| Author |
Message |
    
Rippedradio
| | Posted on Tuesday, July 30, 2002 - 6:29 pm: | 
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i was just wondering is anyone has ran into this problem, it recives excelent but an am there is no audio 5 watt dead key but no audio, on ssb it is like humming and doing 22 watts also no audio, looks like it has not been golden screwdrivered! any help would be appreciated! thanks and 73's chris |
307
| | Posted on Wednesday, July 31, 2002 - 8:24 pm: |
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Hmmm...I will take a guess...I believe the Audio IC may be bad (oscillating). I can pin point it IF you tell me "what noise" you can hear on SSB on another radio with the 146 keyed up on SSB...Do you hear a hi or low pitched tone?
307 |
Rippedradio
| | Posted on Thursday, August 01, 2002 - 7:00 pm: |
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307, thank you for replying it is a low to mid pitched hum, not a squeal though! it looks to me like the audio ic has been replaced along with the green voltage regulator right next to it if this helps at all! thanks, chris p.s. i do not know if it was replaced with the right part it does not look like a stock part, it is a nec pc1224hthe one next to it looks org it is an a473! thanks again and 73's |
307
| | Posted on Friday, August 02, 2002 - 9:14 pm: |
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The Audio Chip must still be bad OR a component near it. The Hum you hear is modulating the SSB up to full power , in AM it is clamped on the IC so I would assume the IC or a component in the area is bad. Most likely a bypass capacitor is shorted.This problem can be duplicated on this radio with a miss-wired mic as well!!!!
307 |
Rippedradio
| | Posted on Friday, August 02, 2002 - 10:18 pm: |
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307, can u tell me what audio ic the 146 is suposed to have or what other component to look at! i have slewes of parts radio's laying around loaded with parts! thanks, chris |
307
| | Posted on Saturday, August 03, 2002 - 6:47 pm: |
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It is a UPC1182H.
307 |
2600
| | Posted on Sunday, August 04, 2002 - 1:39 am: |
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For starters, the uPC1242 is a DROP-IN replacement for the old discontinued uPC1182. It has one more pin, but it's a ground, right next to where the single ground pin on a 1182 goes. The rest of the pins on each side of the ground pins line right up with the board foils in the same positions as the 1182. I'm persuaded that the 1242 is a bit tougher, and less likely to fail than the old 1182. But this is just a distraction. That part has NO transmit function at all in this radio. The Cobra 146GTL was the first radio on the market that I saw using a new-fangled ALL SOLID-STATE AM modulator with NO transformer on the audio side. It used a PNP transistor to keep the voltage drop to the final at a minimum, (less than the NPN transistor in a 148etc.) and looks just like the AM modulator in all (but a few) Superstar, Connex, Galaxy and RCI radios for years.
My point? The speaker amp chip is not used for any transmit modulation purpose at all in this model, either for SSB or AM. If the receiver audio sounds okay, leave the uPC1242 alone. My advice is to look around the mike amplifier section for electrolytic filter capacitors that are marked "10 Volt" rating. If this radio is 15 or more years old, these parts are ready to start failing. The ones marked 16 volts or higher seem not to have this problem, but the 10-volt parts just don't age well, and cause some weird noises in Cobra 148/2000/142/Washington/Madison radios that get to that 15-year mark. If it hasn't been screwdrivered, the odds point to a filtering problem, shutting down the mike audio and/or making it oscillate.
73 |
Rippedradio
| | Posted on Monday, August 05, 2002 - 1:02 am: |
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thank you 2600 for the reply also thanks to 307, how and what do i need to check these capicators! thanks again, chris |
307
| | Posted on Monday, August 05, 2002 - 10:31 am: |
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Good call 2600....Did not even think of that...I see the capacitors in the older Export Jackson go bad.
307 |
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