FT-90R Internal Voltmeter Error

[W6EM]

I have an FT-90R that has a 2.8V error on its internal voltmeter.  Reads 11.0V when the incoming is 13.8V.  I have tried a master reset to no avail.  There's nothing in either the manual or the service manual about how to calibrate the internal voltmeter.

If I wasn't going to use it mobile, I could live with the problem.  It did have a bad tantalum capacitor on the incoming DC to the CPU 5V regulator.


Lee
 

[AC5UP]

How do you know the radio really is seeing 13.8 VDC?

If you measured the voltage at the radio end of the power cable, or better yet downstream from the input filter at the PC board connection inside the radio, then you know the DC voltage at the radio. Measuring the output of the power supply doesn't include any voltage drop in the connectors, fuse holders or internal (choke) noise filter. Also wouldn't hurt to measure the DC voltage while in RX and TX, full power into a dummy load, CW, FM or RTTY. Then you'll know how well the PS is doing its job.

Might want to double check the calibration list in the service manual as there should be a step that at least confirms the voltmeter setup.

[W6EM]

The radio is otherwise operating normally.  50W out on high power into a dummy load.  11.0V on receive, 10V or so on transmit.  :-(

If there is an incoming "filter," with 2.8V drop, I should be smelling something.  Looking at the schematic, I'm not even sure how they sample the incoming 13.8V.

I suspect that the fault may have messed up some stored value used for calibration, but the tech manual has no directions on how to recalibrate the voltmeter.

[KB1GTX]

There is a service menu in the ft90, but be careful.  also the volt meter will only be right if the radio is reset with 13.8 volts at the radio..

"Radio Alignment
Connect the radio to a 13.8VDC regulated power source for use on all steps. To access your Alignment Menu, you must build a plug that plugs into the microphone jack of the radio. Wire it so pins 1,4, and 6 are shorted together. Insert the plug while turning the radio on. Upon entering the Alignment Menu, take the plug out. . Use the arrow buttons on the front panel to switch between each alignment item. To save levels , press the DIAL or the microphone's [VFO/MR] button. To adjust manual settings, rotate the DIAL. To change bands while in the Alignment Menu, press [SET] on the front panel. Press [DISP SS] on the front panel to save settings and exit (once alignment is complete). It is suggested that you refer to the "FT-90R Technical Supplement" provided by Vertex Standard."

[W6EM]

Thanks.  I'll take a look.  There is a voltage divider consisting of R2011 (100K) and R2012 (39K)||R2153 that drops the 13.8V down to about 3.8V, the scaled value that the microprocessor sees.

If the alignment menu will permit voltmeter adjustment to correct the error, I'll try that.  If not, R2153 will have to be changed/adjusted to match.  The value of R2153 is not shown ( three *'s) and apparently is unique to each radio.

The radio had a high temperature fault not too far away, and also has been modded, so there's a chance that the resistor values were affected.

[KB1GTX]

There is a menu setting for the volt meter.
Also, if not careful you WILL over heat that radio, it really really cant be in a hot car in the summer or have heat blowing on it.