The cause was the large (2-3"?) gear in the bottom of the radio. It was loose on the shaft because the setscrews were loose. Since the MHz seek switch is on the same shaft as the MHz synth, the synth shaft will always be in the correct position during this failure, but the motor, gears, and drum will have turned past the correct position. Most gears and shafts in this train are pinned, but the large gear is set by setscrews.
Fixed by setting the unit to 15 MHz, powering off, and with the setscrews loose on the large gear, manually rotating the worm shaft of the motor until the drum shaft points to 15MHz, and then aligning the MHz synth shaft to match. Tightened the setscrews, and all is well. This was a field repair by the way :)
If the amp keys up and immediately the high voltage cuts out, you may have a shorted 4CX350 final tube. The short may not show up with an ohmmeter, but the tube is arcing inside. Pull the tubes and re-try. Also measure the screen voltage and grid bias to see that they are present. If the HV stays up, put one or the other tubes back in, and determine which one (or both) may be shorted. Be careful, the deadly high voltage is about 2000 volts.
The amp will not complete the operation of the TUNE function.
Check to see of one of the two DC gearmotors which rotates the capacitors and switches in the PA tank assembly is not operating. If the elements are not in the right position for the MHz selected, the amp will never complete the tune operation.
Additional Sources for GRC-106 parts:
Jim Williams Surplus: 5W23@aol.com
Mike Murphy : murphy@cts.com
Starks Electronics : whole-sale-radio@juno.com
Barans Surplus, John Baranosky : BARANOSKYBUNCH@aol.com
American Trans-Coil : http://www.atc-us.com/
Mark Masin : mmasin@atc-us.com
Stuart Goldberg : sgoldberg@atc-us.com
Ken Winheim : ken@atc-us.com (better results making a phone call!)
Steve Haney tc0654@mesh.net Haney Electonic Company 8012 CR 1009 Godley, TX 76044-3688 817-309-2220 Best hints I can give you on the GRC-106 is:
1). carefully take the radio drawers out of the cases, carefully oil every bearing, gear, busing, and thru-panel busing. The radio will change channels much faster, more reliably, etc.
2). Go to STBY (stand by) BEFORE changing freq selectors to a LOWER frequency!
3). Make sure that all fans are functioning and that the heat exchanger is CLEAN
4). Use headset when communicating
5) if you have the TTY modem, use it to get a "closing" of the audio passband, it sounds better!
Larry, 1). sounds like your antenna output is not in a "tuned" state, meaning that there is too much reflected power. Try tuning into a 50 Ohm dummy load then transmit and see what happens
2). oil all shaft bearings, bushings, gears in both exciter and PA
3). determine that the band switching in the PA 'tracks' the exciter freq setting. Change freq UPWARD ONLY while the PA is in operate, listen as the drive changes the lumped elements and STOPS!
4). Check that the PA lumped elements drum stops with ALL contacts aligned and making contact. This requires setting a freq, shutting down, open the PA and look at the drum & contacts.
The PA can be operated out of its case but you have to make a connection between the back of the chassis and a voltage controller board mounted on the case. Its std DB connector with all contacts made up as straight through. I purchased a cable from the computer store.
--- In armyradios@yahoogroups.com, "Larry Tighe"
Does the AN/GRC-106 NEED 27 VDC? I'm operating mine on two car
batteries delivering about 25 VDC.
Should be fine. 27 volts is listed but 24 to 28 volts is ok. Use the
AM-3349's built in test meter to check primary power. It should read
in the proper green scale at all times (27 volts is about midscale).
At first turn on of the power amp there is a 60 second initial time
delay and no operation is possible (AM-3349 warm up).
When I go into tune or operate and key with the exciter, the RF
comes up and
drops out in a few milliseconds on the AM 3349. The meter readings
head
toward normal. There is good momentary RF output.
During a tune procedure RF output is lower than the normal 200 watts
(400 PEP) ; about 50 watts. The tune and load meters are also made
more sensitive (electrically) during tuning.
Is the RF output of the RT remaining constant? About 100 mW is
normal. Check if the fault condition is present on all settings of
the MC (MHZ) control; 2 to 29. I have seen a bad 100-kc module 1A2 in
the RT make all kinds of problems but it (usually) shows up only on
certain combinations of frequency settings. Also RT modules 1A5, 1A7,
1A8, 1A12 can cause TX troubles.
Lower rear corner of RT (remove from its main case) there is a toggle
switch, S11, it should be down when the RT is used with the AM-3349.
Up only for testing the RT transmit when no ALC signal from the
AM-3349 is present.
I'm wondering if it is sensing low voltage and shutting down. I
expected
the unit to operate on a nominal 24 VDC but the book references 27
everywhere.
Unless the AM-3349 is overly sensitive to an undervolt condition
(electrical fault) I don't think it is your problem... but do the
batteries hold up ok? Put a voltmeter on them when you try to run the
amp to make sure.
When you have the RT service selector in any position other than oven
or off and the AM-3349 power switch on the two fans should be running
immediately. If not there is a DC-AC inverter and/or power supply
fault or problem in the RT/PA control circuits.
There are two protections built in to the internal DC-DC converter of
AM-3349. Under volt and over current. The DC-DC converter only
operates when the amp is "keyed" or in the tune mode. Over current is
when the PA plates draw more than 450 ma for about 200 ms. Relay A3K1
is the current sensing relay in the tubes plate circuit. Reset is
done by moving the tune-operate switch from one position to the other
and back.
If the voltage at capacitor A7C3 falls under 10 volts, diode A7VR2
will stop conducting and the under volt shutdown is initiated. Reset
is done by moving the tune-operate switch from one position to the
other and back.
***Do you have to do a reset in order to try transmitting again? If
so then the AM-3349 itself is shutting down by fault or to protect
from some type of internal/external problem. If not then there is
lack of RF drive from the RT, tuning code problem, etc.
The PA's main DC power input is circuit breaker protected by A2CB1.
The primary power on/off control will move towards the off position if
the breaker trips.
The best way to check the GRC-106 set up is to have the long PA
control cable CX-10099, an appropriate length of coax for the RF
drive, and build a test cable to connect the AM-3349 to the rest of
the electronics when it is pulled from its case (connectors 2A6XA1 and
JA1A1 rear right looking into case). Have the RF output connected to
a 50 ohm dummy load. Set the RT to several random MC frequencies (KC
knobs don't matter for this check) and each time set the AM-3349 to
tune. Check if BOTH the RT and AM-3349 turrets are keeping up with the
selected MC (MHZ) selection. Also check the AM-3349 rough tune (2
motors) on the antenna coupler 2A3 and associated gear train,
switches, inductors, and variable capacitor C27. Insure the (large)
vacuum variable capacitor C26 is not shorted and it as well as
inductor L1 is properly timed with the front panel counters (load and
tune controls).
Is the GRC-106 output power poorly adjusted causing an overdrive
condition? In the RT, on the inside of the front panel are three
multiturn pots. APC, PPC, and TUNE. APC is average power control and
greatly affects the output power. PPC is peak power control and
affects the peak power. Tune is the tuning procedure power control.
All three are very important and the TM should be followed to properly
set them.
I advise, if you have not already, obtain TM 11-5820-520-35. It will
help you. The radio is all but impossible to work on without it.
Last night I was curious about a metal plate marked "A2" screwed to the bottom
of the chassis and located just below the two PA tubes. I removed the six
screws and removed the plate.
On that plate was a sub-module with several wires going to
terminals marked E-1 thru E-6. One wire, white/black/brown was not
connected....apparently had broken away from the module.
I cannot locate this 5 transistor module on the prints. Started tracing
that wire and will probably find where it goes tonight. Any idea
what the module is and why I can't find it on the schematics?
Update to my previous post:
switch, labeled as S1 (actually 2A1A2S1) is an air pressure activated
switch to detect failure of the internal blower fan. It closes its
contacts when a slight pressure is produced in the plenum. You should
be able to lightly blow into the switch (plenum side) and activate
it... less than 1 psi will easily do... if it takes more pressure than
that the switch is no good. The small circuit board is (from what I
can tell) an interface for the switch to the rest of the AM-3349
protection circuits. You are correct in that the module is hard to
find in the schematics.... because it is not printed in them. This
air pressure switch appears to have been a revision to the original
design. There is a picture in the manual of the plenum cover and if
you look closely there is no rubber grommet for the switch and the two
mounting screws are not shown. The parts location data is also not
printed. Apparently a later manual would have a revision change but
I've not seen it.
A loose wire on the board, or switch, as you indicated you have in
your unit could easily shut the DC-DC converter down. Here are the
wire colors and where they go on module A2 on the plenums cover:
blk/brn E3
blk/org E6
blk/yellow E5
red/wht E2
brn/wht from air switch S1 E1
blue/wht from air switch S1 E4
red/blk E4
As I'm sure you figured out the other parts listed as A1 on the plenum
cover are the components inside the plenum chamber. Board A1A1 is the
power level control board.
Fumio Miyato of B.M Electronics Co., Ltd. Makes a very fine set of replacement
filters for the GRC-106's I bought and installed a set of these filters in my
RT-662 and I am very happy with them! I used a small relay from a RT-524 to
switch between USB and LSB. I used a switch and matching knob from a DOA Ls-166
speaker. I drilled the hole for for the switch where the NB switch in the
front pannel would have been. Looks like it belongs there. I run RTTY every
weekend using a MD-522A and TT-4A, the filters work very well and there is
no change other then to check carrier balance and RF drive levels to the Amp.
Here is the link to his web site, scroll down to the bottom of his main page
for the filter info...
For the MD-522