| Author |
Message |
    
123upmichigan
| | Posted on Sunday, December 07, 2003 - 7:11 pm: | 
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hello i am stumped. i have a 142 gtl and the volume no longer works.. was working good one minute then none the next.. i checked the knobs and the value on them reads good.. this radio does receive, the meter still works, and if you get close to the radio you can hear it receiving.. i also did check the mic so that is not the problem. can anyone help me? |
Mr_Rf
| | Posted on Monday, December 08, 2003 - 6:11 am: |
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Does it have an earphone jack, does it work?
Does it have an external speaker jack, does it work?
Do you have transmit audio? If not, the Audio Amp IC is most likely bad.
Most of the time the ext. sp. jacks have a built in switch to turn off the internal speaker and the contacts will become tarnished/corroded with age and cause this symptom. |
123upmichigan
| | Posted on Wednesday, December 10, 2003 - 8:49 am: |
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i have an external speaker jack, but that does not work either. i do not have schematics for this radio so if someone could be so kind as to give me the ic number it would be greatly appreciated. thank you |
307
| | Posted on Wednesday, December 10, 2003 - 3:40 pm: |
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Does the squelch still "pop" (while rotating)when you stick your ear down near the speaker? If so and the "S" meter still works and you don't hear anything , it is most likely the Audio Amplifier , i.e. Audio IC , is blown. However if you have modulation on TX , you probably have a squelch problem.
307 |
123upmichigan
| | Posted on Wednesday, December 10, 2003 - 8:45 pm: |
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i could try to change the audio ic but i am not sure which ic number it is . i have an extra one lyin around but not sure which part to change i have no schematics. |
2600
| | Posted on Sunday, December 14, 2003 - 2:43 am: |
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Don't change the audio IC yet. The simplest test for that chip AND the connections to the speaker is dirt simple.
Moisten one fingertip. My once-long-ago boss who taught me this trick would just say "Stick you finger in your mouth".
Lay the wet surface of that finger along all ten pins of the chip, power turned on of course.
If the chip itself is still alive, you will get some nasty screech, squawl and hum noises. Probably pretty loud. If you got your finger TOO wet, it will still make noise when you let go. Just dry off the pins.
The 142 was made for about 14 years. If yours is old, there are a few 10-Volt rated electrolytic capacitors that routinely just "die" when they feel like it. One of them is on the transistor that feeds receiver audio into that chip. Don't just blindly pull the TA7222P without doing at least a simple test.
Even simpler test. Select AM mode, key the mike, turn up the mike gain and talk. If it has normal AM transmit audio, the TA7222 chip is good. Guarantee.
If the chip is okay, there's a good chance this radio is old enough to have the "ten-Volt Blues", and needs a 220 uF electrolytic capacitor, right next to the audio chip. A higher voltage rating for the replacement is okay. A 25-Volt or higher part is best, just as cheap insurance that it will be reliable after it is replaced.
I'll check back here, and try to scare up a picture of the capacitor if your test of the audio chip proves that it is okay.
Testing the capacitor is pretty simple, you remove the solder from one of the two legs. This takes it out of the circuit. If the receiver audio comes back, but weak and tinny-sounding it means the capacitor is shorted. Installing a good one will restore the full sound of the receiver audio.
73 |
123upmichigan
| | Posted on Monday, December 15, 2003 - 8:14 pm: |
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ok, well i tried the audio chip and it was good thank you. saved me some work.lol i replaced the capacitor you told me to and i do not think that was the problem. with the capacitor removed the volume was louder but not by much.. but; the squelch does not seem to work at all, cannot hear it pop or nothing and the volume is low just like the squelch is set.. does anyone have any idea's? |
Bruce
| | Posted on Tuesday, December 16, 2003 - 4:41 am: |
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hummmmm sounds like the squelch is always on....
too bad you dont have a 2nd one to compair the squelch ckts.... |
123upmichigan
| | Posted on Tuesday, December 16, 2003 - 8:44 am: |
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well i have a washington that is still working, and a washington for parts.. i have all the parts i need just need a push in the right direction if ya know what i am saying.. radio was working fine i set the squelch came back to it 2 hours later and the squelch would not back off at all. tried replacing the knob on the radio and it did no good but not quite sure where the squelch is inside the radio to start checking. lot of work going from the front to the back of the radio looking for 1 little bad part.lol |
Tech808
| | Posted on Tuesday, December 16, 2003 - 8:57 am: |
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Cobra: Model 140GTL, 142GTL, President P-400, Uniden Washington.
VR1 - "S" Meter
VR2 - Squelch
VR3 - TX Frequency
VR5 - Carrier Balance
VR6 - AM Power
VR7 SSB Power
VR8 - Driver Bias - (35ma TP8)
VR9 - Final Bias (45ma TP7)
VR10 - TX Power Meter
VR12 - Modulation Meter
Hope this help's.
Lon
Tech808 |
Viking
| | Posted on Tuesday, December 16, 2003 - 10:53 am: |
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I recently had a radio (Pres. McKinnley) that lost rec. and trans.. The problem ended up being the 8V regulator.
Voltages for the 142GTL are supposed to be:
1- 8.05
2- 13.78
3- 8.05
4- 0
5- 13.78
6- 8.05
7- 0
8- 0 |
123upmichigan
| | Posted on Tuesday, December 16, 2003 - 9:24 pm: |
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i still have good transmit, and i tried to adjust the vr for the squelch but it does not seem to do any good. it has me puzzled for sure. you would think with 2 radio's right side bye side that it would break the squelch but it does not seem to work. is there an i.c for the squelch that might have gone bad possibly. i have never worked on a radio with a problem of this sort before so i am really not quite sure where to start i do not even know where the squelch circuit is located in these radio's. i have tried to trace the wires back from the knob but they go in 2 totally diffrent locations. does anyone possibly have schematics or something to help me out? i would appreciate it very much. |
2600
| | Posted on Tuesday, December 16, 2003 - 10:21 pm: |
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Quick test for squelch trouble in that radio:
Find TR14, a 2SA733 flat-faced plastic transistor. It is located at the front edge of the main circuit board, about two inches to the left (your left, looking down inside) from the right (your) edge of the circuit board.
Unsolder the center pin of TR14, and isolate it from the copper around the hole. Or just pull TR14 out completely, whichever seems easier. This will completely disable the squelch. If your audio trouble has anything to do with the squelch circuit, this will bring it back.
I really can't tell you how to trace back from TR14 for the real trouble, if this gets you the receiver audio again. Unless you have a 'scope, anyway. Been so long since I had to do this without one I can't remember how. If you have one, speak up. We can take it from there.
73 |
Rattlesnakejake
| | Posted on Wednesday, December 17, 2003 - 1:13 pm: |
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i personnaly would go with a more practical approach. To me, it sounds like the speaker might have became unsoldered. CHeck it. |
Viking
| | Posted on Wednesday, December 17, 2003 - 1:52 pm: |
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If it's of any consequence, on the McKinnley I mentioned above, one of the 8V outputs made the receive pop in and another one made the transmit work. Which one I don't recall, but there's only 3 choices here. I wonder if the IC could be partially blown? |
123upmichigan
| | Posted on Thursday, December 18, 2003 - 11:42 pm: |
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ok i have had to work the last couple of days so i will get back with you all here tomorrow i really appreciate the help... talk to you in a couple. |
123upmichigan
| | Posted on Thursday, December 25, 2003 - 8:48 am: |
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well, i am back been a grueling couple of days. but back to the hobbies.lol ok i pulled out tr14 and it did not seem to make a diffrence at all. was not a squelch problem i guess. so i am figuring speakers.. i changed the audio ic, run my finger acrossed it and it is working fine. i also replaced the capacitors that you all suggested and that does not seem to help either. but.. when there is no capacitor in there at all the volume is louder when it is down as low as it goes than with it wide open with the capacitor in. just not quite sure which way to go from here.. thank you for your time. |
Bigbob
| | Posted on Thursday, December 25, 2003 - 9:16 am: |
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Wow I got a p-400 with same problem,put it away working fine got it out 1 year later absolutly no speaker sound meters and tx worked fine,to bad,clarifier had 25 kcs slide,so bought an eagle 2000,ruined that with my golden screwdriver,so bought a dx2517 and the little silver thingy is still intact,but meter lights are burnt out.Will cut two little strips of 1/8 inch mirror and add two lights exterior and glue them to bottom front of meters for reflected light,got gobbs of little power supplies. |
2600
| | Posted on Friday, December 26, 2003 - 1:11 am: |
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The one clue I'm hearing from your results so far is the the volume goes UP with the capacitor removed. If the capacitor was good, the volume would drop when it is unhooked. If this is the 220 uF 10 Volt cap, put in a new one. A good cap will show you MORE volume when it's in the circuit than you get when it is removed.
May not be the whole problem, but NO WAY should it sound better with the cap OUT than with it in the circuit. Try a new one.
73 |
Big_mike
New member
Username: Big_mike
Post Number: 2
Registered: 3-2005
| | Posted on Saturday, December 03, 2005 - 4:52 am: |
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You do have your mic. pluged in write! It wouldnt hurt to check the mic. to make sure it's compleating the receive circut.
Big Mike 8113 |
Kid_vicious
Advanced Member
Username: Kid_vicious
Post Number: 919
Registered: 9-2004
| | Posted on Saturday, December 03, 2005 - 9:52 pm: |
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hey big mike, you might want to check the dates of this thread. i dont think those guys are listening anymore.
matt |
Cdn_superpower
Junior Member
Username: Cdn_superpower
Post Number: 22
Registered: 6-2005
| | Posted on Monday, May 22, 2006 - 12:33 pm: |
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My cobra 2000 has this problem too, but I shorted a audio wire in the radio testing the speaker switch.... no tx audio or receive audio |
Bc910
Advanced Member
Username: Bc910
Post Number: 722
Registered: 7-2004
| | Posted on Monday, May 22, 2006 - 11:02 pm: |
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CDN
I would BET that in your case, the audio IC is bad...
MIKE!!!! You hit the nail on the head with 123upmichigan 's problem, I was just reading the posts and thinking to myself.."MIC, MIC, MIKE!!!!" Oh well this guy most likely is long gone, but hopefully the info will help someone.
BC |
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