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

hi all,
here i have a president lincoln pb-111ae,it came to me with only 1 watt coming out ,i suspected blown final i noticed the mrf477 has been replaced with a 2sc1969 ,
anyhow decided to try it out localy ,1 watt was fine every one local could ear me then all of a sudden the watts out went to zero so no tx power attall .so could this have blown somthing other or will i be ok just changing the final.
also if i fit another c1969 what pots would i need to turn down so it doesent blow again "vr113 driver bios"??.
thanx in advance for any help or advice

The easy way to find out what as gone on is un-solder the driver and final and test them.

As for setup, use the alignment data, that what it's for.

What is "bios"??. " I this my PC one of them lol.

hi rick thanx for speedy reply,
i have noticed with another radio in the same room on the same channel i can ear the lincoln ok modulation and low signal so does this mean the driver is ok,and lol i spelt bios instead of bias hehe i guess its my age,

Rip out the 1969 and replace it with a MRF455 instead, I have done it, and it works very well, it just requires some minor mods to capacitors, and possibly to the pre-driver circuit in order to nicely re-tune the RF section for the new final.

The MRF455 is what is used in the newer lincolns (well, it is actually a sub, but essentially the same part).

hi scott,i looked at getting a mrf455 but they are more than i want to spend,so i have allready orderd a new 2sc1969,i will be happy with say around 8 watts fm and 12watts ssb,so would be gratefull if someone could tell me what will need adjusting,so it doesent blow the new c1969.

thanx a

The best I have got out a 1969 in a lincoln is 4 watts (for acceptable AM modulation), any more than that is not a good idea, so the last time I had to relace a final I bit the bullet and upgraded to the more expensive part, it is MUCH more robust, and will probably never need replacing again.

yes scott i probly will invest in a mrf455 or maybe a mrf477,when i no the radio works ok but for now 4 watts will be fine. what pot tuning do you advise,??driver bios or is there an high power pot.

thanx a

When you use a 2SC1969 as a Final in the Lincoln, it can be unstable and can self oscillate and be very un-linear due to the lack of feedback, which will destroy the 2SC1969 and may cause other damage.

You can cure the problem by using some R/C feedback network components.
Solder one leg of a .0047uf or 4700pF Disc Ceramic to the Collector of your 2SC1969 and the other leg soldered to a 330-Ohm resistor and solder the other leg of the resistor to the Base of the 2SC1969, mount the components on the trackside of the PCB and keep all the leads as short as possible.

Set the Driver and Final Bias current 50mA in the SSB mode with no modulation, VR113 is for Driver Bias and VR112 is for Final Bias.

Rick (Euro Radio Co).

rick i checked the old c1969 and it was broke,so i fitted a new one with your
instructions with the cap and resister,but thers only about .2 of a watt coming out.i havent checked the driver or final bias ma yet.
do you think c2166 could be gone to.modulation is coming out fine tho.

thanx angus

You need to do some fault finding for you self, you cannot expect us to know all the components which may have failed.
When you us a sub device like the 2SC1969 any think can happen.

I would start by check the input and output of each transistor in the PA stage with a scope or RF probe, or you could just change components until you get it working again.

thanx rick your help is very much appreiciated,im only an amature with cbs and only no some basic stuff,
i do like to try and fix things if i can,with a little help on the forum from you top boys and by looking at the forums, you seem to be very good at what you do.and i dont mean to affend,just asking for some help like if there was something i could do for you i would,
i pulled the c2166 out tonight it seems fine.

cheers a

hi all,
i took some tranny volt tests on
q124-all ok in tx and rx
q134 rx ok /tx c=ok e=2.33 b=3.01
q132 rx ok /tx e=ok b=ok c=7.9 and going higher and higher the longer the key not stable
q133 rx ok /tx e=ok b=ok c=6.5 and going lower and lower the longer the key not stable.
what you thing guys,thanx in advance for any help

I did tell you without the right test gear it not easy.
It looks like you have something loading the final, bad cap, short on a coil, diode, and resistor.

The components may look all right (E.G not burnt) but some components fail and show no outward signs of failing.

Of course, you could have blown the new final, if you have just replaced the faulty part and have not found what caused the fault in the first place, then the chance are you have blow the new final.

hi rick and thankyou for your input,
i think what probly happend was when i first got the radio ther was about 1 watt coming (i think this was cos the final was blew)i then stupidly used the radio for about 1 hour localy without replacing the final on 1 watt then all of a sudden it droped to 0 watts coming out i must of blew somthing else ,now i have just rechecked the new final and the driver and they are fine,they did make a small improvement about 0.2 watt out.im also trying to find some bits to make a probe.

Check for 13.8 V at the driver and final, as a common failure on these radios is for the track that supplies the DC power to burn open when a final blows and shorts out.

Check for 13.8V at the final and driver, and if missing then check the jumper PCB for it, if missing carefully check the tracks that go between the jumper PCB common, and the main DC input for the radio, you will either find a burnt out track, or a melted solder connection / dry joint, it is best to re-solder all the joints in the DC line to be sure that they are OK.

hi scott,yes ther is 13.8v in rx and yes the track has been blown before and repaired.so its something else close i think

You should still be getting the full 13.8V at the driver and final in TX, if this isn't happening, then there is a DC supply problem.

checked these 2 again

q132
rx collector 13v
tx collector 7.9v and going higher and higher the longer the mic key

q133
rx collector 13v
tx collector 6.5v and going lower and lower the longer the mic key.

Test the DC voltage at the radios 13.8V power wire (where it attaches to the main PCB) during TX, to be sure that it is not getting dragged down, it should stay at 13.8V.

If that is OK then run a wire (a thickish one) directly between the jumper PCB common (where you get 13.8V when the jumper is removed) and the main 13.8V power input connection where the power wires attach to the main PCB, this will ensure that any poor conductors are bypassed allowing the full DC supply to get to the jumper PCB, so it can be passed to the final and driver (as it should), once you have done this, re-check the voltages at the driver and final in TX.

If there is still a voltage drop then check the voltage at the jumper PCB during TX, you should get 13.8V.

If this checks out re-solder ALL connections between the final, driver and the jumper PCB, including the jumper PCB connections, and re-try.

I

hi scott and thanx for helping.
i did what you said and now q132 is reading spot on,but still only o,watts output.

and q133 still reading
rx collector 13v
tx collector 6.5v.

thx angus

Resolder all the joints between the jumper PCB and the driver, and all the joints in the RF section around it, if it still does not help, replace the driver again, even if it tests OK, I have come across drivers/finals that have tested OK, but when used the stresses cause them to not work.

Also make sure that BOTH the driver and final have new insulators installed, and that the screw that holds them in is not shorting the mounting tab to the panel.

hi scott,i have found on the coil L134 from q133 to power rail.
it reads 13v all 3 legs in rx

but in tx

collector of q133 6.5v_______ left leg of coil L134 right leg ________9v

|
|
|
bottom leg of L134 to power rail 13v

Here are the voltages that you should be getting for Q132, 133, 134
I suggest that you try replacing Q133.