[TenTec] Omni C + new Ham = Oops.

[Mike Bryce]

Paul and the gang


Every service tech has a different way of fixing and resolving problems, and I've had my hands inside a lot of radios, Here's some tips on getting it back together.

Of course you used drawings and took photos of the PA before you unsoldered anything. You'll need those when it comes time to reassemble the parts.

PA are not hard to work on, they're just tight inside. Remember they were built in layers and you need to remove those layers to get to the transistors.


The feedback control components are mounted last and therefore they are the first that need to be removed. Depending on how the PA was constructed, you can sometimes unsolder on side and push the part (s) away.

Use extreme caution with the small toroid transformers, their leads can break off easily. 

When you move enough layers out of the way to get to the transistors, you'll need to un-solder them from the pcb. The emitters are the hardest as they mount on the largest hunk of copper. Use wide solder wick and a good sized iron. My 35 watt weller WTCP and a chisel tip works fine. You don't want to linger on the pcb too long as that will cause the copper to lift. 

When you got as much solder off the pads, take a sharp knife or a very small screwdriver and wiggle under the emitter lead. While you apply heat to the tab, lift and wiggle the tab until it's off the pcb. 

NOW! Before the copper has cooled, get the other emitter lead.

The base of the transistor will have a matching network and few other parts. Make a note of what goes where and remove those components. 

Remove as much solder as you can, then repeat the process described above and gently lift the base pad.

The collector will have a stiffer wire as this is where the +13 volts come in. The wire will come out of the toroid transformer that look like they have been made with copper pipe. There will be a few caps,too. 

Remove the the pad from the pcb

Now you'll notice there are two screws (with washers) that hold the flange of the transistor to the heatsink.

Remove the screws and before you lift the device out, make a note of how it goes in. It's so damn easy to get on back in 180 deg out of whack.

You may have to wiggle the case a bit as the thermal goo acts like a glue. It will pop out easily.

Now, you got the bloody thing in your fingers, check it with your vom and see what it looks like. A collector to emitter short usually cause smoke to come out of the PA while a base to collector short will toast components on the base side of the circuit. No resistance means the poor thing had blown. Thats the case of too high of voltage on the output (read that as super hi swr on the antenna or no antenna)

Putting it all back together

I checked the new transistors before I put them back in. It's just me.

Shake the PA to un-lodge any solder balls.

Notice the collector lead had its tab cut at an angle. Make sure you put it back in the pcb correctly

Use your soldering iron and reflow the solder around the mount. You don't want any mountains of solder.

Apply a bit of thermal goo (and while some don't use them, the drivers have a mica insulator that must be used)

Attach the transistor to the pcb and mount it to the heatsink BEFORE you solder it down. If you don't and you get it mis-aglined you're seriously screwed!

After you have it mounted, the apply a small amount of solder to the base tab.

Install the second one, as described above.

Once you have them physically attached, solder the pads and re-attached the base and collector wires/caps/transformers/etc

There are usually a dozen screws that hold the pcb to the heatsink. While you're there, tighten them down. You want ground to be ground.

Smoke test

There usually is enough slack to allow you to connect the low level driver to the PA and the PA to the filter board. If you can, then do so without mounting the pa into the back of the radio----just incase you need to remove it.

double check all the connections. Remember, you need a ground on the pa case if you don't have it mounted in the radio.

If you haven't messed with the bias control, it should be good to try.

Power up the rig, and into a dummy load, with the drive and alc all counter clockwise, put the transceiver into lock.

advance the alc (front panel) and watch to see RF output raise and DC collector current raise.

If all is good, then go for the gusto and full power. Most of the Ten Tec PAs draw about 15 amps at full power

Turn drive all the way down and in lock with no RF the standby current should be under 500 ma.

You may need to reset the bias, and do so by following the instructions in the manual. Gary Green told me that as long as you see 500 ma or so standby, you're good to go.

Button the radio up, and enjoy one of the finest CW radio ever made. They sound damn nice on SSB, too.

I have the following:

Omni A
Omni B
Omni C
Omni V
Omni VI
Omni VII

Like I said; once you name 'em you've got to keep'em!

Mike, WB8VGE