Mfb 587 mid doesn't work

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spolat75
Berichten: 8
Lid geworden op: 21 mei 2022, 19:53

09 sep 2023, 00:49

Hi everyone,

I noticed that the mid driver of my one of 587 doesn’t work however the mid sounds come from the bass. It’s like two ways box like 586. I tested the boxes using a 700hz fixed slgnal. The sound was from only the mid driver on the right box as expected however on the left box it was from the bass driver and mid driver was silent. I didn’t feel any movement when I touch it. Is it something that can be fixed easily or I need an expert?
snameroc
Donateur
Berichten: 8348
Lid geworden op: 01 mei 2010, 13:45

09 sep 2023, 10:02

Mostly is the relay the problem. Sometimes is the coil of the midspeaker broken. It is possible to repair if you have some electric skills. Do you have a multimeter and test the coil of the mid?
spolat75
Berichten: 8
Lid geworden op: 21 mei 2022, 19:53

09 sep 2023, 11:44

I have multimeter and I can check the mid driver coil. However I don’t understand why I hear mid sounds from woofer. There should be no sound if mid driver was broken. Does the circuit send mid frequencies to woofer when mid is broken?
snameroc
Donateur
Berichten: 8348
Lid geworden op: 01 mei 2010, 13:45

09 sep 2023, 12:02

Normally not.
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Thomas
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Berichten: 12285
Lid geworden op: 16 jun 2005, 15:55
Locatie: Lochem, Gelderland
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09 sep 2023, 12:14

It is possible that you hear some midrange Sound from the woofer because of overlap frequencies. You can exchange the electronics to check what happens. Another option, maybe someone has been working on the box and did not replace the connectors correctly? In that case, speakers get incorrect signals.
Thomas Baur
webmaster http://www.mfbfreaks.com
De Enige Echte Philips Motional Feedback Website!
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Remi
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Berichten: 12072
Lid geworden op: 16 jun 2005, 21:04
Locatie: Didam

09 sep 2023, 13:32

The 587 is also know for muting the mid due to a bad capacitor (small elko) in the signalpath of the mid.
If you can measure a decent resistance on the mid connector it is very likely the capacitor is causing your problem.
"Hoezo nu wel genoeg? D'r is toch nog plek!" jaja, waar dan? "Ha! d'r kan nog wat in de auto!"
spolat75
Berichten: 8
Lid geworden op: 21 mei 2022, 19:53

09 sep 2023, 16:31

I replaced the electronics and it worked well. So the driver is good. The connections were exactly the same as the other box, so it looks like something is wrong with the electronics in that box. I will take the box to an electronic guy to check the capacitors.

Thanks for your helps !
spolat75
Berichten: 8
Lid geworden op: 21 mei 2022, 19:53

11 sep 2023, 18:34

When replacing the electronics I noticed two capacitors (or whatever) soldered on circuit back side (the pictures below). I don't know what was the problem, so they did this repair. Maybe some of you can understand if it's a good solution or just a quick shortcut just to keep it working.

Thanks,
Bijlagen
IMG_1332.jpg
IMG_1331.jpg
IMG_1334.jpg
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Thomas
Site Admin
Berichten: 12285
Lid geworden op: 16 jun 2005, 15:55
Locatie: Lochem, Gelderland
Contacteer:

11 sep 2023, 21:18

These capacitors like all others Will fail in time. Those two were already replaced by someone who did not want to open the board to put them on the correct side. Not pretty but it works.
Thomas Baur
webmaster http://www.mfbfreaks.com
De Enige Echte Philips Motional Feedback Website!
snameroc
Donateur
Berichten: 8348
Lid geworden op: 01 mei 2010, 13:45

11 sep 2023, 22:32

If you got complete nothing of sound out of the mid the capacitors are not the reason. The are indeed oftley the reason of trouble and mostly the mid and or the tweeter are lower in output than normal, but if you got compleet silence there is at least something els.
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