The Defpom Forum, for RadioMods, S&M Software and Music by The Defpom

Hi all good people. Good to see that forum.

But not to make this too long: I am having as below:

Radio Make and Model: President Lincoln, late ASC version (MRF455 final)
PCB Number: PB111AE
PLL Number: PLL0305A
Test gear available: DVM, Freq, dummy,
Symptoms: No RX within any mode/frequency, low bias noise. No TX, no power output, TX icon seldom appears on the display, no switching between RX and TX mode.

What is working: CPU thats for sure cause I can change bands/channels/frequency. All the other functions are displayed. ASC/squelch works. Modes are switchable (FM noise high, AM/SSB barely audible). All the front panel buttons works, frequency dial works. CW key down produces talkback sound and TX icon shows up but no signal is transmitted.

What has been tried: I was trying to cycle the power on/off, PTT on/off, PA button on/off. I heard of oxidized glue under the voltage regulators (CPU board) causing short circuits. I found them as described - both with brown cracked adhesive - both were cleaned up. No signs of PCB damage, both are giving specified voltage (5V and 8V).

Did it suddenly happen ?: Yes. Day before had a good ragchew with my friend and he was happy with the signal and modulation alike. The rig was ok. That night there were stormy and rainy hours so I took out the antenna plug off the rig. But here were no thunderbolts and no signs of burned tracks in it. On the other hand I have two other rigs which were connected to the same power supply and their antennas (Kenwood and Yaesu) and none of them suffer anything. Next evening I was trying to power up that Lincoln with antenna hooked up, and heard nothing nor transmit.

Anything else that may be of help?: I dismantled the front panel day before to wash it (too much greasy dirt since the rig was laying ages somewhere in the kitchen waiting for its big day) and put the parts back together same evening. All of them were dry (i hope...) and rig preformed excellent for another few hours (tx/rx). But might not be sure about PA button (and others) since there were loads of the dust which I dusted off with clean soft paint brush.

The CPU board was pretty dusty underneath nearby the PLL chip, I dusted it of but it did not help to wake up the radio.

I think that it might be something stupid as dry capacitor or aged crystal, since rig was ok one day and went dead another without any particular reason. But all what I am short off at the moment is that precious Lincoln experience to dabble with, so got stuck and have no idea where to put the spanner into (not)working.

Is the squelch audible?

had an old president lincoln years ago this was...

same problem, was a dodgy crystal, could hear harmonics from a radio next to it with the squelch back, and pressing/flicking (not flicking hard, just a general poke) the crystal, used to make it work, swapped the crystal and presto!

Hi,

first: how much AMP does it draw in Standby? Is it > 0,5 Amps (1, 2, 3 or what): checkout the Final and Driver. They could short-out and then the receiver also can go "dead" (this often happens in several rigs, when the final is "killed").

Second: Try to make the VCO/PLL-Allignment. Its not hard to manage and you will find the dead road. If not the Finals, its something in the PLL or VCO, so they cant lock probably. Due to oxyd on a trimmer, or a coil, that pays for the warm-up-cool-down-cycles over the years - or, as suggested before, you find a crystal, thats out of range. Something you miss, or is out of range, and there the fault will be very close. If on the coils, dont use metal. Not only for sensitivity -> they are *VERY* brittle...

Third: You telling about RX/TX-switching-problems. This can be an indication of improper PLL/VCO, but also just a faulty diode or transistor on the PTT-Line. Checkout the voltage on Mic-Plug, must be 5V - and grounded on TX ("0" V). Then go backwards to the diodes and so on.

Good luck!

I would say to start off by trying to do an alignment and seeing what frequencies are missing or incorrect, as that can give a clue as to the location of the fault.

A common problem with this chassis is aging surface mount ceramic capacitors or electrolytic capacitors on the MPU PCB, some of the elect. dry out around the PLL and need replacing, or the surface mount capacitor on one of the VCO circuits / xtal goes off value, the only way to know for certain is to take some freq. measurements as part of an alignment and see if it is out of whack.