Electronics > Repair
CH341A Serial Memory Programmer Power Supply Fix
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impetus_maximus:

--- Quote from: DavidAlfa on June 25, 2023, 09:22:41 pm ---Killing chips is rare, but do you really want to take the risk?
Furthermore, the modification is really simple.

--- End quote ---
well i risked it, and was victorious. (this time)
Ian.M:
Do you also boast about jaywalking on the freeway?

The only reasons *NOT* to do the mod are if you lack the skills to lift a SOIC pin and run some bodge-wires, or if it isn't your CH341A board.  Even the need to work with 5V memory isn't a reason not to, as the switchable version of the mod isn't much more expensive or difficult to do.
Starfox:
Hi I´m new to this Forum and found the 3.3V Fix from here on Google.

So I have modded my CH341A Black Edition, because i want to Flash a Winbond Chip with 3.3V

Only to be sure i have attached a Picture. On the above Pins for 25xxx Chipsets i have now 7 Pins with 3.3V and one Pin with GND (see Picture)

Is this correct ?

Schematic shows 3 Pins are 3.3V original without the 3V Fix

Pin 11,12 and 7 has 3.3V original
Now i have additional 3.3V on Pins 5,6,9,10 (called MOSI, MISO, CS and CLK)
Pin 8 is GND

Only to be sure before i Frie my Bios Chip 
Starfox:
This Voltages are correct i have attached in Picture post above.

Also a new CH341A don´t have to be modified, it switches automaticly to 3.3V when connect to Chip.
uski:

--- Quote from: jakeisprobably on July 16, 2020, 04:32:26 pm ---I think the ACT pin should go low if the chip has enumerated correctly. I have no idea why they made the jumper thing on the side, but according to the chinglish datasheet I believe the ACT pin is just supposed to connect to cathode of an LED with a resistor. The pin already has a 2k2 resistor in series and pin "3" has no connection, but is right beside a power trace. Just add a solder bridge and LED...or check with a meter.

--- End quote ---

I was wondering too... I removed the jumper and realized the CH341A enumerates in serial port mode. With the jumper on, it enumerates as the programmer.

Upon further research I found this in the datasheet:

--- Quote ---To avoid effect 2-wire
synchronous serial interface when using SCL and SDA to configure, the ACT# of CH341 is set to low-level
through 2KΩ resistance during configuration time. The CH341 is enforced as EPP/MEM parallel interface
and synchronous serial interface, it doesn’t detect outside configuration chip forwardly
--- End quote ---

The datasheet is a bit confusing. This double-function of the ACT# pin is only specified deep inside the datasheet and not where the ACT# pin is described. So that's why many people, including myself, are confused as to why this jumper was there.
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