GRUNDIG GDM313 mic disassembly?

[ben]

I picked this up some time ago at a flea market, but the cable has been abused and sound is intermittent. I want to open it up and replace the lead, but can't for the life of me work out how to get the head off. Anyone know? TIA!

[Reelman]

I have wondered the same thing myself for the last 50 years! I reckon either there is a screw under the label or the metal head is glued in. Never had the courage myself to investigate further, nice mics, came included with TK121, 141 etc tape recorders. Dual impedance I believe via internal transformer.
Do let us know how you get on, good luck.

Peter

[DMcMahon]

I had one of these (or maybe the GDM 314 which I think is basically the same) apart a while back because it had stopped working, could not easily find the fault.

Cannot remember it being difficult as such, I need to find it to refresh my memory.

David

[vidjoman]

The RM site says 'made of plastic, head glued on'

[ben]

Thanks for the responses. So far no joy. I have tried gripping and 'unscrewing' the head from the black body but it won't budge (may try this with a vice). Must be fixed with Garrard Grease or something I also tried 'lifting' the metal mesh over the mic insert by inserting and levering a small hook in some of the holes, but that too wouldn't shift.

The loose connection is either in the lead where it exits the body, or inside on one of the connectors. It's so frustrating, as this would be a 5 minuite fix.

I think the hacksaw may have to come out soon!

[DMcMahon]

I have found my GDM 314 and I now see I previously only got inside the DIN connector to check the wiring and the transformer (which resides in the DIN connector) and like Ben I also cannot remove/get inside the head.

David

[Reelman]

Any developments?

Peter

[ben]

It's still sitting on the desk looking at me, daring me

So far I have only tried gripping, twisting, pulling, but will likely end up putting it in a vice and using more force.

I would really love to know what the hell they glued it toghether with.

[DMcMahon]

No progress on my 314 either, like Ben will have to resort to extreme force I think.

David

[ben]

I peeled away the silver trim/model badge and the exposed recess suggests that the metal head extends down into the black body some way, there's a sort of internal collar by the look of it.

[DMcMahon]

I tried unsuccessfully to remove the silver badge label on my GDM 314 but only managed to scratch the surface.

After eating spinach I tried extra hard and managed to remove the top black piece by twisting the body in one direction and the black top piece in the opposite direction. With the top microphone insert lifted out there is a large circlip visible which I have not tried to remove yet.

David

[DMcMahon]

Looking at some photos of the GDM 313 I see that although similar to the GDM 314 there are differences so the 313 head fixing method may be different.

On my 314 the head was not glued to the body.

David

[DMcMahon]

On my 314 removed the circlip which just fits in a groove around the inside of the body, its only purpose appears to be for the microphone capsule assembly to sit down against, the screen of the 2 core screened cable from the DIN connector is also soldered to the circlip.

I think the capsule flat wire screen may also have been soldered to the circlip, this broke off when removing the head.

The microphone capsule is shown on the schematic as 200 Ohms impedance, my one is totally open circuit so looks like this microphone will be heading for the bin.

David

[DMcMahon]

Originally Posted by DMcMahon

After eating spinach I tried extra hard and managed to remove the top black piece by twisting the body in one direction and the black top piece in the opposite direction.

David

This was achieved by holding the microphone body in left hand with the head pointing to the right, then using right hand strongly trying to rotate the head clockwise while keeping the body either stationary or trying to rotate the body anti-clockwise. This feels like it is the incorrect direction to loosen the head.

If the head moves then after around 45 degrees rotation it can then be pulled away from the body.

David