Cobra 146GTL Taiwan. SSB Probs....

[15minigrass]

Just got a 146 on a trade. theres a carrier/deakey on SSB. how do I adjust it????? or fix it???? AM works fine.....

Mahalo, James.....

 

[ExitThirteen]

Greetings, James!


If you're modulating okay on SSB modes, but have a carrier, do the following:

Remove the covers and with the front of the radio facing you, look in the front/center area of the board for VR4. This is your SSB carrier balance adjustment.

Set the radio to channel 19, USB mode, and key the mic, and adjust VR4 until no carrier is registering on the 10W scale of your power meter. Switch to LSB, and repeat, make sure you balance USB and LSB for lowest carrier. If this adjustment doesn't remove (or greatly reduce) the carrier, I'd say the balanced modulator IC may have gone fault. Good luck!

-Exit

 

[15minigrass]

Well I guess its the balanced modulator IC. Tried tuning VR4 no change. sometimes its o.k. but only for a little while then Dkeys on SSB.

Ill try it aagain today. If not I might have to replace it (IC)

Thanx EXIT13, Aloha James....

Greetings, James!


If you're modulating okay on SSB modes, but have a carrier, do the following:

Remove the covers and with the front of the radio facing you, look in the front/center area of the board for VR4. This is your SSB carrier balance adjustment.

Set the radio to channel 19, USB mode, and key the mic, and adjust VR4 until no carrier is registering on the 10W scale of your power meter. Switch to LSB, and repeat, make sure you balance USB and LSB for lowest carrier. If this adjustment doesn't remove (or greatly reduce) the carrier, I'd say the balanced modulator IC may have gone fault. Good luck!

-Exit

 

[freecell]

if it's "okay sometimes" then the problem isn't the IC.

 

[15minigrass]

if it's "okay sometimes" then the problem isn't the IC.

Would you know what IC is it?

I see IC 1, 2, 3, 4, & 5.
1 = TA75902P
2 = uPD2824C
3 = AN612
4 = uPC1182H
5 = SO42P

 

[15minigrass]

O.K. It must be IC3----

 

[ExitThirteen]

Yep,

IC3 is the balanced modulator IC (AN612). Like Freecell said, though... if it acts up sometimes, I'm not sure that would be the fault... almost sounds like a cold solder joint somewhere in that area. I'd look for cold solder joints if it acts up once in a while. Also wouldn't hurt to shoot VR4 with a little contact cleaner too.

Cheers and good luck!


-Exit

 

[15minigrass]

Cant seem to isolate the cold solder but heres what I found out.

still acting up. WR on QS said to try to touch TX pin to ground, I touched pin 3(TX) to ground nothing happened. but it hums on the other end of my 959 when keyed w/carrier but it modulates fine. (I dont mind it keyeing up but dont wanna ruin the transistors.) plus if i tap the top of the radio it unkeys and drops carrier to 3-4 watts. when you modulate, it swings full forward then all the way back then back to normal key of 3-4 watts. The needle is usually burried to the corner when keyed on SSB.

AM side is all good.

Well, thats all i got. Is it the chip. I already have 1 on the way. Any other tests i could do before changing out the chip???

O.k. then. Aloha. Jim.....

 

[15minigrass]

Well Changed out the chip, still acting up. VR4 still dont tune it. HELLLLLLPPPPP!!!

Needle bends kinda carrier.

Aloha Jim...

 

[Bionic Chicken]

Just wondering...........does it have the key if you turn the mike gain off? Maybe you are getting some background audio out of the mike?
One other thing that can cause the carrier it that someone tuned the radio for AM only and the whole kit and caboodle is out of kilter.

BC

 

[15minigrass]

No mic gain on a 146GTL

 

[15minigrass]

Well thru messing w/this baby shes off to the doctors office. Mahalo forum. Aloha, Jim...

 

[jazzsinger]

Well thru messing w/this baby shes off to the doctors office. Mahalo forum. Aloha, Jim...

try checking the coil on the mike input,sometimes using a power mike can fry them,i've seen it on a ss3900,the symptom was a constant carrier on ssb,am/fm fine.