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#1
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Help fixing Panasonic RF-B300
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. |
#2
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"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 |
#3
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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. |
#4
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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. |
#5
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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. -----= Posted via Newsfeeds.Com, Uncensored Usenet News =----- http://www.newsfeeds.com - The #1 Newsgroup Service in the World! -----== Over 100,000 Newsgroups - 19 Different Servers! =----- |
#6
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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 |
#7
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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. |
#8
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"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 |
#9
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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 -----= Posted via Newsfeeds.Com, Uncensored Usenet News =----- http://www.newsfeeds.com - The #1 Newsgroup Service in the World! -----== Over 100,000 Newsgroups - 19 Different Servers! =----- |
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