TM-741 backup battery (Strange DISPLAY!)

Mike S.

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Jan 3, 2008, 11:52:06 AM1/3/08

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I have a newly purchased TM-741; It was reported to have HUM on the
transmitted signal at times. I purchased it as-is, and dug into the
unit. (Unfortunately, I have retired from the radio-communications
field, and am still feeling bold...)

The backup battery is weak, at 3.0 volts; I am considering that the
very intermittent hum on transmit may be caused by a the radio's CPU...

The unit seems to TX fine, but the power on 2 Meters is just a bit
low at 35 or so watts. This is of no real concern to me but this might
be a clue to YOU, if this is related to the HUM ISSUE I was told about!
(My DC cabling is less than ideal, so this might be the reason for the
low TX power.)

The backup battery is 3.0 volts; I have new batteries that measure
at about 3.3 volts, so I removed the original. I cannot make one of the
new battery side take solder, so I must get a replacement; I am assuming
that I'd be best off to go to a local battery-specialty store.

Now that I have the battery out, I powered up the TM-741, and see
very STRANGE looking entries on the UHF and VHF MEMORIES. The VFOs work
just fine, and the memories will take a setting; This goes away when
power is removed, of course. I need your words of wisdom on this
matter, also. I am assuming this is a manufacturer-initial-power up
condition.

Thank you!

-Mike-

baw

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Jan 3, 2008, 9:37:29 PM1/3/08

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Your battery was just fine at 3 volts. Just because it was 3 tenths of a
volt lower than a new one was not a problem.

Sarge

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Jan 4, 2008, 4:54:10 AM1/4/08

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Put the batt. back in. When you say tx power is low, what voltage are you
feeding it with.? If you're not giving it a good 13.8 to 14 volts the tx
will be low. as for the hum, could it be a mic problem?

"Mike S." <s3ha...@yahoo.com> wrote in message
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Fred McKenzie

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Jan 5, 2008, 2:48:12 PM1/5/08

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In article <Wo8fj.1355$Sa1....@news02.roc.ny>,
"Mike S." <s3ha...@yahoo.com> wrote:

> I have a newly purchased TM-741; It was reported to have HUM on the
> transmitted signal at times. I purchased it as-is, and dug into the
> unit. (Unfortunately, I have retired from the radio-communications
> field, and am still feeling bold...)
>
> The backup battery is weak, at 3.0 volts; I am considering that the
> very intermittent hum on transmit may be caused by a the radio's CPU...

Mike-

I agree with Sarge. I have the TM-742, and replaced the battery before
it was necessary. I had no trouble with the ten-year-old battery!

The hum is more likely due to either a loose shield connection in the
microphone cable or a magnetic coupling between the microphone and a
power supply transformer (or nearby wall-wart). It could be from a bad
filter capacitor in your power supply, but that would probably not be
intermittent.

One other possible cause of hum, is tone-coded squelch (CTCSS). When
you have the tone turned on, it is a sub-audible audio signal with about
3/4 KHz deviation. Its frequency is in the range of about 50 to 200 Hz,
which compares to 60 Hz (or 120 Hz) power hum.

Fred
K4DII

Stanley Miln

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Sep 25, 2008, 3:38:46 PM9/25/08

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The Hum could also be over loading your power supply.
The 741 should pull about 8 to 10 amps for
50 Watts on Two Meters.
Also Make sure the Hum is not your PL Generator
on Simplex or a Carrier Squelch repeater..
The 741 go back into the Late 1980's and early
1990's.
Stan
"Sarge" <sa...@myhouse.com> wrote in message
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