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Uniden Grant XL problem

no offence taken. AM reg's with those chassis's have been a on again off again commond problem. Using stronger ones would have more then likely nipped it in the butt from the get go. Another part I've seen go on those chassis's (more then a few times) is the MB3756 ic regulator, again , another fairly cheap part and easy fix. When those go , the lights are on and nobody is home. :( Casper has a good radio here , if it's not the AM reg. ? it still is nothing serious and fixable from what he has discribed.
 
ok replaced the voltage reg, took out the james brown box, took out the echo box. hooked all the wires that needed to be hooked up... and still nothing after i put the new voltage reg in i took it out to the car hooked it up and this time no sound at all, still can hear myself on talk back and on pa but not getting out passed there, so reading up on the past posts im gonna guess the audio chip is gone,,,,,:headbang so on to the next thing,lol the audio chip, im willing to go thru everything at this point just so i can have it back up and running,lol but its ok guess ill have to live with out if for a little while longer,,,, i do have a cobra that i am using now but would still like this one back up and running,,, thank you to every one that has helped out this far and am looking forward to more tips on this one,,,,,mark
 
ok i know its been a little while since ive posted,,,,, since i last posted ive had the chance to work at a cb shop in TN, I was there for over a month but never brought the grant xl in,,, sitting around and talking with the radio tech there ive come to teh conclusion that i didnt use the same am reg that i had in it, they also had a few grant xl there on the back shelf as parts ive studied all pretty close and saw that i didnt have the same am reg so thats one place to look at,,,,, im back in MN now and have been looking and looking at the grant xl just sitting there,,,,,, with the info i learned on here and down there, ill have it back up and running soon, for the time being im running a pc66xl which is swinging up to 24 watts so im not to worried bout teh grant xl at this time, when i do get it done ill be a base unit and let it run with a kicker maybe who knows,,,,, i know that i would like to get a kicker for the pc66xl but im not sure yet,,,, ive been more then satisfied with the results ive gotten from the 66,,,,, i think the only thing ill change on that one would be the channel light from red to blue which i have in the meter as of now,,,,,, and from working at the shop i learned that i didnt know how to solder at all,lol kind of interesting the things you learn from jobs,,,,, i enjoyed working around the big rigs all day doing installs on them,,,, i was labeled an installer at the shop,,,,, i did everything from the outside in,,,,, when i get the chance to go back to TN im planning on going back and trying to get back into teh shop and learn as much as possible,,,,,,,,,,,thank you again for everyones support and tips,,,,,,, yall have a safe one and a good one,,,,,,,mark
 
ok ive been letting this radio sit for a bit and have gotten around to working on it again,,, planning on gettin a new am reg and also a new audio chip,,,, my next question is,,,, were is the audio chip located at,,,, ive looked at the board and nothing looks burnt anymore,,, only thing i found burnt was the black wire and white wire going to the mic plug,,,, i took and cleaned the wires all up and still nothing,,,, ive had this radio aprat a few times lately looking to see if i missed any peice that may have gone bad,,,, but to no luck everything looks clean only place that had a smell was back around the 2 wires that had gotten burnt so hopefully with replaceing the am reg and the audio chip it should work,,,,, i hope,,,,, after i get these 2 things replaced im planning on changeing out the meter light and channel light and maybe adding nitro knob lights behind the stock knobs,,,,, it was a good radio when it worked and thats why i want it back up and running,,,,, as far as the swr check goes the anttenna i have now is set,,,, im getting a 1.6 on 1 and 1.6 on 40 and reading a flat 1 on 20 so that will not be a worry once its back up and running,,,, when i had the radio hooked up before i thought the swr were fine but i was more then likely wrong now that i have gotten to learn more about it, plus i have a better anttenna to work with,,,,,,, mark
 
Ok here's one for y'all. Is it possible to put a MOSFET final kit into this radio. If so which one and where can I get it. I'm hopeing that there is a kit out there for this radio. Like I said I been using the radio most every night. It work on lsb and USB. But still no am. The radio is pushing around 12 watts one side band but I would like a little bit more out of it. I have a Royce 639 that I'm getting 20 watts on sideband. Everyone I've talked to on the Royce says the little jump I'm power said it has made a big differance. So that's why I would like to see about a MOSFET final kit for my grant xl.
 
caspear1978 said:
Ok here's one for y'all. Is it possible to put a MOSFET final kit into this radio. If so which one and where can I get it. I'm hopeing that there is a kit out there for this radio. Like I said I been using the radio most every night. It work on lsb and USB. But still no am. The radio is pushing around 12 watts one side band but I would like a little bit more out of it. I have a Royce 639 that I'm getting 20 watts on sideband. Everyone I've talked to on the Royce says the little jump I'm power said it has made a big differance. So that's why I would like to see about a MOSFET final kit for my grant xl.
Click to expand...

There may be a MOSFET kit for it; as it is similar to the Cobra 148GTL.
But why do that? Sounds like this radio is the perfect candidate for a low-drive/low power amp - like a 50 or 100 watter. Cheaper this way - and far less work too...
 
hi All some of the am regs are on th side of the chassie 2"or so back from the channel selector on the later grants if you have sound on ssb and hear talk back the audio chip is ok put a nte 152 for the am reg thanks Ben
 
ok replaced am power reg, am voltage reg driver final mb8719 c174 c188 and q21, volts are good on all replaced items, still no tx, checked d40, volts are good as well, was looking at q71 and wondering what q71 was for in the grant xl, radio still rx fine but still no tx and keys up at 10 watts, ssb works wonders, so any ideas from here would be great, thank you Mark
 
Q71?

sure thats not a typo?

as far as i remember, they only went as high as Q47.

what section of the radio is it in?

since it works on SSB, we know the final and driver are good, the audio chip is good, and that the problem has to do with something that is being used in
AM mode but not in SSB mode.

yes, the most common cause of this problem is the shorted MB3756 voltage regulator, but we know you have already replaced this.

is there a chance that there is a component near the voltage reg that is shorted causing the new one to act just like the old one?

here are a couple of tests that will help me, and others who read this thread help you.

first, set the radio to AM mode, and turn the mic gain all the way down.

using a voltmeter set to read DC volts, key the radio, and while TXing, measure the voltage on all three legs of the final (Q36), the driver (Q38), and Q41 (AM reg).

all three of these transistors are BCE from left to right. (Base-Collector-Emitter.

so, if you were looking at the final, and reading where it says 1969 on it, the left leg would be the Base, the middle leg would be the Collector, and the right leg would be the Emitter.
also remember that when you turn the radio upside down, the Base and Emitter legs will be on the opposite sides as they were.

make sense?
good.

so, in your answer; tell us which transistor you are measuring, which leg you are measuring, and what the voltage on that leg is while transmitting.

black lead from voltmeter is to PC board ground for all measurements. Red lead goes to each transistor leg.

this will help us understand what is going on.

oh, two more quick tests that will help.

1. with your voltmeter set to measure continuity (shorts and open connections) put one lead on the metal mounting tab of Q41, and the other lead to the metal chassis of the radio.
is there a connection there?
there should not be.

2. measure the deadkey of the radio in AM mode with the AM POWER pot (VR10) turned all the way down, and all the way up.
what are those numbers?

good luck,
hope you find some help here,
LC
 
Last edited:
Ok heres what i came up with for volts,

Driver - B - 1.04, C - .05, E - 1.94
Final - B - 2.80, C - .10, E - 1.70
Am Reg - B - 8.55, C - 9.47, E -7.57

Q41 metel mount tab to metel chassis
No connection

Am DK VR10 Up
10 watts

Am Dk VR10 Down
10 watts

as far as Q71 it is to the right of L3 and just above FT3

Thank You Mark
 
i cant find a Q71 anywhere in any schematics or parts list.

are you sure it doesnt say Q21?

i will look at the other things and post more tomorrow.
later,
LC
 
Yea it says Q71 its small round and black has 4 legs , the legs are comeing out in the left top right and bottum in a plus pattern, it says 68 k85 on the top of it, thanks mark
 
loosecannon,

Q71 is indeed in the UNIDEN GRANT XL, if your looking at the schematic for the Cobra 148 GTL it is labeled in that radio FET-1. In the GRANT XL (I checked mine too) it is a 3SK85 DUAL GATE MOSFET & appears to be in the IF section.
 
Mine says 6Bk85, but yes that is the part im talking about, i was just wondering what that part was used for in these radios,,,,Thank You Mark
 

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