PC 244 wacky wattage!!

[jj074]

Radio Make and Model: Uniden PC244
PCB Number:
PLL Number:
Test gear available:
Symptoms: I only get about 1-2 watts when modulating on SSB.. unless i whistle real loud right into mic i will get about 16.. but when i do regular talking i get the 1 watt thing going on..doesnt seem to make a difference to what microphone i use either. On AM i have my 3 watts which swings to 5 or so with a strong whistle. The mic gain is completely turned on too..

What is working:

What has been tried:

Did it suddenly happen ?:
Anything else that may be of help?:

[lbcomms]

Are you sure it's a 244, and not a 122 (i.e. PC122) or 144 (as in AX144, AR144)?

I only get about 1-2 watts when modulating on SSB

That's all a cheap (RMS) meter will show, unless you shout really loud into the mike.

Are people receiving you OK, or are they saying you are scratcy/fuzzy/distorted?

Incorrect bias settings can cause this, but will always be accompanied with distortion (hard to describe, but it sounds like you are talking with a mouthful of sand).

If your modulation is clear, then DON'T play with the bias to try and increase your output - there is a chance of frying a transistor or two if you overdo it.

You need a PEP reading meter like this to properly how your average talk power on SSB:



Note the "PEP moni" pull switch on the CAL control. This will show the PEP watts your SSB is measured in.
Without this, your average SSB power will look a lot lower than what it really is.

[jj074]

Hello and thanks for response! ,, yes, its a uniden pc 244.. guess same board as cobra 146 gtl from what i heard? Anyway the audio sounds off on SSB,but on am it sounds clear.. just very low.. My meter is pep, and it works fine on my other radios.. but with this pc244 SSB only doing 1-2 watts talking loud into mic unless i whistle it will go to 15 or so.... thanks again for help -John

[lbcomms]

audio sounds off on SSB,but on am it sounds clear

By "sounds off" I'm assuming that you mean distorted, not off-frequency.

First thing to check then is the biasing. On the driver and final in SSB TX mode (with the mic gain turned all the way down!) you should have zero volts on the emitters (these are connected to PCB ground), 13V or so on the collectors (centre pin + tab) and about 0.7V on the bases (the other side pin). Is this what you have?

If the biasing is way out (sounds non-existent in your case, without seeing it in front of me) the lower level SSB signals will be cut off, up to the point where the signal itself provides the bias (i.e. the circuit will be operating in class C).
This will show up as "grainy" distortion in the audio and low power output. The fault is easy to spot, you will have close to zero volts on the bases. Time for the multimeter...

Sue

[jj074]

ok great ty i will do so when i get a little time and post my findings! thanks again -john

[jj074]

Ok.. i have approximately those volts... 6.8's and 13.7ish and 0.1's ... man i hate when radios dont work right lol

PS.. just got a contact on skip.. he said my audio is clear.. just very low modulation..

thanks again -John

[jj074]

well i found an alignment page for checking bias amp draw as well across a couple test ports after removing the bias shorting board.. i made some adjustment.. i also adjust L40 L39 L38 L37 slightly.. i get an average of 5 watts now on SSB when i have power mic maxed and right at my mouth.. is there a way to boost the radios mic sensitivity? dont need to "eat" the microphone or set to max for radio to put out modulation on my other radios... thanks in advance -john

[lbcomms]

i found an alignment page for checking bias amp draw.... i made some adjustment

Did you check the circuit was working correctly first?

i have approximately those volts... 6.8's and 13.7ish and 0.1's

When replying with multiple answers, tell us where you measured each voltage.
The numbers above are open to interpretation... where did you measure 6.8?

If this was on the bases, either you are setting / reading the meter incorrectly, or you have a serious fault there

Until you clear the fault (or give us a correct reading) there's not a lot we can do to help.

Repeating: On SSB TX with no audio (mic gain all the way down) you should have about:
0.7V on base, 13V on collector, and 0V on the emitter.

i also adjust L40 L39 L38 L37 slightly

Until you get the part above (in red) correct, it's pointless looking elsewhere.
That would be like pumping more air into your tyres to stop the engine leaking oil.

[jj074]

ok i checked voltages again ..0.7V on base, 13.4 on collector, and .01V on the emitter.... I also have another question.. i was looking at a block diagram and saw a few parts labeled "mic amp" was TR25 and TR26 i believe... so i looked at the board in that area and TR26 had a hard brown material all over legs of it and onto other close parts.. not sure if that has anything to do with this, just wondering if its possible that something leaks out of faulty parts? ... thanks again -john

[lbcomms]

0.7V on base, 13.4 on collector

That's good. Now that you know that's OK, look elsewhere.

"mic amp" was TR25 and TR26

The mic amp is common to AM and SSB, so it it's working on AM then these must be working OK.

The light brown stuff is just a glue used when the board is made to stop some components floating away when the soldering is done (they put all the parts into the board first, then cut all the legs in one go with a cutting wheel, then float the whole board in a bath of solder for a few seconds to solder all the components in).

If you have a circuit, follow the audio path from the mic amp to the balanced modulator - there will be a resistor and capacitor in series connecting the 2 sections.
A rare fault is for the cap to "go low" (lose some of its capacitance) which causes tinny audio and low power on SSB transmit.
Only seen this about 3 times in 20 years, in all makes of radios, so not very common.

What is the PCB number (usually starts PC-) of this radio? If I could get a circuit diagram it would make it a bit easier to follow.

[jj074]

ok.. the board is PC-833AF .. and same modulation issue on AM.. thanks again -John

[lbcomms]

I think that's the later version of the original large upc2824 Uniden chassis - looks something like this:

Does this look the same as yours?

The earlier version is almost identical, except:
- there are 4 trimpots top-centre of the picture instead of 3
- the 6 cans in a row bottom-centre of the picture are smaller
- the audio IC (next to the green transistor on the right side) is a different larger type that has 2 screws, not 1

First, is the mike and mic gain pot OK? I had a Cobra 148 with tinny modulation a while back that took ages to find the fault - somebody had previously swapped the 1K log pot for a 100K linear one!

Does it sound OK in PA mode? That will clear the mic and mic gain pot.

If it is this chassis, there is a known problem with low voltage electrolytics.
Change the ones circled in red - if they haven't failed yet, they will soon...


If changing the caps and checking the mike /mic gain pot don't solve the problem, it's just a matter of tracing (easy with a CRO) where your gain has dropped.
Let us know how you get on.

[jj074]

Sorry for no recent updates.. been very busy with work.. yes the pic you posted looks like my board.. I will do some more testing and let you know.. Thanks again for all the help -John

[jj074]

ok.. not sure if PA is working "correctly" it sounds good and loud when i "eat" the microphone, but if i turn my mic gain down even a little it drops completely off.. not sure if that means much.. just figured id add it in -John

[lbcomms]

Have you tried a different microphone?

[jj074]

Yes.. I've tried 3 different microphones.. And they work fine on other radios as well .. Just this 1 for whatever reason doesn't seem to pick up the audio from mic unless very close to it and talking loudly.. I actually haven't looked at it much lately.. Maybe it's time to send it out lol.. -John

[spikeselectronics]

Okay. The driver is bad. All the other stuff is just hog wash. That's why you have a low dead key and not much swing. replace the driver and it will cure your problem.