Yaesu MH-31 microphone: Replacing dynamic cartridge
A couple of months ago – while I was staying in Tyrol and did some portable activities as OE6FTE/7 – I rigged up my gear at a nearby hill to do some contest QSO’s (my common routine on weekends, HI). Desperately trying to make some contacts I finally noticed an outstandingly low SWR. Since I used a manually tuned HF-P1 portable antenna this seemed by far to good to be true. Praying not to encounter a worst case scenario (blown finals, damaged modulator, etc.) I double-checked the setup as well as every single transceiver (FT-857D) setting.
The ALC level finally gave a vital clue: It remained 0 during SSB transmission. A second test on FM confirmed: Microphone damaged. I was happy and mad at the same time. Happy, because a damaged mic is just a bagatelle. Mad, because the microphone had been in use for just 6 months.
For the rest of my stay in Tyrol I used a MH-59 microphone. Back at my primary QTH I talked to Stephan (OE6SWG) at our local ham radio club meeting. He experienced exactly the same problem.
Looking for proper replacement cartridges to fix both microphones I came across the rather inexpensive Monacor SA-18 (approx. 5 € per piece). The replacement procedure is extremely easy:
1. Unscrew the Yaesu MH-31 enclosure
2. Unscrew the PCB
3. Desolder the wires from the broken dynamic cartridge
4. Replace wires with longer ones
5. Solder the two wires to the Monacor SA-18 cartridge
6. Keep the new cartridge centered and fill the void space with hot glue
8. Do some DX with it, HI
Another possible fix would be to replace the dynamic element with an electret capsule as described by OM John, M0UKD.