I just got some of these to. Do you need to replace the batteries at all? Mine are dead also but they sound fine. Hope you can get an answer and if I find out I will let you know. Tom.
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Here's how they work.First thing - series 80's are not a APOC as used in later 801's and other B&W's. The 80's protection circuit is powered by the battery.If you beat the guts out of this speaker ( with a 9V battery installed) - the speaker will disconnect from the amp (no sound) and the red LED will light up. Turn the volume down and hit the button that has the slash thru the lightbulb and the red LED goes out and the speaker comes back on.The button with simply a lightbulb icon on it apparently is a test button - press it and the red LED lights and the speaker disconnects from the amp. Again -reset by pressing the ligtbulb with slash thru it button.
Later APOC circuits charged a capacitor when you entered the idiot range and disconnected the speaker from the amp and lit a LED so that those truly impaired might notice another symptom beyond the lack of sound.No button needed to reset - just turn down the deafness control and they come right back on.
I'm not sure how great the old relays in these protection circuits sound ( maybe ever sounded?) - but most of the APOC equipped speakers are getting tough to source replacement drive units for - so removing the APOC circuit is something you probably would want to at least think about a bit before hauling out the soldering iron?
Based on Stonedeaf's info that the APOC circuit uses relays, a battery with one quarter the current spec of the original battery may not trip the relays, or trip just a few times then go dead.
This is just a hunch, so you may want to try the lithium batteries and see how long they last in actual usage.
If they are pin & size compatible, any battery is better than no battery.
Geting at the battery is pretty easy.
1.) Use a coin to loosen and remove the bolt that goes down thru the center of the head. It's got a fairly long thread on it - so when completly loosened you'll be able to simply pinch it with your fingers and remove it.
2.) Lift the head off the speaker a few inches - it's got a coiled connecting cable plugged into the top of the bass box.Pull on the plug at the bass box end of the cable - it may be somewhat tight - but will pull straigt up out of the matting socket. Plug is polarized with a notch - so you can't plug it in the wrong way.Don't pull on the cord itself.
3.) Lay the head aside.
4.) The fabric frame is held onto bass box on the corners by a pretty sturdy rubber gromet and metal post combination. From the bottom of the fabric frame- Pull up on the corners and move around the box and you'll find it simply pulls off from the top.
5.) You're going to see a circuit board with two "button" switches on it and a LED - right behind that will either be a long dead ( maybe leaking) battery or a pair of battery leads/clips. This stuff is all located on the right front top corner of the bass cabinet.
6.)Somewhat to my surprise - the batteries are available - must have some industrial application I'm not aware of?
7.) Would suggest replacing them - since in no way will this affect the sound over no battereies at all - and s$#t happens! You have a perfectly functioning and quit wonderful sounding set of speakers -but very understandably - factory parts are no longer really available for the woofers or mids and the tweeters require a X-over replacement in order to be replaced. A working protection circuit just seems like it's worth the trouble.
The only way to tell would be by bypassing one speaker's protection circuit and leaving one stock - playing a mono signal and rolling the balance control.Personally _ I'm not interested - simply because I am more concerned with keeping 'em working so I can continue to enjoy them - over what is probably a subtle improvement ( especially to my abused old ears).John Bowers was pretty damm serious about what he wanted from these speakers - his track record is very impressive and I wouldn't want to bet that what he designed doesn't sound good ( even 30 years latter).
One final note: One of the original ideas for the head was that it would be somewhat decoupled from the bass box - there's a rubber ring that was supposed to help accomplish this on the top of the bass box - if you remove the heads for battery service -consider adding a little "rubber' tape
on top of this thirty year old stuff and when reinstalling the heads - screw them down just tight enough that you can still rotate them side to side - this should be about right.
If anyone knows where i could find a schematic for this series 80 battery powered protection circuit/X-over - I'd be real interested in seeing that -even by the time they got to the next model (F model) - B&W had gone to the self powered APOC that was used for years.