Yaesu: FT900 Repair Questions

[RFI-EMI-GUY]

I have an FT900 that has been in my closet for many years. It is like new condition, but now apparently not working.

What I have done is the usual CPU reset, both soft and hard.

But I don't think there is a CPU or VCO problem. The radio seems to operate normally from all the controls and display.

What it does not do is transmit or receive. If I operate TX in 10M FM, there is some small amount of carrier and in RX there is FM noise in the speaker. But not a lot of FM noise. Other modes have no sound or apparent RF power. I am thinking the problem is in the IF section of the RF board. I am suspecting the minus 9V inverter. Unfortunately there is no easy point to measure the voltage of this circuit other than inside the can on the exposed lead of the diode and one resistor. The chip iR3M03n2 is on the underside of the board.

I would do more poking but the service manual I downloaded is low resolution.

Has anyone fought this battle before? Thoughts?

Thanks Joe K4SAT

 

[K7MH]

I have an FT-900 but have never had any problems with it...Yet...!
There is a yahoo user group for the FT-900 and there are a few people there that are very knowledgeable about repairing them. Someone there may have a better service manual as well. In fact, it may be in the files section for downloading.

 

[RFI-EMI-GUY]

I have an FT-900 but have never had any problems with it...Yet...!
There is a yahoo user group for the FT-900 and there are a few people there that are very knowledgeable about repairing them. Someone there may have a better service manual as well. In fact, it may be in the files section for downloading.

I requested a subscription and will inquire there. I think the -9V convertor-regulator is bad. There was a bulletin about changing the diode because it apparently burns out the IC. But the bulletin is cryptic. Looks like a very simple fix except that I can't probe -9V directly anywhere on the board as it is apparently all happening on the backside of the board and the one connector it should appear on is a tiny ribbon cable arranged such that I cant probe the pins. Looking inside, these are really pretty nicely built radios. My other radios are all ICOM 575H and 970's so this is new to me. I intend to upgrade so having a working HF radio is next on my list.