Friday, August 8, 2008

Blown VHF Finals in a Yaseu 857D

I am officially a member of the infamous "Blown Finals Club" of Yaesu 857 and 817 owners.
Today, after a $230.00 repair bill and FedEx shipping both ways I have my radio back from the Yaesu Service Center in California and other than a huge void in my wallet, life is good once again.

So how did this happen?

I'll never know what caused the final VHF transistor and several capacitors to suddenly fail but at the time I was using the radio to transmit thru a 45 watt in - 170 watt out linear amplifier. The antenna is a 2-meter 5/8 wave ground plane that I've been using for months. Likewise, the 857 has been transmitting thru this amplifier for many months though the amplifier is almost always off.

This time I was transmitting about 45 watts FM on 146.52 into the amplifier (now switched on) and carried on a simplex QSO for a few minutes. We then switched to 144.20 SSB and continued the QSO briefly. I was still using the amplifier, only this time the rocker switch was switched to SSB. Having an unsuccessful QSO I switched the Yaesu 857 back to FM and changed frequency back to 146.52. I keyed the mike and became aware that I was not transmitting. I noticed the amplifier was still switched to SSB so I flipped the switch on the amp back to FM. Still no transmit power from the 857.

I tried several tests in various configurations, first without the amplifier. I found that I was actually able to be heard on the local repeater although I was reported quite noisy. This led me to conclude that I was transmitting with at least the driver stage of the transmitter. I switched to a good dummy load and then monitored my 2-meter transmissions on a VX5R handheld I had in the shack. Everything sounded well -- good audio etc.

At this point it became painfully obvious I had a blown PA transistor. By the way, the radio continued to function properly on the HF frequencies. Only 2-meters and above were affected.

I carefully packaged the radio in its original box and with a humble letter enclosed I sent it on its way to the Yaesu hospital in California.

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