More tape machine woes: crosstalk in sync only

[juanito2008]

I don't know what that last bit is about, if it's a dig at my ability to align a machine or just an unfortunate way of expression.

I don't question your ability to align the machine. I'm only wondering what can cause the problem.

 

[EmilFrid]

@juanito2008 sorry if I came off a bit dry, I've had a crap day and interpret everything in a negative light.
But yes, I'm wondering the same. I did adjust the bias traps since I swapped the head (as described) and thought that maybe I cracked the connector board when pulling and putting back channel cards, but I haven't managed to track down any cracks on the board. I even went through it with a magnifying glass looking like I was a hundred years old trying to find my own obituary in the morning paper. But no crack anywhere. I will keep looking. I will examine everything with the scope first and foremost. As the only thing that has happened is the head swap and bias trap adjustments, the problem is in a broad sense localized. Just need to find the final coordinates.

 

[RoadrunnerOZ]

I agree with you. But how he brakes a ground plane or whatever if he only swapped two connectors ?
He should have done something else in the machine. Recapping, wiring...

Old wiring can go brittle, crack, erode from oxidation and cause all sorts of problems. PCB connections can have dry joints, plugs when pulled and reinserted can cause print to crack - sometimes the cracks are invisible. I fix vintage gear every day and I find sometimes there’s board erosion under the solder mask (the green coating on circuit boards) that’s almost invisible to the eye - the copper is eaten away by either salt or moisture creep corrosion underneath the mask - the only clue is a blackening of the print traces. Sometimes you pull a cable when accessing others and don’t even notice but it causes a fault, you can break a connection where there’s corrosion by simply pulling a plug and slightly moving the connectors. You just need to use logic to look at the actual fault and think of what could be shorted/open circuit/blown and where it could be. Since this is common to all channels and affects all adjacent channels it’s likely a common cable or print trace that has failed - question is where.