Power Up Test DSO 068

[bigxo]

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

[bigxo]

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 !!!!!!!!!!!!!

[bigxo]

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

[jye1]

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.

[bigxo]

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.

[bigxo]

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 ?

[planet581g]

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

[bigxo]

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

[bigxo]

Got It Working

[leonardmuresan]

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 !