Batboard

I know there are a few posts over the years on how to "blank" then re-initialize GM300 logic boards, but I have NEVER been able to get that method to work. And others have had the same error I found.
Which is that as you try to re-initialize the now "blanked" board, the RSS doesn't find the data to tell it what model radio to initialize.
So you are locked out of the init process because the board must not have enough info in it. Or perhaps this version of RSS doesn't know how.
What I found that seems to work well on corrupted logic or lower tier logic boards is a process where for all practical purposes I "clone" the radio with Maxtrac LAB.
You need a working radio that you want to make a duplicate of. Example, an 8 ch UHF with scan but masked logic board, and your bad logic board in a chassis with any RF board (just don't try to TX UHF thru a VHF PA),
Power up both radios.
Start LAB, go to the F9 EEPROM access and read the first block of memory from the GOOD radio.
Unplug your RIB from the GOOD radio, and plug it into the BAD radio, write the data ( I think F8).
Move the cable back to the GOOD radio, hit F4 to increment memory block.
Move the cable back to the BAD radio and write the data again.
Repeat the process about 18 times.
Sounds longer than it is. Takes maybe 3 minutes.
Once you have the bad logic board "recovered", everything in it will be exactly as the starting "good" radio.
Even the serial number will be the same.
I go back in and change the serial do something different, but if you do, you will have to make changes that leave the checksum the same.
The FIX CHECKSUM feature in MAX LAB won't fix it. I will make it worse.
Just increment one digit up and one digit down equal amounts.
You know you got it wrong if you get the long error tone.
If it is right, you get the usual reset beep.
I have used this to recover a few logic boards in radios that have been on the "back burner" for awhile.
Also used M10 or M120

Dang Keyboard... Sent before I was done.
Also used M10 or M120 masked logic boards to "repair" 8 channel GM300's where the logic board completely died.
So, if you have a pile of GM series parts, you may be able to get some working for ham stuff, or receivers, or GMRS radios.
Better than throwing them away.
I have not tried this with the expanded logic board,( I didn't have any dead expanded boards to try) but there is no reason that I can see for it not to work.
But, I bet there would need to be many more "read / write" evolutions.
Still probably worth the trouble. To me it is anyway.

Hello:
Easier way to recover a defective GM300 /M120/M10 logic bd is DO NOT BLANK IT.
If you do youd better like bit banging or reinitiate it as a maxtrac but since a maxtrac has a different logic bd than the gm300 then you wont have rx audio and will need to do a modification on the gm300 logic bd to regain the rx audio.( Note : If you do reinitiate a GM300 as a Maxtrac and do the rx audio mods on the GM300 logic bd )(THEN YOULL NEED TO READ AND PROGRAM THAT GM300 AS A MAXTRAC WITH MAXTRAC RSS AS ITS A MAXTRAC IN A GM300 CHASSIS NOW)
I recommend skipping the blanking unless all else fails
If your getting any error codes such as Error 58 after read attempt and radio when first turned on as in powered up gives a long error tone saying radio test failed to pass then id suggest you get a known good working code plug that matches your radios model number and clone program it into the radio. ( Serial Number Does Not Have To Match )
After you clone in the good code plug this should get rid of the long error tone on power up but might and in most cases youll still get the error 58 meaning code plug checksum isn't correct due to needing logic bd recalibrated.
In the correct rss program for the radio your recovering the logic bd select service menu and select the replace logic bd section and go through the recalibration process in order it shows as you cant skip one so need to go through the process and program those parimeters needed per the screen.
When done program the new settings into the radio.
Then power off and back on the radio and you shouldn't hear the long error tone but rather a short beep meaning radio passed its power up testing and is good.
Then you should now be able to read and program the radio with its correct rss without error 58 bad code plug or any of the several other error codes.
If you get error code 21 radio not supported error code then you have the wrong rss or radio was last programmed with a newer rss program than you are trying to read it with as in its older rss than the newer rss version it last was programmed with.
Satelite