My new MK-312BT is also suffering from "Failure 20".
Because all the measurements and scope screenshots I decided to create a new topic - I hope it is OK.
To be honest I am lost. I cannot say I fully understand the signal generation and the test procedure. So debugging is quite a challenge for me.
I will be grateful for any suggestions or observations.
My PCB is 1.3B.
FW is mk312-bt/firmware/Custom Boot Message f005-MK312-BT/ElectrodesReady.bin.
I did few modifications to the MK-312BT but I don’t think any of them is “Failure 20” related.
- R35 and R46 are 220k instead 200k (I guess 10% off is not the problem).
- I didn’t use MAX232.
- I didn’t use battery VREG – I am powering it from lab PSU directly to the battery input.
- I added a reverse protection diode (inspiration from 1.3R).
- I modified MIC input like it is in 1.3R.
- I used 22pin IDC cable and used only 2GND pins (instead of 4).
- I used 42TU200 transformers – some other user tested it and it is supposed to work just fine. Center tap output is not connected.
- I used two 1R resistors in parallel for R30 – I also tried 3 and 4 in parallel to fight the 42TU200 lower DC resistance.
Sometimes the ATMEGA does not startup correctly. The LCD is not correctly initialized (I guess) the top row is full of rectangles, the backlight is ON. The crystal oscillator is ticking correctly at 8MHz. Fuse bytes are correct. I tried to add 100nF cap between RST and GND to slow down the startup time – It made it even worse. The power consumption is 55mA in this case. 5V and 9V rails are OK.
Question – with a “Failure 20” on the LCD the backlight is OFF – is this normal? Also every 10s or so the backlight and output LEDs flashes and nothing else happens.
Power consumption 42mA at 12V.
5V rail: 5.10V
9V1 rail: 8.92V (I might replace 9V VREGs for more precise ones in the future)
9V2 rail: 9.20V
**Signals after power up – Yellow = 5V rail, Red = signal
PB0: no signal
PB1: no signal
LTC1661 OUT A:
LTC1661 OUT B:
LTC1661 – Red = OUT A, Yellow = OUT B:
Red = OUT A, Yellow = U10A output:
Red = OUT A, Yellow = R30 current sensing resistor:
LTC1661– Red = DIN, Yellow = SCLK:
Red = Q1 gate, Yellow = Q2 gate (against ground):
Red = Q3 gate against 9V1 rail (floating scope):
Crystal when the ATMEGA does not startup correctly:
Crystal when the ATMEGA does startup correctly:
// OK, I found it is documented already
I also managed to enter some kind of a test mode. It happened when I tried to measure signal between ground and Q3 gate (floating scope). It also happens when the R30 value is too high – 1R instead of 0.5R. The MK-312BT then boots into this – see the photo. Buttons pressed change one number, Multi Adjust changes other number, and output intensity pots do nothing.
Test mode? When I disconnected one of two 1R in parallel (R30).
Can someone confirm these waveforms?
- Is the voltage at R30 suppose to be so low - peaks are only 100mV?
- Is the output coming from the DAC correct?
- Is the output from U10A correct?
I am unable to measure impulses across transformer coil (floating scope) - it keeps getting into “test mode” - not sure how is this possible.
I will try to desolder and measure all FETs. But I measured each of them before soldering.
Any ideas, please?