More tape machine woes: crosstalk in sync only

[RoadrunnerOZ]

Normally across a large board I’d expect 1 - 1 1/2 Ω maximum total plus of course meter lead resistance but 15 Ω is big. Maybe try 1 - 8, 9 - 16 see if they’re half and identical

 

[EmilFrid]

Will do!

 

[EmilFrid]

Update: measuring directly on the back plane connectors I get only 1.5 ohms between GNDs of channel one and sixteen, and the same goes for digital GND, so we can at least rulle out any weirdness on that front. Tonight, I will hopefully have time to go through the machine with ny scope. It's an old tube scope with very few features but maybe it could tell me something.

 

[RoadrunnerOZ]

Set your ground for the scope at the same place as the tape machine. I assume the wall ground is ok and that the tape ground is not being achieved via audio connections but is fully achieved from the wall socket - ie the mains power cable ground is intact?

 

[EmilFrid]

Yes, wall ground is intact. Thanks for the instructions. So am I looking for DC offsets in GND? Haven't done this particular work before, so excuse my stupid questions.

 

[RoadrunnerOZ]

Yes, wall ground is intact. Thanks for the instructions. So am I looking for DC offsets in GND? Haven't done this particular work before, so excuse my stupid questions.

DC offsets and also audio on grounds at the various ground points in the machine like the power supply individual DC supply grounds, cable harness frameworks, head cable shields, headstock and the card grounds - there are different ground runs for the different voltage supplies - three I think on the connector board. Just look for audio leakage where it shouldn’t be.

 

[EmilFrid]

Alright, thank you!