Maker Pro
Maker Pro

Whirlpool oven up/down display not working properly

bill313

Sep 16, 2021
3
Joined
Sep 16, 2021
Messages
3
I have a 1994 Whirlpool oven who's control panel display lights went dim. Thank to this website I replaced the capacitors and the lights came back. The problem now is somewhere along the line the up and down touch controls don't work now. Instead of incrementing when the screen is pushed they run so fast that they cannot be controlled. Otherwise the oven is fine. I cannot find any schematics/information on the board (oven model number RS385PCBWO, control panel number 4389366) and there are no boards to be bought anywhere. I resoldered all the pads, looked under a microscope for cracks, checked signals with o-scope (work at an engineering /manufacturing firm so I have access to tools), I am working blind since I have no idea what the 64 pin processor is under the VFD and the other major IC is a Robertshaw custom 24 pin IC that I cannot find information on either. I do see the voltage toggle low on the buttons, as expect, looking on the processor pins. I do see a 4 MHZ clock on processor and some 60 and 77 Hz clocks on the board but other than that I don't where else to look. Anyone have any ideas.I hate to buy a new oven just for up/down counters, especially now. Thanks for the help.
 

Harald Kapp

Moderator
Moderator
Nov 17, 2011
13,769
Joined
Nov 17, 2011
Messages
13,769
I do see the voltage toggle low on the buttons, as expect,
Is this a clear high(low signal or does the signal maybe show excessive bouncing when the buttons are pressed? In the latter case a small capacitor from the buttons' signal lines to gnd may help. Try 1 nF or 10 nF.

Another possibility may be that still some electrolytic capacitors in the power supply are bad. The supply voltage may be stable enough to power the processor, display etc, as long as the current drained is steady. As soon as there is a dynamic current, e.g. from the change in the display while counting up/down, the supply voltage may show dips low enough to interfere with the operation of the controller. An oscilloscope can easily show you if this is the case. Re-check the capacitors and replace ones you may have overlooked. For quickly testing it may suffice to temporarily solder a new capacitor across the pins of an old one.
 

73's de Edd

Aug 21, 2015
3,636
Joined
Aug 21, 2015
Messages
3,636
Thir bill313 . . . . .( pardon my lispth)

Looks like that unit might REALLY be from another pool of manufacturers product ( GE / Robertshaw/ FSP) that is then being "rebadged" with a Whirlpool brand marking.
Plus I believe that the actual number of the whole board assembly is actually being a . . . . . # 4389570 . . . . . with the part number that you gave, as being for the symbolized front switch overlay . . . . . peel off panel.
I find no pics of the PCB of the . . .570 unit, except this one which sports the Robertshaw marking, but it is having no visible chips agreeing with what you mentioned . Its only visible chip is being the ULN2003 . . . . which is an interfacing driver chip, 2 sections feeding the Q4 - Q1 relay driver transistors for the two large BAKE and BROIL power relays.

https://cdn1.bigcommerce.com/server...oard-back__62304.1576533129.1280.1280.jpg?c=2

Can you supply us some GOOD working photos of your board ? Including the control push buttons.
That display is multiplexed such that it starts a cycling thru the numbers when a push button is initially pressed down, but apparently is not getting its stop command when you let up on the push button.
With a pic and your telling us the E-caps changed, we might then speculate if any other ones are suspect . . . . unless have you changed ALL OF THEM on the unit, already.

73's de Edd . . . . .

1*5DAQEDPv_5opTqr-y6yEag.gif

.
 
Last edited:

bill313

Sep 16, 2021
3
Joined
Sep 16, 2021
Messages
3
Harald:
The logic is a simple pull up resistor to 5V with the pushbutton shorting the signal to ground. There is no external debounce logic but looking on the scope the signal stays low when the button is pushed, with no noise showing on the signal. The counter runs rapidly the whole time the button is pushed so I don't think signal integrity is the issue. The signals and power supply hold close to their levels,namely 5V ( 4.9V), 12V ( 11.8V) . I cannot think of any other signals to check going to the processor that might affect the controls to the VFD. I did replace all the (qty 8) electrolytic capacitors initially. I almost think the state machine in the processor is corrupted somehow. Thanks for the feedback.

Edd:
Pics of the fronts are attached. I can post the back side if desired. Sorry I do not have the touch panel - it is at work at the moment. I got the board number from a website that sells this hardware (partsselect.com). Revisiting that website it looks like 4389366 is the panel and the control board is 389570, as you mentioned. The '2003 is on the board - not legible in the pics due to limited photo size. There is also an EEPROM (93C46) . Those are the only two ICs I could find data sheets on. Interesting how the counter works. I was thinking it was just an edge detect increment then stop. The other issue with your comment is when the button is pressed it is not incrementing slowly, it is flying through the numbers so that the numbers are not readable, only stopping when I let off the button. Note this happens both for time setting and for temperature setting (i.e., any use of the up/down controls). I bought 2 of each cap so I could go back and replace them. Thank for your feedback also.IMG_3506_001.jpg IMG_3508_001-2.jpg
 

bill313

Sep 16, 2021
3
Joined
Sep 16, 2021
Messages
3
One more note. C11 is not show in the pics - that was an operator error. I initially tried to unsolder the cap with my cheap home solder gun and ruined the pads. The cap is on the back with jumper wires for now. Signal levels in and out of it look good- 77 Hz clock that is decoupled between the processor and the Robertshaw IC. The Robertshaw has 60 Hz clock to/from the processor also. Only other clock I see on the board is the 4MHz oscillator for the processor.
 
Top