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Uniden Grant XL problem

Caspear1978,
The one in mine also says:
6B
K85

But the complete part number appears to be 3SK85 if your looking for a datasheet.

Just thought I would throw my 2 cents in on that part you were referring to.

I hope you get your radio going, the GRANT XL is a nice radio. Take care!
 
I likemy grant xl as well, it is the best one i have had so far and i do hope i can get it figured out, im sure it has to be something simple, but i just haent come across what it is, Im not sure how ill react to haveing a completely working grant again, i think it was working for about 4 months after i bought it and then the am side messed up, i looked at the tech bullitin for the 148s and tryed what they said on there and that didnt work as well, im waiting for LC to come back and tell me if my volt numbers are good or bad so far and then go from there,,,,Thanks Mark
 
those numbers are not right, and it seems like the voltage is not getting to the collectors of the final and driver.

you should be getting about 5.5 volts on the collectors of the driver and final in AM TX.

you also should be getting 13.8 volts to the collector of Q41.
trace out the middle leg of Q41. most likely you will see the trace go to a jumper wire, and connect right to a trace that connects to the positive lead of C172, the main filter capacitor (also the biggest one on the board)

you should be reading 13.8 volts or close to that on the pos lead of C172. are you?

what are you getting for voltage on pin 1 of the MB3756 8 pin voltage reg?

should be right at about 8 volts.

i know you dont want to hear it, but it still seems like power supply issues to me, meaning the MB3756 isnt doing what its supposed to do.

do you have a D78 on your board?
should be right near pin 1 of the MB3756.
if so, remove it from the board and do a diode test on it with your voltmeter. (instructions found by googling "diode testing with a multimeter")

sure hope we get this figured out,
LC
 
i dont mind hearing the bad noise on the radio LC whts the worst i can find out that its shot,lol well part of it is right now, but thats why im here, to figure out whats going on and how to fix it, ill check them parts as you specified and well go from there, Thanks Mark
 
ok heres what ive come up with

D78 test forward
559

D78 test backward
1640

Pin 1 is 8 volts

C172 is 12 volts

thats what i came up with,,,, if the number seem a little low, it is because im useing a battery in the house here, so i figure everything that suppose to read 13.8 will read around 12 if im not mistakeing, ,,,


Yea i agree LC i hope we get it figured out also

Thanks Mark
 
if the positive lead of C172 is 12 volts, then you should read 12 volts on the middle leg of Q41.
try measuring the middle leg in receive first. you will most likely see 12 volts.
if that 12 volts is not there when you key the mic, there is some component that is shorted or open and is pulling that voltage down.

the numbers you gave me for the final and driver were taken while transmitting in AM mode right?

i dont see how you can have 10 watts output without any voltage on the collectors. (middle legs)

the only thing i can think to tell you is to check all the components near Q41.
you will have to remove them from the radio to get accurate test results.

start with Q42, using the diode function on your voltmeter. (instructions online)

then check D54 and D63. then check C173 and C191 for shorts.
remove VR10 and make sure the resistance is changing as you turn the pot.

yes, im starting to guess now, but without having the radio in front of me thats about all i can do at this point.
im afraid if you dont find the problem there, then im out of ideas at the moment.

also remember that if you do find a faulty component near Q41, it might have blown the one you just put in, so you might have to replace it again after you replace the faulty component.

make sure you look very closely for traces that might be touching other traces because of a solder bridge.

good luck,
LC
 
on Q41 its not solder to the board it has a llittle pcb board soldered to it and mounted to the back of the radio, its got three wires comeing from the little board and running to the main pcb board, i will follow the wires and test them parts as you instructed and see what i come up with,, i do have another mb3756 her so if i need to replace that i can when the time comes, i think i will order up another am reg just to be on the safe side, and will replace that when i replace mb3756, i will get the volts for you later this after noon, and i do thank you for all the help so far, Mark
 
ok so everything checked out on those parts, as i was sitting here looking at everything, i decided i was going to check all the vr pots, , i found that vr7 has no power at all going to it, i traced that back to r131, r131 had power to one side and nothing on the other side, looking closer at r131 i found that it had been clipped, with r131 clicped would this also cause my problem, if so what is the resister that i need to put back in there to make it have contact?,,,Mark
 
well thats a bummer.

keep looking around the MB3756 for shorted caps and such.
did D78 check out ok? open in one direction and somewhere around .4 to .6 volts in the other direction using the diode test function of your multimeter?

R131 is the AM mode modulation limiter. very common to see it clipped.
if you put it back in the circuit and turn VR7 all the way up, its basically the same thing.

it would not be causing the problem you are having.

keep on keepin on,
LC
 
well , I came across another slight problem, i replaced r131 with another risistor and i keyed up and it still went to 10 watts, that was am, so i flipped over to ssb dand to talk to a buddy and i had no modulation on ssb,, so yea ive got a problem,lol all i did to get ssb modulation back was clip r131 again, maybe i should redo r131 again and go through and check voltages again, i have a feeling the problem is eluding me with it clipped, d78 checked out good, i will keep looking around mb3756, i might just replace it and see what happends and go from there, Thank you for your help LC, ill let ya know more as i go on with it, if i have anymore questions ill be back,Thanks again,,,,,mark
 
wow, im not sure what to make of that last one. LOL

R131 causes the SSB modulation to go away?
as far as i know it has nothing to do with it.

you might want to look at your AM/SSB switch for signs of previous work or corrosion, or, i dont know...

good luck with it.
LC
 
yea LC, i had to giggle about that one also, im not sure anymore whats going on with it, all i know is i replaced r131 and flipped over to lsb and low and behold no mod, i dont know aht to think about it anymore, all i did to get lsb back was clip r131, oh well the search continues i guess, unless i can find another grant xl, i know where there are 3 sitting on a work bench and all work, so i think its time to call and see if i can pick one up, ill let ya know how it goes, after i get it in, im going to do some comperisons and see what is really going on, the other grant xls are all stock, never been touched, so ill beable to get a good idea where im at from there, Thank you LC for all the help, it has been all helpful to me,,,,mark
 
well after letting the radio sit for aa long time and not having am, i got back into it the other day and found a couple of things wrong,


1. the protection diode was bad, couldnt see that it was bad until i pulled it out and clipped it over, looking at the side facing the board i saw a nice crack down the length of it, replaced that.

2. Q42 was bad, after sitting there staring at the radio for about an hour, i spotted what looked to be a crack, took it out and sure enough there was a crack going from the top to the bottom, so i replaced that.

3 replaced the am regulator just to be on the safe side, after doing so i had modulation back on am, when i plugged the radio back in and keyed up the red wire going to the regulator started smoking and started to melt, further inspection i found that the reg was grounding out on the chassis, pull the reg out, hand wired the wires going from pc board to reg,

so now i detuned the radio so i can run an amp behind it, , have a dk of 2 watts swinging up to about 8, so that should do ok with the amp behind it,

wanted to get it fixed for a trip ill be taking next week to south dakota to see some family so now im happy,

and to think the problem was as simple as a 945 transistor, but atleast its fixed now and working good, thanks to every one that has helped out on the radio,,,,,,mark
 
gee, seems to me that someone suggested that you test this part many months ago. LOL

"i dont see how you can have 10 watts output without any voltage on the collectors. (middle legs)

the only thing i can think to tell you is to check all the components near Q41.
you will have to remove them from the radio to get accurate test results.

start with Q42, using the diode function on your voltmeter. (instructions online)"


just messin' with ya'!

glad to hear you got it all sorted out.

just to make sure, when you say you "detuned" the radio, do you mean that you adjusted the transmit coils for less than their peak?

if so, re-peak them while saying "ahhh" into the mic, and use VR10 to set the deadkey where you want it afterwards.

if you did use VR10 already, and the TX coils are peaked, then you're all set.

have fun on your trip!
LC
 
ha ha funny guy, i guess i had that coming tho, and yes you are right you did mention it,
as far as tuning, ill get back into it tomorrow and do as you instructed, and i will use vr10 to set the dk down,

the only reason i detuned it was for the fact the am reg that i am using isnt the right part but will get me by until i pick up an nte 152, so i fiugred trun it down that way i dont over power the reg,

im not longwinded when it comes to keying up, so that should be fine to bring it back up and turn vr10 down,

i tested the radio today for about an hour and everything seemed to stay cool, so now all i need to do is get it tuned right,

thanks again LC
 

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