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

frogman296

i have done the mod to the general lee with the mosfets with no issues

frogman296

Radio Make and Model: uniden pc 68xl PCB Number: PA-339AB1/4 PLL Number: NPC 992D SM5126BP Test gear available: BK 1040, BK 2040, watt meter, Multimeter Symptoms: radio has great modulation on BK 1040, but zero watts What is working: the only thing that i can find that is not functioning is the tx p...

frogman296

this radio never gives up.... now if i turn the volume over 3/4... the speaker squeals, without the mike even keyed..

frogman296

i might add... i Replace 11.1125 crystal with a 11.3258 crystal. and the radio wont do anything...does this mean that the crystal is bad??

the radio had a 11.1125xtal in it when i got it.... technically... it should have been changed in order for the channels to work...am i wrong???

frogman296

finally got the clarifier back to normal... the radio is txing with some watts..1.5 swinging back on AM.. and around 1.5 forward on lsb, and usb

on am... channel 19... it is txing on 27.1859.... i cannot get it onto the exact freq

where to next, scott??

frogman296

any new info??

frogman296

i have a NEW one here

frogman296

im the process of getting a first hand account of where the wires go... will keep you updated

frogman296

The Defpom wrote:One side of the pot goes to R415 (3.3K)

are you sure it isnt r145?? i just dont see a 415

frogman296

i will try my best to remove the clarifier mod... i will need to see another radio to figure out where they go...unless you can tell me where the 2 outside wires on the pot go to.

frogman296

Now check the freq TP10 and see if it is stable when you are injecting each of the following 1V, 3V, 6V. it does not drift with the fixed voltages OK, in that case check for a stable 10.240MHz on pin 7 and pin 8 of the PLL, if it is unstable replace C64, C65, C66, C67 and re-check. If that still fa...

frogman296

You will have to use tantalums, as they are critical parts, they form a special filter circuit to smooth out the pulses and steps which are generated by the PLL to control the VCO, using electrolytic caps probably won't work. You may also want to check C72, that is supposed to be a tantalum as well...

frogman296

the tantalum caps, can i replace them with another type?? for instance c63 is a 2.2uF 25v tantalum cap

frogman296

there is a 20k trimmer and resistor added on the board...looks like some sort of clarifier mod, the red wire you see goes to the clarifier pot http://i171.photobucket.com/albums/u287/frogman296/radio%20mod%20pics/060.jpg http://i171.photobucket.com/albums/u287/frogman296/radio%20mod%20pics/061.jpg h...

frogman296

The Defpom wrote:
Now check the freq TP10 and see if it is stable when you are injecting each of the following 1V, 3V, 6V.

it does not drift with the fixed voltages

frogman296

the audio amp i replaced the original came out of a used/parts radio, for what its worth The odd voltage on the audio amp may mean the used one you put in could be faulty as well, if you have a new one try putting that in and re-checking the voltages, if they are about the same and it still has no ...

frogman296

I am a little confused, it is 20KHz off frequency ? if the loop is running in the 40-50MHz range then something is not right if you are getting the TX being only 20KHz off. yes is is 20khz off on the tx Is the loop freq the same (or very close) on TX/RX ? the readins creep from 33.xxx to 37.44x(am)...

frogman296

the loop osc freq are high... in the 40 - 50.0000 mhz range

the offset osc freqs are pretty much spot on

frogman296

very low tx power... less than a watt... it is txing about 20 kHz off freq

the audio amp i replaced the original came out of a used/parts radio, for what its worth

frogman296

just got done changing ALL elect caps.. fired it up... the needle is moving at least now... not swinging very high on ssb but... i will get it on the watt meter later now for the rest of the voltages TR 34...........................RX.........................................................TX .........

frogman296

TR 9..................RX............................................TX ...............E........C........B.............................E......C......B USB.........2.32.....1.57...8.36........................0.03.....0......0.56 AM..........2.32.....1.57...8.36........................0.02.....0......0...

frogman296

There is usually (but not always) a variable VR on the power supply PCB. I think I had some notes here for adjusting the voltage when the VR is not present, I will have to have a look. What is the PCB number on the power supply board, there are different versions. PC-570AB TR34, 35... are these the...

frogman296

IC6 ....RX.....................AM..................USB.................LSB 1..... 0 VOLTS FOR ALL 2. 0.1 .................... 8.14...............7.87..................7.80 3. 0.01.....................8.07................7.44.................7.70 4. 0 VOLTS FOR ALL 5. 0........................8.26......

frogman296

I kind of forgot about this one.. Have you tried doing an alignment on it, and did you notice anything that seems incorrect during the alignment ? no not yet It is likely to just be a capacitor (or a bunch of them) somewhere that are killing the DC supplies to certain parts of the circuit, the volt...

frogman296

anybody??

frogman296

i am in dire need of a magnum s9 pcb layout, bottom view(solder side)...

help would be much appreciated... have to bring this hack job back to life

thanks in advance guys

frogman296

checked the others... added correct values.... still no luck... i went back to the unlocked clarifier...

radio works A+

frogman296

The TX alignment issue is probably due to the original clarifier mod, check for correct component values for the resistors that are connected by VR5. On the TX side R187 should be 2.7K, R186 should be 100 Ohm, there should also be diodes in D75 and D52. On the RX side R175 should be 3.3K, R174 shou...

frogman296

replaced pll

now i can align the RX on freq... but i transmit off freq.... it seems as though there is not enough adjustment to the tx freq VR 5

on a side note... when i unlocked the clarifier.... the radio will align...

looks like the pll crapped out... thanks a million Scott

frogman296

Of course, no CH9.. but yes, check the path and source of the voltage feeding pin 11, if you disconnect it from the ch selector and test the ch selector side for voltage it should say whether the selector is at fault, or if there is a short circuit somewhere (it should be feeding 0V), the PLL pin w...

frogman296

thanks scott

much appreciated

frogman296

the radio does not have the instant channel 9 function.

so i should check pin 11 of the pll and its path through the radio??

frogman296

1. 1 1 0 1 1 1 1 2. 1 1 1 0 0 0 0 3. 1 1 1 0 0 0 1 4. 1 1 1 0 0 1 1 5. 1 1 1 0 1 0 0 6. 1 1 1 0 1 0 1 7. 1 1 1 0 1 1 0 8. 1 1 1 1 0 0 0 9. 1 1 1 1 0 0 1 10. 1 1 1 1 0 1 0 11. 1 1 1 1 0 1 1 12. 1 1 1 1 1 0 1 13. 1 1 1 1 1 1 0 14. 1 1 1 1 1 1 1 15. 1 1 0 0 0 0 0 16. 1 1 0 0 0 1 0 17. 1 1 0 0 0 1 1 18....

frogman296

bump for new info

frogman296

I think you checked IC4 instead of IC5, IC4 is the audio amp, IC5 is the MB3756 you are right IC5 rx AM USB LSB 1. 8.51 8.45 8.51 8.51 2. 12.47 12.34 12.44 12.44 3. 8.52 8.47 8.53 8.53 4. 0.00(all modes rx/tx) 5.12.47 6. 8.51 0.52 0.56 0.56 7. 0.00(all modes rx/tx) 8. 0.24 8.45 8.51 8.51

frogman296

The Defpom wrote:It should be an 18V Zener diode.

stripe towards the IC??

frogman296

The Defpom wrote:D60 is mounted between pin 2 of the MB3756 and 0V, it is on the track side of the PCB, it was a factory addition, to help protect the device, not all radios have it in place, if not add it.

so its a 1n4004 type?? or a 1n4148??

so i solder it from pin 2 to chassis ground??

frogman296

There is a capacitor near the audio amp that can short out when it is old, it kills the audio, check C107. replaced c107 and a ton of other elect caps Also what voltages are you getting on IC5 ? RX TX am TX usb TX lsb 1. 12.48 12.41 12.45 12.45 2. 6.00 5.97 5.99 5.99 3. 0.00 for all modes(rx/tx) 4....

frogman296

You may want to re-check the clarifier mod, in case it is shorting the TX and RX lines together, it sounds like the MB3756 may have failed. Make sure you connect your negative test lead to one of the metal cans on the PCB, and not the chassis, as the chassis is not a true 0V. i will recheck the cla...

frogman296

zodiac wrote:I thought you wanted the test points for adjusting the frequency not the bias.
You should find the information your after on CBTricks under radio information.

i have since found them on the site...

thanks for the heads up though

frogman296

You need to check the binary code going into the PLL, pins 16 through to pin 10, it is likely that a solder blob is shorting a couple of pins out, causing the PLL to jump to the wrong frequency, or there is some other fault causing an incorrect binary code. So what you need to do is tell me what th...

frogman296

thanks a bunch 1096

frogman296

Radio Make and Model: uniden washington PCB Number: PC 385AG PLL Number: MB8719 Test gear available: multimeter, watt meter...bk2040, 1040 Symptoms: no output on any mode, no rx audio, What is working: radio lights up perfect, tx/rx light changes when keyed...no rx audio, meter does not move on rx, ...

frogman296

went through the radio.... reversed the channel mod, and clarifier is now locked. replaced the crystal with the stock crystal....changes mike plug to 4 pin powered the radio up... worked perfect... 5 minutes later..... no power output in any mode... no mike audio through talkback, and no "tx li...

frogman296

where the devil is d60??

i cannot for the life of me see that diode

frogman296

so are these the only two that are important??

i have since found a diagram that lists em

frogman296

yes it is very easy to make... cheap and it does the trick... enjoy

frogman296

did you ever get this issues solved... i had one do the same thing... lower the mike gain... no more problem

frogman296

hmmm you are rigged to go

you can find the full alignment on radiomodz homepage for the cobra 29..

are you looking for a tune to add some modulation and power??

frogman296

The Defpom wrote:Personally I put a 1K series resistor on the middle leg of TR24, and change R124 and R126 to 4.7K, that increases your mod level on all modes with no ill effects.

tried this mod with great success

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