Oven software headache

[BurningTantalum]

I have a domestic oven bought new a few years ago. It has been plagued with problems, almost exclusively caused by mains transients especially during electrical storms and on reinstatement after a power outage (very common in my area.). The agents have been NO help at all apart from sending a new PSU PCB free of charge at one point. Unfortunately it was not installed until 2 years after purchase.
I installed a switch on top to disconnect the supply from the electronics during storms. On switching it back on the other day I watched the Power On Self Test and was surprised to see the legend: 'Ver 600' in yellow on the display (3 colour led touch switches and 3 colour 7 segment temp/time display) It should show 'Ver 900' in green, indicating, I assume, that it is the 900mm high double oven model. There was a 600mm high single oven model sold.
Now pressing the controls for the top oven does nothing but give a 'DOOR' alert on the display (the bottom oven has an integral microwave with standard door switch)
The microcontroller is an Atmega16.
I have a horrible feeling that this will be one of the few electronic or mechanical faults that I will not be able to overcome.
Purely out of interest- can anyone explain how this reversion to a software version for a different model oven could occur.
Why is the 'VER 600' text in the program at all? I suspect that if I connected the panel into a 600mm oven that it would operate correctly.
Regards, BT

[Ian.M]

Its probably a single control board that fits multiple models, and is configured either at the factory, by populating/ not populating resistors or zero ohm links, or by jumpers or switches that can be set by a repairer, or by sensing the wiring connections, to select the model it is to control.   If the selection mechanism is damaged, by a board or wiring fault, other component failure or a blown pin on the MCU, it could easily misidentify what it is installed in.   At this point, unless the preprogrammed MCU is available as a spare part, you probably need a replacement control board, as I'm betting its disabled the second oven due to the detection fault.

[CJay]

I think I'd be looking for an EEPROM on the board in addition to the ATMega internal EEPROM

[Ian.M]

Why would the manufacturer even do that?  (I'm assuming the oven isn't an IOT device so doesn't need a MAC address.)

Adding an external EEPROM, unless its needed for storing user program settings, adds cost and complexity with no benefit and configuring the board by EEPROM (external or internal) would require an extra process, and some sort of jig to do so.  You might as well simply flash the MCU with model specific firmware.

Its possible that it does use a stored configuration that is configured by a test mode probably accessed by a jumper or some obscure button combo, but that increases the risk of mis-configured ovens being shipped to the customer.   Its a lot simpler to configure it by physical components that are inspectable or by detecting what its plugged into.   It also depends on the number of possible combinations of options - if you need more than 8 bits of configuration, hardware configuration gets unwieldy to the point where soft configuration may be the least evil option.

[CJay]

Why would the manufacturer even do that?  (I'm assuming the oven isn't an IOT device so doesn't need a MAC address.)

Adding an external EEPROM, unless its needed for storing user program settings, adds cost and complexity with no benefit and configuring the board by EEPROM (external or internal) would require an extra process, and some sort of jig to do so.  You might as well simply flash the MCU with model specific firmware.

Its possible that it does use a stored configuration that is configured by a test mode probably accessed by a jumper or some obscure button combo, but that increases the risk of mis-configured ovens being shipped to the customer.   Its a lot simpler to configure it by physical components that are inspectable or by detecting what its plugged into.   It also depends on the number of possible combinations of options - if you need more than 8 bits of configuration, hardware configuration gets unwieldy to the point where soft configuration may be the least evil option.

I can't explain the logic behind it and I agree, it makes little sense but I have seen boards with EEPROM chips and CPUs with plenty of EEPROM space in washing machines and central heating boilers (and those are just the few I've had my hands on).

I can think of a few reasons for it, especially if the chip is socketed but who knows what the designer was thinking or required to implement?

Given that it's changed overnight it would seem as reasonable to suspect that there could be an EEPROM chip somewhere that could have been corrupted as a hardware link or something has given up the ghost. As it only takes a few seconds to look for chips which could be EEPROMs, it'd be better to have a look than buy a new board and kick yourself later?

[Ian.M]

Sure its possible, and it may even make sense from a production viewpoint, even if not socketed,  as inventory costs of keeping reels of different preprogrammed EEPROMs may well be lower than either different preprogrammed MCUs or tracking what firmware has been flashed to a specific board by the ATE jig.

However EEPROMs are most usually connected direct to the MCU, and if so the only reasonably likely ways they can get corrupted without damage is a power glitch or software failure while writing to them, and the odds are that you'd need a dump from one on a known good board to fix it.   There is a possibility that fitting a blank replacement *might* cause default settings to be loaded into it, or that its absence is used to identify a lower cost model, so if one is found, replacing it should be an absolute 'hail Mary' last resort before scrapping the board.

[CJay]

Sure its possible, and it may even make sense from a production viewpoint, even if not socketed,  as inventory costs of keeping reels of different preprogrammed EEPROMs may well be lower than either different preprogrammed MCUs or tracking what firmware has been flashed to a specific board by the ATE jig.

However EEPROMs are most usually connected direct to the MCU, and if so the only reasonably likely ways they can get corrupted without damage is a power glitch or software failure while writing to them, and the odds are that you'd need a dump from one on a known good board to fix it.   There is a possibility that fitting a blank replacement *might* cause default settings to be loaded into it, or that its absence is used to identify a lower cost model, so if one is found, replacing it should be an absolute 'hail Mary' last resort before scrapping the board.

It's sometimes possible to reverse them and 'fix' problems, I've done that a few times, in car stereos and on an electronic dashboard, often it can be just a few bits or bytes that've been corrupted and I have to admit to being lucky as I found there were duplicate/multiple copies of the data in the same chip on both.

I also managed to work out the coding in a corrupted calibration token to repair and 'recharge' it, an interesting couple of days and rather fun to do, especially when I got a 'hit' and unlocked calibration mode.

All blue sky thinking though for the OP's situation and just a suggestion to look for such a chip, it may be fruitless.

[BurningTantalum]

Thanks for the info- I can mull over it today. There is no EEPROM on the PCB.
At the risk of turning this into a saga: I worried about a failure on this PCB so last year I scored an entire oven (65kg) on eBay in the UK for £1. It was listed as working but with a broken door hinge. I am in Australia! The seller stored it until I visited the UK when I lied to my 92 year old father about 'going to the shops' and borrowed his Mr Magoo car to drive 100 miles to fetch the oven. It was pouring with rain and I had to scour the area for some packing to stop the oven resting on the rear window. There was an incident after I found a suspected dead body wrapped in bed linen at the side of the road. A horrible day where we thought that we would end up in the nick "You said that you came to Manchester from Nottingham, but now you are telling us that you came from Australia...", but Mrs BT and I have started to laugh about it !
I dismantled the oven at a friend's and brought all parts that I could carry back to Oz.
A few months ago I fired up the display PCB on the bench where it failed the POST despite having all temp sensors and switches simulated. NOTABLY it displayed 'Ver 600' in yellow.
I hardly dare install it to test in the oven...
BT

[BurningTantalum]

The first post should have stated that the oven itself was not installed for 2 years thus the warranty had expired- a lesson for all.
BT

[Ian.M]

There are no signs of any PSU or high power control circuits on that board.  I presume there is a power control board, and if it handshakes with it or the model ID mechanism is on the power control board then you wont be able to run the display board standalone.

Did you salvage the FULL wiring harness?

The minimum to bench test would be all boards, controls, sensors, and fan motors with incandescent lamps in place of the heating elements.

[BurningTantalum]

Thanks Ian- the story was truly too long for this thread but I have the PSU and switching PCB supplied by the Oz agents, plus the one from the eBay oven in the UK, plus the thermal sensors and wiring looms (and heating elements ++). I will investigate further when I have time and we don't mind the 65kg behemoth standing on a table in the kitchen. Western Australian wiring regs don't require any form of switch or isolator between an 8.4kW device and the fuse board (in fact such a switch doesn't seem to be available here anyway...) so the whole job is a pain (and illegal for Mr BT to perform).
It seems that the control and display PCB is common to both the 900 (mm high) 2 oven unit and the 600 single oven unit, and I can see that it would be logical for the software for both to be installed in the MCU, with a hardware or software 'bit' set or not to select.
As I said- I don't think this will be fixable. Result is no more cheese on toast 
Regards,  BT