After some further tracing / checks I've identified a potential suspect component (circled in orange on the attached image.
Red line shows the path of the signal (either squarewave when another function is selected, or locked low when squarewave function is selected).
It's an SOC-143 package marked up T5V. I can't find any reference to that online, but based on the readings I've seen and it's position I'm thinking it's a Parallel Pair Schottky Diode. Example would be a BAS40-07 from Infineon.
Datasheet at... (
https://www.infineon.com/dgdl/Infineon-BAS40series.-DataSheet-v01_00-EN.pdf?fileId=5546d4626d66c2b1016d73f7e0bb20ca)
Reading left (+ve) to right (-ve), I get....
Left T5V top pair: 0.311v
Left T5V bottom pair: 0.311v
Right T5V top pair: 0.312v
Right T5V bottom pair:
0.107vReading right (+ve) to left (-ve), I get
Left T5V top pair: open
Left T5V bottom pair: open
Right T5V top pair:
1.227vRight T5V bottom pair:
0.099vI can't see anything obvious in the circuit to indicate why I would see different readings on the right hand T5V to the left, hence I currently suspect this may be faulty.
It would be great to know....
- If anyone agrees / disagrees with this theory (and why)?
- If anyone can determine what the T5V's actually are - does a Parallel Pair Schottky Diode seem likely here?
Thanks.