Need Help with SB-104A transmit problem

[mike bryce]

ted...

it may be the carrier balance is out of whack... or an oscillation in the
audio chain. or a defective part in the t/r switching... or...

first, and I assume you already have looked, make sure there is a jumper in
the acc socket. this allows the high power function to work. you can tell by
pressing in the high power button and then the tune button. the relay should
click in.

now take some contact cleaner and clean the tune and high power switches
along with the rest of the switches in that row.


pull the "C" "D" and "E" boards up and reset them several times.

if the jumper is in place, select cw


select high power

push in tune

advance the drive control while watching both current from the supply (you
can can't you?) and rf power on watt meter into dummy load

current should increase to about 20+ amps and rf should go to at least 80
watts, depending on band.

release tune button

release high button

select tune button

you should see about one watt across the band with about 5 amps of current
from the supply

if not.. then take a clip lead and ground the AUDIO line. select usb and key
the ptt line with a clip lead. you should see no more than one watt of rf
regardless of the drive setting.

if you do see power, then start looking at the vox and t/r control lines on
board b


dig out your scope. monitor pin 4 of ic201b. there should be nothing, nada
zero, zip on it's output. if you see audio on this output, something is
singing between the microphone and the mic gain control.

now monitor pin 9 of board "B" with a vtvm. During TX this pin should go +11
volts. At RX .2 volts. Move to pin 7. During TX this pin is .2 on RX +11
volts

If these are not correct. Q701 on "G" board is suspect. Hint... if TX line
is high all the time, suspect Q206 on board "B"

IF the relay does not pull in, and you have made sure the jumper is in
place, then Q207 on board b is at fault.

this should get you started in the right direction


let me know how you make out



Mike Bryce WB8VGE
SunLight Energy Systems

http://www.seslogic.com
http://www.theheathkitshop.com

"Electricity at the speed of light"

> From: TJLee <tlee at WCOIL.COM>
> Reply-To: TJLee <tlee at WCOIL.COM>
> Date: Fri, 28 Dec 2001 22:09:48 -0500
> To: HEATH at LISTSERV.TEMPE.GOV
> Subject: Need Help with SB-104A transmit problem
>
> Hello to all
>
> I am presently working on an SB-104 with the SB-104-1 modification kit
> installed.  I am troubleshooting the transmitter.  Here is my problem.
>
> When I press tune I get an ever so slight power output surge with the
> button is released.  I also get this power output when rig is turned
> on.  When I key the mic I am getting full output (100 watts) with no
> audio input in LSB and USB modes.  Any ideas from anyone.  I have
> replaced the "B" board with a good one and I still have the problem.  I
> know there could be lots of solutions but any help would be appreciate
> from the technical experts out there. Your help may save me hours of
> troubleshooting.
>
> 73  Ted  N8GPQ
>
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