First time post here, joined to say I have successfully converted a MD3200 to a MD1200 by reprograming the backplane. Big thankyou to this thread that has given me pointers of what to look for. I would guess this should work for the MD1220 and MD3220 as well.
Firstly this is definitely not my area of expertise and this has been a five day crash course for me so please excuse any mistakes.
There is very mixed views on if you can convert a MD3200 to MD1200 or even the other way round, yes they use identical parts with identical part numbers but at least for me just plugging in a MD1200 controller didn't work. The back/mid plane has two EEPROM chips which as mentioned in this thread are programmed at the factory to suite the model being shipped.
So with no modification the MD1200 controller in a MD3200 chassis would have a amber light on the controller and after a few minuets the fans would spin up to full speed, oh boy are they loud. At first I tried to use the serial interface of the controller to reprogram the backplane but found it far to difficult.
Highlighted in red are the two EEPROM chips that sit in the middle of the backplane, not to be confused with the two temperature chips that sit on the outsides of the board. The black covering is easily removable by pressing a small screwdriver into the back of the pins, then it can be fitted again later.
Next I needed a EEPROM programmer, these can be found very cheaply and fast from amazon or ebay.
I got a CH341A programmer, they are very cheap but make sure you get one with the clip included to save you soldering and unsoldering. Software wasn't included or any instructions with the programmer but there is lots of info on YouTube about how to use this. In short, jumper on pin 1&2, attach the clip into the board making sure pin one lines up with the red cable on the clip, clip the clip over the chip with the red cable over pin one of the chip that is marked with a white dot on the backplane PCB.
For the software there are multiple different programs that work with the programmer, I used AsProgrammer 1.4.1 some of the other software would just repeat the first line over and over.
To set up the software you need to tell it that the chip is a 24C64 that's under IC > l2C > _24Cxxx This should match what is printed on the top of the chip. Also check the hardware tab is set to CH341A
You should now be able to read the chips, adjust the clip if not, it can be a bit tricky to get it perfect.
So this is my MD3200 dump
Highlighted are a few key parts, the serial number is here but split into two parts, should match what's on your sticker. Also the model here as a MD3200 and the HOGS_SAS not entirely sure but its important. Also the firmware version of the last connected controller I believe is the 1.06 The rest of the chip is blank with 00's after the random bit at 0x000002F0 was different on all of my boards, not figured out what it's for.
So first thing is you can't just change the model number and be done, that would be too easy. The MD1200 has some sort of checksum which I haven't been able to pin down. Here is a reading from my working stock MD1200:
I was well out of my depth here but All I could figure out was that every 8 bytes (I think) the 8bit checksum (2's complement) came back as 00. But it being a checksum you can rearrange numbers that are already there and get the same checksum, important if you are converting multiple MD3200 as they won't work with the same serial number here, just swap a pair of numbers in the serial number section.
Finally if you are testing outside of the chassis, the control panel card must be connected otherwise the out port won't work and you won't get any drives showing up, this added a whole day on to the job for me.
I have attached a zip folder with both the MD3200 and MD1200 dumps, they don't open properly in notepad but they work in AsProgrammer.
Another Final important thing, Both chips need to be programmed the same, that's the FRU and the VPD chips are marked on the PCB. a mismatch is what causes the MD3200 to go onto lockdown.
You can just take my files and program them straight to the chips or if you are converting multiple devices to work together you will need to rearrange the serial number so they are unique, as always take backups before modifying.
Obviously this is all at your own risk and don't expect any help from dell with this.