Altec Model Nineteen High Frequency Problem

[QntmLpr34]

Hi. I'm looking for someone who may be able to point me in the right direction to begin troubleshooting/fixing a problem with one of my Altec Model Nineteen speakers. First off, I am a novice... So, I apologize in advance for not using proper technical terms.
I have a set of Model Nineteens that I bought from a garage sale in 1999/2000ish. They both worked perfectly from the time I bought them, until I disconnected them in July 2012. They sat in storage from July 2012-Aug 2016. When I tested them this week, I found that one of them still works perfectly, but the other has no sound coming from the high frequency horn. I undid the bolts on the horn and checked the wires and connections to the crossover. All of those appear normal visibly, when compared to the known-working speaker. I also touched a multimeter to the ends of the wires that clip into the driver at the back of the horn on both speakers and got the same reading.
Does anyone out there in A/V land have a clue as to what the problem could be... Or maybe a suggestion of any further testing I could do to determine the problem?
Any help or suggestion would be greatly appreciated.

[grumpy]

if you've already got the horns out, try swapping them and see if the problem stays with the box/crossover.

[DavidF]

If not tried already, give the response adjustment knobs several turns to see if there has been some build up of oxidation on the contacts.

[QntmLpr34]

Thank you! I'll try that after work tonight. I think I had considered doing that, but worried I might damage the known-working speaker. As I said, I'm a novice. (This might be a dumb question but... ) If I connect the suspect horn to the working speaker first, would there be a danger of it damaging the crossover?

[grumpy]

Keep the volume down, then Nope :)
(you already measured resistance with your multi-meter, right?)
+1 on exercising the knobs.

[QntmLpr34]

(you already measured resistance with your multi-meter, right?)
I'm going to be honest with you, I don't know how to properly read a multimeter. I just know that the one I have was set to test a household electrical appliance. I removed the HF horn from both speakers and touched the black lead to the black wire, red lead to red wire. The meter's needle jumped to, then stayed in, the same position on both speakers. My assumption being, if the meter showed no movent on the suspect speaker, the crossover and/or internal wiring could be malfunctioning. I know I sound like a fool... But I'm trying to learn. Your patience is appreciated.

[grumpy]

No worries. If you are on an "ohms" or "resistance" setting then you'd want
to use a range where you can read something on the order of 5 to 10 ohms.

You may also hear a small scratchy noise coming from the horn while you're connecting the multimeter.

[QntmLpr34]

Since last we spoke, I tried the following:
1st- set multimeter to 10 ohms and touched the leads to the red and black posts on of the driver section of the horn. (Warning: I may be mis-naming the short black cylinder attached to the horn by 2 smallish nuts/bolts by calling it the "driver") During this test, the needle on the meter didn't move, and if a crackling noise is possible during a test like this, I didn't hear one.
2nd- I hooked the suspect horn to the known working speaker. No sound from the suspect horn.
3rd- I hooked the known working horn to the suspect speaker/crossover. Perfect treble sound came out of the known working horn.
Conclusion: the suspect horn is now known to contain the problem.
If you fine folks would be so kind, I will still need help determining what the specific problem is and how to properly repair it (or have it repaired). Any more ideas/suggestions?

[grumpy]

It's odd that it would quit while in storage, but worth checking connections under the driver cover to make sure nothing is loose before investing in a new diaphragm (what DavidF showed).

Sometimes the flat wire loop (visible on the diaphragm's convex side) that becomes the voice coil ... breaks. Then it's a fiddly band-aid fix or a new diaphragm.

[DavidF]

So, I had to delete my prior screwed up post.

I had an original pair of 802 diaphragms that had one of the leads to the voice coil snap. These are shown as the two small red-brown loops feeding down onto the metal diaphragm from the connector on the rim of the diaphragms. The resin coating likely deteriorated and lost its flex taking the thin wire lead along with it.

I ended up sending these off to Great Plains Audio for replacement diaphragms and magnet recharging. That was some years back so not sure of options today.

Anyway, I now you mentioned looking at the wiring of the drivers but not sure you knew to check on these two leads.


73303

[QntmLpr34]

Thank you both, for all the help! That is it, exactly. One of the brown arches that run in right angles between the black edge ring and the silver membrane has snapped. I'd imagine I need to find an authentic replacement pair of diaphragms for optimal performance... But I might at least try to get a used or import replacement from eBay as a temporary fix unless you helpful chaps have a method for repairing that delicate of a piece? Seems pretty much broken. But this thing was so fun and user-friendly to take apart and fit back together that I'm sure it will soon be fixed and see many more years of use here in my living room. Thanks again, Grumpy and DavidF!

[audiomagnate]

That's fixable, but sometimes it's a little tricky; especially if you're not experienced with a soldering iron. The good news is you have nothing to lose so why not give it a shot.