I have an FT-101E that's been recapped, trimmers peaked, and has a strong set of tubes that have been neutralized and put out full output on all bands. Everything is operational except for a pronounced hum on transmit. I was hoping for some insight on how I should proceed in tracking down the source....or likely culprits. Any troubleshooting approach would be greatly appreciated! It is still present if the mic is unplugged and the mox is keyed on the front of the radio. All of the boards were pulled and reseated with no change. Thank you in advance!
Yaesu: Ft-101e transmit hum
- Thread starter Champo
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Any chance you have a 12VDC power supply and connector for the radio? Bypassing the internal power supply would narrow down the issue (e.g. no hum with DC supply = internal supply issue).
Regrettably no. I have a DC power supply but unfortunately no DC plug for the radio.
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- Retired 40 Year Firefighter NW Tenn
A hum would be a filter cap in the power supply. Who did the recap job recheck all the caps.
It has been described as if a fan is running in the background during transmit. I know it's not ambient noise being picked up by the microphone because it's present if the radio is keyed without the mic. I was asked to perform a test last night to rule in or out the VFO and or crystal oscillators by using a radio that receives FM next to the FT-101E during transmit. It was definitely more prevalent on AM than FM....if it was on FM at all. I just figured I'd add that to the mix. I have a scope at my disposal. Where would be the best test location to start probing?
prcguy
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Monitor the received audio from another receiver with an oscilloscope and determine the frequency of the hum. If its exactly 60Hz or 120Hz then consider something in the power supply like a bad diode in a bridge rectifier. If its something other than 60 or 120Hz then its coming from another part of the radio.
I'll give that a go tonight and let you know what I find. Thanks!
I think I've isolated the problem to the external fan on the heat pump unit....or it's at least 1 potential cause. The radio ran fine for several hours tonight. It then experienced the hum during transmit. It seemed to coincide with the external heat pump kicking on. I'll need to explore this more. It was only momentarily though (60 seconds) tonight and then it was gone. It wasn't for a prolonged period of time like the other night. I also didn't pay much attention to external causes the other night since it did it from the get go. Nonetheless it was clearly heard during the conversation I was having tonight. I'm not sure if it's the only cause or one of many that the radios susceptible to. Presuming that it is indeed external, and not some intermittent internal issue, is it likely interference coming in on the AC line or external RF? If it is the AC line would a ferrite bead be of any help or something like the Isobar Tripp Lite to isolate the radio enough to potentially reduce it? Any and all solutions would be greatly appreciated.
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Some outside heat pump units use a two connection capacitor (or sometimes two separate caps), one for start capacitance and the other for run capacitance. Not knowing what brand heat pump unit you may have, you'll have to open the panel and look. It sounds to me you may have a run capacitor going bad. They are very easy to identify and replace. Good luck and 73!
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