Pix Request, 148 GTL / Grant XL

[redlght]

Also test the pre driver

 

[LeapFrog]

Also test the pre driver

I will do this in a few hours, thank you!
EDIT: Installed Antron 99 instead, sorry.

 

[Robb]

Leave the wax alone; it isn't a problem. Glue is.

Why didn't you take the bias diodes out and test them?

 

[sonoma]

the wax in the back of the radio was just to hold wires and parts in place while soldering at the factory and more than i have seen before may had been messed up during the wax app/ the back area you were pointing to is not the vco area, it is the RX area.you can glue a 4148 diode to the final and driver to replace the mvy1 I think is the part number. the ones from the factory are temp sensing diodes. to verify the direction of the diode that would be simple to do since you say they still work. just check the voltage flow of the ones installed and then check the flow of the 4148 by using a ohm meter in the diode testing mode. if you are just getting a slight difference in the reading on the stock diodes I would say they are just fine .
sounds like you have some week caps in the TX stage that are old and going south. I would change them out , especially the ones in the 10 volt range and put 16 plus volts back in. the 10 volts are bad about getting bad. you said you turned 3 cans on the right side of the board. if you did theat and did not know what they were for and not hooked up for proper adjustments could have started thing dropping out. when you say cans the 1st thing I think of is the L can adjustments. if it is the variable resisters the are VR's. what can numbers did you turn to 1/4 position. some VR.s adjust back wards to others depending on how the board layout is done and the ground position on the VR 's

 

[Robb]

All 10v caps - gotta go!

 

[LeapFrog]

Glue a 4148 diode to the final and driver to replace the mvy1 I think is the part number. the ones from the factory are temp sensing diodes. to verify the direction of the diode that would be simple to do since you say they still work.

One has failed i think, they test different from eachother in circuit.
I should remove them but i just want to temporarly install the 4148's to continue testing for TX.

You said you turned 3 cans on the right side of the board. if you did theat and did not know what they were for and not hooked up for proper adjustments could have started thing dropping out. when you say cans the 1st thing I think of is the L can adjustments. if it is the variable resisters the are VR's. what can numbers did you turn to 1/4 position. some VR.s adjust back wards to others depending on how the board layout is done and the ground position on the VR 's

No, when I got this radio the bias trimmer pots, were all full right, so I turned them back to 1/4 way open just to test the radio. I talked on it fine for an hour like this, and the driver/final ran cooler.

 

[Robb]

Sooo; you didn't adjust the bias pots? What are you afraid of? Get out that DVM and learn how. Your predicament dictates your involvement.

Test in SSB mode with mic gain set to zero. One lead to the board post to the DVM, and the wire to the other DVM lead. The posts on the board is where the + lead of the DVM + wire goes; and the removable lead on the board is connected to the - DVM lead goes. Set DVM on mA range. Key the mic for the reading and adjust accordingly.

Read the Service Manual to get the appropriate mA settings for the final and driver. Do the driver first and then the final last. IIRC, the driver is 35mA and the final is 50mA.

You can do it!
It isn't that hard.

 

[sonoma]

if the VR's are getting bad you may have turned the bias off. do as ROBB said and set them to spec.the settings you did may have worked a few times then the vr may have gone bad and not putting out any voltage. never set the bias this way just by turning it and not checking the milli amps it is to be set at.

 

[sonoma]

you said you turned 3 VR's. is this a dual final radio or single final. if it is a single final it only has 2 VR's for the bias adjustment. I am now wondering what the 3rd one was you turned. you say 148 and grant XL. which are you working on. the service manual for the 148 is on cbtricks . the grant xl is basically the same radio as the 148 so the manual will work on either one.

 

[Sideways]

Leap, the bias diodes are different, and why the readings arent the same.
According to Rick Jackson's schematic on cb tricks for the 148, the driver diode is labeled d50 and is a MV1Y.. The final diode is labeled d49 and is a MV13YH.

I remembered thinking the same thing one time while troubleshooting an old 148.
Hope this helps

 

[LeapFrog]

Hi Guys, it doesn't not TX anymore, how can I set the bias without TX lol
I spent yesterday installing my Antron 99 so I never got back to the Grant XL, I had a problem when I first set the bias for the driver it never would reach the spec. it would get close then if I tried to increase it more it would read 0.

I have to check the tp8 tp7 I think a voltage reg died somewhere.
I am familiar with the bias procedure thanks to the help from this forum, already.
Members like Robb, Loosecannon, ExitThirteen, Tallman, Sonoma, and many others have already helped me grasp the process. I am doing it correctly.

Sooo; you didn't adjust the bias pots? What are you afraid of? Get out that DVM and learn how. Your predicament dictates your involvement.

Test in SSB mode with mic gain set to zero. One lead to the board post to the DVM, and the wire to the other DVM lead. The posts on the board is where the + lead of the DVM + wire goes; and the removable lead on the board is connected to the - DVM lead goes. Set DVM on mA range. Key the mic for the reading and adjust accordingly.

Read the Service Manual to get the appropriate mA settings for the final and driver. Do the driver first and then the final last. IIRC, the driver is 35mA and the final is 50mA.

You can do it!
It isn't that hard.

Thank you Robb, I tried when I first got the radio, I was doing everything to spec, but the driver would not bias high enough it was 10-15 mA too low. When I tried to raise it any higher the meter read 0, so I changed the pot, same issue. No I just want a flicker of TX output and I will set the bias, something else is wrong though, I spent yesterday putting up an Antron 99, so I never got back to the Grant XL.

Today it's my goal to get her going again, and finally set the bias correctly.

you said you turned 3 VR's. is this a dual final radio or single final. if it is a single final it only has 2 VR's for the bias adjustment. I am now wondering what the 3rd one was you turned. you say 148 and grant XL. which are you working on. the service manual for the 148 is on cbtricks . the grant xl is basically the same radio as the 148 so the manual will work on either one.

Grant XL, the third one was for modulation, somebody set this radio for the "full tilt boogie". I tried to undo that and teast it, I had a failure soon after I tried to set the bias and couldn't get it nailed.
The radio was originaly "all the way to the right" and it keyed and talked like that (with reverse swing)
I was spooked when I saw them all the way to the right so I put the 2 bias pots a quater of the way open, and also temporary set the modulation adjust halfway (if that is what that pot was, i forget but i did look it up befoire messing with it).

Now that I think about it the 3rd pot they had cranked was for the S-meter lol.
So to some it up, I need to check voltages, and the pre-driver.

Leap, the bias diodes are different, and why the readings arent the same.
According to Rick Jackson's schematic on cb tricks for the 148, the driver diode is labeled d50 and is a MV1Y.. The final diode is labeled d49 and is a MV13YH.

I remembered thinking the same thing one time while troubleshooting an old 148.
Hope this helps

If the two diodes are not the same, I need to reference that scematic Rick Jackson shared.
Surely I could lose (all) TX if one of these failed?

The TX led does change from green to red, no output on SSB or AM.
Going to poke about it some more after coffee!

 

[LeapFrog]

All 10v caps - gotta go!

They are, thanks LOL.
I don't need any ten volt blues (or greys for that matter) lol.

 

[sonoma]

sounds like you have some bad VR's in the radio if they go dead to zero. or they are bad and taking the voltage over 200 milli amps. if it does that your meter will show zero's.

 

[LeapFrog]

sounds like you have some bad VR's in the radio if they go dead to zero. or they are bad and taking the voltage over 200 milli amps. if it does that your meter will show zero's.

So if the amount of bias current is too high (over 200 mA), my meter will show 0?
Thank you. I would hate to have to change out all the VR's, I'm going to look over the radio somemore and see if a signal is at the pre-driver or driver stage.

 

[sonoma]

not sure why you would hate to change out the VR's. they are very simple to change out. you will need to get new ones. used ones out of another radio can also be bad.