I know it's a Diode, can't read what the number is for it on the schematic. I have an old Phillipines Grant XL here with MB8719, has a shattered D44 and seems to not want to work on channels 38,39,40. but seems to work on all other channels, maybe some low voltage to the IC IDK, but also it seems to be stuck 1 channel down or up, like channel 6 is 7. I am like WTF? I don't see a 10Khz mod anywhere, but it's off by exactly 10Khz, and like I said won't work at all really on channels 38,39,40. I don't see anything grounding pin 16 on the MB8719. Help. Thanks.
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Uniden Grant XL D44 what is it?
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- Start date
http://www.cbtricks.com/radios/cobra/148gtl/graphics/cobra_148gtl_sch_b_size.pdf
If the D44/SR1K2 diode is the same as the Cobra 148GTL - it should be - then it is a part of the voltage regulator circuit 'anti spike' diode and should be replaced.
http://www.cbtricks.com/radios/cobra/140gtl/graphics/cobra_140gtl_142gtl_148gtl_tb1226.pdf
I would check the VCO voltage and make sure it is within specs.
I would also check the 1st and 2nd oscillators for alignment to be sure that it is up to snuff.
If you didn't find any problems in those adjustments, then I would consider the channel board for bad joints.
That is the extent of what I could tell you; but I am not a tech either . . .
If the D44/SR1K2 diode is the same as the Cobra 148GTL - it should be - then it is a part of the voltage regulator circuit 'anti spike' diode and should be replaced.
http://www.cbtricks.com/radios/cobra/140gtl/graphics/cobra_140gtl_142gtl_148gtl_tb1226.pdf
I would check the VCO voltage and make sure it is within specs.
I would also check the 1st and 2nd oscillators for alignment to be sure that it is up to snuff.
If you didn't find any problems in those adjustments, then I would consider the channel board for bad joints.
That is the extent of what I could tell you; but I am not a tech either . . .
I know I don't have an diodes around with numbers like that. Does it cross to a 1N part number diode of some kind?
Thanks for the reply. I will check all that (VCO voltage and Alignment) today, didn't have everything ready for that last night, was just looking around inside of it and only had a solder iron with me...
Thanks for the reply. I will check all that (VCO voltage and Alignment) today, didn't have everything ready for that last night, was just looking around inside of it and only had a solder iron with me...
Something else goofy I have found:
In the actual radio:
R44 = 8.12K Ohms
R174 = 12.0K Ohms
On schematic (which appears to be right for the rest of radio):
R44 = 2.7K Ohms
R174 = 4.7K Ohms
Any ideas why it would be so different? I am checking other various resistors in the radio to see if they match the schematic or not, this is a Uniden GRANT XL made in the Phillipines, the schematic is from CB Tricks, it IS labeled PC-409, which may not be the right Grant, this radio main PCB is labeled PB-208AB.....
In the actual radio:
R44 = 8.12K Ohms
R174 = 12.0K Ohms
On schematic (which appears to be right for the rest of radio):
R44 = 2.7K Ohms
R174 = 4.7K Ohms
Any ideas why it would be so different? I am checking other various resistors in the radio to see if they match the schematic or not, this is a Uniden GRANT XL made in the Phillipines, the schematic is from CB Tricks, it IS labeled PC-409, which may not be the right Grant, this radio main PCB is labeled PB-208AB.....
They extended the range of the clarifier 'slide' by increasing those values is all.
http://www.worldwidedx.com/cb-band-cb-radios/49063-cobra-148-gtl-review-4.html
Pulled up the schematic for the Cobra 148GTL, PC-412 and it DOES have the 8.2K and 12K resistors in the schematic for R44 and R174.
So this Uniden Grant XL PB-208AB must be the PC-412 board or VERY similar... Thinking I am on the right track now.
Still confused about the D44... Is that supposed to be a 16.2V or 18.2V? 1N part number anyone? I don't have a clue who makes a SR1K2 diode, sounds like some antique diode part number from a specific manufacturer, which I am sure crosses to some normal 1N diode part number.....? Thanks again for the help Robb.
So this Uniden Grant XL PB-208AB must be the PC-412 board or VERY similar... Thinking I am on the right track now.
Still confused about the D44... Is that supposed to be a 16.2V or 18.2V? 1N part number anyone? I don't have a clue who makes a SR1K2 diode, sounds like some antique diode part number from a specific manufacturer, which I am sure crosses to some normal 1N diode part number.....? Thanks again for the help Robb.
Found this tidbit of info using google:
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by what you are telling me, it sounds as if the voltage regulator has shorted out.
its IC4 and its an MB3756. not too hard to find, but an NTE1271 will work just fine.
after replacing the voltage reg. DO NOT turn the radio on until you have also replaced D44 with an 18.2 volt zener diode, and added a 1N4001 diode from pin 1 to pin 2 on the MB3756 voltage reg.
on D44 the UNBANDED end goes to ground.
on the 1N4001 diode the BANDED end goes to pin 2, and the UNBANDED end goes to pin 1.
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So I guess I should replace D44 with 18.2V Zener and add a 1N400X diode from pin 1-2 on the MB3756... Pretty sure the MB3756 is good in this radio, it had AM modulation and Receive and did not have a high deadkey, matter of fact I think the Final 2SC1969 is bad, only the driver putting out... Radio did not have much output last time I checked...
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by what you are telling me, it sounds as if the voltage regulator has shorted out.
its IC4 and its an MB3756. not too hard to find, but an NTE1271 will work just fine.
after replacing the voltage reg. DO NOT turn the radio on until you have also replaced D44 with an 18.2 volt zener diode, and added a 1N4001 diode from pin 1 to pin 2 on the MB3756 voltage reg.
on D44 the UNBANDED end goes to ground.
on the 1N4001 diode the BANDED end goes to pin 2, and the UNBANDED end goes to pin 1.
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So I guess I should replace D44 with 18.2V Zener and add a 1N400X diode from pin 1-2 on the MB3756... Pretty sure the MB3756 is good in this radio, it had AM modulation and Receive and did not have a high deadkey, matter of fact I think the Final 2SC1969 is bad, only the driver putting out... Radio did not have much output last time I checked...
It already has a Diode (1N4003 with blue paint on it?) from Pin 1 - 2 on the MB3756... On the circuit board it is labeled D78... So now I am like WTF again... So confusing, how many different versions of this radio did they make, LOL.
Update to this, got everything fixed up on the Grant XL, the problems with it were due to someone screwdrivering it in the wrong places I guess when they attempted the switch mod (channel expansion for MB8719). The reason it would not get 38-40 at all is because VCO was way too high, set it back to 3.6VDC on ch 40 and worked like a champ. Also peaked the receive and the transmitter output and set the AM TX Freq (SSB was already on Freq, just perfectly) and now the radio is good as new, works like a champ.
Only 1 minor issue, when you switch the radio to AM mode, the S/RF meter goes up to about 1-2 S-units and sits there with no input, yet there is no noise to make it do so, switch to SSB and it drops back right on 0, not sure what is up with that. I did not find an adjustment to calibrate the RX AM S/RF Meter. Does anyone know if there is such adjustment in this radio? Or is it only adjustable for TX on the S/RF Meter?
Only 1 minor issue, when you switch the radio to AM mode, the S/RF meter goes up to about 1-2 S-units and sits there with no input, yet there is no noise to make it do so, switch to SSB and it drops back right on 0, not sure what is up with that. I did not find an adjustment to calibrate the RX AM S/RF Meter. Does anyone know if there is such adjustment in this radio? Or is it only adjustable for TX on the S/RF Meter?