Maytag stove just displays OFF.

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?

On 8/2/2019 12:43 AM, Rheilly Phoull wrote:

Here is photo of the control board:

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.

Thanks for your reply.

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David Farber 
Los Osos, CA

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 ?

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

...

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.

Thanks for your reply.

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David Farber 
Los Osos, CA

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."

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

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

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.

Thanks for your reply.

--
David Farber 
Los Osos, CA

d

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 :-#)#

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.

Thanks for your reply.

--
David Farber 
Los Osos, CA

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

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.

Thanks for your reply.

--
David Farber 
Los Osos, CA