No video on transmit

[G4HTZ]

Well rewired connections over the weekend and this morning fed FM board into minitoune at suggested via attenuation but still nothing decoded .

Timing lock doesn't seem to alter , if it does it just jumps about then stops again .

No access to scope
Tried to upload screen shot of minitoune but won't upload .....another faliure

No internet in shack in garden so will have to bring it indoors at some point to try the other suggestions

At least ugly mode working

[G8GKQ]

Hi Steve

Some questions to help us help you. With the unit set to transmit in IQ mode, 333KS and pattern input:

Using a test meter, please measure the voltage at the I+, I-, Q+,and Q- testpoints near U41 on the F-M board.

Next measure the voltage on each pin of J01 (all 4 pins in turn please)

Then, the voltage on each pin of J02, (again, all 4 pins in turn)

With these 12 readings, we might be able to work something out.....

Dave

[G4HTZ]

Hi Steve

Some questions to help us help you. With the unit set to transmit in IQ mode, 333KS and pattern input:

Using a test meter, please measure the voltage at the I+, I-, Q+,and Q- testpoints near U41 on the F-M board.

Next measure the voltage on each pin of J01 (all 4 pins in turn please)

Then, the voltage on each pin of J02, (again, all 4 pins in turn)

With these 12 readings, we might be able to work something out.....

Dave

Dave
Measurements as requested ....sorry meter is only a cheap eBay one

I+ 0.437mv
I- 0.91
Q+ 395mv
Q- 0.91

JO1
1 10.7mv
2 1.5v
3 10.7mv
4 1.51v

JO2
1 10.7mv
2 10.5mv
3 3v
4 10.6mv

[G8GKQ]

Hi Steve

I have an idea. Please could you check the voltage at the junction of R03 and R09 under the same conditions? It's easy to find at the left side of R03 as shown with my probe on it in the photo below.

Dave

[G4HTZ]

Hi Dave
Voltage reading 4.53 volts

There does seem to be a 1/2 volt low discrepancy on my meter after checking it on too different 13.8v supply's ...just for info
Regards
Steve

[G8GKQ]

OK Steve

That voltage should be 2.5V when you are on transmit (and the J01 voltages are about 1.5V). I think that you might have the pin numbering reversed on J01 (ie 1-4, 2-3, 3-2, 4-1) as, although you have a signal at the input to the opto-isolators, you have no signal at their output.

If that is the solution, it might be worth double-checking J02 as well.

Dave

[G4HTZ]

Hi Dave
Just checked gpio to fm board wiring and all seems ok ...assuming that the square solder pad is pin 1 in all cases
Regards
Steve

[G4HTZ]

Also checked it against the picture that's on the internals of .G4KLBs ? On the wiki and it's wired the same

[G8GKQ]

OK Steve

The problem seems to be (referring to this circuit diagram https://wiki.batc.tv/images/5/5b/PdFM_V2_Sht_1.pdf) that the signals on J01 pins 1 and 2 (which you have measured at 1.5v - the value I would expect if they were alternating between 0 and 3.3v from the PI) are not causing any change in the voltage at the output of the opto-isolator (pin 5 of U01). This is the 4.53V that you measured at the junction of R03 and R09. The same seems to be happening for the Q channel.

As a test, you could disconnect J01, so that RPi is isolated. Then connect J01 pin 1 to ground (it is not grounded through the PCB) and J01 pin 2 to +5v. Then measure the voltage at each end of R01 (between U01 and J01. One end should be at +5v, the other at between 2 and 3v. With the 5v still connected to J01, check the junction of R03 and R09. It should be less than 1V, rising to 4.5v or so when you disconnect the 5V from J01 pin 2.

Please let me know if this works.

Dave

[G4HTZ]

Hi Dave
Results more or less in line with your predictions....given my low reading meter !!!

Volts at RO1 junction UO1 and JO1 4.6v and 1.5v

Test at junction RO3 and RO9 43mv 5v on ......4.5v when 5v disconnected

Cheers
Steve