| Electronics > Repair |
| CH341A Serial Memory Programmer Power Supply Fix |
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| FazzaGBR:
I purchased one of these a while back, such great value for money and I'm so glad the topic of the voltage came up on a YouTube video I saw and when I checked the voltage on my device it was wrong so did the lifting up of the pin and soldering a wire to the 3.3V supply and hey presto it was safe to use! |
| Tantratron:
--- Quote from: Ian.M on November 20, 2024, 12:38:16 pm ---VESA DDC I2C (on VGA ports) used 5V signal levels - see page 18 of https://www.eevblog.com/forum/projects/i2c-over-cat5e-problem/?action=dlattach;attach=185318 If you are using VGA port I2C, for a 3.3V (or lower) target, you need one of these: https://www.adafruit.com/product/757 or equivalent from Amazon, Ebay or the usual far east 'eBazaar' suppliers. It should follow Philips AN97055, with one N-MOSFET per signal line. It needs a 3.3V supply to biass the MOSFET gates, but that can usually be tapped from the target device as very little current is needed. The various CH341x 3.3V mods are all good for both SPI and I2C. The switchable version of the CH341x mod can be wired to auto-set the target Vcc voltage, so you dont need to jumper 3.3V to 5V to short out the regulator when programming 5V devices. This is actually a simpler mod - lift Vcc (pin 28) and link it to the regulator output. Wire a SPST switch, common to regulator output, one end to V3 (pin 9) and the other to the regulator input (+5V). With the switch in the 5V position, confirm the regulator does not get hot, and that there is 5V at the programmer socket Vcc pins. Ideally replace the zero ohm link in the R1 (marked F1) position on the CH341x programmer PCB with a 250mA polyfuse to protect your PC if the programmer Vcc gets shorted in 5V mode. --- End quote --- The reason i'm asking is related to firmware reading and/or writing this LCD driver board based on RTD2660 processor. The board has a SPI NOR flash memory which is clearly 25xx (3.3V) then one option is to use the CH431A programmer and grabber to flashrom, this is why I purchased the CH431A. Another approach which is documented here consists of using an adafruit FT232H and make specific wiring as shown. The LCD driver board has VGA connector but its 2 pins dedicated to SDA/SCL are directly connected to the RTD2660H panel processor via 100R with 4.7K resistor. So there are 2 ways to hack or flash the SPI eeprom: either direct via CH431A programmer or indirect via the VGA-i2c where the RTD2660H will internal route the commands to the actual SPI eeprom. This is why I was wondering if OK to use the CH431A with modification to explore hacks. I do know from reading the datasheet of RTD2660 than its pins 58 (SCL) and 59 (SDA) says not 5V power tolerant so we kind of go back to the 3.3V story with CH431A except here I'd use its 24xx outputs instead of using the FT232H interface. What would be unique or universal modification to make sure wether 25xx outputs or 24xx would be always 3.3V |
| Ian.M:
A cheaper alternative to the Adafruit FT232H board is CJMCU FT232H breakout board from the usual far east suppliers. Same chip but no fancy I2C mode switch or Stemma connector, so you have to patch D1 and D2 together, and probaby add pullups for SDA and SCL to either 3.3V or 5V yourself. Most programming or configuration software that uses a FT232H to 'talk' I2C cant use a CH341x and visa versa. Check what interface ICs the software you need to use supports. |
| Tantratron:
--- Quote from: Ian.M on November 20, 2024, 03:08:03 pm ---Most programming or configuration software that uses a FT232H to 'talk' I2C cant use a CH341x and visa versa. Check what interface ICs the software you need to use supports. --- End quote --- Many thanks Ian for this hint and guidance so i'll go after a FT232H board to VGA-i2c dialog with the RTD2660 re-directing R/W to the external SPI NOT memory and CH431A with 5V-3.3V modification to directly R/W with grabbers the SPI NOR memory. Normally I should get the same binary image unless the RTD2660 is bricked. Merci beaucoup |
| Ian.M:
That should work. The FT232H chip has 3.3V logic levels but 5V tolerant so can be used with either 5V or 3.3V SPI and I2C with no problems. N.B. The CJMCU FT232H board I suggested does *NOT* have a seperate 3.3V regulator, but the FT232H has one internally, good for only a few tens of mA - enough for I2C pullups and small 8 pin EEPROMs, but *NOT* enough for any target board and maybe not enough for big Flash memories. Be careful *NOT* to short its 5V, its 'raw' unfused USB Vbus and if you short it, either it will burn the board or maybe damage your PC. |
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