No signal < 0.5V/Div

jaaxx
Posts: 4
Joined: Tue Nov 15, 2016 1:38 am

No signal < 0.5V/Div

Post by jaaxx »

When attempting calibration I noticed that I get a flat trace when I adjust V/Div less than 0.5.

I verified the 0.1 test signal is working correctly with another scope.

All voltages tested correct. R1 and R2 were tested and good. Also re-flowed U1.

Could C2 or C3 be causing this?
jye1
Posts: 1228
Joined: Wed Feb 20, 2013 4:58 pm

Re: No signal < 0.5V/Div

Post by jye1 »

Did you get the same issue if J2 and J4 were used to connect the two boards? Please check the soldering ofthe pin-headers.
jaaxx
Posts: 4
Joined: Tue Nov 15, 2016 1:38 am

Re: No signal < 0.5V/Div

Post by jaaxx »

Re-flowed pins. Same result using either header.

I'm stuck.
jye1
Posts: 1228
Joined: Wed Feb 20, 2013 4:58 pm

Re: No signal < 0.5V/Div

Post by jye1 »

Please check R3, R4, C5, and C6. R3 open or R4, C5, C6 short would cause the problem.
jaaxx
Posts: 4
Joined: Tue Nov 15, 2016 1:38 am

Re: No signal < 0.5V/Div

Post by jaaxx »

Tested R3,R4,C5,C6 out of circuit and all were perfect. Voltages are perfect. Using a JYE140 for power.

Since V2 is 0 with switch to GND, I am assuming U1B is working properly. Could this be U2 then? How to test it?
jaaxx
Posts: 4
Joined: Tue Nov 15, 2016 1:38 am

Re: No signal < 0.5V/Div

Post by jaaxx »

With input set to DC and Test signal set to 0.1V I am measuring 45mV at V2 and 3V at V3
jye1
Posts: 1228
Joined: Wed Feb 20, 2013 4:58 pm

Re: No signal < 0.5V/Div

Post by jye1 »

I might have misunderstood your first post. By V/div < 0.5V/div you might mean settings like 0.2V/div, etc, which represent higher sensitivity. I was thinking the opposite. If this is the case you need to check the branch of R1, R2, C2, and C3. When scope is set to 0.2V/div or higher sensitivity signal will take this branch. For other sensitivity settings the R3, C4 branch will be taken.
Jlough
Posts: 3
Joined: Tue Nov 29, 2016 7:02 pm

Re: No signal < 0.5V/Div

Post by Jlough »

I am having the same issue. During Step 5: Probe Calibration, when I set the TS amplitude to 0.1V and adjust V/DIV from 0.5V to 0.2V the trace becomes a mostly flat line with no zoom in. At 50mV it's a flat line so there is no way to adjust C3.
With the TS amplitude set to 3.3V and the sensitivity at 1V, everything is as expected. When I zoom in on the trace by adjusting V/DIV from 1V to 0.5V, the trace gets taller as expected. At 0.2V and all the way to 5mV, it is off the screen as expected. If anyone has a solution or some ideas, please respond.
jye1
Posts: 1228
Joined: Wed Feb 20, 2013 4:58 pm

Re: No signal < 0.5V/Div

Post by jye1 »

Please check R1 for opening and R2, C3 for shorting.
Jlough
Posts: 3
Joined: Tue Nov 29, 2016 7:02 pm

Re: No signal < 0.5V/Div

Post by Jlough »

I'm new to electronics and inexperienced at testing circuits, so please correct me if I did this wrong. From both sides of the board I did a visual inspection for obvious shorts and couldn't find any. I tested R1 for open from the top of the board by touching a probe to its lead at its label on the board and the other probe to C2's lead at its label and also at R2's lead at its label, and found continuity. I probed the other lesd of R1 with the other lead of C2 and also C4's lead at its label, and found continuity. I probed the other end of R2 to ground and also to the lead on the round side of C3 and found continuity. Continuity from ground to the round side of C3 but not the flat side of C3. Continuity from the labeled leads of R1 and R2 and the flat side of C3, but not to ground. At this point everything looks good.
I have another issue now that I am sure is related. The last time I had it assembled, D2 on the main board smoked and burnt out. D1 is OK. I'm not exactly sure of all that transpired prior to this. I know that after I turned it on I had a flat trace . I was trying to enter test signal mode at 3.3V amplitude, because that is where I had a square wave, but either I couldn't get there or I got there and had a flat trace. Anyway, I'm not sure if the rotary encoder was responding correctly. I tried to do a factory default restore and then it smoked and quit. Any ideas on the cause and how to proceed next?
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