TR751 Power Out and APC adjustments

[John]

I have just got my TR751 working. (Kenwood 2m multimode transceiver)

Does anyone have details of the APC adjustment procedure? Also details of
which pot controls power output in Hi power position. I am getting nearly
40 Watts out on FM in to 50 ohms whereas the spec says 25 Watts. I want to
turn power out down so as not to stress the output brick.

Thanks

[John]

Post by John
I have just got my TR751 working. (Kenwood 2m multimode transceiver)
Does anyone have details of the APC adjustment procedure? Also details of
which pot controls power output in Hi power position. I am getting nearly
40 Watts out on FM in to 50 ohms whereas the spec says 25 Watts. I want to
turn power out down so as not to stress the output brick.
Thanks

I'm not sure what you mean by "APC adjustment procedure".
The complete transmitter adjustment covers two and a half pages and
requires a lot of test equipment. RF voltmeter, frequency counter,
power meter, DC voltmeter, linear detector, oscilloscope, spectrum
analyzer, and AF voltmeter to name most of them.

The power adjustment is the easy part.
Place the radio in front of you with the controls toward you.
Remove the top cover.
In the right rear you will find VR4, VR3, and VR7 close together
on the composite unit (TX) board. They form a triangle.
VR3 is the low power adjust
VR4 is the high power adjust
VR7 is the CW break in delay

Low power is supposed to be adjusted for 5 watts
High power is supposed to be adjusted for 27 watts

Power should be adjusted with the radio in CW mode.
A VHF capable 50 ohm dummy load must be used for the adjustment.

Be careful - there are three VR3 and two VR4 pots in the radio.

John

[John]

Post by John

Post by John
I have just got my TR751 working. (Kenwood 2m multimode transceiver)
Does anyone have details of the APC adjustment procedure? Also details of
which pot controls power output in Hi power position. I am getting nearly
40 Watts out on FM in to 50 ohms whereas the spec says 25 Watts. I want

to

Post by John
turn power out down so as not to stress the output brick.
Thanks

I'm not sure what you mean by "APC adjustment procedure".
The complete transmitter adjustment covers two and a half pages and
requires a lot of test equipment. RF voltmeter, frequency counter,
power meter, DC voltmeter, linear detector, oscilloscope, spectrum
analyzer, and AF voltmeter to name most of them.
The power adjustment is the easy part.
Place the radio in front of you with the controls toward you.
Remove the top cover.
In the right rear you will find VR4, VR3, and VR7 close together
on the composite unit (TX) board. They form a triangle.
VR3 is the low power adjust
VR4 is the high power adjust
VR7 is the CW break in delay
Low power is supposed to be adjusted for 5 watts
High power is supposed to be adjusted for 27 watts
Power should be adjusted with the radio in CW mode.
A VHF capable 50 ohm dummy load must be used for the adjustment.
Be careful - there are three VR3 and two VR4 pots in the radio.
John

Thanks a lot for the info John. Have now adjusted power o/p as you suggest.
Am I right in thinking that you have a TR-751 ? On SSB mode my 751
receiver background noise is very quiet although the RX is quite sensitive.
What is the background noise on SSB mode like on your 751 ?

Does the service manual run to many pages ? Do you have a scanned copy by
any chance ? I do have access to all the necessary test equipment in your
list.

John G3UGY

[John]

Post by John

Post by John

Post by John
I have just got my TR751 working. (Kenwood 2m multimode transceiver)
Does anyone have details of the APC adjustment procedure? Also

details

Post by John
of

Post by John

Post by John
which pot controls power output in Hi power position. I am getting

nearly

Post by John

Post by John
40 Watts out on FM in to 50 ohms whereas the spec says 25 Watts. I want

to

Post by John
turn power out down so as not to stress the output brick.
Thanks

I'm not sure what you mean by "APC adjustment procedure".
The complete transmitter adjustment covers two and a half pages and
requires a lot of test equipment. RF voltmeter, frequency counter,
power meter, DC voltmeter, linear detector, oscilloscope, spectrum
analyzer, and AF voltmeter to name most of them.
The power adjustment is the easy part.
Place the radio in front of you with the controls toward you.
Remove the top cover.
In the right rear you will find VR4, VR3, and VR7 close together
on the composite unit (TX) board. They form a triangle.
VR3 is the low power adjust
VR4 is the high power adjust
VR7 is the CW break in delay
Low power is supposed to be adjusted for 5 watts
High power is supposed to be adjusted for 27 watts
Power should be adjusted with the radio in CW mode.
A VHF capable 50 ohm dummy load must be used for the adjustment.
Be careful - there are three VR3 and two VR4 pots in the radio.
John

Thanks a lot for the info John. Have now adjusted power o/p as you suggest.
Am I right in thinking that you have a TR-751 ? On SSB mode my 751
receiver background noise is very quiet although the RX is quite sensitive.
What is the background noise on SSB mode like on your 751 ?
Does the service manual run to many pages ? Do you have a scanned copy by
any chance ? I do have access to all the necessary test equipment in your
list.
John G3UGY

Yes I have a TR-751. In SSB mode, in the absence of a signal, there is
considerable background noise if the squelch is off and the RF gain
is at maximum. The squelch knob works in SSB mode. I recently had
to replace both the volume and squelch pots in my TR-751 and my
TR-851. I took one of the bad ones apart and found that the metal
wiper had come loose from the plastic piece that supports it. If I had
a surgeons hands I probably could have repaired it.

I have an original service manual. I don't have a scanned copy.
The service manual is the equivalent of 94 8-1/2" x 11" pages. There
are several double and triple fold out pages. Quite a few pages are
taken up by the parts list, the schematics, and colored images of both
sides of the circuit boards. The adjustment section is 12 pages.
The circuit description is 12 pages. The element function description
is 7 pages.

It looks like the manual may be available from

http://www.amateurmanuals.co.uk/

If not, I can probably scan at least the adjustment section for you.
You can get my email address by looking up my call sign at

http://www.qrz.com


John WA3TSW