AKG BX 20 problems

[vineyardgray]

Hi SEPP -

Is the new coil wound by yourself or someone you know?    Is the intent to mass produce?

Regards,

Matt

 

[s_e_p_p]

Hej Matt

Yes, it's wound by myself. I still have to tune the maschine a little. It's quite time consuming and complicated to wind it and to apply it to the springs since the diameter of the wire is 20um. But I'm optimistic to bring the BX 20s ( btw the BX15 got the same driver coils) back to life.

Happy new year to you all
Cheers,
Sepp

 

[Sammas]

I managed to fix a busted coil in my BX15 today. It redefines fiddly. That is for sure! I have pretty good eye sight but still couldn't make out where the wires from the figure-8 coils went. I had to pull out a bright light and the biggest magnifying glass you have ever seen.

It was a bit of luck in the end. I wasn't measuring the usual 180 ohm resistance through one of the coils and snooped around. It turned out to be the result of one of the 20um wires had detached from one of the four brass pins as seen in the above pictures. Lucky it was one of the pins on the top! With a bit of gentle prodding with a 1mm (massive in comparison!) tipped soldering iron I managed to get it reattached and working. Touch wood. Hopefully it lasts a while.

Just for some perspective on how fiddly it is, the gap between the magnet in the attached photo is about 5 or 6mm. The wire running out of the coil by that tiny little spring actually contains 4 wires - 2 for each coil.

It is incredible workmanship. You would be better tooled as a watch maker than an audio tech to repair on of these things!

 

[vineyardgray]

SEPP - that is incredible news!    I think mine are all testing good right now, but was worried for the future.    Less worried now!!!

You may have just saved a bunch of BX20's from the dustbin.  Congratulations! 

What resistance readings are you getting? 

 

[s_e_p_p]

They measure 174 ohms. If I tune the length of the coils a little they will end up between 180-190ohms.
Cheers
Sepp

 

[vineyardgray]

Do you know roughly what resistance the pickups should read if they are good ??

The service manual says resistance between pin pairs (+/- 10%):

11 and 12, 21 and 22 = 260 ohms
13 and 14, 23 and 24 = 180 ohms
15 and 16, 25 and 26 = 260 ohms
17 and 18, 27 and 28 = 180 ohms

Hi Sepp,

This was quoted from earlier in the thread.  Looks like there are two different coils - one that should measure 180 and one that should measure 260 unless I'm confused.  Which could be...

 

[blindjohnny]

Yes, this is kinda confusing. No clear explanation in the manual. I suppose it's different for in- and outputs? The BX15 manual states:

2 and 3, 5 and 6 should be 260 ohms
7 and 8, 7 and 9 should be 180 ohms (+10%)

Now more confusing: Mine measures the other way around! It looks like someone has been prodding here before so maybe there was a good reason for changing the connections around?

Anyway I found that one of the connections was intermittent from connector to coil, so hopefully my problem will be solved by replacing one of the connector cables. Then I'm going to close up the box as fast as possible. This scares me... Interesting read though. Keep up the good work!

 

[[email protected]]

And again,

I have removed my last post at Sepp's request, as he is also planning to sell replacement coils.

I have no interest in selling them, just buying some to repair my unit and I know a guy who is making some!

If anyone has interest in following my tech's progress on his run on replacements, feel free to PM me.

Hope that clears things up!

Thanks,

Simon.

 

[s_e_p_p]

Hi

There is something strange with the coil resistances in the BX20 and BX15 manual.
In the BX 20 manual and schematic the 'send'-coils are 260Ohms and the 'receive'-coils are 180Ohms

In the BX15 Manual it's the opposite:
it says 260 Ohms for the 'receive'-coil and 180Ohms for 'sending'.

pin 7 is ground

Sorry for the screenshots of the german manual.
Since I don't own a BX15, just BX20s, I can't proof it. A friend got one and I will measure his soon.
Taking the measurements of blindjonny in account I would say that the manual could be wrong.
What about yours? are there different manual versions out there? Is it worth a new BX15 thread?

S

 

[chops]

How on earth do you solder these impossibly small wires onto the terminals on the gold can?? 

 

[[email protected]]

Hi All,

my tech installed the replacement coils in my unit yesterday and checked all the impedances, voltages etc. Everything is on spec and after a little tuning of the trimpots on the cards we have gotten it to a place where it sounds even with the side of my unit that was not broken and now in general it all works and sounds fantastic!  Feel free to PM me and I will pass on his contact.

Thanks,

Simon.

 

[s_e_p_p]

@chops
solder it 'passively'. put some turns around a wire and heat it up. sometimes it's possible to repair a broken spring end.

 

[musiclandstudioslondon]

s_e_p_p -

in case you were still wondering, Adam @ Funky Junk has just serviced a BX15 we bought and the only issue was the voltages were the opposite to the manual. So it would appear that they are the same as the BX20 and the BX15 manual is a wrong.

Cheers

Graham