Radioddity GD-77

Tuning & alignment project

 

Alignment, tweaks, and flash memory corruption recovery for your Radioddity GD-77

 

version 2.2 --- 18th January 2022


This information is primarily intended for amateur ’ham’ radio operators who wish to maintain and adjust their GD-77. Any regulatory authority approval (e.g. FCC certification) may become invalid by the use of this information. Users should ensure their radios are operating in accordance with their licence conditions. In any case, the user alone accepts all responsibility and risk from the use of this information and tools provided here.


The Radioddity GD-77 is becoming quite a popular entry level dual band DMR handheld for amateur ’ham’ radio use. The GD-77 family takes it’s design cues from DMR radios designed for purely commercial or business two way radio usage. In that arena, should a problem develop with the equipment, the user would return the radio to their supplier for repair. The very low cost of the GD-77 means repair isn’t generally feasible, and so replacement rather than repair is the most cost effective strategy.


Ham radio operators don’t have this time/cost constraint. We often prefer to repair our own radio equipment, and have the time to experiment, tinker, and adjust the equipment until it is ’just so’ for our needs. The GD-77 tuning project was born of this philosophy. The only problem was that there were no tools, information or references to enable us to maintain the GD-77. Seeing the need for this information inspired Roger VK3KYY, Colin G4EML and Jason VK7ZJA to put the GD-77 under the microscope in order to derive the tools necessary for hams to maintain the GD-77


This information and tools have come about by deep investigation and experimentation. Radioddity have their own tuning process for the GD-77, something that is mentioned in the FCC certification documents, but is hidden from the general public in order not to reveal anything commercially sensitive. Since Radioddity don’t have a repair facility, presenting this information isn’t going to deprive Radioddity of any revenue. Indeed, the very availability of this information could improve the appeal of the GD-77 to the amateur radio community and might even result in increased sales for Radioddity, in a similar way to how MD380 Toolz must have caused an explosion of sales for TYT. I know of some ham radio operators who refuse to own any equipment for which they can’t obtain service manuals or other information necessary to maintain that equipment.


In order for you to read, change and write tuning data to the GD-77, a tool called Flash Manager has been produced.


CAUTION: The GD-77 Flash Manager software is a very low level tool and can cause serious and unrecoverable damage to your radio. Indiscriminate use can ruin both the software and hardware of your radio. Make sure you understand exactly what it is you are doing, and use with care.


Download links:
Download GD-77 Flash Manager here (61kb)

If you need a good hex editor, download HxD in your preferred language here (about 860kb)

There are four types of memory in the GD-77:
1) EEPROM 64kbyte: half of the codeplug is stored here.
2) External flash memory 1Mbyte: the other half of the codeplug, DMR IDs written by ActiveClient.exe, RF alignment data and even display character font data is stored here.
3) Internal MCU flash memory 512kbyte: this is where the radio firmware lives.
4) Internal MCU RAM 128kbyte: used by the MCU for it’s own internal operational use.

The GD-77 Flash Manager operates with the external flash memory. All 1Mbyte (8Mbits) of this flash memory are readable and almost all of the flash memory is writeable with this tool. Flash Manager can't correctly read or write any data to flash addresses 0x0000 to 0xFFFF but there is no active data stored there anyway, so this will not matter. You could edit half of the codeplug or the DMR IDs, though it would be easier to use the CPS software and ActiveClient.exe respectively to edit those.

The data of particular interest to us here is the RF alignment data. This lives in flash memory at addresses 0x08F000 to 0x08F0DF. If you are browsing other parts of flash memory, you might also find other copies of the RF alignment data at other locations, but the ’active’ data is always located at 0x08F000-0x08F0DF. Having other copies of this RF alignment data is quite handy, especially if the active data becomes corrupt. More on this later.


Your first step should be to take a backup of the entire flash memory and save it to file, so you have a copy to fall back on should something go wrong at some point. Begin by turning the GD-77 off, plug in the programming cable, and turn on the GD-77 while holding down the following key combination: side blue key, green menu button and the * (lock symbol) key. The radio will power up normally with no other unusual visible indication. This can be a tricky key sequence to get right and you might need a few attempts to successfully get this mode started up correctly.
Start up Flash Manager and carefully note the warning message, and click ’yes’ to proceed. Enter the Start address (hex) as 0, and enter the Length (hex) as 100000- that is a one and five zeroes. Click Read. You should now see the display of the GD-77 respond with ’Memory Prog’ and the top panel LED flash red, and a percentage progress bar on your PC increase. To read the entire flash will take around five and a half minutes. Then Save File and give it a .bin extension, and keep the file somewhere safe. If the file is filled with all 00s then it means the radio didn’t start up in the flash reading mode properly, and you should try the side blue key, green menu button and the * (lock symbol) power up key sequence again.


In order to begin changing parameters, refer to the table below that displays what byte (or bits) at each address in flash is used for. When altering these values, you need to keep in mind that flash memory is not like EEPROM, you can’t just overwrite data. The data you are changing first needs to be erased. Flash memory can be erased in 4, 32 or 64kbyte blocks. The GD-77 firmware performs a 64kbyte block erase for this area of flash, which means if you want to change just one byte, the flash memory will erase that 64kbyte block and you’ll need to re-write that 64kbyte entirely. With that in mind, your first step is to read the 64kbyte block of data that contains the RF alignment data. As above, put the GD-77 into the special flash read/write mode with the following power up sequence:
Blue side button + green menu button + * (lock) button held down while powering up the radio.

Begin reading at address 80000 (hex) and read for 10000 (hex) bytes. Save this block of data to a file if you like. Scroll down to address 8F000 and you should see data beginning with bytes A0 0F C0 12 A0 0F C0 12. Change the parameter you want, then write the data, again using 80000 as the start address and 10000 as the length. Each read or write for this 64kbyte block will take around 25 seconds to complete.


There are a few handy features in the Flash Manager to assist you manipulate the data:
Ctrl-F is a find feature, where you can search for data from the cursors present position onwards. Hex or ASCII strings can be searched for. F3 will find the next occurrence.
Ctrl-G will go to an address that you specify in hex, which can save a lot of scrolling in large fields of memory displays.
Alt-F12 will make visible three new buttons to read, adjust and write calibration data. The adjust calibration button will give an easy interface to adjust RF tuning parameters without having to edit raw hex data. Be aware this feature is still under development and may not work completely as intended.

SERIOUS WARNING: carelessly altering certain parameters can be hazardous to your radio. For example, setting RF output power to a level significantly higher than what is already calibrated for your individual radio might well give increased RF output, but it will also dramatically increase the risk of RF PA burnout. Altering DMR I&Q parameters will definitely cause your DMR transmitted signal to become corrupted.
YOUR USE OF THIS INFORMATION AND TOOLS PROVIDED IS ENTIRELY AT YOUR OWN RISK.




Address in flash memory Typical value Usage Notes
UHF SECTION
8F000 A0 Not known, must be set to this value for UHF transmitter to work CRITICAL VALUE
8F001 0F Not known, must be set to this value for UHF transmitter to work CRITICAL VALUE
8F002 C0 Not known, must be set to this value for UHF transmitter to work CRITICAL VALUE
8F003 12 Not known, must be set to this value for UHF transmitter to work CRITICAL VALUE
8F004 A0 Not known, must be set to this value for UHF transmitter to work CRITICAL VALUE
8F005 0F Not known, must be set to this value for UHF transmitter to work CRITICAL VALUE
8F006 C0 Not known, must be set to this value for UHF transmitter to work CRITICAL VALUE
8F007 12 Not known, must be set to this value for UHF transmitter to work CRITICAL VALUE
8F008 E8 DAC word for frequency reference oscillator at UHF, fine tune. CRITICAL VALUE, typical range DC-E9
8F009 03 DAC word for frequency reference oscillator at UHF, coarse tuning. Should be no need to adjust this away from value 03. CRITICAL VALUE
8F00A E9 Frequency fine tune for DMR mode only, UHF CRITICAL VALUE, typically same as 8F008 or +1 of that value
8F00B 83 Low RF power output setting, UHF freq 400 MHz 00=lower power, FF=higher power, typical low power value ranges 65-80
8F00C C6 High RF power output setting, UHF freq 400 MHz Typical high power value ranges AA-DB CAUTION: Excessively high settings will burn out electronics
8F00D 82 Low RF power output setting, UHF freq 405 MHz Suggestion: lower value to 40 hex gives about 30mW output, value of 20 gives no detectable output.
8F00E C5 High RF power output setting, UHF freq 405 MHz CAUTION: Excessively high settings will burn out electronics
8F00F 81 Low RF power output setting, UHF freq 410 MHz
8F010 C6 High RF power output setting, UHF freq 410 MHz CAUTION: Excessively high settings will burn out electronics
8F011 81 Low RF power output setting, UHF freq 415 MHz
8F012 C7 High RF power output setting, UHF freq 415 MHz CAUTION: Excessively high settings will burn out electronics
8F013 80 Low RF power output setting, UHF freq 420 MHz
8F014 C9 High RF power output setting, UHF freq 420 MHz CAUTION: Excessively high settings will burn out electronics
8F015 80 Low RF power output setting, UHF freq 425 MHz
8F016 CA High RF power output setting, UHF freq 425 MHz CAUTION: Excessively high settings will burn out electronics
8F017 81 Low RF power output setting, UHF freq 430 MHz
8F018 CB High RF power output setting, UHF freq 430 MHz CAUTION: Excessively high settings will burn out electronics
8F019 81 Low RF power output setting, UHF freq 435 MHz
8F01A CB High RF power output setting, UHF freq 435 MHz CAUTION: Excessively high settings will burn out electronics
8F01B 81 Low RF power output setting, UHF freq 440 MHz
8F01C C8 High RF power output setting, UHF freq 440 MHz CAUTION: Excessively high settings will burn out electronics
8F01D 81 Low RF power output setting, UHF freq 445 MHz
8F01E C6 High RF power output setting, UHF freq 445 MHz CAUTION: Excessively high settings will burn out electronics
8F01F 81 Low RF power output setting, UHF freq 450 MHz
8F020 C5 High RF power output setting, UHF freq 450 MHz CAUTION: Excessively high settings will burn out electronics
8F021 81 Low RF power output setting, UHF freq 455 MHz
8F022 C5 High RF power output setting, UHF freq 455 MHz CAUTION: Excessively high settings will burn out electronics
8F023 7F Low RF power output setting, UHF freq 460 MHz
8F024 C4 High RF power output setting, UHF freq 460 MHz CAUTION: Excessively high settings will burn out electronics
8F025 7E Low RF power output setting, UHF freq 465 MHz
8F026 C6 High RF power output setting, UHF freq 465 MHz CAUTION: Excessively high settings will burn out electronics
8F027 7D Low RF power output setting, UHF freq 470 MHz
8F028 C6 High RF power output setting, UHF freq 470 MHz CAUTION: Excessively high settings will burn out electronics
8F029 7D Low RF power output setting, UHF freq 475 MHz
8F02A C6 High RF power output setting, UHF freq 475 MHz CAUTION: Excessively high settings will burn out electronics
8F02B 3D Unknown
8F02C 3B Unknown
8F02D 3A Unknown
8F02E 38 Unknown
8F02F 37 Unknown
8F030 36 Unknown
8F031 35 Unknown
8F032 A9 Unknown
8F033 1D Unknown
8F034 0D Unknown
8F035 0D Unknown
8F036 11 Unknown
8F037 11 Unknown
8F038 0B Unknown
8F039 0B Unknown
8F03A 0F Unknown
8F03B 00 Unknown
8F03C 00 Unknown
8F03D 00 Unknown
8F03E 00 Unknown
8F03F 18 Unknown CRITICAL VALUE range typically 17-1E
8F040 16 Unknown CRITICAL VALUE range typically 15-1C
8F041 14 Unknown CRITICAL VALUE range typically 14-1C
8F042 13 Unknown CRITICAL VALUE range typically 13-1C
8F043 16 Unknown CRITICAL VALUE range typically 16-1C
8F044 14 Unknown CRITICAL VALUE range typically 14-1D
8F045 15 Unknown CRITICAL VALUE range typically 14-1D
8F046 12 Squelch sensitivity gain. Lower value=more sensitive squelch. Do not go below value 08.
8F047 3E UHF Mute strict, wideband, close Higher value=lower RF level / more sensitive. NB: Strict and normal values interact somewhat
8F048 3C UHF Mute strict, wideband, open
8F049 3E Unknown
8F04A 3A Unknown
8F04B 53 UHF Mute normal, wideband, close
8F04C 51 UHF Mute normal, wideband, open
8F04D 34 UHF Mute strict, narrowband, close Higher value=lower RF level / more sensitive. NB: Strict and normal values interact somewhat
8F04E 32 UHF Mute strict, narrowband, open
8F04F 34 Unknown
8F050 32 Unknown
8F051 53 UHF Mute normal, narrowband, close
8F052 51 UHF Mute normal, narrowband, open
8F053 1C UHF Received signal meter, low end Suggestion: leave as is
8F054 20 UHF Received signal meter, high end Suggestion: set to 60 for more realistic RSSI indication. 1 bar= -113dBm, 2 bars= -95dBm, 3 bars= -80dBm
8F055 3C UHF 405 MHz DMR TX 4FSK CRITICAL VALUE Don’t adjust, typical range 3C-41
8F056 3A UHF 415 MHz DMR TX 4FSK CRITICAL VALUE Don’t adjust, typical range 3A-40
8F057 39 UHF 425 MHz DMR TX 4FSK CRITICAL VALUE Don’t adjust, typical range 39-3E
8F058 38 UHF 435 MHz DMR TX 4FSK CRITICAL VALUE Don’t adjust, typical range 37-3D
8F059 36 UHF 445 MHz DMR TX 4FSK CRITICAL VALUE Don’t adjust, typical range 36-3C
8F05A 35 UHF 455 MHz DMR TX 4FSK CRITICAL VALUE Don’t adjust, typical range 35-3A
8F05B 34 UHF 465 MHz DMR TX 4FSK/td> CRITICAL VALUE Don’t adjust, typical range 34-39
8F05C 33 UHF 475 MHz DMR TX 4FSK CRITICAL VALUE Don’t adjust, typical range 33-38
8F05D 1D UHF DMR receive audio gain & beep volumes (not independantly adjustable) Higher value=more gain
8F05E 0F UHF TX DTMF deviation Higher value=more deviation
8F05F 0D UHF TX 1750Hz tone burst deviation Higher value=more deviation
8F060 11 UHF TX CTCSS deviation, wideband Higher value=more deviation
8F061 11 UHF TX CTCSS deviation, narrowband Higher value=more deviation
8F062 0B UHF TX DCS deviation, wideband Higher value=more deviation
8F063 0B UHF TX DCS deviation, narrowband Higher value=more deviation
8F064 0F Unknown, but do not adjust - affects both RF power out and modulation in all modes CRITICAL VALUE Do not adjust
8F065 0E Unknown, but do not adjust - affects both RF power out and modulation in all modes CRITICAL VALUE Do not adjust
8F066 31 UHF analogue only mic gain (both wide & narrow band) do not exceed value 7F Higher value=more gain
8F067 05 Unknown
8F068 27 UHF analog overall (CTCSS, DCS, DTMF & voice) deviation, wideband, fine setting Higher value=more deviation
8F069 00 UHF analog overall (CTCSS, DCS, DTMF & voice) deviation, wideband coarse setting. Should be no need to set above 00 Higher value=more deviation
8F06A 27 UHF analog overall (CTCSS, DCS, DTMF & voice) deviation, narrowband, fine setting Higher value=more deviation
8F06B 00 UHF analog overall (CTCSS, DCS, DTMF & voice) deviation, narrowband coarse setting. Should be no need to set above 00 Higher value=more deviation
8F06C 0F UHF analog only receive audio gain. Valid range 00 to 0F. 8F06C & 8F06D are added to give total gain value
8F06D 0E UHF analog only receive audio gain. Valid range 00 to 0F. Higher value=more gain
8F06E 00 Unknown
8F06F 00 Unknown
VHF SECTION
8F070 50 Not known, must be set to this value for VHF transmitter to work CRITICAL VALUE
8F071 05 Not known, must be set to this value for VHF transmitter to work CRITICAL VALUE
8F072 CC Not known, must be set to this value for VHF transmitter to work CRITICAL VALUE
8F073 06 Not known, must be set to this value for VHF transmitter to work CRITICAL VALUE
8F074 50 Not known, must be set to this value for VHF transmitter to work CRITICAL VALUE
8F075 05 Not known, must be set to this value for VHF transmitter to work CRITICAL VALUE
8F076 CC Not known, must be set to this value for VHF transmitter to work CRITICAL VALUE
8F077 06 Not known, must be set to this value for VHF transmitter to work CRITICAL VALUE
8F078 EB DAC word for frequency reference oscillator at VHF, fine tune. CRITICAL VALUE, typical range E0-EB
8F079 03 DAC word for frequency reference oscillator at VHF, coarse tuning. Should be no need to adjust this away from value 03. CRITICAL VALUE
8F07A EE Frequency fine tune for DMR mode only, VHF CRITICAL VALUE, typical range E4-EC
8F07B 40 Low RF power output setting, VHF freq 136 MHz 00=lower power, FF=higher power, typical low power value ranges 33-64
8F07C AA High RF power output setting, VHF freq 136 MHz Typical high power value ranges 8B-F0 CAUTION: Excessively high settings will burn out electronics
8F07D 41 Low RF power output setting, VHF freq 140 MHz Suggestion: lower value to 40 hex gives about 125mW output, value of 20 gives no detectable output.
8F07E BD High RF power output setting, VHF freq 140 MHz CAUTION: Excessively high settings will burn out electronics
8F07F 4E Low RF power output setting, VHF freq 145 MHz
8F080 BE High RF power output setting, VHF freq 145 MHz CAUTION: Excessively high settings will burn out electronics
8F081 55 Low RF power output setting, VHF freq 150 MHz
8F082 B6 High RF power output setting, VHF freq 150 MHz CAUTION: Excessively high settings will burn out electronics
8F083 56 Low RF power output setting, VHF freq 155 MHz
8F084 B1 High RF power output setting, VHF freq 155 MHz CAUTION: Excessively high settings will burn out electronics
8F085 56 Low RF power output setting, VHF freq 160 MHz
8F086 B5 High RF power output setting, VHF freq 160 MHz CAUTION: Excessively high settings will burn out electronics
8F087 59 Low RF power output setting, VHF freq 165 MHz
8F088 B8 High RF power output setting, VHF freq 165 MHz CAUTION: Excessively high settings will burn out electronics
8F089 5C Low RF power output setting, VHF freq 172 MHz
8F08A B8 High RF power output setting, VHF freq 172 MHz CAUTION: Excessively high settings will burn out electronics
8F08B FF Not applicable
8F08C FF Not applicable
8F08D FF Not applicable
8F08E FF Not applicable
8F08F FF Not applicable
8F090 FF Not applicable
8F091 FF Not applicable
8F092 FF Not applicable
8F093 FF Not applicable
8F094 FF Not applicable
8F095 FF Not applicable
8F096 FF Not applicable
8F097 FF Not applicable
8F098 FF Not applicable
8F099 FF Not applicable
8F09A FF Not applicable
8F09B 40 Unknown
8F09C F0 Unknown
8F09D 40 Unknown
8F09E F0 Unknown
8F09F 40 Unknown
8F090 F0 Unknown
8F0A1 FF Not applicable
8F0A2 FF Not applicable
8F0A3 0F Unknown .
8F0A4 0F Unknown
8F0A5 0F Unknown
8F0A6 1B Unknown
8F0A7 1B Unknown
8F0A8 1B Unknown
8F0A9 FF Not applicable
8F0AA FF Not applicable
8F0AB 00 Unknown
8F0AC 00 Unknown
8F0AD 00 Unknown
8F0AE 00 Unknown
8F0AF 1D Unknown CRITICAL VALUE range typically 1D-20
8F0B0 1D Unknown CRITICAL VALUE range typically 1D-1F
8F0B1 1D Unknown CRITICAL VALUE range typically 1D-1F
8F0B2 1C Unknown CRITICAL VALUE range typically 1C-1F
8F0B3 1C Unknown CRITICAL VALUE range typically 1C-1E
8F0B4 1C Unknown CRITICAL VALUE range typically 1C-1D
8F0B5 1B Unknown CRITICAL VALUE range typically 1B-1E
8F0B6 1B Squelch sensitivity gain. Lower value=more sensitive squelch. Do not go below value 08.
8F0B7 3E VHF Mute strict, wideband, close Higher value=lower RF level / more sensitive. NB: Strict and normal values interact somewhat
8F0B8 3C VHF Mute strict, wideband, open
8F0B9 3D Unknown
8F0BA 3A Unknown
8F0BB 53 VHF Mute normal, wideband, close
8F0BC 51 VHF Mute normal, wideband, open
8F0BD 34 VHF Mute strict, narrowband, close Higher value=lower RF level / more sensitive. NB: Strict and normal values interact somewhat
8F0BE 32 VHF Mute strict, narrowband, open
8F0BF 34 Unknown
8F0C0 32 Unknown
8F0C1 53 VHF Mute normal, narrowband, close
8F0C2 51 VHF Mute normal, narrowband, open
8F0C3 20 VHF Received signal meter, low end Suggestion: leave as is
8F0C4 27 VHF Received signal meter, high end Suggestion: set to 5D for more realistic RSSI indication. 1 bar= -113dBm, 2 bars= -95dBm, 3 bars= -80dBm
8F0C5 B1 VHF 136 MHz DMR TX 4FSK CRITICAL VALUE Don’t adjust, typical range B0-C3
8F0C6 AB VHF 140 MHz DMR TX 4FSK CRITICAL VALUE Don’t adjust, typical range AA-BD
8F0C7 A5 VHF 145 MHz DMR TX 4FSK CRITICAL VALUE Don’t adjust, typical range A4-B7
8F0C8 A0 VHF 150 MHz DMR TX 4FSK CRITICAL VALUE Don’t adjust, typical range 9E-B1
8F0C9 9B VHF 155 MHz DMR TX 4FSK CRITICAL VALUE Don’t adjust, typical range 98-AB
8F0CA 95 VHF 160 MHz DMR TX 4FSK CRITICAL VALUE Don’t adjust, typical range 93-A5
8F0CB 90 VHF 165 MHz DMR TX 4FSK CRITICAL VALUE Don’t adjust, typical range 8F-9F
8F0CC 8E VHF 172 MHz DMR TX 4FSK CRITICAL VALUE Don’t adjust, typical range 8A-9B
8F0CD 1D VHF DMR receive audio gain & suspected beep volumes (not independantly adjustable) Higher value=more gain
8F0CE 10 VHF TX DTMF deviation Higher value=more deviation
8F0CF 0D VHF TX 1750 Hz tone burst deviation Higher value=more deviation
8F0D0 11 VHF TX CTCSS deviation, wideband Higher value=more deviation
8F0D1 11 VHF TX CTCSS deviation, narrowband Higher value=more deviation
8F0D2 0B VHF TX DCS deviation, wideband Higher value=more deviation
8F0D3 0B VHF TX DCS deviation, narrowband
8F0D4 08 Unknown, but do not adjust - affects both RF power out and modulation in all modes CRITICAL VALUE Do not adjust
8F0D5 0E Unknown, but do not adjust - affects both RF power out and modulation in all modes CRITICAL VALUE Do not adjust
8F0D6 31 VHF analog only mic gain (both wide & narrow band) do not exceed value of 7F Higher value=more gain
8F0D7 05 Unknown
8F0D8 27 VHF analog overall (CTCSS, DCS, DTMF & voice) deviation, wideband, fine setting Higher value=more deviation
8F0D9 00 VHF analog overall (CTCSS, DCS, DTMF & voice) deviation, wideband coarse setting. Should be no need to set above 00 Higher value=more deviation
8F0DA 27 VHF analog overall (CTCSS, DCS, DTMF & voice) deviation, narrowband, fine setting Higher value=more deviation
8F0DB 00 VHF analog overall (CTCSS, DCS, DTMF & voice) deviation, narrowband coarse setting. Should be no need to set above 00 Higher value=more deviation
8F0DC 0F VHF analog only receive audio gain. Valid range 00 to 0F. 8F0DC & 8F0DD are added to give total gain value
8F0DD 0F VHF analog only receive audio gain. Valid range 00 to 0F. Higher value=more gain
8F0DE 00 Unknown
8F0DF 00 Unknown

If you manage to work out what some of the unknown use parameters do, please let me know via e-mail: vk7zja at gmail dot com


Remember, you need to work with a minimum size of 64kbyte block of data, you can’t just change a few bytes on their own. Read memory from (hex) 80000 for length (hex) 10000, then edit the parameters you want and write that entire block back to the radio.

There are three pairs of bytes that also need discussing. These three lots of vital flash memory values are located at D0000-D0001, D0B30-D0B31 and E93D0-E93D1. Do NOT change them, otherwise access to flash memory via the blue button & green menu button & * (lock) button power up sequence will be lost and the only way to recover from this is to desolder the flash memory IC and program it externally.

RECOVERY FROM DATA CORRUPTION AFTER MEMORY / FACTORY RESETTING

Memory and / or factory resetting the GD-77 with certain versions of firmware, specifically between 2.6.7 and 3.1.1 (with 3.0.6 and 3.1.1 being the most common) can corrupt information in the RF alignment data block at address 8F000 onward. Typical symptoms are very low or no RF output from the radio, in either analogue FM or digital DMR modes.
Previously some users have been able to recover from this corruption by downgrading to earlier firmware versions and then performing a memory reset and re-upgrading again. This may or may not work for more recent firmware versions, reports of success vary from user to user, and I suspect it may have something to do with pre-existing conditions within the flash memory.
Described here is a method of restoring the corruption, which is both more reliable and quicker than the previous downgrade-reset-upgrade method of recovery.

As always, use these tools and information with caution, as serious damage can result from careless use.


Step 1: Download Flash Manager, and if you don’t already have a hex editor, download and install HxD. Download links are given above.

Step 2: Turn off the corrupted GD-77, connect programming cable to the radio and to the PC. Do not turn on the GD-77 yet.

Step 3: Hold down the side blue key, green menu key (above left arrow button) and the * / lock key (just below the right arrow button) while turning on the GD-77. The radio will appear to power up normally.

Step 4: Launch Flash Manager.

Step 5: Read the entire flash. Set Start address (hex) to 0, and set Length (hex) to 100000 - that’s one followed by five zeroes. Click the Read button, and wait about 5-6 minutes for the read to complete.

Step 6: Export the read data to a file using the Save File button. Call the file something like corruptGD77.bin In Windows the file should show as being 1.0 Mbyte in size.

Step 7: Launch HxD or your favourite hex editor. Open the file you just saved from Flash Manager.

Step 8: Now search for other copies of RF alignment data that should be hiding in other locations of the dump of flash memory. We are relying on the fact that some RF alignment data never changes from radio to radio. One such item of data shows up as an ASCII string of SQ4242 (note upper case / capital letters SQ). So perform a search from the beginning, looking for the ASCII string SQ4242

Step 9: Once you’ve found this occurrence, look at the data around it. About 75 (decimal) bytes prior to this SQ4242 sequence, there should be a set of repeating bytes A0 0F C0 12 A0 0F C0 12. If you do find this, then you have very likely found a valid and uncorrupted copy of your radios RF alignment data. If you don’t find this, continue searching until you do find valid RF alignment data. A common address to find such data is typically 50100 to 501DF (hex)

Step 10: From the start of the sequence of bytes A0 0F C0 12 A0 0F C0 12, copy a block of 224 bytes. So if you do find valid alignment data starting at address 50100, copy the data from address 50100 to 501DF, and paste that data into address beginning at 8F000. You can highlight, copy and paste in HxD which is very handy.

Step 11: Once you’re satisfied that you have valid RF alignment data copied over to address 8F000 to 8F0DF, save the file to disk, calling it something like repairedGD77.bin Again, the file should show as being 1.0 Mbyte in size under Windows.

Step 12: Back in Flash Manager, use the Open File button to load your repairedGD77.bin file. Scroll down to, or use the Ctrl-G feature to jump directly to address 8F000 and confirm that valid RF alignment data is present. As above, it will begin with bytes A0 0F C0 12 A0 0F C0 12. If it does not appear there, something has not gone quite right and you should go back to step 7 above and try again.

Step 13: Turn off your GD-77 and power it back on with the special power up sequence again, same as step 3.

Step 14: Now it is time to write the valid RF alignment data back to the radio. We don’t need to write the entire flash contents, but do need to write at least a 64kbyte block for this to work. Enter Start address (hex) of 80000 - that’s eight followed by four zeroes, and enter Length (hex) as 10000 - that’s one followed by four zeroes. Click Write and wait about 25 seconds for the write to complete.

Step 15: Turn off your GD-77, remove the programming cable, and power on normally, and test. Your GD-77 should be working nominally now.

It is not recommended to use the typical values in the table above to reconstruct a new RF alignment data block from scratch unless used as a last resort. The reason for this is that some parameters can be quite critical, especially the frequency tuning and DMR 4FSK values. It is always best to find copies of the RF alignment data that is specific and unique to your radio. The typical values are given as a guide only and give some context to potential adjustments you may wish to make.


Other useful links for the GD-77:

GD-77 Modifications

GD-77 Frequently Asked Questions FAQ & answers

Absolute beginners guide to DMR

GD-77 Review

© Copyright Jason Reilly (SK), 2018-2022



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