Two BC660K modules don't register (worked yesterday)

IoT Modules LPWA Module
1

I need to say that all this worked till yesterday.
Today I updated my prototype’s firmware, and the built-in modem could not register any more. Need to mention, I use self-built modems based on BC660K, one is in my prototype device, the other is connected to my PC through USB TTL Converter. Both modems are sitting side by side on my desk, so radio-situation is identical to both of them.

My prototype worked well over night, so I wanted to proceed with firmware (data transmission part) today…
After flashing the new firmware, I could see +CEREG:0, two seconds later I saw +CEREG: 2. Normally this changes to +CEREG: 5 within one minute.

I was waiting really long, but the modem permanently stays on +CEREG: 2 now! At same time, the second modem was able to re-register when I used AT+CFUN=0 and AT+CFUN=1. Also a AT+QRST=1 changed nothing.
I get
RDY
+CFUN: 1
+CPIN: READY
+CEREG: 2
… and here it remains…

So I guessed that this possibly is related to the SIM card. I swapped the SIM cards. After that, both modems didn’t reach +CEREG: 5 any more. I swap the SIM back, still the same.

Entering AT+CSQ returns +CSQ: 99,99 now, yesterday I saw “15,0”.

Some technical things:
I followed all things mentioned in Quectel’s Hardware Design Guide. VBAT modem supply is 3.30V from a LVD linear regulator (LD1117AS33TR), with 200uF Tantalum + all capacitor values written in AN.
The only difference to Hardware Design Guide is: I have no TVS diodes between GND and SIM-CARD wires. But as the SIM appears to correctly work (-> +CPIN: READY), this cannot be the reason.

Can somebody tell me what is wrong here, please? I didn’t change anything of BC660K’s settings! Meanwhile I am inclined to assume the problem is on mobile network side.

2

Through our communication, I suggest you to use cat1 type module more suitable for your project

3

Herbert,
I have meanwhile also reached the point for using a better module. I chose EG800Q model. Is this model suiting my needs? It is difficult to find useful PDFs for it.
Can you provide me links to (or the PDFs directly) for EG800Q module? It appears to be the right choice then. I need documentation similar to BC660K for:

  1. Hardware Design Notes
  2. Complete AT Commands list
  3. TCP/IP commands

But I still have minor questions for BC660K…

  1. Documentation shows at several AT commands that new settings are immediately written to NVRAM. A little bit stupid to provide no command for revert to factory settings, but also not writing the default setting in the documentation. Isn’t it?
  2. NVRAM is a very relative naming, as it only says “Non Volatile”. But what hardware is behind of it? Differnet types of Hardware allow different numbers of writes (guaranteed), then they will start to fail. So it is never wrong to never do unnecessary writes of same content (except this BC660K only physically writes when there IS a difference? (I didn’t write the firmware inside, so I can only ask)
  3. How often can officially one AT setting be usually written/changed before I risk damaged NVRAM? I ask, because this is important for lifetime of devices.
4

I have sent the document of EG800Q to you