hw1XX and SB1XX no tune in tune position fix

[mike bryce]

I've seen several requests for a fix to the above problem.

to get everyone up to speed, it seems that some radios won't go into tune
when the tune mode is selected. PTT works, and that's been the work around.

Select tune
ground the PTT
tune radio


Well here's the fix!

I did this on a HW-101 but should be good for any of the tube based HW and
SB transceivers.

Open up the radio so you can get to the top side and bottom chassis.

power up the radio

Measure the cathode of tube V12. That's pin 8. Looking down from the top of
the radio, pin 8 is near the edge of the right side of the radio. Count the
pins going counterclockwise. Pin 1 is pointing towards the PA deck

You should see 14-15 volts of voltage on the cathode. This voltage is
supplied by D202, a 15 volt zener diode.

No voltage? R129 is open, D202 shorted.

Voltage too high? D202 open

Measure +300 volts at pin 1. IF you see this voltage, then RY1 and RY2 have
good coils.


place mode switch in tune.

take a clip lead and a cut off resistor lead and ground pin 8 of V12. Relays
will click in and radio will go into tune mode. by using the resistor lead
you can get on to pin 8 from the top side of the pc board.

deselect tune from the mode switch.

Flip radio over to expose chassis.

At the microphone connector there should be TWO black wires connected
together and then the pair is connected to pin 2 on the ORIGINAL TWO PIN
socket.

If you don't see the two wires connected, that's the problem.


When someone changes from the ORIGINAL two pin to a FOUR pin they left out
the second connection. This is the wire that goes to the MODE switch. IF you
only see one black wire, one that runs to the large wire bundle, it's goes
to pin 8 of V12. WIthout the second wire connected to pin 20 of the mode
switch, NOTHING happens when the rig is placed in TUNE mode.


Here's how it works....

By design, it's quite simple

Both relay coils, RY1 and RY2 are in series. +300 volts is applied to one
end of this string.

The other end goes to relay driver V12.

This end is connected to the plate of V12.

In CW or VOX mode, when the VOX amplifier conducts, it sends a voltage to
the grid of V12. the allows the tube to turn on. WHen the tube conducts, the
relays are pulled in.

Life is good.

In PTT or TUNE mode, there is no input from the vox amp, so to KEY the radio
the cathode is pulled to ground. this does the same thing, causing the tube
to conduct and thus pulling in the relay. The PTT line goes directly to pin
8 of V12.

again, life is good


SO, if you have VOX and PTT working but nothing in the TUNE mode, you are
missing a second black wire from the circuit.


Mike Bryce WB8VGE
SunLight Energy Systems

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

"Electricity at the speed of light"

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