President Lincoln II+ V4 board question

[TimmyTheTorch]

Finally, a problem that's not of my doing. I loaned my Lincoln II+ V4 to a friend for a week for him to try out. When it came back to me, it would not even turn on. I think he may have had a high SWR issue or amp issue, but really could not be certain and ca't get a straight answer. All I had to do to at least get it to turn on was replace the fuse in the power cord.

However, while the receive now seems to be working properly, when I key the mic the wattage stays at exactly 0 on both the radio's meter and the external watt meter and does not move with modulation. This is on AM/FM/SSB, all power levels, all modulation levels, with two different mics. I pulled the finals out and one of them was bad so I replaced all three of them with new 13N10s like the ones that were in there. I also put in a new TIP36C. Still no transmit. I was told it could also be the RF pre-drive amp 2SC2314 or the KA7808 voltage regulator. They're cheap so I am getting a few of those sent this week to try.

I saw something strange when looking over the board and I don't know if this is by design or a sign of something gone bad. Does it look normal to have the stuff apparently barfing out of the barrel? Is this a capacitor? I think to the left of it is a TDA2003L audit amplifier and to the right is a KA7808 voltage regulator.

 

[sp5it]

That's a glue to keep capacitor in place.
To trace failure I recommend to get/build RF probe.
Mike

 

[TimmyTheTorch]

That's a glue to keep capacitor in place.
To trace failure I recommend to get/build RF probe.
Mike

Thanks. I just looked again at both sides of the board and found it in two additional places and gently poking it with a toothpick showed it to lack any sort of gooiness at all.

 

[TimmyTheTorch]

That's a glue to keep capacitor in place.
To trace failure I recommend to get/build RF probe.
Mike

My buddy is going to take care of the repair costs. I wonder if I can get the RF probe added to the bill as part of the repair service.

 

[Handy Andy]

Do some continuity checks - make sure you're getting voltage's to the Finals and if you are aware - the radio uses jumpers to adjust bias trim, check them too.

The "blown finals" issue can also arrive from improperly wired radio - as in reverse polarity. So since you have receive back, you can also double check the condition of the TIP36C by simply testing it's legs for voltage when it's powered on.

No power? Presume blown part or you'll have to locate that voltage source to that TIP36C and keep checking that trace back until you find power.

 

[TimmyTheTorch]

I was told this morning that my broken Lincoln II+ has been repaired and my friend footed the bill. I hope it works as well as before the big ape got his hands on it. Should know in a few days.

Here's the tech's notes:

PROBLEMS: No transmit power output.

ANALYSIS: Trace problem to no connection from Q55 base to Q54 emitter. Evidently the board multi-layer connection had been damaged.

RESOLUTION: Add point-to-point wire.
Adjust for 12 Watts AM carrier (40 W "swing" PEP) and 35 Watts PEP SSB.
Use monitor scope and spectrum analyzer to test - clean output signal.

 

[Handy Andy]

Hmmm...

Murphys Law...

The most expensive parts in any equipment - will blow first - to save the 2¢ fuse.

Your friend was lucky - it was a blown trace - but at least fixable - not that it required a new board dropped in because of too many blown traces and parts from whatever caused this issue.

 

[Dr. Frankenstein]

Just a thought........

These point-to-point repairs should be cataloged (with pictures) for future reference........ being as it's the only way for others to be able to repair their radios in the future.