I bought bad Mission 753's, T's and x-overs fried, worth fixing?

[planet10]

The tweeters could also be SEAS. I have had some of the models with the 19mm tweeter. They had SEAS part numbers and the same snap-in butterflies.

dave

[rabbitz]

Just to confuse things more, that looks like a Peerless part number (811877) and seems to follow their labelling with Qc etc.

[sreten]

Hi,

Rabbitz is correct - Peerless used that snap in magnet arrangement.



You have a choice of 5 versions from madisound for $7 each ......

/sreten.

[timbert]

Yes, I just found that page, noticed the Peerless snap-in similarity, could not find the exact 811877 number, but looked at the Madison page, and they list part numbers those diaphrams replace but none match exactly, and none are the aluminum ones. Well, for $7 each I'll get a pair of fabric ones and try them. Now, do I need to do anything about the fluid?

[justblair]

Originally posted by timbert
justblair, I've looked at your other helpful posts. I do not have an inductance meter, and was thinking of just replacing the resistors and checking the caps and hoping for the best. I saw your schematic in the other post and will look to see if it appears the same, but I'm no expert.

You certainly could try this. Nothing looks too badly damaged. If your lucky the resisters have acted as fuses for your main drivers. The caps look good. You could replace them with similar values for very little money even for better caps.

Originally posted by timbert
For the tweeters, they are the same as yours and I believe they are Vifa but could not find a current model that looks like this. Here are some pics. Looks like the coil is fused to the magnet because when I pulled it off it started to come unwound. Also, the outer metal shell looks like it was in contact with the outer dome screen, and you can see what appear to be abrasions on the outside surface of it. Is that oil that leaked out of the magnet?

I would guess that the coil will remove with some pressure applied. Looks to me more that the glue holding it together has melted. it probably is just knotted up inside the groove. It may come out

Cant really see abrasions on the tweeter in your picture, but yep that tweeter must have been moving some to damage it. The dome is pretty scratch resistant (I'm clumsy, I know this for sure)

No its not oil (well not really) thats reached out of the magnet, its ferrofluid. It normally sits in the groove, held there by the magnet (Its magnetic you see) You will probably have heard the term before, the stuff basicly acts as a coolant for the tweeters voice coil. Looks like your tweeter had a violent enough death that the fluid splashed out.

Originally posted by timbert
So I guess I need a source for the tweeters, but don't know the original model or its specs so if I have to substitute a more current model and make it fit physically I'd like to not have to mess with the crossover. I guess I'll contact Mission as I doubt I would be able to find tweeters that would just fit right in.

I would be very interested in where this quest takes you. Replacement drivers may be an upgrade I would be interested in.

FWIW, When researching the speakers, I could find little information about them in the public domain though i am rather talentless when it comes to googling. However I believe (from what I have read anyway) the missions cross their tweeters at about 2.1khz. You should be looking I believe for a replacement thats flat in its response to below this figure.

[justblair]

Originally posted by timbert
Yes, I just found that page, noticed the Peerless snap-in similarity, could not find the exact 811877 number, but looked at the Madison page, and they list part numbers those diaphrams replace but none match exactly, and none are the aluminum ones. Well, for $7 each I'll get a pair of fabric ones and try them. Now, do I need to do anything about the fluid?

You were posting as I was.

You can inspect the magnet assembly and find if there is any fluid still there.

I actually just searched it on ebay, it seems an easy item to buy.

Someone else can perhaps advise on how necessary it is etc.

[timbert]

Give me a few days for the parts to arrive and I'll post my experience. I have not heard back from an email to Mission, but I ordered the closest approximate replacement voice coils, in fabric not the original aluminum, and a couple 2.2 ohm resistors, but they only had 10W, not the original 5W, from Madisound. I assume that higher power handling is ok, and that the cylindrical shape, not square cross-section like the original, is ok. I also found these discontinued Peerless tweeters for $10 each on ebay, and they are close to the original model number and appear to be aluminum-domed, but are listed as 8 ohm when my originals are 4. I think I will leave the old fluid in the old tweeters and just put the new coils in and see what happens. Then if that doesn't work I'll install the 8 ohm tweeters, figure out if I have to modify the crossover, and try it. Until today I had never taken a tweeter apart, so I appreciate the confidence and expertise you guys have all given me. Also justblair's schematic appears to be the same as what I have, though the layout is different.

[sreten]

Originally posted by timbert
Yes, I just found that page, noticed the Peerless snap-in similarity, could not find the exact 811877 number, but looked at the Madison page, and they list part numbers those diaphrams replace but none match exactly, and none are the aluminum ones. Well, for $7 each I'll get a pair of fabric ones and try them. Now, do I need to do anything about the fluid?

Hi,

811877 will be a Mission only driver. As I recall the tweeters are
are sandwich, i.e. aluminium foiled fabric domes. Ideally you should
keep the ferrofluid, any differences in the tweeters can be adjusted
carefully with kitchen paper edging mopping up oil.

I'd go for the 811830 diaphragm, level may need adjusting in the c/o.

TBH the main voicing of a speaker does not depend on the tweeter.
I think you will be fine with new diaphragms - also see :

http://www.speakerdesign.net/tweeter...er_tweaks.html

/sreten.

[justblair]

I have had that tweak on my bookmark for some time. Just haven't seen the lambswool that is reffered to on my travels since I vowed to try it.

There is a scholl store in town, I must remember to sweep by it and get some of the lambswool.

The foam blug in the tweeter looks very low tech. I guess there is room for improvement there.

Very keen to hear howyou get on with the fabric dome. If it works, I will try changing over from metal to fabric. Its relativly cheap, and may be an improvement.

[DIY_Peter]

Originally posted by ashok
You should contact Mission first.
When my 780's had problems I contacted them. They offered to replace the woofers for free under warranty but I was the second owner and the warranty was not transferrable. However they sold me two woofers for a very reasonable sum.

Try contacting them.

I have a friend who also had a bad woofer in a mission 780. The man from the shop said that the 78 series all had bad woofers. He had to replace dozens of them. They were made by AUDAX and had a problem with some coating that burned into the isolation of the wires.
After a year or 2, mission noticed the problem and the later models had a new type of woofer.
You should replace the 2 woofers, because the other one will also go bad.