[Yaesu] FT-897 Won't Turn On...

[Dr. Gerald N. Johnson]

Chasing the circuit as far as I could with a faulty main board schematic 
in the TS I downloaded from Mods.dk, I see there is about the same main 
power relay as in my 857. That the power switch on the front panel 
grounds the power switch wire and that ground can come from the 
microphone jack or the front panel power switch. Likely it goes to a 
microprocessor that times the button push and if its short switches the 
tuning rate (on the 857) rather than controls power.

I see two circuits to chase. The ground from the power switch on the 
panel unit that goes to the main unit through the RS45 cable and the 
drive to the transistor that runs the power relay, including that 
transistor and the power relay on the PA unit.

The problem reminds me of Motorola Spectra where the front panel power 
switch couples a square wave that's always present with power on to the 
control processor, but when a certain surface mount electrolytic leaks 
liquid out it losses capacitance and won't couple enough power. The next 
stage is that leaked electrolyte eats a trace off the board from under 
that capacitor adding complication to the repair. Nearly every Spectra 
our county bought from the DOT has failed that way. That's why the DOT 
sold them, too great a failure rate. But from what I can tell the power 
control in the Yaesus is DC, not AC.

There has to be some regulator getting standby power to the processor 
that acts on the power switch ground.

Maybe there would be a useful response in trying to power up and do a 
minimal reset, that standby power was consumed by the radio not being on 
often enough, though I've let one of my 857s sit for probably a year at 
a time and not had a problem powering it up yet. I didn't trace circuits 
enough to find that processor standby power.

73, Jerry, K0CQ

On 3/12/2013 1:55 PM, KBØNLY wrote:
> Got another dead Yaesu, seems like its been a recurring trend lately.  This time it’s a FT-897 and it won’t turn on.  Here is what I know, brand new radio, was installed in a emergency communications center and used maybe once a month.  Then one day they went to turn it on and it wouldn’t turn on.  It was connected to an external Yaesu power supply and only a VHF/UHF dual band antenna, no other connections to it.  It had sat for a month or more with the power supply and radio off.  The power supply turns on and output is a perfect 13.8v and I put a load on it, with a 20a load it drops to 13.72v, power supply seems to be no issue.  I tried the radio on my power supply on the bench as well, no dice.
>
> Took it apart and found that Q1031 on the back of the main board was dead and seems to be a common problem, it’s a 2SJ355, part ordered and replaced, no other components seem to be bad that I can find tracing it out.  Everyone says check R1595 which is on the output of Q1031 and its supposed to be a 6.8 ohm resistor, this radio has a 15 ohm resistor in that position, and its marked as such so its not just out of value.  Not sure why this radio has a different value but I know nobody else ever worked on it.  I checked the voltage regulator that R1595 feeds with some micro clip leads and feeding it 12v I got 5v output so the regulator is ok, its on the back of the board and no way to check it while in the radio and connected.
>
> I have checked all the regulators in the radio, all fine when fed power.  The spots on the main board marked 13.8 all have input voltage on them, no drop over the ribbon cable as some have reported.  The radio still will not power up and I can’t find any other faults.  Any suggestions what I should be looking for now?
>
> 73,
>
> Scott KBØNLY
>
>