[Russell Dawkins]

Could someone please explain how a remote control works, at least how the buttons work.

I have an old Sony VCR remote with numerous non-functional buttons. I can't tell from looking what the operating principle is. I see the squiggly traces on the circuit board and that the part of the button that contacts it is flat black, as if covered with carbon, but I don't know whether this is capacitive or conductive.

In any event, cleaning with alcohol doesn't seem to help.

Any information would be welcome.

Russell

[Brian T.]

Russell,

The main building blocks of a remote control are the buttons, encoder chip and IR transmitter.  The buttons are arranged as a grid connecting rows and columns.  A typical example is shown on page 6 of this application sheet:
http://www.innotechsystems.com/ic4001.pdf#search=%22remote%20control%20IC%22
It sounds as if you have conducting foam buttons which are pressed onto the grid tracks thereby making the circuit.  If cleaning the tracks has not done the trick I would suspect the encoder IC.  Trace the circuit and see if the offending duff switches share a common column or row track.  You may have a faulty chip or a dry joint on one track connection.  If the encoder IC has a type marking you could try looking up the pinouts and putting a meter on the output whilst shorting faulty button potions.

Brian
 

[Russell Dawkins]

thanks for the information, Brian.
Seems to me that remotes often seem to go bad one button (usually the most often used one) at a time.
I never was able to find out whether the basic operating principle was one of conduction or capacitance, perhaps because cleanings I had done using a fine abrasive pen with glass fibers, followed by Caig deoxit seemed to have no effect where if conductivity were the thing, matters should have improved.

I will follow your advice, though, and look carefully for a dry joint.

Russell

[ctviggen]

Using capacitance would be unlikely, as resistance is cheap and easy.  It usually is as simple (row, column) as Brian has suggested.  I worked on a project that was a bit more complex, in that the keypad had a separate chip that would encode the (row, column) output into a 4-bit value (i.e., pressing the number 1 was converted into "0001").  I doubt they use that in remotes, though.  You may also be able to examine the output of the button portion to determine if something is stuck (perhaps one row/column is shorted).  If one column is shorted, selection of a button in another column would mean that the encoder chip could not determine an appropriate column. With no buttons pressed, the output should be either low for all outputs (columns, rows) or high (columns, rows), depending on whether pullup or pulldown design is being used.  Try to figure out which buttons work and what columns/rows they belong to.

Is there a reason why you want to fix this remote?  Usually, one just buys a cheap "universal" remote when a remote breaks.   

[Russell Dawkins]

I need to try to fix it because, not working properly, I can't use it to program a programmable remote!
It is an old near top of the line Sony Beta VCR ($1700 in '87) that I still use to makes copies on. It is one of the few consumer decks that records in Beta I.

The remote is huge and complex (for the time), with a jog shuttle wheel.

At this stage I would  be happy to have just the play, FF, rewind and stop buttons working.

thanks for taking the time, ctviggen

[Rom]

Hi Russ,

Try cleaning the conductive rubber for that button,try alcohol and let it dry. This is how I normally clean those contacts on calculator and it should be of similar technology for those old Sony remote.

I hope these help.

cheers
rom