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Uniden Grant XL No Transmit

No TX. Everything else works great. Changed final, driver,ic4 voltage reg,mode switch and a few others. No TX? TP7 and TP8 have no voltage? 0.11volts. I no it should be 12.8volts. Pa mode works. Also radio next to it will move the meter. Any help? Thanks, TJ

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  • Thejerb Feb 02, 2009

    Thanks wood butcher for the help. I replaced the driver, final and the am regulator. Still no tx. There is no voltage to the test points 7 and 8?? Anybody???

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On the back of the radio you will see a small circuit board with a transistor on it this is your am regulator.check to see if that has gone bad

Posted on Feb 02, 2009

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Radar 1731 shuts down when tx is hit


There are a couple of things that could cause the radar to power off when going into the transmit mode.

The first thing to eliminate is input power. When in the standby mode the radar draws less current than in the tx mode so if you have low voltage for whatever reason, that could cause a shut down. Check all connections and measure the voltage to the unit while it is on.

A problem with the antenna motor or gear box could also be the problem. The antenna doesn't rotate unit the unit is switched to the tx mode. You would need to remove the dome cover (with unit off) and verify that the array will turn freely by hand. Typically, a bad motor will not cause a shut down but a physical obstruction could.

Focus on the power issue because that's the most common problem. Be aware that you need to measure the voltage as close to the radar display as possible and watch the voltage as you switch the radar from standby to transmit for a quick dip in voltage.

Jun 25, 2014 | Furuno Navnet 1834C/NT vx2 Radar C Map Nt

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NO TRANSMITT


failed driver final transistors or voltage supply to driver and final

if your RX is aok then chances are the PLL and TX mixers etc are aok leaving only the first answer or a broken mic or TX switching circuit caused prob by a bad mic cable

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1 Answer

When i try to calibrate my 148gtl mk 2 the needle is very erratic,why?


can you be more specific please ?
TX meter or RX s meter ? check power supply voltage is stable,
obviously on RX its essential to use a constant signal, of course,
if you're doing it without test gear & just doing a quick 'tweak' comparing with a good know s reading off a known set - a s9 signal is usually the standard point they calibrate to. although on a CB set its not a greatly important. on TX you may first want to check RF power out is constant first, so a dummy load (in case aerial swr is changing while on TX) needs to be used.
If actual RF power is changing, suspect drying electrolytic capacitors, these sets are 30 years old, so its not unlikely. dying driver or PA transistors or dry joints are also possible. or if everything checks out, possible voltage regulation probs, so check 2SA1012 AM reg isn't dying and the other ****** too.
If you're lucky, its just the variable resistors giving up.

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My cobra148gtl will not transmit


First check voltage of IC 4 (mb 3756) pin #8 in TX mode should be 8.0 volts. Check the voltage of the center leg of Tr36 (Final) and of Tr38 (Driver) RX=13.78 volts DC, TX=4.5 to 6.5 volts..

Jan 06, 2011 | Cobra 148 GTL 120-Channels Base CB Radio

1 Answer

Radio 29 ltd no modulation, no receive and good carrier, no capacitor shorted or blowm,changed ic audio by a new one and get still the same problem


did you change IC4=TA7222AP ?
check input ic4 pin1 is it supply voltage?=12vdc.
check C48 couple cap,also check C39 replace
with a 25 watt and C42 also C45.
check R130 1.1 ohm. also R121 180 ohm.
if pin 1 on ic4 is low volt or missing,check TR23
and D22,C119
maybe this will help some

Sep 28, 2009 | Cobra 29 LTD CB Radio

1 Answer

Low TX PWR/ATU won`t tune. No SWR and ALC metwr reading?


You've replaced the pre driver, the drivers and finals. Set bias and still low output. The pre driver is the same transistor used as the tx exciter transistor on other pcb chassis on bottom of radio. Follow the gray coaxial wire from the pre driver on the RF circuit board back to the tx/rx i.f. Circuit board. The gray coax cable plugs right next to the tx exciter transistor on this pcb. Again it's on a different pcb all together and on the bottom of the radio and also. Replace it! And check for open bias or emitter to ground chip resistor next to it. You will get your drive back. Very few rigs have I seen the actual Finals blown in the mosfet or the bipolar version. Just the driver stage with a week pre driver and the SMT "pre" pre driver on the same RF pcb. And the tx exciter on the other pcb.

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1 Answer

No receive cobra 29 ltd classic


Hi and welcome to FixYa,

Initially, pls confirm that there is modulation (transmit audio). The reason I asked is if IC4 (TA7222P) is blown, then the radio would have no audio amplifier which would explain no receive audio. Additionally, the final and pre-final (TR15 & 15) gets is modulated TX+12 through D8 from T1 which in turn is the output of IC4 through C48.

Perhaps a schematic diagram may be of further help.

Good luck and Thank you for using FixYa. Happy Holidays.

Dec 18, 2008 | Cobra 29 LTD CB Radio

2 Answers

Cobra 29 nw


Hi and welcome to FixYa,

Initially, pls check the final and pre-final (TR15 & 15) and that it gets modulated TX+12 through D8 from T1 which in turn is the output of IC4 through C48.

Perhaps a schematic diagram may be of further help.

Good luck and Thank you for using FixYa. Happy Holidays.

Dec 08, 2008 | Cobra 29 LTD CB Radio

1 Answer

Cobra 29ltd classic : no rx / tx


Hi,

D23 is the reverse protection diode and it shorting is the primary reason your fuse blew. As you posted, power was applied in reverse, hence other components would also fail. Pls check:
1. D22 - 9.1V Zener Diode
2. TR23 (2SC1096) 9 Volts regulator
3. D19 - 5.1 Zener Diode
4. IC4 (TA7222) - Audio Amp
5. TR14 (2SC2029B/10) - Finals
6. TR15 (2SC2028B/20) - Driver
7. Most capacitors over 220uF (like C123, C114 & C112)

Hope that this be of help/idea. Pls post back how things turned up or should you need additional information.

Good luck and kind regards.

Feb 04, 2008 | Radio Communications

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