Dead speaker repair / diagnosing? - Page 1
Forum section: electronics / beginners

author: Mp3
author_rank: Frequent Contributor
timestamp: September 08, 2018, 02:05:26 am
content: Hello everybody,I repair a lot of old Alesis MIDI sequencers. They are pretty simple, so failures aren't too common besides a few causes, however this one i am a little confused byIt has a speaker that is not much different from a PC "beep" speaker. You can tell it to turn the click track on or off, and it'll output a "tock" sound over the speaker. It also is supposed to make a "tock" on power on and power off.This is the first one i've come across though where the speaker does absolutely nothing. I opened it and checked the wiring, no problems there. I then removed the wires from the speaker to test the impedance, and it varied between 8 and 15. It is an 8 ohm, 0.5w speaker so i assume that is fine.I then tried connecting a known good 9V battery to the two speaker terminals but still nothing. I then set my multimeter to AC voltage and put it on both leads going to the speaker. When the click track was supposed to be going, it went back and forth between 0.002v and 0.750v so i assume the click track output is working.edit: I checked the service manual and it makes no mention of the speaker or how to test it if not working.

author: floobydust
author_rank: Super Contributor
timestamp: September 08, 2018, 04:50:08 am
content: Connecting & tapping a 1.5V battery should make the speaker click loudly.If it doesn't, with the battery still connected, press lightly around the paper cone to see if there is a bad connection.Sometimes the bad connection is on the speaker's terminal strip and lead-in wires, so soldering/unsoldering can make the problem come and go.You should get around 8 ohms and not 16 ohms. Otherwise the voice coil goes open-circuit.If you get 8 ohms continuity and no sound, the magnet gap can be jammed stuck, but rare to see this.

author: Mp3
author_rank: Frequent Contributor
timestamp: September 08, 2018, 05:26:07 am
content: Quote from: floobydust on September 08, 2018, 04:50:08 amThank you for your thoughtful reply!First thing i did was tap a 1.5v battery, and was able to get a small amount of fuzz but rarely and was difficult to get. Since you said it should click loudly, i thought maybe it was dead / dying.Then i resoldered the wire and added lots of new solder to the terminals, but still nothing. Still, since it did not pop but make occasional fuzz with a full 1.5v battery, i assume the speaker was dead.i have no idea the history of the machine. Could have been handled roughly. I ordered 3x 8 ohm 0.5w speakers from AliExpress for $3.50 including express shipping, so i will try again with those when they get in.Thank you so much for your help!

author: Brumby
author_rank: Unknown
timestamp: September 08, 2018, 06:07:38 am
content: I'm thinking there might be some contamination or distortion in and/or around the voice coil area, causing it to bind and not move freely. This will give you all the normal electrical test results, but little to no sound. You could try to measure the resistance between the voice coil and the frame. If the insulation of the wire in the voice coil has been compromised and there is contact with the frame, you will see a low resistance. In this case, there is definitely a failure in the voice coil alignment - as it should read infinite.Note - getting an infinite reading doesnotmean the voice coil geometry is OK. It just means there is no metal to metal contact. Things could still be jammed up.Since this isn't anything critical or expensive, simply replace it.

author: Mp3
author_rank: Frequent Contributor
timestamp: September 08, 2018, 07:02:47 am
content: Thanks for the replies guys!I do have the new speakers on the way but i've discovered some more interesting problems with this unit. I will bring it to a new thread, instead of changing this thread's topic & purpose.