Yaesu MH-31

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.

Monacor SA-18

left: Original Yaesu MH-31 cartridge, right: Monacor SA-18

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
7. Re-assamble
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.

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