locked somehow?

From page 8 of the Magic Chef 500 manual, To unlock:

Press and hold the CANCEL and Cook & Hold pads for three
seconds. (Press CANCEL pad first.)

Restoring the clock display is on the same page

To restore the Clock display:

Press and hold the CANCEL and Clock pads for three
seconds. The time of day will reappear in the display

http://www.manualsdir.com/manuals/119283/magic-chef-500.html?page=9

[Fox's Mercantile]

On 8/6/19 12:31 AM, Mike S wrote:
>
> From page 8 of the Magic Chef 500 manual

And over on page 9, is "Please learn how to use your editor."

--
"I am a river to my people."
Jeff-1.0
WA6FWi
http:foxsmercantile.com

[David Farber]

>> Hi John,
>>
>> I don't have an EPROM reader/programmer and therefore I've come to the
>> end of the troubleshooting road with this board.  I've looked over
>> every connection with magnifying glasses, checked the ESR of the two
>> electrolytic caps, and have exhausted all my tricks.
>>
>> By the way, the chassis ground with respect to Vcc is -5V. Therefore,
>> anything that reads 0 volts is Vcc.
>>
>> I'm going to order a used control board because you can only go so
>> long without being able to use your stove!
>>
>> Thanks for your reply.
>>
>> --
>> David Farber
>> Los Osos, CA
>
> Is there any chance the controls are locked somehow?
>
> From page 8 of the Magic Chef 500 manual, To unlock:
>
> Press and hold the CANCEL and Cook & Hold pads for three
> seconds. (Press CANCEL pad first.)
>
> Restoring the clock display is on the same page
>
> To restore the Clock display:
>
> Press and hold the CANCEL and Clock pads for three
> seconds. The time of day will reappear in the display
>
> http://www.manualsdir.com/manuals/119283/magic-chef-500.html?page=9
>
>

Hi Mike,

I tried pressing and holding those key combinations but it did not make
any difference. The display is still blank until you press Cancel. Then
it displays "OFF" for 15 seconds and goes blank again.

[John Robertson]

Did you check that the switches show continuity? If a matrix check that
the rows and columns show appropriate connections when switch X is
pressed - powered OFF!

Also, chances are the EPROM is OK if it will reset. Bad EPROM usually
locks up the CPU and it will be completely unresponsive.

John :-#)#

[David Farber]

The oven control schematic that came with the oven is incomplete.It
shows the relays on the control board and external connections to it but
it does not show any of the supporting circuitry such as the keypad,
semiconductors, power supply, etc. I have no idea how you would do a
matrix check of the keypad without a detailed diagram. In one of my
previous posts, I explained how the keypad was working after I was able
to trigger the alarm and then power cycle the board. But after a second
power cycling, it reverted to its "OFF," display.

[peterw...@gmail.com]

A bit late into this.

I have found that with older appliances, re-assembly can be a bit of by-guess-and-by-god, not because the tech mis-wires, but because connectors are often old, sometimes brittle and so forth.

Go back, pull it all apart, clean anything relevant, check for any marginal, loose or cracked connectors, check the traces on the boards where possible, and then re-assemble with extreme care.

Might help. Can't hurt. Remember, the alternative is land-fill.

Peter Wieck
Melrose Park, PA

[David Farber]

Hi Peter,

The circuit board and connectors are in very good condition. I found a
used control board with keypad for sale on eBay. It should be arriving
tomorrow.