Cobra 148gtl No Modulation and...

[Handy Andy]

I tend to agree, the foil on these two pads is easily lifted so when you find "crooked-ly" mounted parts - it means the Wave flow Soldering machine hit a few bumps loosening the parts it supposed to solder in.

Look carefully to the LEFT in the photo - midsection - there are two traces with a solder tail in-between. You may find that a lot in newer boards that "ran cold" thru the machine - the flux didn't clean the pad, and the solder "wicked" to a dust bunny or other hair between the two pads.

How to know it was cold? Look to the bottom of the EMPTY pads, wicked solder adherence to cold metal changes the level of flow - the hole filled in, but note the dimple, that section stayed molten longer. As it cooled, the outer ring of the pad solidified faster - so the solder "stretched" the hole.

 

[Gunner357]

I re-soldered those 2 area best I could No changes so the search goes on ...I think Im still going to put the finals in I dont know if that would help the WeaK modulation problem or not but Ill give it a try.....

 

[Handy Andy]

When you say that the parts are not matching up to the schematic, did you ever find your board number?

PA-4XX or PB-3XX - somewhere on top of the board...

PC-78

Cobra 142
​

OR even on the Foil side, but earlier ones used to print them on edge but you can find it anywhere...

Let us know what you find...

 

[Gunner357]

When you say that the parts are not matching up to the schematic, did you ever find your board number?

PA-4XX or PB-3XX - somewhere on top of the board...

PC-78
View attachment 39115
Cobra 142
View attachment 39116​

OR even on the Foil side, but earlier ones used to print them on edge but you can find it anywhere...

Let us know what you find...

Ill have to open it up to see the numbers I put those finals in just for the hell of it and like i thought the 1969's are clones will not work the 2166's are OE and work good.....

 

[Gunner357]

Im sorry its been a while since i finished this issue, here is the only number on this board.....also a few things arose... I have very little modulation now if I turn power mic up all the way and whistle as loud as i can it may go to 5-10% on my modulation meter (external) the radio's meter just DK to 5 watts and no swing at all, And yes I tried the MIC on another radio and it worked..... There is no AM, SSB, or PA. now all I can hear when I key up is a crackle . I looked at every solder point ,and the ones I don't like the looks of I re-soldered with no changes...... what next the TA7222AP?

 

[Handy Andy]

This is a Ranger board - the EPT gives it away...

 

[Handy Andy]

NZ8N has the right PC board so this might be a good idea to take a trip over to "CB Tricks" website and see what they have for this 148...

You may need to replace a LOT of capacitors on this board. For if it's as old as I think it is, the caps dried out and will have to be replaced.

They -Ranger- only did this board for a little while - Hey! while you have your ability to take pics, it would be a good idea to locate the PLL chip too - the Date code on it would help - for the CB Tricks site has a service manual for it - but that manual is only good thru 1998.

This isn't anyone's fault except for not using the radio enough - the caps - when not used, will fail

 

[Gunner357]

NZ8N has the right PC board so this might be a good idea to take a trip over to "CB Tricks" website and see what they have for this 148...

You may need to replace a LOT of capacitors on this board. For if it's as old as I think it is, the caps dried out and will have to be replaced.

They -Ranger- only did this board for a little while - Hey! while you have your ability to take pics, it would be a good idea to locate the PLL chip too - the Date code on it would help - for the CB Tricks site has a service manual for it - but that manual is only good thru 1998.

This isn't anyone's fault except for not using the radio enough - the caps - when not used, will fail

Thats a ez its the RCI-8719A then 549 under that, the plate on the back of CB says
1996

update : I checked the voltages on the IC4 all showed that the VDC was in range pin 8 which is the TX (8.24 vdc) (200 mA) I get (8.24vdc) and (.71mA) when I key it up. and 200mV and 0 mA when not keyed up??

 

[1iwilly]

lift one leg of r128 and see if you have modulation also check TR26 sometimes they go bad

 

[groundwire]

Im waiting for the outcome. I have a very similar problem with mine as well. Its brand new in the box and was never ever used. Same problem with no audio, except on mine the rx/tx light flashes back and forth red green red green giving it an orange color. Output Power and receive are perfect.

 

[Gunner357]

Im waiting for the outcome. I have a very similar problem with mine as well. Its brand new in the box and was never ever used. Same problem with no audio, except on mine the rx/tx light flashes back and forth red green red green giving it an orange color. Output Power and receive are perfect.

yup i can receive and when I key I can DK up to 8w its set at 5 right now But no modulation no swing on the radio meter or the ext meter ....

what is the production date on yours?

 

[groundwire]

yup i can receive and when I key I can DK up to 8w its set at 5 right now But no modulation no swing on the radio meter or the ext meter ....

what is the production date on yours?

I dont know, its a taiwan though. I know that much

 

[Gunner357]

its is Taiwan mines Malaysia dunno if thats the same lol

 

[Gunner357]

lift one leg of r128 and see if you have modulation also check TR26 sometimes they go bad

this really sux i cant find r128 i see r131 r129 r120 the tr 26... any hints lol

TR26 AM (E) 4.12v not keyed 1.975v keyed up and was slowly climbing (C)6.20v (B) 1.036v

 

[loosecannon]

did you say you adjusted VR5 for the modulation?

if that's the case, then what you adjusted was the frequency the radio transmits on when you key up the radio.
unless the clarifier has been unlocked in which case it would do nothing at all.

the VR to adjust for modulation in the 148gtl is VR7, located in front of the big soda can looking capacitor toward the rear right.

this could have just been a typo, but i thought it would be worth a check.

weak modulation is a different problem than no modulation.

if the radio seems to receive ok and you can hear voices coming in through the speaker at a normal volume then your audio IC is probably fine.

if you are going to tune L38 over near the final, do that while putting a tone or your voice into the mic. don't just tune it for max deadkey.

also be sure that the power source you have the radio connected to can deliver at least 3 amps continuous.
your radio never draws anywhere near the same current while receiving that it does while transmitting audio.

if your radio can deadkey 4 watts, you final and driver are fine.
you might try some contact cleaner in the DYNAMIKE potentiometer and work it back and forth, as your mic audio passes right through it, and if it seems hard to turn there could be a bunch of gook in there.
LC