Yaesu: HT Battery Terminals on old radio

[Murphy625]

My neighbor gave me an old Yaesu FT-51r with a dead-as-a-rock battery. I'd hate to see a fine piece of equipment go to waste as this was apparently one of the better HT's made back then.

I'd like to see if I can get the radio powered up but am a bit confused on the terminals.

The radio has four pins that connect to the battery and when I downloaded the schematics, they're labeled as ADAPT, BATT SEL, GND and BATT.

Upon reviewing the diagrams, I can not figure out what the ADAPT and BATT SEL terminals do.

When I went through the service manual, the calibration procedures call for 11 volts to be applied to the two small PCB terminals in the bottom left corner of the diagram. The PCB test terminal is electrically the same as the ADAPT terminal.

The radio can take three different batteries.. either 4.8v, 7.2v or the larger 9.6v pack which allows a full 5 watts.

Can I just apply 9.6 volts to the BATT terminal and ignore the ADAPT and BATT SEL contacts? Anyone know anything about this?
Here's the diagram:

 

[mmckenna]

ADAPT is the AC or DC adapter connection. If I recall correctly, the adapter connection looked like a battery holder with a cord coming out. You can see it's got a protection diode and some capacitors that the battery connection doesn't, likely for filtering noisy AC-DC power supplies.

BATT SEL was probably for sensing different chemistry/size batteries and might have adjusted the RF power output level depending on which one you were using.

Looks like you could apply +9.6 volts to the batt connector and the negative to the ground connector and it should work fine.

Manual is here: http://www.radiomanual.info/schemi/YAESU_VU/FT-51R_user.pdf
9.6v gave you the full power output, lower voltage batteries reduced the RF out.

 

[Murphy625]

ADAPT is the AC or DC adapter connection. If I recall correctly, the adapter connection looked like a battery holder with a cord coming out. You can see it's got a protection diode and some capacitors that the battery connection doesn't, likely for filtering noisy AC-DC power supplies.

That makes sense.

BATT SEL was probably for sensing different chemistry/size batteries and might have adjusted the RF power output level depending on which one you were using.
.

At the lower 4.8 and 7.2 volts, the unit only puts out 2 and 4 watts.. but with 9.6 volts, it puts out the full 5 watts.

If I plug 9.6 volts into the BATT terminal, am I going to get 5 watts? Or is the lack of any connection to the BATT SEL terminal going to reduce power?

 

[mmckenna]

I can't tell, you'd need to give it a try.

 

[Murphy625]

Thanks for the help, really appreciate your input..

 

[AK9R]

Replacement battery packs are still available for that radio from 3rd party battery dealers like Batteries America.

 

[Murphy625]

Replacement battery packs are still available for that radio from 3rd party battery dealers like Batteries America.

I know, but I don't want to invest in a $50 battery pack before I'm sure the radio works properly.

This thing has crossband repeat.. can you believe that? An HT that does crossband repeat is just to cool to throw out in the garbage.

Besides, if I can get it working, I might just 3d print a battery case for it.. even if its not perfect, I don't care, so long as it works.

 

[jaspence]

FT-51r

I still have my 51r in very good working condition. They were a big step forward at their introduction. The FT-11 and FT-41 followed and are also quality radios. Very expensive for the time, $400+ if I remember correctly for the 51. See RigPix or https://www.eham.net/reviews/detail/376 for more info. Programming software was available as they were more complex than the average radio of the day. Great find. Have fun!