Here are the technical details of the modifications that I described above.
The meter has a 24C02 EEPROM in SOIC package. This has 256 bytes of data which includes some configuration and some calibration data. I modified specific parts of the configuration without changing calibration data. It is important that you understand that you must read your EEPROM data, then modify only the specific bytes for these changes; the other data must remain intact. If you simply copy my EEPROM, you will ruin your calibration.
For the reason above I will not post a binary of my EEPROM, only an image of the changes to be made. Attached is a screen capture showing the data in my EEPROM with all changed bytes in
RED.
Address 0x10,0x11 is the nominal full scale, changed to 8000 (0x1F40), note the byte swap for all two-byte data values.
Address 0x12,0x13 is the range-up value, changed to 8001 (0x1F41).
Address 0x14,0x15 is the range-down value, changed to 750 (0x02EE).
The rationale for choosing 8000 as full-scale is explained in the previous post.
Addresses 0x80-0xBF configure the various switch positions. There are 16 possible switch positions (not all are used for this meter), and 4 possible functions for each switch position. The switch positions are labeled in the attached image of the meter. The attached chart shows the data to place in a memory location to enable the associated function.
Note that 0x80, 0x90, 0xA0, 0xB0 control the four functions for switch position 0, so 0x81, 0x91, 0xA1, 0xB1 control the four functions for position 1, etc. On this meter, there are 11 switch positions (plus "OFF" which doesn't count). You can see that the "ACV" position is shown as "9" which means that the four memory locations for functions under that position are 0x89, 0x99, 0xA9, and 0xB9. Looking at the data dump, you can see 0x89=0x06 and 0x99=0x05. This means the first function is ACVmV and the second is DCVmV. 0xA9 and 0xB9 are zero which means no function. So setting the switch to "ACV" and pressing "Select" will toggle between the ACV and DCV measuring functions.
Address 0xFB is the automatic power off in minutes. 0xFC is the backlight off timer in seconds. Set either to zero to disable.
To facilitate easy repeated modifications, I removed the EEPROM, then attached a DIP socket to the pads with short lead wires. I soldered another 24C02 EEPROM into a SOIC-to-DIP adapter board, so that I can easily remove it to program it in the TL866, then place it back in the socket.