[NJARC] Hall Sensor follow-up story...

[Matt Reynolds]

All,


For those of you who replied with advice and comments on the saga of the Betamax hall sensor issue, thank you.  I thought I'd at least bring you up to speed on my findings, in case some of you ever encounter the same problem for some reason...


Quick refresher for the reasoning, I picked up a Sony Betamax SL-2710 at one of the InfoAge auctions out of curiosity.  It powered up, belt was fine, and output RF modulated signal.  If I hit play, FF, or REW it would run for 3 seconds or less then stop.  Reading into it, I found there was a flaw in many of the Sony machines where the glue used to hold the hall effect sensor in place ends up shorting out the sensor over time (it becomes conductive with age).  Some people have had luck scraping it away, some do not (like me).


Reading online I found a very common way to fix this was to harvest a sensor from other devices that have one in them.  Among things that commonly have them are VCRs, other Betamax players, anything with flat drum motors, like 5.25" floppy drives, etc.  As luck would have it, another Betamax player showed up on a free add (facebook) that was also broken (wouldn't load tapes), so I snatched that.  Lo and behold it had 3 of these sensors (mine only needs one).  Since the machine I picked up was also not working (all the belts were shot, and it seemed to be a "kit" as parts were rattling around in it), I pulled the sensor from this machine.  They looked identical, but mine had no markings, and this one had markings, but nothing intelligent enough for me to figure out which way the sensor should be oriented (is pin 1 on the left or right, on either one? don't know).


I flip flopped around between installing the replacement in the same orientation as it was in the unit I took it from (which was the opposite of the Sony) and hooking it up so that it "looked the same" as the Sony did.  Both sensors had a round "dimple" on one side of the plastic packaging.    I guessed that this could have been a "key" like how transistors generally have a flat side.  Good, bad, or otherwise, I seemed to have guessed correctly (or it's polar and doesn't matter), because the sensor worked, and the video head motor started to spin again.  Yay!


Unfortunately, either the head was already damaged, or is severely clogged, or I damaged it separating the servo motor from the head itself to fix the sensor (I'm going to go with it was already bad.  I don't think I hurt it, but I'm clearly not a trained VCR tech), as the picture is pretty telling that it's shot.  I may have come to the end of the journey on this project for the time being (unless any of you have a NOS Betamax VCR head for some reason?), but at least the sensor portion of the puzzle was solved.


I found sporadic pieces of information on how to test them, and what the difference is between them.  Evidently 4 wire sensors generally use the outer two pins for power, and the inner two for the signal detection.  On three wires they tie one of the power and signal pins together.  I still don't know if there are different sensitivity ratings, orientations, etc.  I'm sure there are.  Whether I got lucky, or it's a "horseshoes and hand-grenades" sort of thing, I dont' know.


Food for thought if you ever run into the issue I guess.


Best Regards,


Matt Reynolds

Capacitor guy

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