| Author |
Message |
    
Boatman
New member
Username: Boatman
Post Number: 2
Registered: 3-2005
| | Posted on Wednesday, April 06, 2005 - 9:54 pm: | 
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no rx audio, but is receiving signal. has key up wattage but no modulation. AUDIO CHIP??????? |
Kid_vicious
Intermediate Member
Username: Kid_vicious
Post Number: 360
Registered: 9-2004
| | Posted on Wednesday, April 06, 2005 - 10:48 pm: |
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check it with a known good mic or short the correct pins on the mic connector to rule out the possibility of a broken mic wire.
matt |
Boatman
New member
Username: Boatman
Post Number: 3
Registered: 3-2005
| | Posted on Thursday, April 07, 2005 - 5:57 am: |
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mic ok |
2600
Advanced Member
Username: 2600
Post Number: 535
Registered: 7-2002
| | Posted on Saturday, April 09, 2005 - 3:08 am: |
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Audio is dead on both transmit and receive?
There is always a reason if the audio power chip is blown. Most common would be a shorted cable on an external speaker. A blown internal speaker can hammer the audio chip, but a speaker that is that bad will sound terrible. Most folks can't listen to the nasty sound of a blown speaker long enough to blow out the audio chip.
Checking for power on pin 1 of the TA7222P chip should show between 12 and 13 Volts, depending on the power supply. The voltage on pin 9, the next-to-last pin at the other end, should be ONE-HALF of that reading, or very close to it. If pin 9 shows a lot lower, or a lot higher than that, a blown chip is likely. Pin 1 should be the end towards the front of the radio.
Any time we replace a TA7222P chip, we replace the output capacitor that feeds to the speaker and to the modulation transformer. Don't have a diagram for the PC78. In the PC76, this capacitor is C48, a 470 uf 16 Volt part. If the cap is bad, it could hammer a new chip soon after it gets replaced. The cap is cheap insurance, compared to the aggravation of replacing the audio chip twice.
73
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Boatman
New member
Username: Boatman
Post Number: 4
Registered: 3-2005
| | Posted on Sunday, April 10, 2005 - 8:28 pm: |
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checked voltages, chip bad. replaced it and output cap. All's well.
Thanks, Art |
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