JYE Tech Forum

Sorry I left off the U2 readings
V4 reading 3.5V
U2
P1 -3.4V
P2 0
P3 -120mV
P4 -4.9V
P5 0
P6 -1.1V
P7 3.5V
P8 4.9V

If you look at the print and V1 is at 0 and V2 is at 0 and V3 is at 0 then should U2 Pin 5 be at 0, then how does V4 call for a 1.6V and I read 3.5V?
I have checked R6,7,8,9,10,12 and R12 and resoldered several times. Along with SW 2 & 3. Does R9,10 and 11 drop the voltage to a 1.6V at V4 but
I see 3.5V (is this what it should be) at Pin 19 of U3 so V4 will read 3.5? Is U3 BAD ?? I am ready to replace U2 or U3 just give me the word !!!!!!!!!!!!!

I should have said R11 and not R12 twice in the last message..
Sorry

If the resistors are good and power supplies are good U2 could be bad. One more test to confirm this. You can disconnect R9. This will make V4 0V since pin 5 is 0V. If V4 is not 0V U2 is bad. I'd suggest you to replace it.

OK I would like to replace U2 and U3. Please tell me the cost and how to order them.
If U2 is the problem then I have a spare U3. If the cost is too high for U3. I will just
order U2. Please let me know.

OK U2 is for sure BAD. With the AV- side of R9 open , V4 reads 1.7V not 0V ?? I guess I don't need U3 yet?
How do I get the U2 Chip (LM6172)??
If you take the 1.7V I read from the 3.5V I see at V4 that makes 1.8V which is very close to the 1.6V that should be at V4 ?

I thought I'd mention my own experience since I've been following this thread while trying to get my DSO 068 working. All voltages were checking out fine for me, but I couldn't get through the first power up test because the bootloader wouldn't work. I had a hunch the crystal might be defective so I ordered a new one from Digikey and I was right. I just replaced the crystal and now LED flashes and the buzzer makes noise. For reference, here is the 20 MHz crystal I ordered from Digikey. It's a little bit larger than the one supplied by the kit, but there is enough space for it.

PN: SER3438-ND

planet581g
Thanks for the info.
I ordered a LM61721M (U2) from Digi-Key and will update the thread when I get it installed.
bigxo

Got It Working

good evening !
I seem to have the dreadful power up test Problem as well. Basically when I press the SW12 Switch it does nothing. A barely squeaking can be herd in the buzzer. All voltages seem to be correct with the exception of V4 that is reading +1,6 V and V5 - 3,33 V. I have checked the resistors and soldering connection. They all seem to be all right. Could it be that U2 is damaged.
I am powering up from USB and I have only installed BOB 4 and BOB 5. The led is not reversed. The capacitors from MCU AT64 seem to be all right.
Thank you very much !