Kenwood model 741 triband mobile: power-on problem
 

I have a Kenwood model 741 three band mobile with a strange problem.
If the power is interrupted momentarily it will not restart properly.
The word "on" appears and remains for about a minute before the rig
turns off automatically. Resetting the microprocessor and replacing
the two lithium backup batteries didn't help. However, if I
deliberately interrupt the power supply many times on and off while it
displays "on" it will ultimately, by chance, boot-up properly and work
perfectly until the next power interruption. I have $1500 CDN invested
in this rig and I would dearly love to fix it; does anyone have any
ideas?

Paul

"Paul Buchan" wrote in message
om...
I have a Kenwood model 741 three band mobile with a strange problem.
If the power is interrupted momentarily it will not restart properly.
The word "on" appears and remains for about a minute before the rig
turns off automatically. Resetting the microprocessor and replacing
the two lithium backup batteries didn't help. However, if I
deliberately interrupt the power supply many times on and off while it
displays "on" it will ultimately, by chance, boot-up properly and work
perfectly until the next power interruption. I have $1500 CDN invested
in this rig and I would dearly love to fix it; does anyone have any
ideas?

Paul

Go to the Kenwood web site and look for the amateur radio
service bulletins. The first two entries describe memory loss
problems for the TM-231A. Basically the power on reset
circuit fails and does a partial reset on power on. I have a
TM-331A and a TM-431A that have this problem. I haven't
tried to do the repair yet. I also have a 741 that is starting to
act up but it's not really bad yet. The 741 is the same vintage
as the 231 and probably has a similar circuit. I would also
make sure the pins that connect the band modules to the
main chassis are clean and not bent. The 4 wire cable that
connects the control panel to the chassis also should be
checked for good connections.

John

"Paul Buchan" wrote
I have a Kenwood model 741 three band mobile with a strange problem.
If the power is interrupted momentarily it will not restart
properly........

I have a couple newer micro-p controlled rigs that act the same way. PIA
compared to older rigs. Simplest solution is to hardwire the mobile to the
battery and *always* turn it off while starting the motor.