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

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, shows a small dk on AM

What has been tried: replaced ic 4 and ic 5, tr37, d44... replaced the caps in front of 3756(c164, c133)

Did it suddenly happen ?: radio had been setting idle for some years...when fired up...
Anything else that may be of help?: has had the channel mod done to it, very neat job i might add

anybody have any ideas...i have been searching through the forum...for lil tidbits of info on these radios... replacing some parts trying to get some wattage or audio.. no luck

thanks in advance fellas

There is a capacitor near the audio amp that can short out when it is old, it kills the audio, check C107.

Also what voltages are you getting on IC5 ?

does SSB TX work at all ? is there an actual carrier getting out on AM ?

The Defpom wrote:
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. 0.00 for all modes(rx/tx)
5. 1.15 1.16 1.16 1.16
6. 1.15 1.16 1.16 1.16
7. 0.00 for all modes(rx/tx)
8. 0.00 for all modes(rx/tx)
9. 6.20 for all modes(rx/tx)
10. 11.75 for all modes(rx/tx)

does SSB TX work at all ? is there an actual carrier getting out on AM ?

no ssb tx. a carrier less than 0.5 of a watt on AM

I think you checked IC4 instead of IC5, IC4 is the audio amp, IC5 is the MB3756

The Defpom wrote: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

bump for new info

anybody??

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 ?

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 voltages you gave for the MB3756 look ok.

What voltages are you getting on IC3, IC6, TR34, TR35 and TR9, TR10, TR18 ?

I have the SAMS for this radio, so I have the voltage info for just about everything for it.

Your audio amp (IC4) voltages seem off, pin 2 read as 6V, it should be about 3V, pin 5 and 6 are also slightly out, read as 1.15, should be about 1.9V (may be normal though), pin 9 is a touch low, should be 7V, pin 10 read 11.75 but should be about 13.1V

Check the voltage coming out of the radios power supply, I think it is only set to about 12.5V, it should be set to 13.8V, it could be throwing the voltages out a bit.

Replace C112 (4.7uF) to rule that out.

The Defpom wrote: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 voltages you gave for the MB3756 look ok.

What voltages are you getting on IC3, IC6, TR34, TR35 and TR9, TR10, TR18 ?

Your audio amp (IC4) voltages seem off, pin 2 read as 6V, it should be about 3V, pin 5 and 6 are also slightly out, read as 1.15, should be about 1.9V (may be normal though), pin 9 is a touch low, should be 7V, pin 10 read 11.75 but should be about 13.1V

Check the voltage coming out of the radios power supply, I think it is only set to about 12.5V, it should be set to 13.8V, it could be throwing the voltages out a bit( it is showing 11.70, how do i turn it up?).

Replace C112 (4.7uF) to rule that out. replaced earlier

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.

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.................8.34.................8.34
6. 0 VOLTS FOR ALL
7. 0........................2.86.................2.86..................2.86
8. 0.01....................2.86.................2.86..................2.86
9...... 0 VOLTS FOR ALL
10. 0.......................0.76.................0.74..................0.74
11. 0.......................1.43..................1.42.................1.42
12. 0.......................0.76..................0.74.................0.74
13. 0.......................1.43..................1.42.................1.43
14......0 VOLTS FOR ALL

IC3
.........RX..................AM....................USB...................LSB
1. 3.11.....................1.36...................3.06...................3.06
2. 3.48.....................3.38...................3.42...................3.43
3. 3.47.....................3.34...................3.42....................3.42
4. O VOLTS FOR ALL
5. 6.25.....................6.08...................6.19....................6.26
6. 7.82.....................7.62...................7.74....................7.69
7. 7.89.....................3.83...................4.24.....................4.24

The Defpom wrote: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 final(tr35) and driver(tr34)????

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......0.51
LSB.........2.32.....1.57....8.36........................0.03.....0......0.55

TR10

USB........0.29.....0.98.......8.23......................0.......0.09....0.56
AM.........0.29.....0.98.......8.23......................0.......0.08....0.51
LSB.........0.29.....0.98.......8.23......................0.......0.09....0.55

TR18

USB........1.23......1.96......7.52......................0........0.54....0.55
AM.........1.24......1.98......7.51......................0........0.46....0.50
LSB.........1.22......1.92......7.52......................0........0.54....0.55

All those voltage check out OK...

TR34 and TR35 are the AM modulators, TR34 is a 2SC945, TR35 is a 2SC1419 they are at the rear right corner next to the audio amp.

I am just trying to figure out what could be causing your radios faults, so far everything has checked out, apart from the slightly high voltage on pin 2 of the audio amp, but you replaced that already didn't you.

I think I am going to have to look at this as different faults, not one common one, and try to tackle each in turn.

Replace C92, I have come across that part killing TX audio before, no harm in replacing it.

As there is a lot of things that are unknown I need you to do an alignment, and confirm that the radio is at least on the correct frequencies and the oscillators are all correct etc, so that doubt is removed.

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
...............E..........................C........B.............................E.........................C......B
USB.........0.2(slowly drops).....0.........0.............................37 slowly drops.....0.......0
AM..........0.39(slowly drops).....0.......0..............................same as above.......0.....10
LSB.........0.36 (slowly drops).....0.......0..............................49 slowly drops.....0.......0

TR 35..................RX.................................................TX
...............E.............C............B......................E............C.........B
USB.........12.47.....12.48...8.02........................12.44.....12.45......8.08
AM..........11.93.....12.48...8.02........................7.19......12.41.......7.85
LSB.........12.48.....12.48....8.06........................12.45.....12.45......8.07

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

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

the offset osc freqs are pretty much spot on

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.

Is the loop freq the same (or very close) on TX/RX ?

What loop freq do you get on CH1 at TP1, what freq do you get at TP10 and what voltage do you get at TP9, I can then work out if there is a problem with the Loop circuit (VCO/PLL/Mixer).

Have you tried adjusting the VCO coil (L13) to see if that corrects it ?

I have had VCO issues with this chassis before, so it can happen, a faulty VCO can cause all kinds of weird behaviour.

frogman296 wrote: 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 audio, then the used one may be OK, so dont chuck it out yet.

OK, so what IS working now, and what IS NOT working, just so I know where things are now, obviously changing all the caps has made a difference.

The Defpom wrote: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)---- 33.50x to 37.44x(usb)-----33.60x to 33.98x(lsb)

What loop freq do you get on CH1 at TP1( 34.640-34.655), what freq do you get at TP10( 1.7040-1.7080) and what voltage do you get at TP9(1.53, adjusted to 2.00 volts), I can then work out if there is a problem with the Loop circuit (VCO/PLL/Mixer).

The Defpom wrote:
frogman296 wrote: 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 audio, then the used one may be OK, so dont chuck it out yet.

OK, so what IS working now, and what IS NOT working, just so I know where things are now, obviously changing all the caps has made a difference.

the radfio will fire up and move the needle when keyed on all modes... wattage is very low, less that a watt... rx is there with no noise... rx/ts light changes when keyed

i get ZERO amperage reading at TP7, TP8

OK, we shall try and fix the loop freq problem first, and go from there.

Because it is a LOOP all parts are incorrect, the frequency drift could be the cause of the voltage shift, or the voltage drifting could be the cause of the freq drift, an easy way to find out if you disconnect the PD output from the PLL which feeds the VCO and inject your own variable voltage to control the VCO frequency, then re-check if the frequency is still drifting at TP10.

So all you have to do is lift one end of R72, and then inject a voltage into TP9, an easy way of doing that is to get a 10K pot and connect each outer terminal pin to 0V and to 8V, at PLL pins 18 (0V) and pin 9 (8V), then connect the middle leg to TP9.

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

A common part to fail is C72 or C71, this loads down the control voltage and causes the voltage to fluctuate, or C73, C74 which effect the VCO itself,so if the frequency at TP10 is drifting when a FIXED voltage is injected it could be one of them effecting the VCO, or it could be the mixer transistor that is the problem.

If the freq at TP10 is drifting even with the fixed voltage feed and C71,C72,C73 C74 are definately OK, then check the VCO output at pin 10 of IC1 (the pin that feeds TR19 from the VCO module), and see if that frequency is stable, if it is, or it is better than TP10 (it can get a noisy backfeed), then the mixer transistor or components are likely to be the problem, in which case you need to look at C68,C69,C70 and the transistor itself, TR19, it is also worth checking C75 as well, just in case that is back-feeding noise into the VCO from L14.

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

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

frogman296 wrote:
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

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 fails to resolve it replace C197, C60, C61, C62, C63 and check R71 (1.5K), R72 (2.7K), R73 (33K), R74 (12K), R75 (33K), R76 (6.8K) and R77 (2.2K), these will all be near the PLL.

I can see a lot of solder flux on the PCB in the pictures, it is a good idea to use some PCB cleaner (flux cleaner) to remove it, especially around oscillators sections, as it can cause problems.

I can also see a couple of questionable solder joints, and there is a smeared solder blob near the end of the yellow jumper wire, which may be bridging to the earth track.

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

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, and could also contribute to the problem.

Tantalum as almost as prone to failure as electrolytic's, just not as commonly used, so they are always suspects too.

The Defpom wrote: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, and could also contribute to the problem.

Tantalum as almost as prone to failure as electrolytic's, just not as commonly used, so they are always suspects too.

i replaced 60 61 62 63 64 65 66 67 with no change

The Defpom wrote:
frogman296 wrote:
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

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 fails to resolve it replace C197, C60, C61, C62, C63 and check R71 (1.5K), R72 (2.7K), R73 (33K), R74 (12K), R75 (33K), R76 (6.8K) and R77 (2.2K), these will all be near the PLL.

I can see a lot of solder flux on the PCB in the pictures, it is a good idea to use some PCB cleaner (flux cleaner) to remove it, especially around oscillators sections, as it can cause problems.

I can also see a couple of questionable solder joints, and there is a smeared solder blob near the end of the yellow jumper wire, which may be bridging to the earth track.

i cleaned the flux off and replaced all the parts mentioned above still no luck... PA function is working A+

Remove that clarifier mod to return the clarifier to original, and re-do the loop alignment and see if that gives better results, if you have replaced C72 as well and the VCO output is still noisy, then the PLL may be at fault.

The reason I want to get the VCO and loop problem sorted first, is that if it is jumping all over the place rapidly, it could cause the TX freq to jump wildly, resulting in loss of output power and distorted TX audio.

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.

One side of the pot goes to R415 (3.3K), which then connects to 0V, the other side goes to the RX only 8VDC supply, as found at the NB switch, and the feed side of the resistor that then connects to the RF gain pot (R417) (there are two, one goes to 0V, the other to the RX only DC).

Once you have the RX side back together, make sure that the TX side is also correct, refer to the partial circuit diagram I have attached which shows how the clarifier and TX only DC supplies are hooked up.

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

It was probably on the back of the pot originally.

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

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??

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???

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

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

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