[NJARC] 4 pin hall effect sensors?

Thu Jul 6 11:11:18 EDT 2017

MattI feel your pain.  This is exactly the reason why modern electronics non-repairable, especially if it is built with surface mounted components.  The real deal killer is if the unit also contains an ASIC (application specific integrated circuit).  I used to work in the cell phone industry and helped make millions of parts.  But they were only designed for a particular cell phone model and the run rarely lasted for more then a year.  Then it was off to design and build the next generation ASIC.  Vicious cycle!
My only suggestion is to put the sensors under a vacuum to remove the moisture.  Very specialized procedure but it does work.  I have recovered carbon microphones using this technique so I know it can work if moisture is indeed the problem.  This works much better then putting the part in an oven.  Heat is the enemy of electronics!
eBay has one for around $55 including shipping, item number 162447384161.  The one I bought was a glass desiccator and used for storing items under vacuum in the laboratory but this seems to be better for the job.  Of course, you will need a vacuum pump too.
Lots of luck!Jim

      From: Matt Reynolds <mattr04 at hotmail.com>
 To: NJARC Reflector <njarc at mailman.qth.net> 
 Sent: Thursday, July 6, 2017 9:16 AM
 Subject: [NJARC] 4 pin hall effect sensors?

All,
I've been playing around with some old analog junque from the 70s-80s recently.   One of the things I've been trying to convince to work is an old Sony Betamax player, (for fun and curiosity, not necessity).
Evidently the Achilles heel in these machines at this point in time are the hall effect sensors.  They were glued to the drum motors with a glue that wicked moisture and shorted them out.  Without the sensor the drum motor won't spin.
I know next to nothing about these sensors.  The threads about fixing these say to harvest them from working machines, as they are hard to find.  Another alternative is harvesting the drum motor from heads that are shot on other players (the drum motors evidently were the same across several vcr\betas of the time).
I found a seller in Spain on ebay that had two sensors for 20 bucks.  Not interested in that price point as I'm not 100% sure it's the only issue, but the ad does give me a picture I can show all you:
http://i.ebayimg.com/images/g/nzgAAOSwTA9X9AZQ/s-l300.jpg
I was just wondering if any of you had any ideas on where to get one, outside of cannibalizing VCRs?  I've seen hall effect sensors on Ebay but they are all 3 leaded, the old ones in these devices are 4.  Green Brook doesn't have any with 4 leads, and IEI doesn't carry them anymore either.
Just curious if anybody has tinkered with this stuff in the past and might have a stash of them.
Matt

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