by hvxl » Fri Apr 08, 2016 1:19 pm
The diagnostics all look good. The high-to-low and low-to-high transitions of each opto-coupler are reasonably close. The difference between the two opto-couplers is not relevant.
The logs show that during the times when you have problems you don't get an error response to each message. This gives the impression that the boiler doesn't receive/understand all messages, in which case it doesn't send a response. And when it does, the gateway doesn't understand that response. So you seem to have problems in both directions at certain times, while at other times communication works perfectly in both directions.
I agree with your colleague that this sounds like a bad contact somewhere. Opentherm uses the same two wires for communication in both directions, so a bad contact could easily affect both directions. However, inside the OTGW, the two paths are split up fairly quickly. A problem past that point wouldn't affect both directions. That limits the area where a bad contact would cause the symptoms you describe. It's either in the cable between the OTGW and the boiler, or the circuitry around X2, D5-D10, Q1, R1-R3.
The first simple thing you can try is to swap the wires of the cable connected to X2. Depending on which wire is + and -, the signal goes through either D8 and D5 or through D7 and D6. If that doesn't change the symptoms, you can rule out D5-D8 (unless you have multiple identical bad contact). Next, try a different cable between the boiler and the gateway. If that also doesn't help, recheck the solder joins of X2, Q1, D9, D10, R1, R2, and R3. Since those are only a limited number of components you may even want to just resolder them.
Schelte