Cobra 139XLR picture needed

[Deleted]

I am in need of a picture of the underside off the CB-PA switch. Used for extra channels. I purchased a radio for restoration. Radio is non-working, so I want to start there. If anyone had one of these radio, it would be greatly appreciated.

[Sandbagger]

Feb 24, 2009 23:08:44 GMT -5 @vinnies said:

I am in need of a picture of the underside off the CB-PA switch. Used for extra channels. I purchased a radio for restoration. Radio is non-working, so I want to start there. If anyone had one of these radio, it would be greatly appreciated.

I actually had this from another time. It took a little digging but here it is:
img3.imageshack.us/my.php?image=139xlrswitches.jpg

[Deleted]

Great job. Thanks !

[Deleted]

OK, I think I have this wired correctly now. I had a bad 10.240 crystal. When I go to check TP6 for 33.855MHz, it is jumping everywhere. I am supposed to adjust CT6 for AM 33.855, them CT4 for USB 33.8574, then CT5 for LSB 33.8526. Why are these jumping so much?

[Sandbagger]

Mar 2, 2009 16:21:46 GMT -5 @vinnies said:

OK, I think I have this wired correctly now. I had a bad 10.240 crystal. When I go to check TP6 for 33.855MHz, it is jumping everywhere. I am supposed to adjust CT6 for AM 33.855, them CT4 for USB 33.8574, then CT5 for LSB 33.8526. Why are these jumping so much?

Typically, when a counter jumps around and the signal is otherwise stable, it's usually for one of two reasons. Either you don't have a strong enough signal for a solid "lock", or you're getting an interfering signal which is "confusing" the counter.

The AM oscillator has to be set in the transmit mode. You would get better results if you disable the final/driver so that the high power 27 Mhz signal does not leak into to your high impedence counter probe. The USB and LSB oscillators are active in both transmit and receive, so you can set it on receive without fear of RF contamination from the transmitter.

If that doesn't help, then you're probably not giving your counter enough signal, and you'll have to find a different point to couple it, or find a more sensitive counter/probe.

[Deleted]

I am going to have to get an alignment procedure, and the schematic and some component locations are different from the TRC-458 schematic.

Dave, I saw somewhere that I should replace all 2SC1419. Is this correct?

[Sandbagger]

Mar 2, 2009 22:35:19 GMT -5 @vinnies said:

I am going to have to get an alignment procedure, and the schematic and some component locations are different from the TRC-458 schematic.

Dave, I saw somewhere that I should replace all 2SC1419. Is this correct?

I've never heard about the 2SC1419 being a problem, and I've never had to replace one. That doesn't mean that there isn't a problem, but I'd have to say it's not a BIG problem. The Cobra 139XLR schematic along with some tech bulletins are on CBtricks. The first bulletin about changing the final bias only applied to the early versions of the radio, when final popping was very common. But check the components out to make sure they've been updated, and set the final bias accordingly.

The TRC 458 and Cobra 139XLR are virtually identical. The chassis is the same. The only differences you will find are in how the radios are wired to the accessory switches and controls (like the mic gain), and stuffing option extras like the modulation meter which are not in the 458.

[Deleted]

I check the bulletins. This appears to be a later model. All fixes were implimented.