Repair for broken Dolby and EQ switches on RX-505

Hints and Tips

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RX-505 Dolby On-Off / Dolby B-C / Eq 70-120 switches no longer lock in place? Here’s the fix:

 

The problem is that there is a tab on the switch shaft which a small wire hook locks into to hold the shaft in place and keep the switch depressed.  That tab breaks – it’s only plastic and tiny.  I’m sure it will break every time if you try to remove the button caps when the switches are depressed.  The three interlocking switches for tape type use the same shaft but don’t use that lock tab so it won’t have broken.  The trick is to switch the shafts.

 

Remove the switch block.  Easiest way I’ve found is to remove the metal face, then the meter / Level / Switch face, dismount the switch board, then CAREFULLY de-solder the switch from the board as it dangles from the face of the unit (not fun but easier than completely disconnecting that board).
Remove the faulty locking switches from the switch block by bending the metal tabs which hold them in place back enough to allow the switch to slide out.
On the interlocking end of the switch block, find the small spring steel plate at the side of the last switch.  Slide a needle or pin through the square hole at that end and slide it under the spring flap.  Slide that plate out far enough so that the hooked tab on its end is clear from the metal face of the switch block.  The purpose of that tab is to move the sliding plate which locks the interlocking switches in place.  You should be able to see the end of that plate through the front square hole at the end of the metal switch block.  Use some pointed object to slide that plate toward the end of the switch block.  This will free all three interlocking  switches for removal.  Leave the end switch in place if you can and remove one or two of the other switches for the swap.
Now comes the tricky part.  Note that each switch has one tab on each side which holds the top to the bottom.  GENTLY pry the tabs from each side just enough to slide the top off.  BE CAREFUL HERE.  THE SPROING FACTOR IS VERY HIGH.  Now you should be able to slide the switch shaft out.  The orientation of each part is important since the shaft is not exactly centered so nothing will reassemble if it’s backwards.  Once you have done this step with both a locking and an interlocking switch, you’ll probably notice that one is DPDT and one is FourPDT.

GENTLY remove the switch contact wipers from the good shaft  and mount them on the bad shaft.  They won’t slide straight off, but will rock off the end, then rock back on the other shaft.  Both switches can now be reassembled.  You need coordination here.  Once reassembled, check all the continuities before going on to make sure all the wipers are making good contact and that none got bent too far in the swap process.

 

Replace the repaired switches into the block, bend the tabs back to hold them in place.  Slide the locking plate back into the block and slide the spring plate back over the end of the plate to apply enough pressure to keep the interlock working.  Solder the block back onto the board and reassemble.
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