| Author |
Message |
    
2ir473
| | Posted on Tuesday, March 11, 2003 - 9:05 am: | 
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I have a Cobra 148 soundtracker.
I tried a clarifier and channel mod that was listed on the forum, and that worked fine, but somewhere along the line, I lost modulation.
The radio keys up and dead keys, the various frequencies are there on the meter, but there is no audio going into the radio.
I must have blown something in the audio input circuit, but what?
Any thoughts would be appreciated. |
307
| | Posted on Tuesday, March 11, 2003 - 12:25 pm: |
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Does it work on Sideband?
307 |
Crafter
| | Posted on Tuesday, March 11, 2003 - 11:55 am: |
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307, Can you help. I have yet to work on a sound tracker model. Does it work on ssb ? |
2ir473
| | Posted on Tuesday, March 11, 2003 - 7:25 pm: |
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Nope, no modulation on AM or SSB.
Don't know what happened, but I suspect something must have shorted out or blown. |
Crafter
| | Posted on Tuesday, March 11, 2003 - 9:23 pm: |
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Hey 307 whats that cap that you change when you change the 7222ap. There is also a diode next to the audio transformer you might check. The little clear one in between the transformer and the chassis. |
2600
| | Posted on Wednesday, March 12, 2003 - 1:21 am: |
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Have you tried another mike? The trouble might not be connected to the mods that were done. Sometimes a mike just dies for no good reason.
73 |
2ir473
| | Posted on Wednesday, March 12, 2003 - 10:20 pm: |
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Yep, tried a different mic, and no modulation. |
2600
| | Posted on Thursday, March 13, 2003 - 12:28 am: |
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I suggest taking a bright light and a magnifier to look for an accidental solder "splash" that has bridged two closely-spaced foils on the solder side of the circuit board. This is a pretty unusual failure for this radio. Probably has an unusual cause. Modifying the clarifier should not have any effect on the mike circuit, except maybe by accident.
73 |
Crafter
| | Posted on Thursday, March 13, 2003 - 2:33 am: |
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Does the clarifier mod work ??? |
2ir473
| | Posted on Thursday, March 13, 2003 - 9:40 pm: |
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clarifier mod worked. Would be better with a 10 turn pot, but the thing tunes almost a full 10kc up and down.
One thing I did different from the listed channel mod was this... the mod said to put SPST switches on pins 14,9 & 10, ground.
When I did this, I did not get frequencies from 27.445 through 27.605.
By adding an SPST switch on pin 11,ground I got the complete range of freqs.
Would a blown transistor, like audio amp, cause this problem?
Could a 2166 driver failure cause a problem like this? |
Crafter
| | Posted on Friday, March 14, 2003 - 3:54 pm: |
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I would say not, did you check the little clear diode next to the audio transformer? I take it that radio has the mb8719 PLL. Did you remove the amc limiter I think its tr 25 or 24? Sometimes someone will accidently connect to two traces. |
Bigbob
| | Posted on Saturday, March 15, 2003 - 5:59 am: |
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sounds like a bridge or a splash did that when i changed tr51 in eagle 2000 smoked my speaker real good. |
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