I'm wondering if anyone can help me track down a problem with a SW radio
I just bought at a garage sale? It's a Panasonic RF-B300 (portable),
and when I tested it at the garage sale all bands worked fine. But when
I brought it home the MW band would just barely pick up my local station
and nothing else (HF and FM still worked fine). I took the back off to
check for loose wires on the ferrite antenna, but everything looked OK.
In fact, everything inside looked really solidly built on this radio.
I put it back together, and when I turned it on the MW band was
working loud and clear, picking up stations from all over. I turned it
off, but half an hour later the MW was dead again (except for our local
station). I hadn't moved it or bumped it in the time between when it
was working and when it wasn't.

Does anyone have any ideas of what could be wrong? Like I said, the HF
and FM bands work fine, and the MW band can barely pick up my local
station (but nothing else). Here's a link to some info on this receiver:

http://www.dxing.com/rx/rfb300.htm

Thanks,
Dave.

"Dave N" wrote in message
...
I'm wondering if anyone can help me track down a problem with a SW radio
I just bought at a garage sale? It's a Panasonic RF-B300 (portable),
and when I tested it at the garage sale all bands worked fine. But when
I brought it home the MW band would just barely pick up my local station
and nothing else (HF and FM still worked fine). I took the back off to
check for loose wires on the ferrite antenna, but everything looked OK.

[snip]

Thanks,
Dave.



Most likely a poor solder connection. It would probably be an easy fix for
somebody who repair electronic items.

Frank Dresser

DN,

Wait a minute . . .
- - - Don't Plug-in that Soldering Iron Yet !

Since the Panasonic RF-B300 has a "Band Selector" Switch with
mechanical contacts. I would first suggest that you get some good
switch/tuner contact cleaner/lubricant and try cleaning 'contacts' of
the "Band Selector" Switch first. Most of the time mechanical
failures will occur before any electrical failure; but both appear to
be electrical failures. Most of the time individual band reception
problems in multi-band radios are related to the mechanical band
selector switching hardware.


wmcis ~ RHF
..
..
= = = "justtis"
= = = wrote in message ...
Most likely still a cold solder joint. I had a Yacht Boy 400 with a
similar problem..."new" from the factory.
Carefully go over any of the soldering points that you think may belong to
the am section. Also examine antenna leads. Flexing the board with a
pointed object such as a pencil or very small jewellers screwdriver (being
careful not to short anything out), usually will uncover the faulty
joint(99% of the time). Look for any discoloured joints. The next area
to look at would be one of the electrolytic capacitors, and not necessarily
near the am section. Barring any of these, it's most likely a thermal
problem, either with one of the semi-conductors or one of the passive
devices(resistor, cap(pf). Freeze mist routes these out quickly. Hope this
has been of some help.
"Dave N" wrote in message
...
I'm wondering if anyone can help me track down a problem with a SW radio
I just bought at a garage sale? It's a Panasonic RF-B300 (portable),
and when I tested it at the garage sale all bands worked fine. But when
I brought it home the MW band would just barely pick up my local station
and nothing else (HF and FM still worked fine). I took the back off to
check for loose wires on the ferrite antenna, but everything looked OK.
In fact, everything inside looked really solidly built on this radio.
I put it back together, and when I turned it on the MW band was
working loud and clear, picking up stations from all over. I turned it
off, but half an hour later the MW was dead again (except for our local
station). I hadn't moved it or bumped it in the time between when it
was working and when it wasn't.

Does anyone have any ideas of what could be wrong? Like I said, the HF
and FM bands work fine, and the MW band can barely pick up my local
station (but nothing else). Here's a link to some info on this receiver:

http://www.dxing.com/rx/rfb300.htm

Thanks,
Dave.

Thanks for all the suggestions guys. Here's something really odd --
today I was fiddling with the radio (MW was dead of course) when I
pushed the dial light button firmly and *poof* the MW came back on. I
shook the radio and bumped it around in an attempt to get the MW to cut
out, but it stayed on strong. I pressed the dial light several times,
and switched the band selector back and forth, but nothing seemed to
have any effect on the MW (it stayed on). I then turned the radio off
for about 10 minutes, and when I turned it back on the MW was dead
again. I pressed the dial light button a couple of times, and the MW
returned! I've repeated this dial light "fix" several times throughout
the day.

OK, I'm no radio expert, but how could a dial light effect one band like
this? Better yet, how can I fix or track down the problem? Any more
thoughts are appreciated.

Dave.

Dave N wrote:

Thanks for all the suggestions guys. Here's something really odd --
today I was fiddling with the radio (MW was dead of course) when I
pushed the dial light button firmly and *poof* the MW came back on. I
shook the radio and bumped it around in an attempt to get the MW to cut
out, but it stayed on strong. I pressed the dial light several times,
and switched the band selector back and forth, but nothing seemed to
have any effect on the MW (it stayed on). I then turned the radio off
for about 10 minutes, and when I turned it back on the MW was dead
again. I pressed the dial light button a couple of times, and the MW
returned! I've repeated this dial light "fix" several times throughout
the day.

OK, I'm no radio expert, but how could a dial light effect one band like
this? Better yet, how can I fix or track down the problem? Any more
thoughts are appreciated.

Dave.

Turning on the dial light could create a voltage transient in the
receiver's power supply that may be temporarily repairing a defective
component such as a transistor. See if you can determine which active
components (transistors and IC's) are used only for the MW section.


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"Dave N" wrote in message
...

[snip]

OK, I'm no radio expert, but how could a dial light effect one band like
this? Better yet, how can I fix or track down the problem? Any more
thoughts are appreciated.

Dave.



I'll guess the switch is on the circuit board, and pressing it flexes the
board a bit and restores the connection in the AM section. Don't trust my
diagonsis 100%, but if you put it in the hands of someone who works on these
things, it should be an easy fix. If you don't want to pay a shop to do it,
or try to do it yourself, maybe there's an electronics repair class at a
junior college or tech school near you.

Frank Dresser

I think that starman may be on the right track here. The light switch
is mounted on a post totally separate from the main board, and I
couldn't get the MW band to come "on" of go "off" by bumping or shaking
the radio. I took the main board completely out of the radio today and
gave it a cursory look-over, but couldn't find anything amiss. I'll
take Peter's advice and give it a thorough going over sometime soon,
just to make sure it's not a solder joint gone bad.

I've put together several radio kits, and have taken electronics "101"
at a local community college, but unfortunately I don't have enough
knowledge to be able to determine which is the MW section of this radio.
There is a shop in the town where I work (Champaign, IL) called "Radio
Doctor", so I'll probably give them a call to see what they would charge
to look at it (if they even work on this sort of radio). I gave $15 for
it at the garage sale, and it's really a nice little rig, but I don't
want to put a bunch of money into it.

Dave.


Turning on the dial light could create a voltage transient in the
receiver's power supply that may be temporarily repairing a defective
component such as a transistor. See if you can determine which active
components (transistors and IC's) are used only for the MW section.

"Dave N" wrote in message
news
[snip]


I've put together several radio kits, and have taken electronics "101"
at a local community college, but unfortunately I don't have enough
knowledge to be able to determine which is the MW section of this radio.

[snip]

Dave.


If you can do that much, you should have a good chance of fixing it
yourself. Pay particular attention to the solder connections around the
ferrite antenna and follow the traces back to where ever they go, and pay
attention to those, too. And touch up the soldering on anything that looks
suspect where ever you find it. Most intermittents are caused by poor
solder joints.

Frank Dresser

Dave N wrote:

OK, I'll look it over later this week when I get some time. Everything
inside this radio is very well labeled, and if a guy had a service
manual and some know-how I'm sure he could fix just about anything that
could go wrong with it. One side of the ferrite antenna is even labeled
"MW", and the other "SW". What could be easier? Thanks for the
suggestion to trace backwards from the ferrite -- that helps a lot.

Thanks again,
Dave.

Try tapping the PC board at various locations with an insulated
(plastic) tool to see if you can make the problem come and go. Try to
find where the board is most sensitive to being touched/flexed. Then
look carefully with a magnifier around that area at the solder joints,
particularly those that have lost their shinny appearance or look
brittle (cracks).

Frank Dresser wrote:
If you can do that much, you should have a good chance of fixing it
yourself. Pay particular attention to the solder connections around the
ferrite antenna and follow the traces back to where ever they go, and pay
attention to those, too. And touch up the soldering on anything that looks
suspect where ever you find it. Most intermittents are caused by poor
solder joints.

Frank Dresser


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