80C32 oven control board problem - Page 1
Forum section: electronics / general

author: fernando68
author_rank: Newbie
timestamp: October 13, 2024, 02:13:27 pm
content: Hello,I am having problems with a control board for a bakery oven. I will really appreciate any help.The board went bad during a relocation of the oven. I noticed the display wasn't showing the actual and target temperatures (shows zero) and the timer was showing zero as well. The oven was not turning on. I opened the area were the control board is located and found that a small piece of wire had landed on the RAM memory. I removed the wire and tried again and the problem persists.I am not very familiar with microcontrollers (I do have experience with electronics in general). Since I can't find anybody locally to work on the board I am trying to troubleshoot it myself. This is what I have so far.The board has 80C32 controller a 27C512 EPROM and a 62256 RAM, there is a HC573 and a HC574 and a RTC-72423 clock.I am including a very incomplete diagram that I put together from continuity checks. the board is very compact and almost imposible to follow the traces. I hope the diagram is enough for some knowledgeable person to point me in the right direction, but I can try to complete it if needed.The thing I notice is that the program seems to be running. I can access some menus, for example for programing steam set points, temperature corrections, I can run self-test that will test the outputs relays, I can test operations of the LEDs, etc.However when I try to save any changes (lets say I want to save a +10C temperature correction) the board does not take it.It seems to me that it is working OK from information that is saved in the EPROM but does not read/save information in the RAM (do you guys agree in that assessment?).When I got the oven I made a copy of the EPROM. I plugged in the back-up EPROM and the problem persists. I replaced the RAM, the 80C32, the HC574, HC573 and the RTC-72423 clock. No difference.One more thing: when everything was working, pressing two keys in the control board allow me to the the firmware version (6.4) now after pressing the keys I don't see (0).Any ideas or suggestions?Thank you very much for any helpFernando

author: ozcar
author_rank: Frequent Contributor
timestamp: October 13, 2024, 02:58:33 pm
content: Quote from: fernando68 on October 13, 2024, 02:13:27 pmYou mean saved to the 93LC86 EEPROM? You don't mention checking that out?

author: fernando68
author_rank: Newbie
timestamp: October 13, 2024, 03:47:58 pm
content: Hi Ozcar,My understanding the 93LC86 is a ROM that contains information for the initial boot of the program.Since I can see parts of the program running I concluded the 93LC86 must be OK (I could be totally wrong in this).I have an oscilloscope and I see "activity" on the pins of the 93LC86.Unfortunately I did not backed up the information in the 93LC86 as I did with the EPROM.To me seems like the data that is constantly acquired (like chamber and steam temperature , humidity, etc) or data that I try to input through the panel (target temperature, timer, etc) is not being stored. Isn't that data stored in the RAM?I tried 3 different RAMs in case it was a speed issue but this did not solve the issue

author: ozcar
author_rank: Frequent Contributor
timestamp: October 13, 2024, 04:15:41 pm
content: If the settings like target temperature were retained in the event of power loss, then most likely they would be kept in the 93LC86.Do you have some inside info to suggest that there is code in there as well?

author: fernando68
author_rank: Newbie
timestamp: October 13, 2024, 05:49:41 pm
content: Ozcar, thank you for your help.This is from the oven manual:"The internal real-time clock and the required battery are particularly necessary for the nightstart-up function. A good operational battery is necessary for a proper function. All otherparameters and baking programs are stored in an EEPROM (function without battery!!)."When they talk about EEPROM I thought they referred to the 27C512. I figured the 93LC86 would not have enough capacity for all the baking programs and all the other settings.Now based on this and since I can't save baking programs or settings I am thinking that the controller might have a problem writing to the EEPROM but seems that it can read from the EEPROM, where for EEPROM I am thinking 27C512.I do not know if there is code in the 93LC86.Do you think the 93LC86 has enough storage for 30 baking programs and all the other settings?Thank you

author: xvr
author_rank: Frequent Contributor
timestamp: October 13, 2024, 06:02:11 pm
content: EEPROM is 93LC86. It has enough capacity to store 30 baking program, because 'baking program' is a set of parameters, not a real program.27C512 is a UV erasable EPROM. It could be programmed ONLY in special programmer, not inside baking oven. It contains program for MCU (80C32 do not have internal FLASH or ROM).

author: ozcar
author_rank: Frequent Contributor
timestamp: October 13, 2024, 06:13:01 pm
content: Quote from: fernando68 on October 13, 2024, 05:49:41 pmThe 93LC86 can store around 546 bits for each of the 30 programs (perhaps less some for a few global settings). That sounds plenty to store several temperatures and times for each program. What other parameters are involved in a "program"?

author: fernando68
author_rank: Newbie
timestamp: October 13, 2024, 07:37:08 pm
content: Thank you guys, this is very helpful.Not many parameters go into each baking program, each program has up to 5 stages, each one has a setting of temperature, time, humidity and steam on or off.How are the readings of actual temperature/humidity being processed? Are they temporarily stored in the EEPROM and then "processed" by the 80C32?Do the 80C32 needs any data "from outside" to boot? is it possible that that information was stored on the 93LC86? I think I read somewhere that the 80C32 needs "to be told" where to look in the EPROM to start the program.

author: PCB.Wiz
author_rank: Super Contributor
timestamp: October 13, 2024, 11:42:29 pm
content: Quote from: fernando68 on October 13, 2024, 02:13:27 pmThat suggests large parts are functional.Quote from: fernando68 on October 13, 2024, 02:13:27 pmAre you saying a default stored cycle runs ok ? - you just cannot save any new settings ?Quote from: fernando68 on October 13, 2024, 02:13:27 pmThat's unclear - does it still show incorrect actual temperature ? That suggests a sensor or connection problem?

author: fernando68
author_rank: Newbie
timestamp: October 14, 2024, 12:41:57 am
content: Hi PCB.WizIt is not a default stored baking cycle that runs OK, I am referring to the fact that some functionality seems to be running.For example I can access the menus that allows adjusting of different parameters. To be more precise, by pressing two keys in sequence I can access the parameters menu, then I can enter a code, lets say code:170, that takes me to the menu that adjusts the steam quantity. It shows 0ml, I can then enter the value 100ml for example, but when I exit this menu, that value is supposed to saved but it is not. When I access the same parameter it shows 0ml again.The actual and target temperatures shows 0, same as the timer, seems stuck at 0 and I can not change it. On powering up, the actual temperature shows 200C for a fraction of a second, then 0.Another strange thing is that by pressing two keys in sequence I should be able to see the firmware version (ver. 6.4) but now shows 0I am not sure if this is of any help but I will post a picture of the main board and of the control panel (before the problem).Thank you very much for your help.

author: PCB.Wiz
author_rank: Super Contributor
timestamp: October 14, 2024, 04:31:10 am
content: Quote from: fernando68 on October 14, 2024, 12:41:57 amIs there a set factory defaults option anywhere ?I'd try and get a 'sign of a pulse' on the temperature, which I presume it shows by default ? ie heat the oven temperature sensor externally.That can confirm part of the analog side is Ok. Check the analog supply voltages ?Usually you would expect the firmware version to read from the EPROM, and it may even be visible in the HEX file if you look ?

author: 5U4GB
author_rank: Super Contributor
timestamp: October 14, 2024, 04:53:51 am
content: Just a thought, from that photo the battery and holder look a bit corroded, if they're as essential as the manual says they are could it be an issue of poor electrical contact?

author: Atlan
author_rank: Frequent Contributor
timestamp: October 14, 2024, 12:35:31 pm
content: Try replacing the eeprom 93xxx memory. It is still possible to load data from the old eeprom and write them to the new one. Remove the old one and install the new one.

author: Njk
author_rank: Frequent Contributor
timestamp: October 15, 2024, 12:52:50 am
content: Quote from: fernando68 on October 13, 2024, 02:13:27 pmIt looks like the PCB is conformally coated so it's unlikely a small piece of wire could do any electrical damage. But once it had landed, it's obviously not present anymore in the place where it came from, making the circuit there broken. Perhaps that makes the CPU program confused.It seems there are at least two PCBs inside the oven, the "power board" (504078.xx, this is what your image shows) and the keypad interface, so called "control board" (504077.xx, something like on the attached image). There are some (logic?) ICs on that board as well. Perhaps it's a keypad-related problem.The other possibility is that the firmware in the 27C512 part is corrupted (or the MCU is unable to read it). You'd already advised to carefully check the power supply voltage for that part. If the voltage is lower than required, it can be problematic for the MCU to fetch the instructions/data properly, it's a known feature of the UV EPROM chips.Since you'd managed to read the firmware from the 27C512 to a file, you can convert it back to the symbolic format (fortunately, it's an old architecture so there must be a lot of available disassemblers, and the code size is relatively small) to make sure the content looks sane. Generally, a FW image contains the code area, the constants, and the empty areas (that usually reads 0xFF). So you can analyze the code to make sure it's seemingly correct because there are no obviously erratic jump instructions, for instance. It can take time, of course, so it's a last resort method. But it's very powerful, you can identify the corrupted areas and fix the code manually. Moreover, you can design your own code.Not sure about the DS series, but it seems the later series has a dedicated connector for diagnostic/configuration SW tool like Miwe BPM (baking program manager). Anyway, there must be at least debug UART pads somewhere on the board.The wiring diagram for a Miwe DS series oven. Not sure if it's about the exact model but definitely of that era:https://xn--b1agge9ai.xn--p1ai/one_pdf/miwe?pdf_id=5121&producer_id=188One more link. Not about your oven at all, but the DS series are mentioned. Just FYI.https://tehnokitchen.ru/assets/vendor_pdf/resources/384883/3e9547f4a76df6fd98cd57b0d7094ebb7b6f2b53.pdf