| Author |
Message |
    
Lonestarbandit
Member
Username: Lonestarbandit
Post Number: 79
Registered: 10-2006
| | Posted on Saturday, May 19, 2007 - 11:55 am: | 
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hey lon or any other tech..... just bought 2 thank god pc68xls off ebay thinking i had a 50/50 chance and turned out to be exactly the case one is fine the other lights up dk and everything else but no sound out and no modulation at all. where should i be looking and what should i be replacing? thanks guys |
Dale
Advanced Member
Username: Dale
Post Number: 873
Registered: 12-2002
| | Posted on Sunday, May 20, 2007 - 10:48 am: |
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well imho that could be a simple soulation or
not.first what mike is on it?if its not a stock
mike it could be wired up wrong.and if thats the case then you would have no sound coming thru
your speakers and radio wouldnt keyup or modulate
on the other hand if ya got a mike that say works on the good 68 that works then ya got more serious problems.like radio out of alignment recieve tuning cans need re-align or just d.o.a
radio.just my 2 cents here.
dale/a.k.a.hotrod
cef426
cvc#64
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Kid_vicious
Senior Member
Username: Kid_vicious
Post Number: 2532
Registered: 9-2004
| | Posted on Monday, May 21, 2007 - 1:00 am: |
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LSB,
definitely check the mic first, if the mic from the working radio has no effect on the poor performance of the broken radio, then i would suspect a bad audio chip.
its one one with about 10 inline pins that is mounted to the side of the chassis.
there is usually a disc cap soldered from the tab of the IC to the metal of the chassis.
i think its IC1.
i will post the correct voltages tomorrow.
shouldnt be too hard to find a replacement.
not sure if they still use the sam part, but it used to be a TA7222p.
hope this helps,
matt
anyone wanting a "clean signal", just look to the left and build one of these!!!
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Lonestarbandit
Member
Username: Lonestarbandit
Post Number: 80
Registered: 10-2006
| | Posted on Monday, May 21, 2007 - 1:05 am: |
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yes. this is a harware issue not a tuning issue. it ws doa when recieved/ go figure fleabay / got one that worked and one that dont. 50/50 but i was asking for what conditions hardware wise cause this. would blown audio ic affect both no transmit audio and no speaker audio or is this 2 seperate issues.... |
Kid_vicious
Senior Member
Username: Kid_vicious
Post Number: 2533
Registered: 9-2004
| | Posted on Tuesday, May 22, 2007 - 10:56 pm: |
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nope, audio chip is for both RX and TX audio.
cheaper that way.
also, semiconductors are the most sensitive components in the radio. usually first to pop.
here are the voltages for that chip.
set your voltmeter to DC voltage, on a scale that will read from 0-15+ volts, touch the black lead to one of the metal tuning cans for a ground, and touch the red lead to each pin, noting its voltage.
radio needs to be on, squelch at minimum, volume set about halfway, NB/ANL off, mic plugged in, RF gain all the way up, mic gain all the way up.
pin 1: 13.77 volts (this may be slightly different, depending on your power supply's output voltage. you should have the same voltage on this pin as on the output of the power supply)
pin 2: 2.95 volts
pin 3: 0 volts
pin 4: .01 volts
pin 5: 1.85 volts
pin 6: 1.85 volts
pin 7: 0 volts
pin 8: 0 volts
pin 9: 6.83 volts
pin 10: 13.15 volts
if any of these voltages are not there, or are way off, then the audio chip needs to be replaced.
if you cant find an original TA7222AP chip, the NTE1278 will work just fine.
be very careful to save the mica insulator between the chip's heatsink and the chassis wall, as the new part may not come with one.
use a very thin coating of heatsink compound on the back of the chip's heatsink, and on the chassis wall where the chip mounts. dont use too much. stick the mica insulator onto the back of the heatsink on the chip, and stick the chip to the chassis. then bolt it, making sure it is straight.
mount the chip with the bolt BEFORE you bend and solder the leads. (hey, you never know.LOL)
be careful about static, and always touch your soldering iron's tip the the metal chassis of the radio before you solder any of the chip leads.
its really not too tough if you are carefull.
to remove the old chip; use a jewelers screwdriver to bend the lead up after heating it with the soldering iron. then unbolt it.
i really think this will fix your problem.
i hope so anyway,
best of luck,
matt
anyone wanting a "clean signal", just look to the left and build one of these!!!
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Dx_freak
New member
Username: Dx_freak
Post Number: 7
Registered: 2-2007
| | Posted on Wednesday, May 23, 2007 - 12:15 pm: |
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Kid vicious sounds like he has a point. I would also check out the rf voltage regulator. I had an PC 78 LTW that light up but did not key, receive or anything. I had the beefer voltage regulator installed and it took care of my problem, and also stopped the radio from diming the lights on key up also. Just another avenue for you too conceder. Good luck.
DX freak
Mad Dog/Short bus operator/Puppet Master
Special for my agitators fan club, im calling myself Puppet Master. I have two puppets that love to hear me key up and they are my #1 and #2 puppets, LOL.
Richey
CEF#885
I can only do the best I can with what I got.
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Kid_vicious
Senior Member
Username: Kid_vicious
Post Number: 2535
Registered: 9-2004
| | Posted on Thursday, May 24, 2007 - 12:00 am: |
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dx freak,
what is the part number of the voltage reg. in the PC78LTW?
and what part did you use as a replacement?
i am very interested in this upgrade.
thanks,
matt
anyone wanting a "clean signal", just look to the left and build one of these!!!
|
Lonestarbandit
Member
Username: Lonestarbandit
Post Number: 81
Registered: 10-2006
| | Posted on Saturday, May 26, 2007 - 12:44 am: |
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hey kid think thats a rat shack available ic? |
Kid_vicious
Senior Member
Username: Kid_vicious
Post Number: 2538
Registered: 9-2004
| | Posted on Saturday, May 26, 2007 - 2:31 am: |
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no.
it really shouldnt be too hard to find one though.
you can probably get one on an internet auction site.
or just google "TA7222AP", and you should get plenty of sources.
good luck,
matt
anyone wanting a "clean signal", just look to the left and build one of these!!!
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Dx_freak
Junior Member
Username: Dx_freak
Post Number: 10
Registered: 2-2007
| | Posted on Wednesday, May 30, 2007 - 1:05 am: |
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Kid, sry for not getting back sooner but I believe the 1 I put in miy radio was a
526-NTE1278 and I got mine from a local cb shop. As for price, I paid a whole 8 bucks or so for it and man did it wake that radio up. Hope this help you.
DX freak
Mad Dog/Short bus operator/Puppet Master
Special for my agitators fan club, im calling myself Puppet Master. I have two puppets that love to hear me key up and they are my #1 and #2 puppets, LOL.
Richey
CEF#885
I can only do the best I can with what I got.
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Kid_vicious
Senior Member
Username: Kid_vicious
Post Number: 2542
Registered: 9-2004
| | Posted on Wednesday, May 30, 2007 - 10:39 pm: |
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hi dx_freak,
thanks for the reply.
not sure how the NTE part "woke the radio up", as the specs are exactly the same for both parts.
both are 5.8 watt devices, and are internally identical.
most likely it was something else done to the radio at the same time the audio chip was replaced that helped.
who knows,
thanks again,
matt
anyone wanting a "clean signal", just look to the left and build one of these!!!
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