Halli SX 100 Problem found, Need help with cause
tchrme
favorite rcvr too. I traced the thunderstorm crashing sounds down to
the 2nd converter subchassis. After I pulled it again, I replaced all
the caps and the resistors since it is such a pain to access. I
powered it up on test leads to the main chassis and still heard the
frying thunderstorms. A 22k resistor that I replaced was starting to
overheat and turned brown. I checked the one I took out and it too was
burned looking. So.... I need help on what would cause the overheated
resistor (R24). I can email a schematic to anyone who can help me out
on this. I double checked all wiring and parts were replaced one at a
time. Help. Thanks ahead of time. 73 Mike KF6KXG
co_f...@yahoo.com
Based on you other posts, I don't think you found the source of the
problem, only another symptom. If the noise stopped when you pulled
the tube/tubes, Did you try pulling them to stop the resistor
overheating? Replace the tube/tubes with a different set, one at
time. Watch the resistor for overheating, again.
If you have indeed replaced all other components, the one you have not
commented on are the tubes. Sounds like a grid to plate short
somewhere.
I have no familiarity with that receiver.
Paul, KD7HB
tchrme
Paul, I tested the tubes and they seemed to be okay. I will try your
suggestions. Much appreciated, MIke KF6KXG
Richard Knoppow
"tchrme" <tch...@aol.com> wrote in message
news:b9d67ae9-3bdb-4398...@v15g2000prn.googlegroups.com...
Have you made tube socket voltage and resistance
measurements? This is a first step and will often point at
problems. I've downloaded the schematics for both versions
of the RX, you appear to have the earlier one (the 22K
resistor is a different value in the later version). I can't
see an immediate suspect but any capacitor in a position to
draw current through the resistor is a suspect. While paper
caps fail mostly by developing a low series resistance I
have encountered shorted ones.
--
Richard Knoppow
Los Angeles
WB6KBL
dick...@ix.netcom.com
Nordic Breeds
news:ybKdncMBq6TLeGDX...@earthlink.com...
Both the Mark 1 and Mark 2 models have the 22K resistor in the Bama
schematics. I would check
both C24 and C26 but a leaky C24 is the most likely cause of overheating
in the 22K resistor. A
quick check on the plate and screen voltages of V5 should point you in
the right direction. A tube
socket extender is handy here, but carefully pulling the tube out and
carefully wrapping a fine wire
around the appropriate pins and plugging it back in will work. C28, C29,
and C30 should also be
checked. Silver migration in C28 and C29 could conceivably case the
noise too.
73, Barry WA4VZQ
COLIN LAMB
caps in the sub-chassis, but that circuit appears to be the offending
circuit. I cannot quite read component numbers, but if noise appeared on
the screen bypass cap, it would be more likely to make the crackling noise
than a bypass cap further up the power supply chain. And, as Barry
mentioned, the coupling caps for that if transformer could be bad,
particularly C30.
Varying the selectivity control will change the load on C28 and C29, so you
might see if there is any change. It could also be one of those caps or the
rotary switch, although having the crashes go away when pulling V5 along
with overheating R24, points to the plate or screen of V5.
Check C27, the plate bypass cap, closely. That is a tuning cap and would
have some affect. Noise can be caused by a cold solder joint, but that
would not result in more current being drawn.
You are getting closer.
73, Colin K7FM
Richard Knoppow
"Nordic Breeds" <wa4...@live.com> wrote in message
news:hdkrt7$no3$1...@news.eternal-september.org...
are sort of low res.
Richard Knoppow
saw one as larger. I agree that C-24 looks suspicious.
tchrme
> "Nordic Breeds" <wa4...@live.com> wrote in message
>
> news:hdkrt7$no3$1...@news.eternal-september.org...
>
>
>
Success! Yes! Thank you everybody for all the help. Because of
the location of V5 in a TIGHT corner of the subchassis I didn't check
its voltages until I used lots of test leads and fired it up on the
bench out of the rcvr. Not only was the screen grid reading low but so
was the plate. It should have been around 270v and was only 17! So
after making sure there were no shorts on selectivity switch circuit
off the screen grid I focused on the plate circuit. The only component
I hadn't changed yesterday was a 100 pf tubular ceramic cap that
ohmed out in the megs. Silly me, I thought it was good. Well it was
the first component to ground after the plate so....I decided to lift
a lead just to be sure. Wow, everything went to normal voltages and
the crackling stopped. I subbed in a new ceramic cap and let it run
for a while on the bench. All was good so I put it back together and
aligned it. Colin, you were dead on. It was C 27. I just figure the
cap was partly open and under high voltage, broke down to a short that
varied in degree that caused the thunderstorms. While I also replaced
V5, V12, and V13 in case of a grid to plate short as Paul suggested,
my Paco tube tester did not indicate any shorted elements, but then
again I am going to check them with an VOM when I get a chance just to
know. Barry, I had the same thought on silver migration, so the first
thing I did was to change the silver micas.
Again, thank you to all who helped to point me in the right
direction. Sometimes we get so close to a problem, we miss it and
another person viewpoint is needed. Have a great weekend, 73 Mike
KF6KXG
MoiInAust
hearing *genuine* static crashes that will mask the cure! Eliminate that
possibility by listening on another receiver (with yours off).