| Author |
Message |
    
Silvereagle
New member
Username: Silvereagle
Post Number: 5
Registered: 4-2003
| | Posted on Saturday, June 17, 2006 - 5:00 pm: | 
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Has been working just fine,now all of a sudden it has stopped keying up.Where do I start looking for the problem? |
Patzerozero
Senior Member
Username: Patzerozero
Post Number: 2992
Registered: 7-2004
| | Posted on Saturday, June 17, 2006 - 10:48 pm: |
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5 pin mic plug....i pull the xmit wire out in my mobile XL weekly.
try another mic 1st |
Kid_vicious
Senior Member
Username: Kid_vicious
Post Number: 1815
Registered: 9-2004
| | Posted on Saturday, June 17, 2006 - 11:07 pm: |
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put a wattmeter on it and confirm that there is NO power out as opposed to VERY LITTLE power out.
first, check the output on SSB by talking into the mic on SSB. if there is output on SSB but not on AM then replace TR41 with an NTE152. this is the AM regulator, and the stock part is underrated and can blow if the radio is peaked.
the NTE152 is a much stronger part, and wont blow. (well, anything is possible!)
if there is no output on AM or SSB try this:
there are some electrolytic caps on this radio that if they go bad, will cut out all transmit.
look at C95, a 47 uF 10Volt radial capacitor. It's located at the rear end of IC3, the balanced modulator chip. IC3 is about two inches to the rear of the front edge of the circuit board, just about centered left-to-right. If you unsolder one leg of C95, or just remove it completely the transmit power will return if that was the problem. Don't just leave C95 out if this fixes it. The part is there to filter noises that could leak into the transmitter from the power supply.
replace it with a 47uF 16volt electrolytic cap.
good luck,
matt |
Silvereagle
New member
Username: Silvereagle
Post Number: 6
Registered: 4-2003
| | Posted on Sunday, June 25, 2006 - 6:47 am: |
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I replaced the tr41 and now AM is transmitting as well as ssb.I do not have any receive at all.Plugged in a known good speaker.Where do I look now. |
Pogo12
Junior Member
Username: Pogo12
Post Number: 41
Registered: 3-2005
| | Posted on Sunday, June 25, 2006 - 1:12 pm: |
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The audio chip on the right side of the radio hooked to the wall.I cant remember FOR SURE but it may be something like TA7222AP and it will have 10 pins.If you change it make sure to put back the insulator and heatsink compond. |
Al_lafon
Intermediate Member
Username: Al_lafon
Post Number: 218
Registered: 3-2005
| | Posted on Sunday, July 02, 2006 - 11:06 am: |
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Hello frist check your S meter on a known busy
channel if its kicking around your problem is in
the audio chip but if its noe moving at all its
most likely the frist recive amp Tr 14 Replace the 2SC1674 (TR14) with an 2SC2999 (or similar low noise and high gain transistor) to achieve this improved signal to noise ratio.
Re-Adjust L4 and L5/L6
The gain will improved with more than 6dB with the same signal to noise ratio.Also if you replace D21 & D22 with ECG 593 it will give you
very nice AM recive This sxme psrt can also be used at D5 & D6 for better SSB AGC.
Hope you get your
Radio back on Air. |
Silvereagle
New member
Username: Silvereagle
Post Number: 9
Registered: 4-2003
| | Posted on Monday, August 28, 2006 - 5:37 am: |
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Where can I find a schematic for my cobra 2000 that has voltage readings.I know it is sams cb radio manual 251 but can't seem to find one. |
Kid_vicious
Senior Member
Username: Kid_vicious
Post Number: 2014
Registered: 9-2004
| | Posted on Tuesday, August 29, 2006 - 12:19 am: |
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you should be able to buy a copy of the sams 251 on CDROM off of the internet auctions
i bought one for about $6.00
good luck,
matt |
