| Electronics > Repair |
| CH341A Serial Memory Programmer Power Supply Fix |
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| fudmuffin:
--- Quote from: pupa on July 16, 2020, 12:07:22 am ---Can it read/write/verify successfully? Some units have errors on PCB. The quality systems from China are difficult to control and maintain. So you should check your unit thoroughly for solder bridges or missing components. --- End quote --- No I haven't been able to get it to work. The lack of any voltage on MOSI and MISO leads me to belive the chip is broken internally, though it's strange that is still enumerates from the USB side. No solder bridges or missing components on this one. I've attached a photo of the unit just in case anything's noticeable. I would like to buy a few replacement CH341A chips to try repairing it but the loose chips seem almost as expensive as the fully constructed units. I do have a different CH341A based programmer and it does work, although when it arrived it had a capacitor installed where there should have been a 2k resistor to enable the SPI programming mode (noticed after reading the datasheet). I haven't verified if the other component values are correct. I also had to remove a solder bridge from the underside. Confirmed on this different model that there is 3.3V on MOSI and MISO by default. Attached a photo of this one too. |
| pupa:
Do you read approximate 3v3 to 3.6 volt from the internal regulator on pin#9 of the Ch341A IC i.e same voltage across C4? |
| fudmuffin:
--- Quote from: pupa on July 16, 2020, 01:12:47 am ---Do you read approximate 3v3 to 3.6 volt from the internal regulator on pin#9 of the Ch341A IC i.e same voltage across C4? --- End quote --- yes, 3.47v on pin #9 3.47v across C4 0v on pin #20 0v on pin #22 5.15 going in to the regulator 3.28 coming out of the regulator. |
| jakeisprobably:
--- Quote from: fudmuffin on July 16, 2020, 12:50:41 am ---"...it's strange that is still enumerates from the USB side. --- End quote --- "Enumerates" according to the host PC or the CH341A? 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. |
| fudmuffin:
--- Quote from: jakeisprobably on July 16, 2020, 04:32:26 pm --- --- Quote from: fudmuffin on July 16, 2020, 12:50:41 am ---"...it's strange that is still enumerates from the USB side. --- End quote --- "Enumerates" according to the host PC or the CH341A? 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 --- Finally got a chance to check on this.. I meant it enumerates according to host PC. Under linux I see: --- Quote ---new full-speed USB device number 4 using xhci_hcd New USB device found, idVendor=1a86, idProduct=5512 New USB device strings: Mfr=0, Product=0, SerialNumber=0 --- End quote --- ACT remains at 5v after I get that message on host PC (also at 5v when I plug it into a USB battery i.e. nothing to enumerate with). My other CH341A (mini-USB version pictured above, which works) remains HIGH too (albeit at 3.3v) after I see the same text. I haven't looked into the CH341A enough to know whether ACT is supposed to go low when recognised by the host pc or later during some USB initialization perhaps before chip programming. Thankfully I was able to program the chip for my project using the other working one, but I'd be curious as to what's wrong with my black CH341A programmer, and will test it further in the coming weeks. I may attach a LED as you (and datasheet) suggest so I can see if ACT goes low during a programming attempt. |
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