N My R-B quit today. I think I might have blown the Uniden. What is the
N simplest way to determine what died so I can fix it post haste. I believe tha
N something has been wrong for about a week, since it doesn't seem to be
N producing any results. It had worked fine before that. I'm no technician, so
N please keep it simple. This is an emergency, as I need my machine to regain m
Everyone working with RF equipment needs to some basic test equipment
handy for problems such as this. A good investment is a dummy load and
a combination RF wattmeter/VSWR meter. With these, you can quickly
verify that your CB, amplifier and tuner are functioning properly.
If you can, obtain a Radio Shack 21-523 SWR/field-strength meter
($19.99), and a Radio Shack RSU 11269479 Dummy Load ($21.99). Using
these, you may easily test your RF equipment.
If you can't obtain any test equipment, a Quick & Dirty test may be
made by connecting a short piece of coax cable to a #47 light bulb.
With no modulation, a CB producing 2 to 5 watts of RF should light the
bulb brightly. Applying modulation will make the bulb brighter, and may
even burn it out.
If you use a clear glass (easier to see the filament) 60 watt 120
volt light bulb and a short piece of coax cable, you can test your
amplifier and tuner. The amp will light the bulb without the tuner,
although not at full brightness.
Connect the 60 watt bulb to the coax output of the tuner, and if the
amp and tuner are working properly, you'll be able to get the bulb to
light quite brightly with no modulation.
The CB by itself probably won't light the bulb so you can see it,
unless you use the antenna tuner. In that case, you can usually see a
dull red-orange glow on the filament if the CB is OK.
The brightness of the lamps should change as you modulate the CB.
Depending on your particular modulation method and modifications, the
bulb may get either brighter or dimmer as you modulate the CB. Of
course, you can also listen to the signal using another CB or a portable
radio placed close to the CB being tested.
Hope this helps!
>From firstname.lastname@example.org Sat May 30 13:23:33 1998
>I am suffering from a frustrating problem which I need a little help with.
>Every time I run my B/R Device with frequencies above 1,300 Hz the tube goes
>out, and the power supply (switching) trips. The unit runs fine at lower
>frequencies, but I still cannot run at SWR's lower than 1.6 - 1.8. Any
Hello George and List:
Personally, I have not run into this problem, but the cause and cure appear
reasonably straight forward. When the modulator is modulating the carrier
in the CB, the current needed to do so is reflected back into the power
supply where it trips the current overload circuit. One of the solutions
for the problem is to filter the D.C. output line of the power supply with
an electrolytic capacitor. I am not certain what minimum capacitance value
will make the problem go away, but I would start with about 4,000 uF and
the voltage rating should be 16 volts minimum. Be sure the polarity of the
capacitor connections is correct. If you could connect the capacitor inside
the CB between the cold end of T2 and ground, it would be more effective.
> Tonight tried putting a choke on the power cable from the wall outlet to
> the Astron power supply. Started up just as sweet as always at 1550 hz,
> had a tone coming from the CB, nice clear tone. This is not unusual, it
> seems to do this sometimes.
It should do it all the time at this frequency level.
> worried about it. Then after about 30 seconds the function generator
> (Heft-modified Kinnaman unit) goes EE on the display, shuts down output,
> and goes through it's startup/power-on sequence like I'd just turned it on.
It's being shut down by the RF. Use a choke on the power cord into it
as close to the box as possible. If it's a thin cord, wrap it through
the choke as many times as possible.
Second, keep the CB to Kinnaman cable as short as possible. Since
you are using the CB cord and microphone, I would recommend making a
CB mike connector to BNC coax cable (RG59). Pinouts are given
in the CB mod file in the Rife notes section of my web page.
Third, (I don't think this is possible in an F1B), ground the func
Fourth, try different component positions and short-as-possible coax
cables (7-12 inches instead of 18 feet).
If these measures fail to prevent the device from shutting down or
going haywire, it is necessary to put an RF choke on the CB to Kinnaman
cable. This should be avoided if possible since it will typically
decrease the amount of harmonics available, but a number of people do
it and get good results. On one system I built, it produced a louder
CB tone (and better harmonics) because the cable otherwise had so much
interference on it.
> Checked the 0.68 cap and it is not continuous so I don't think the cap
> blew. Even after removing choke SWR seemed much higher than it has been in
> earlier runs, like .3 or so. Back of CB seemed more warm than usual, so
> took off cover and smelled, couldn't find any 'burned part smell' in it.
> Have noticed the rear of the CB usually gets pretty warm.
Put a fan under it blowing up with the bottom of the case removed.
This will provide optimal cooling. Some people get by with merely
putting a heat sink on the back of the CB using the small nut and bolt
which hold the power transistor which gets hottest (glued to the back
of the case).
Rick... I happen to be working on a blackface Palomar 225. The 4.7uF 50V cap
positive is connected to the +12V feed (same foil connecting the center-tap of
the large output transformer). The negative is connected to ground.
Rick Gressel wrote:
> Wonder if anyone can help me-just blew the little 4.7uF 50v electrolytic
> capacitor in front of the large trans in my blackface palomar-got another
> replacment, but I don't know enough electronics to know which lead goes
> where-I traced the positive lead on the board, but does that hook up to the
> positive lead on the capacitor?
>If anyone has had the unfortunate experience of frying a linear from to
>much SWR, could you please share with me the symptoms of a damaged amp.
>What can I expect to see if I goof?
Greatly decreased output power. Like if it was 100 before and it's 20 now
at the same input tone (5000 Hz, for example), you're probably looking at
either a fried tuner, fried cable or a fried linear. The first is actually
the worst in my experience!
You can tell if you fried the CB by hooking it directly to the antenna
tuner using just one cable and seeing how much power it's putting out.
That, of course, is if you have a tuner with a dummy load -- on the
MFJ-949E you can turn it to 30 watt range and get a direct readout of the
power coming out of the CB. If it's putting out 7 watts or more at 5000 Hz
input it's OK.
Then try swapping cables if possible. If a cable melts down it usually
fries the linear when it shorts... :(
It's quicker to buy a second amp than swap those big power transistors in
the linear. If you can afford it I highly recommend it. Otherwise, hope
you're either good at soldering or have a good friend who's into TV/radio
repair. I just met such a man, great guy. Do get your first amp fixed
though. Try RF Parts for the transistors -- the 2SC replacements for the
455's were on sale last month, might still be.
Been down the road you're on. Good luck!
This morning during a routine session, I heard a "pop"
or "thud" sound come from my RB unit, and the tube went out. I
shut it down immediately. I tried restarting it, after giving
it a chance to cool down, but with no success. My system
consists of the following components: Kinnaman F1 frequency
generator Uniden 510 proXL CB unit, modified as per James Bare
black faced Palomar 225 linear amp MFJ-962D tuner 1" tube with
flat braid wrapping & clamps The CB & linear, and linear &
tuner, are connected by 18' coax cables. I have limited
knowledge of electronics, and need to figure out what blew. The
tube looks OK, and my guess is the Kinnaman is fine. the CB
lights up and sings when the switch is on. The linear clicks
and lights up as well. The indicator needles on the tuner swing
up into the SWR infinity range, and will not move when the
antenna or transmitter knobs are adjusted. Could I have
burned out the internal balun in the tuner? What else should I
be checking? Are there simple tests I can do to locate the
problem? I would greatly appreciate any assistance, as getting
my unit back on line is a high priority. Thank you in advance.
Yours in Health,
Steve, It sounds like the problem is in the tuner, probably one
of the connections inside flashed open when you heard the
"pop". Your tuner meter readings and unresponsive tuning knobs
indicate that the CB and Linear are working OK, but no RF is
being fed to the transmission line and plasma tube.
You should open the tuner and inspect all the wiring and switch
contacts for any open/burned connections. Unfortunately, I'm
not familiar with the wiring of the 962D. I have a 962C, but if
it is similar, try the following...
Disconnect all equipment from the tuner and put the Antenna
Selector on "Bal. Line". Get a continuity meter (ohm meter).
Test for continuity between the center pin of the "Transmitter"
jack on the rear chassis and one side of the "Transmitter"
tuning capacitor (the side with the wire going to the Antenna
Test for continuity between the "Balanced Line" wingnut (with
the white wire attached internally) and one side of the
"Antenna" tuning capacitor (the side with the wire going to the
If either of these checks fail, suspect that the Antenna
Selector switch is bad. If the switch contacts are fried, you
could always solder a jumper wire in place to "force" the
If these check OK, test for continuity from the junction of
both tuning capacitors, to the chassis. If open, suspect a
defective Inductor switch (or bad roller inductor contact, if
this is the model that has it).
Someone who owns a 962D may be able to give additional hints.
Blown Amp -
All indicator lamps were lit. What Jim told me to do is: with
everything still hooked up and powered up, key the mic. If you
hear the relay pull in and no output, the finals are blown. If
the relay doesn't energize, the switching transistor that
controls the relay is bad.
N> This morning during a routine session, I heard a
"pop" or "thud" soun N>come N>from my RB unit, and the tube
went out. I shut it down immediately. I tried N>restarting it,
after giving it a chance to cool
N>The tube looks OK, and my guess is the Kinnaman is fine. the
CB lights up and N>sings when the switch is on. The linear
clicks and lights up as well. The N>indicator needles on the
tuner swing up into the SWR infinity range, and will N>not move
when the antenna or transmitter knobs are adjusted.
It sounds as though either the balun failed or the coax
cable between the tuner and the balun melted and shorted out.
Plug a dummy load into the coax out connector on the tuner and
see if you can get normal power and VSWR readings with the load
in place of the balun and tube.
If you don't have an RF dummy load, you can make one from a
standard 60 watt, 120 volt incandescent lamp. Simply connect
the screw base of the lamp to the ground terminal of the
antenna tuner, and connect the center pin of the lamp base to
the center pin of the Coax Out jack on the tuner.
If you like, you can connect a short length of coax cable to
a PL-259 connector, and strip the other end, connecting the
shield to the lamp outer shell, and the center of the coax to
the center pin of the lamp. That way, you can easily connect
the load for tests. The center pin of the lamp will take
solder OK, but the aluminum outer shell of the lamp will not.
Simply twist a length of #14 bare copper wire around threads
of the lamp base and then twist the wire in place like a
Twist-tie. If you like, you may use a standard CERAMIC light
bulb socket, available at your local hardware store. That way
you can use different wattage lamps.
Now, you RF purists will cringe at the thought of using a
horrible thing like a lamp for a dummy load, but this is not a
precision use, just a quick & dirty test to see if things are
working. Light bulbs are cheap, and if you blow one out, you
can easily replace it with another. They don't require any
fancy meters, either, if it's bright, things are right!
Note that using a light bulb for a test load will require
that you use your antenna tuner. An incandescent lamp will
have varying resistance as it heats up. VSWR will change as
the power changes, nevertheless, you will find a setting that
will give you a low VSWR at whatever power you are using.
WARNING - do NOT connect this directly to your amplifier
without using the tuner between the amplifier and the lamp
load. The cold (lamp of) resistance of the lamp is very low,
and may damage the amplifier if the amplifier is powered up
abruptly at a high power setting.
The RF power transistors used in the linears are "multiple
emitter" types. Most often when the amplifiers put out reduced
power and all other factors are normal, it means that some of
these emitters are blown open, necessitating installment of new
Incidentally, these transistors will typically show no signs of
stress visibly and they also pass the "diode" test on a
multimeter. The only conclusive test would be to dynamically
test them in an RF test bed environment.
Just the same, I would first open the linear and visually
inspect for anything burned first.
If you decide to replace the transistors yourself, I'd be glad
to e-mail some tips on how to perform this.
Best regards. Tom
===== The Equipment =====
* Soldering gun: You need a soldering gun with enough heat to do a
proper job -- don't even attempt it with only a 20 or 30 watt gun. My
weapon of choice is a Weller model 8200. It is a 100/140 watt
trigger-switchable gun with a perfectly angled chisel-head tip for this
kind of work. It is available for US $30 to $40 from *many* suppliers,
including Mouser Electronics, MCM Electronics and Tech America (Radio
Shack used to carry this model, but no more). Can probably do alright
with Radio Shack #64-2193.
* Screwdriver: A good-quality small screwdriver (jewelers) with about
1/8" wide blade. Can use Radio Shack screwdriver assortment #64-1948.
* Desoldering braid: For best performance, try to obtain braid that's
at least 0.1" wide. Can use Radio Shack #64-2090.
* Heatsink compound: Can use Radio Shack #276-1372.
* Solder: Any good rosin-core solder for electronics. Radio Shack
===== The Procedure =====
* Remove the two screws on each transistor that secure them to
the heat sink.
* Each transistor is a "helicopter" with four tabs coming out
of it at 90-degree angles. On each tab, use the gun's chisel
tip to hold a section of desoldering braid against it. Trigger
the gun and as soon as the braid starts soaking up the solder,
move the tip around to gather as much solder from around the
tab as possible, feeding fresh braid as necessary. Alternate
doing the tabs from one transistor to the other to minimize
heat buildup of surrounding components. In other words, don't
spend a lot of time with the tip in one place! When all eight
tabs are done, let everything cool down for a few minutes.
IMPORTANT: Make note of which tabs have the angled corner.
* Alternating tabs as you did before, use the gun and the
screwdriver together to lift each tab from the circuit board.
Carefully apply heat to the outer corner of a tab and using the
screwdriver blade, dig under the loosened tab and "rock" the
screwdriver under the tab to lift it. As the tab slowly lifts,
keep rocking the screwdriver while pushing it forward and
gradually "peel back" the tab to the point where most of it is
curled up in the air. If you notice that there is still a blob
of solder under the tab holding it to the circuit board, simply
push some braid under there with the hot tip to soak it up. On
each transistor, the first two tabs are the hardest to do.
While doing the last two tabs, the transistor should begin
lifting out of the hole, which makes removal much easier.
* Prepare for installing the new transistors... With the
transistors out, clean out the heatsink compound (the white
goop where the transistor was). Use the gun and braid to melt
and remove any excess solder from the circuit board where the
tabs will lie for the new transistors.
* Apply fresh heatsink compound to the underside of the new
transistors, and set them in place on the heat sink. CAUTION:
Be sure the tabs with the angled corners are oriented the same
way as the original transistors.
* Screw the transistors to the heat sink. If you did a good
job preparing the circuit board, all of the tabs will be lying
flat against the board, ready to solder.
* Alternating tabs as before, heat the top of each tab
beginning near the outside and slowly melt fresh solder onto
and around the tabs. A correct job will leave each tab with a
very slight "mound" of shiny solder surrounding it. That's it,
===== Additional Tips ===== * If you just bought a new solder
gun (or a new tip), you must "tin it" first so it will solder
properly. The first time you trigger the gun, let the tip heat
up for a few seconds and flow solder over the end of the tip.
* NEVER trigger the gun unless you are applying it to the work
(except for the reason above). Whenever you pull the gun away
from the work, let go of the trigger.
* NEVER touch near your eyes after your fingers are exposed to
heatsink compound. It's an extreme eye irritant, the itching
will last for days! Wash thoroughly after procedure.
I'm sure that something is missing in all this, but it should
be good for starters. As always, comments are welcome. Hope
it was helpful.