Yaesu FT101EX... where should I start looking for these 2 problems?

I was screaming into a known-good mic. Not nice words either.

 

Do you have anything plugged into the patch port on the back? That will mute the mic. Also, do you get any modulation when it's in AM mode or just a carrier?

 

Nothing plugged in. I get modulation when in AM mode if I'm reading the oscilloscope correctly.

 

Do you see peaks that move along with your voice when looking at the oscilloscope? Or is it just steady?

 

When I key the FT101 in AM mode, the 2 lines get fat but appear to have no wave forms. When I key it in LSB/USB, nothing changes-- the oscilloscope lines stay steady and flat.

By contrast, when I key my (functioning!) Kenwood 520 in LSB or USB mode, one line shows regular triangle wave that doesn't change amplitude and the upper line goes nuts. I can't compare AM because the 520 doesn't have it.

 

What kind of microphone are you using? I found the microphone needs to have at least about -60 to -50 dBV output. Many low impedance dynamic mics do not have sufficient output.

 

I have tried both the microphone that came with the unit (of uncertain provenance), and a Kenwood MC50. Both work on the TS520.

 

The MC50 should work if it is set for 50K output impedance ( output -56 dB ). If set to 600 ohm output impedance, it will not work ( -76 dB ).

 

It's at 50k. Too bad...

 

Okay so what happens if you drive some audio into the rig via the patch port on the back. Put a tone from a computer or something into it and set the PTT to MOX and see if you get any output at any level that way. Have you cleaned the mode switch? All of the audio and control routing goes through there. If one of those connections aren't clean the AF amp won't get turned on, which is what sounds like is going on here.

 

I will clean it again. It certainly won't hurt anything, as long as I don't make the waferboard break down. Thanks for the word.

I'll also figure out how to inject some tone in there.

 

All of the inputs and outputs for the Audio board are easily accessible from the underside of the edge connector. Also you may want to try reseating the AF board if you haven't already.

So the AF board, it outputs its signal from Pin 8 to the Mod/Osc board Pin 9. You can monitor the AF amp output here, you could also inject audio directly into the mod/osc board if you like. If you get modulation injecting audio at Pin 9, it's at the AF board. If you still get no modulation then its the mod/osc board.

 

As above - that's what makes these rigs one of the easiest to work on !

Have you checked that your Mic is wired to the correct pins on the plug?

If so, it sounds like you have a problem with the Mic Amp. I presume you have cleaned the Mic Gain pot? Have you tried simply unplugging the Audio board and cleaning the edge connector?

While it's out, visually inspect the components around the Mic amp circuit (the photo in the Handbook will help you identify them) . . . I've never seen it here in Britain, but some of those brown capacitors have been known to split in the USA.

Also . . . you said you adjusted the Voltage pot to set the S Meter . . . I presume you meant the S Meter pot, not the 6V Regulator pot?

Even so, it should be reading about S9 + 40dB on the Calibrator signal on 80m ! (the correct place to set it properly is on 14.200 . . . with a Dummy load connected, it should be set to S9 + 25dB)

Roger G3YRO

 

It's been decades since I've own either radio but it appears the mike wiring is different.

 

They all seem like they're different to me