Uniden Grant XL Receive issues

[Shrav]

Hi all
Just picked up an XL from ebay. Transmit is great. Reception isn't. Swapped in 2 other units and I hear all kinds of distant chatter. Had my son drive from the house as a test and he heard me about 7 miles away. I lost him after 1. Plugged in a spare unit and I can hear. I think L4/L5 are the pots to tune for the receive. Made only a minor difference. Anything else to check or should I put this thing back on ebay and move on? Thanks in advance!

[The Defpom]

This sounds more like the AGC or RX front end has been overloaded and failed, the radio probably needs to have some parts replaced.

[Rick]

Farley common fault with this radio, check D12 and D13 you will probably find one the diodes open circuit if so replace and also replace Q14 (2SC1674L) has it will have gone low gain. You will need to retune L4 to L10

Rick.

[Shrav]

Farley common fault with this radio, check D12 and D13 you will probably find one the diodes open circuit if so replace and also replace Q14 (2SC1674L) has it will have gone low gain. You will need to retune L4 to L10

Rick.

Hi Rick
I checked both diodes and they seem ok (work one way, nothing with leads reversed). I also pulled Q14 and using the red tip on the base got a reading on the collector and emitter. Reversed no reading and also no reading testing collector to emitter (tried both directions). I did notice a variance from the reading of the base to collector and the base to the emitter. Should their be a slight variance or should they be bang on? Thanks again for you help!
Glenn

[Rick]

I would just replace Q14, you can not test for low gain with a mutilmeter, also check the AGC voltage. The common fault is front end fault I wish I had a pound for ever one I have fixed.

Rick.

[Shrav]

I would just replace Q14, you can not test for low gain with a mutilmeter, also check the AGC voltage. The common fault is front end fault I wish I had a pound for ever one I have fixed.

Rick.

I'll make the long drive to Toronto to a parts supplier tomorrow and grab a replacement. They list a 2SC1674 but I believe mine is a 2SC1674L. Any difference? Any other possible ones to put instead since I'm this far into it anyways?
For the AGC voltage what/where should I be checking? If that voltage is low what other part should I be testing/replacing? I figure I should get my parts list now as the return trip for parts is about 2.5 hours from home. Thanks again for all your input. I'll get this fixed yet!

[Rick]

The 2SC1674 is the same as 2SC1674L. You can check the AGC voltage at the Anode for D13 it should be about 4.8 to 5.8vdc with no signal and 1.5 to 2.0vdc and S9. To see if ot is a AGC fault clamp the AGC line to 4.0vdc but do not transmit while the AGC is clamped.

Rick.

[Shrav]

The 2SC1674 is the same as 2SC1674L. You can check the AGC voltage at the Anode for D13 it should be about 4.8 to 5.8vdc with no signal and 1.5 to 2.0vdc and S9. To see if ot is a AGC fault clamp the AGC line to 4.0vdc but do not transmit while the AGC is clamped.

Rick.

I looked on cbtricks and don't see a schematic for my xl. I understand it shares the same board as a cobra 148. It that correct? If that is the case where would I apply the 4v to and is their a 4v tap point in the unit that I could jumper from? Thanks again for your patience!

Glenn

[Shrav]

All it took was a drive to a shop and they tuned it and replaced a few parts. Tried a test with my son driving until out of range. We got almost 8 miles. Last time we got 7 and he couldn't hear me. Last time I only heard him for the 1st mile. Long story short... you can't tell with used and unless you find that magic knob inside thats says "twist me to fix your radio" bite the bullet and get a pro to look at/align it. At least you have a baseline to start from if you go messing around with it later.

On a personal note a massive THANKS to Rick for all the help and guidance he gave me. He knows his stuff!