| Author |
Message |
    
Buck
| | Posted on Sunday, February 02, 2003 - 4:33 pm: | 
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I found a 148GTL at work that is in mint condition. The covers dont look like they have ever been off and it isnt hacked up...Everything works great except for the transmit.It dosent have a carrier or modulation, but you can slightly hear it key up on another radio on my bench. The PA works just fine and the recieve is fine. Any Ideas on what the problem might be?? |
2600
| | Posted on Monday, February 03, 2003 - 1:32 am: |
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Did you try to transmit on SSB? If SSB still transmits and ONLY AM is dead, that's a large clue, and would narrow things down a lot.
Does the name plate on the back say "Made in Malaysia" ???? Those have a list of routine troubles like this that the Taiwan, Philippines, China and Thailand radios usually don't. The model number alone only narrows it down to a half-dozen or so actual radio types.
73 |
Buck
| | Posted on Monday, February 03, 2003 - 5:15 pm: |
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Thanks for the reply 2600...It dosent have any TX...no Am, no SSB, nothing. However, like I said on another radio on the bench there is a little bit of faint static or "scratchyness" when you key it up. I should have mentioned in the first post that this is a Taiwan model.
Thanks
Buck |
2600
| | Posted on Tuesday, February 04, 2003 - 1:25 am: |
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A Taiwan model, eh?. I gotta hunch on this one. Seen it before. Find IC3, the AN612 balanced modulator chip, near the front-center of the circuit board. It's about 3/4 inch long, 1/4" tall black plastic. It has seven pins in line soldered to the board, oriented parallel to the sides of the radio. At the rear end of this chip on the left (your left) side of IC3 is a tiny electrolytic capacitor C95, marked 47 uF, typically rated at ten Volts. Unsolder one (either) leg of this guy, or take him out completely. If your wattmeter comes back to life when you key it now, install a replacement capacitor. Use a higher voltage rating. We never use any under 25 Volts. No point. Any value up to about 220 uF should serve okay, if you can make it fit.
Uniden saved a half-cent or so using this 10-Volt part instead of a higher voltage rating. The ten-volt parts just have a consistent habit of failing first. There is a 100 ohm resistor R108 that feeds this spot, next to C95. If it looks overheated or discolored, it should go, too.
You may want to seek and destroy, replacing all the remaining 10-Volt rated electrolytics. A Taiwan radio is getting old, and more of these will probably fail if you leave them in it long enough, and/or use it a lot.
Only now do I realize that nobody asked if the transmit light goes red when you key. If it does, try my suggestion above. If it stays green when you key the mike, or goes dark, this may not help at all.
73 |
Sparkomatic
| | Posted on Tuesday, February 04, 2003 - 12:18 pm: |
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A while back I bought a 148 off of EBAY that was made in Malaysia and the radio had NO line filtering whatsoever. The tech replaced a few parts and charged me 50 bucks to get rid of the noises. |
Buck
| | Posted on Tuesday, February 04, 2003 - 8:39 am: |
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Thanks 2600...I will try this tonight when I get home. The Tx light does go res when I key up so I hope this is it. I will keep you posted
Thanks
Buck |
Buck
| | Posted on Tuesday, February 04, 2003 - 7:59 pm: |
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2600 your hunch was dead on....I removed C95 and got my transmit back....now where can I get ahold of a few replacement caps???
Thanks for all your help
Buck |
2600
| | Posted on Friday, February 07, 2003 - 11:57 pm: |
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Hmmm. Small quantities of electrolytic caps? Used to be all but the smallest town had a parts distributor who supplied repair shops. They seem to be as extinct as the repair shops they sold to nowadays. www.mcmelectronics.com is pretty good. www.mouser.com is a reliable source. Both have large catalogs. Seems there's no such thing as a "small" parts supplier any more.
73 |
Buck
| | Posted on Saturday, February 08, 2003 - 8:25 am: |
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I was able to find what I needed at rat shack...Do you know what years the tiawan radio was manufactured??? |
2600
| | Posted on Sunday, February 09, 2003 - 8:58 pm: |
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Best I can recall, it was made in Japan until about 1980, in Taiwan until '88 or '89, and in the Philippines until 1993, when Cobra stopped buying from Uniden. After that, it got a little crazy.
73 |
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