Search found 433 matches

by The Defpom
Tuesday 3rd Mar 2009, 18:23
Forum: CB Radio Repair and Troubleshooting
Topic: UNIDEN WASHINGTON, no sound(tx,rx,pa)
Replies: 37
Views: 43620

Re: UNIDEN WASHINGTON, no sound(tx,rx,pa)

I think you checked IC4 instead of IC5, IC4 is the audio amp, IC5 is the MB3756
by The Defpom
Tuesday 3rd Mar 2009, 18:20
Forum: CB Radio Repair and Troubleshooting
Topic: Uniden Washington Keys Up, No TX & No RX
Replies: 8
Views: 11423

Re: Uniden Washington Keys Up, No TX & No RX

It should be an 18V Zener diode.
by The Defpom
Tuesday 3rd Mar 2009, 16:14
Forum: CB Radio Repair and Troubleshooting
Topic: Cobra 148GTL, only 2 channels functioning
Replies: 15
Views: 17449

Re: Cobra 148GTL, only 2 channels functioning

Also make sure that any diodes or resistors on the clarifier circuit have been restored and are not bridged or anything, often they are, which could put too much strain the the MB3756 if the clarifier is turned fully in one direction.
by The Defpom
Tuesday 3rd Mar 2009, 14:42
Forum: CB Radio Repair and Troubleshooting
Topic: Uniden Washington Keys Up, No TX & No RX
Replies: 8
Views: 11423

Re: Uniden Washington Keys Up, No TX & No RX

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.
by The Defpom
Tuesday 3rd Mar 2009, 14:40
Forum: CB Radio Repair and Troubleshooting
Topic: Cobra 148GTL, only 2 channels functioning
Replies: 15
Views: 17449

Re: Cobra 148GTL, only 2 channels functioning

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.
by The Defpom
Tuesday 3rd Mar 2009, 14:37
Forum: CB Radio Repair and Troubleshooting
Topic: UNIDEN WASHINGTON, no sound(tx,rx,pa)
Replies: 37
Views: 43620

Re: UNIDEN WASHINGTON, no sound(tx,rx,pa)

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 ?
by The Defpom
Sunday 1st Mar 2009, 10:23
Forum: CB Radio Repair and Troubleshooting
Topic: President Lincoln USB off freq,
Replies: 2
Views: 5284

Re: President Lincoln USB off freq,

All of these units, (including the HR2510) have problems when they get older, what you need to start out with is to replace ALL of the electrolytic capacitors on the MPU PCB, there is only one which you do not replace, the large one that is next to the MPU, as it is a special memory backup capacitor...
by The Defpom
Saturday 28th Feb 2009, 10:10
Forum: CB Radio Modifications
Topic: Getting 40 Channel Coverage on an old 23ch Cobra 135?
Replies: 3
Views: 6335

Re: Getting 40 Channel Coverage on an old 23ch Cobra 135?

Crystal sets are not my area, but I do know that there are two versions of the 135, I have a diagram for one of them, and that version (which may or may not be like your one) does not give any easy way to add more channels, yes there is one crystal that can be switched but it will only work on RX, n...
by The Defpom
Friday 27th Feb 2009, 22:45
Forum: CB Radio Modifications
Topic: Getting 40 Channel Coverage on an old 23ch Cobra 135?
Replies: 3
Views: 6335

Re: Getting 40 Channel Coverage on an old 23ch Cobra 135?

Because it is a crystal radio instead of a PLL based one it complicates things a fair amount. I suspect that it MAY be possible to instal a crystal mixer PCB, to shift one of the frequency banks to another range, to give higher channels, but it is not something I have done on a crystal radio, so I c...
by The Defpom
Friday 27th Feb 2009, 8:28
Forum: CB Radio Repair and Troubleshooting
Topic: Sadelta Echomaster Plus - Echo Fading Out
Replies: 9
Views: 12845

Re: Sadelta Echomaster Plus - Echo Fading Out

If you have a scope there, it may be an idea to check pin 2 and pin 4 of the MN3101, it generates the clock frequency for the MN3008, check to see if the clock frequency drops off on those two pins when the echo fails, if it stays OK, then the fault is probably with the MN3008
by The Defpom
Friday 27th Feb 2009, 8:01
Forum: CB Radio Repair and Troubleshooting
Topic: Sadelta Echomaster Plus - Echo Fading Out
Replies: 9
Views: 12845

Re: Sadelta Echomaster Plus - Echo Fading Out

I would say to check all the resistors and capacitors, if they are OK try replacing the LM324, it is a common part, and will rule that out, failing that it could be one of the echo IC's themselves.
by The Defpom
Friday 27th Feb 2009, 7:51
Forum: Wanted !
Topic: Dummy Load
Replies: 5
Views: 10158

Re: Dummy Load

INteresting, and pretty clever. I do wonder though if the resistance and tuning changes with temperature, as it warms up it may increase its resistance as the molecules expand, perhaps if you build it you could check the SWR at room temp, and again when it is hotter after it has been used and see if...
by The Defpom
Thursday 26th Feb 2009, 11:44
Forum: CB Radio Repair and Troubleshooting
Topic: Cobra 18 Ultra No TX and no RX - WX works OK
Replies: 8
Views: 11927

Re: Cobra 18 Ultra No TX and no RX - WX works OK

it looks like the VCO signal is missing, check for the same frequencies at Q402 (it is just a buffer/amplifier), check all three legs, one is 0V, so wont have anything, the other two should have the frequencies on it I mentioned.

If there is nothing, then check Q403 and the alignment of L401.
by The Defpom
Thursday 26th Feb 2009, 8:53
Forum: CB Radio Repair and Troubleshooting
Topic: Sadelta Echomaster Plus - Echo Fading Out
Replies: 9
Views: 12845

Re: Sadelta Echomaster Plus - Echo Fading Out

Check the voltages across the IC's, specifically pin 1 and 3 of MN3101 and see if it drops off when the echo does.

Also check pin 3 and ground of the LM324, in case of a problem with the 100K resistors.

Does the TX LED light up and stay lit up the whole time, even when the echo fails?
by The Defpom
Thursday 26th Feb 2009, 8:39
Forum: CB Radio Repair and Troubleshooting
Topic: Cobra 18 Ultra No TX and no RX - WX works OK
Replies: 8
Views: 11927

Re: Cobra 18 Ultra No TX and no RX - WX works OK

OK, if the VCO and PLL are functioning, you should see 16.270 MHz on CH1 in RX, and 13.4825MHz in TX on PLL pin 23. If the signal is missing, then I would suggest you start by checking power supplies, the radio uses Zener diodes, it is possible one has failed, or a capacitor is shorting dragging dow...
by The Defpom
Thursday 26th Feb 2009, 7:20
Forum: CB Radio Modifications
Topic: Cobra 148 GTL mod confusion...
Replies: 7
Views: 19713

Re: Cobra 148 GTL mod confusion...

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.
by The Defpom
Wednesday 25th Feb 2009, 22:46
Forum: CB Radio Alignments
Topic: uniden pc68xl alignment points
Replies: 4
Views: 11673

Re: uniden pc68xl alignment points

I am pretty sure that alignment info is on the main radiomods site too, my memory is failing me, but I expect it is there.
by The Defpom
Wednesday 25th Feb 2009, 22:35
Forum: CB Radio Modifications
Topic: Cobra 148 GTL: Unlocking the Clarifier
Replies: 16
Views: 24469

Re: Cobra 148 GTL: Unlocking the Clarifier

If you think about it you will understand that you only need to slide by about 6K down, as the upwards slide from the channel below it would cover the gap, giving full coverage.
by The Defpom
Wednesday 25th Feb 2009, 11:38
Forum: RadioMods Web Site
Topic: Forum Search Not Working.
Replies: 5
Views: 9655

Re: Forum Search Not Working.

Glad to hear it :-)
by The Defpom
Wednesday 25th Feb 2009, 11:38
Forum: CB Radio Repair and Troubleshooting
Topic: Sadelta Echomaster Plus - Echo Fading Out
Replies: 9
Views: 12845

Re: Sadelta Echomaster Plus - Echo Fading Out

Please post the diagram for the mic.
by The Defpom
Tuesday 24th Feb 2009, 21:48
Forum: CB Radio Modifications
Topic: Cobra 148 GTL: Unlocking the Clarifier
Replies: 16
Views: 24469

Re: Cobra 148 GTL: Unlocking the Clarifier

I would definitely keep what is done to a minimum, the more slide range you give, the more it will drift, AM would be OK, but SSB will really suffer for it. As far as a super diode goes, I have no idea, someone once used to market them as such, but as far a an actual part number goes, I do not know,...
by The Defpom
Tuesday 24th Feb 2009, 21:44
Forum: CB Radio Repair and Troubleshooting
Topic: Cobra 18 Ultra No TX and no RX - WX works OK
Replies: 8
Views: 11927

Re: Cobra 18 Ultra No TX and no RX - WX works OK

I would start by looking to see if the PLL and VCO are functioning correctly, I would definitely be looking for things common to both RX and TX.

Can you please post a copy of the diagram here, I do not have that one.
by The Defpom
Tuesday 24th Feb 2009, 21:42
Forum: CB Radio Repair and Troubleshooting
Topic: cobra 148 gtl no tx in am rx ok.
Replies: 2
Views: 5042

Re: cobra 148 gtl no tx in am rx ok.

Do you have the exact circuit diagram for the radio, I do not have a very good one for the KEPC-332, it is only just readable in places.

I would say to check (in order) R41, TR42 and the 220 Ohm 2W resistor, it looks like it is either R193 or R183 (I cant make it out), VR10, C174, R228, R194, C173.
by The Defpom
Tuesday 24th Feb 2009, 7:39
Forum: CB Radio Modifications
Topic: Cobra 19 DX IV mods???
Replies: 24
Views: 74802

Re: Cobra 19 DX IV mods???

OK, but why did you remove the mod info you posted ?
by The Defpom
Monday 23rd Feb 2009, 22:30
Forum: CB Radio Modifications
Topic: Cobra 19 DX IV mods???
Replies: 24
Views: 74802

Re: Cobra 19 DX IV mods???

Thanks for posting the info, however, your post is on the verge of being a bit too abusive... be careful, abusive comments are not tolerated.
by The Defpom
Monday 23rd Feb 2009, 7:09
Forum: CB Radio Repair and Troubleshooting
Topic: Cobra 25 LTD : Dead Channel LED after attempted replacement.
Replies: 2
Views: 4859

Re: Cobra 25 LTD : Dead Channel LED after attempted replacement.

Have a look fr a decimal indicator on the displays, and see f that will tell you if they are both the same way up, the part marking is not always on the same edge. If you have a multimeter with a diode test function you can use that to probe the pins, and you will see that it makes some segments lig...
by The Defpom
Saturday 21st Feb 2009, 9:20
Forum: CB Radio Repair and Troubleshooting
Topic: Help... Cobra 148 GTL no voice TX in AM FM SSB- RX OK
Replies: 11
Views: 13807

Re: Help... Cobra 148 GTL no voice TX in AM FM SSB- RX OK

Do you have audio in PA mode ?

If not trace all the way from the audio pin on the mic socket through to the main PCB, and confirm that there are no shorts or missing connections, a solder blob could kill the audio entirely, even with connections being correct.
by The Defpom
Saturday 21st Feb 2009, 9:16
Forum: CB Radio Repair and Troubleshooting
Topic: Cobra 148GTL, only 2 channels functioning
Replies: 15
Views: 17449

Re: Cobra 148GTL, only 2 channels functioning

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 the...
by The Defpom
Saturday 14th Feb 2009, 14:21
Forum: CB Radio Modifications
Topic: Cobra 148 GTL: Unlocking the Clarifier
Replies: 16
Views: 24469

Re: Cobra 148 GTL: Unlocking the Clarifier

Those green axial type are the ones you would want. A warning though, adding a inductor to the varactor has some tradeoffs, firstly, it gives you more down slide than up slide, and it also then requires you to re-align the loop oscillator section, it can also increase LSB instability and cause more ...
by The Defpom
Friday 13th Feb 2009, 22:52
Forum: RadioMods Members Assistance
Topic: cannot search
Replies: 2
Views: 7086

cannot search

This forum has been getting a bit buggy of late, I may have to look at dumping the entire thing and getting a newer version, this one has not been updated in years, apart from the improvements I have done to block spammers and tweak certain functions.
by The Defpom
Tuesday 3rd Feb 2009, 14:17
Forum: CB Radio Repair and Troubleshooting
Topic: HR 2510 BLOWN VOLTAGE REGULATOR
Replies: 10
Views: 13016

HR 2510 BLOWN VOLTAGE REGULATOR

You will need to replace the final as well, it is very likely that it has been damaged, they rarely survive being reverse wired.
by The Defpom
Tuesday 20th Jan 2009, 4:40
Forum: RadioMods Web Site
Topic: Forum Search Not Working.
Replies: 5
Views: 9655

Forum Search Not Working.

I had to empty out the search database, so it will not find existing matches, it will add things from this point on from new posts.
by The Defpom
Monday 19th Jan 2009, 14:38
Forum: RadioMods Web Site
Topic: Forum Search Not Working.
Replies: 5
Views: 9655

Forum Search Not Working.

I have cleaned out the database, I think it just got too clogged up.
by The Defpom
Saturday 17th Jan 2009, 10:16
Forum: CB Radio Repair and Troubleshooting
Topic: Cobra 29 Modulation stuck at 45%
Replies: 5
Views: 7749

Cobra 29 Modulation stuck at 45%

Yeah, the tuning slug is the way that it is designed to be adjusted by, so try screwing that slug in to reduce the output power and see if that helps. It could just be an issue with the mosfet conversion, I have never done one (not seen the point), so I cannot help if it is something do do with that...
by The Defpom
Saturday 17th Jan 2009, 10:03
Forum: CB Radio Repair and Troubleshooting
Topic: Cobra 29 Modulation stuck at 45%
Replies: 5
Views: 7749

Cobra 29 Modulation stuck at 45%

Reduce the power output. it sounds like it is just trying to run too much power so the audio amp cant match the output to give enough drive.
by The Defpom
Sunday 14th Dec 2008, 8:23
Forum: CB Radio Modifications
Topic: Dumb question for cb experts.
Replies: 4
Views: 7354

Dumb question for cb experts.

The MFR455 (or equivalents) has been used in the President Lincoln radio, to replace the obsolete MRF477.
by The Defpom
Thursday 11th Dec 2008, 23:20
Forum: CB Radio Repair and Troubleshooting
Topic: malaysia 148 GTL sideband transmit problem
Replies: 3
Views: 6172

malaysia 148 GTL sideband transmit problem

Warbling on TX SSB can be caused by poor voltage regulation, this can happen if the clarifier has been modded, the extra current drawn in TX puts more strain on the regulators, so it effects TX a lot more than RX. My first port of call would be to see if the clarifier has been modified to give TX sl...
by The Defpom
Sunday 7th Dec 2008, 20:51
Forum: CB Radio Repair and Troubleshooting
Topic: tx meter hardly oves
Replies: 13
Views: 17320

tx meter hardly oves

As the Lincoln is using the high power 455 transistor that is very likely to have fried the linear amp, as the radio would have been putting out more power than most amps can handle, which in turn has probably weakened / blown the final in the Lincoln. Try plugging the radio into the DC supply, and ...
by The Defpom
Friday 5th Dec 2008, 22:54
Forum: CB Radio Repair and Troubleshooting
Topic: Test your knowledge Uniden (President) Grant PC-409
Replies: 43
Views: 115396

Test your knowledge Uniden (President) Grant PC-409

The idea of this is to troubleshoot, you asked me if it had failed, and I responded that I did not know, and that it was up to you to work out if it had or not, you asked me directly if it had failed, you did not ask for me to test it, or tell me how to test the VCO module. So while yes your guess w...
by The Defpom
Friday 5th Dec 2008, 9:46
Forum: CB Radio Repair and Troubleshooting
Topic: Test your knowledge Uniden (President) Grant PC-409
Replies: 43
Views: 115396

Test your knowledge Uniden (President) Grant PC-409

WELL DONE, it was the VCO module, IC2 ! I said you were all close !! The fault was with IC2, as the DC supply going in was clean, the PD control voltage was clean (when injected), all external components were OK, but the outputs were noisy, this meant it could have only been one thing, the VCO itsel...
by The Defpom
Friday 5th Dec 2008, 1:02
Forum: CB Radio Repair and Troubleshooting
Topic: Test your knowledge Uniden (President) Grant PC-409
Replies: 43
Views: 115396

Test your knowledge Uniden (President) Grant PC-409

OK, let me put it this way...to sum up what has been covered. It has been confirmed that there is no noise in the power supply to the PLL/VCO/TX mixer/11MHz Oscillator. There are no bad solder joints. There is noise on the outputs of the VCO, The PD input of the PLL, and the PD output of the PLL, an...
by The Defpom
Thursday 4th Dec 2008, 22:09
Forum: CB Radio Repair and Troubleshooting
Topic: Test your knowledge Uniden (President) Grant PC-409
Replies: 43
Views: 115396

Test your knowledge Uniden (President) Grant PC-409

Everything requested, tests OK...

Do you want me to tell you the answer ?
by The Defpom
Thursday 4th Dec 2008, 10:38
Forum: CB Radio Repair and Troubleshooting
Topic: Test your knowledge Uniden (President) Grant PC-409
Replies: 43
Views: 115396

Test your knowledge Uniden (President) Grant PC-409

All solder joints are now OK, on the entire PCB.
by The Defpom
Thursday 4th Dec 2008, 7:17
Forum: CB Radio Repair and Troubleshooting
Topic: Test your knowledge Uniden (President) Grant PC-409
Replies: 43
Views: 115396

Test your knowledge Uniden (President) Grant PC-409

euhara: L16 tests OK. ================ Rick: Signal voltage at pin 10 is normal, but noisy. There are no cold solder joints on IC2, there was one on pin 8 but that has already been fixed. The frequency at TP10 is correct, but noisy. Pin 1 of IC2 is noisy. There is no noise on Pin 1 of the PLL. L19 s...
by The Defpom
Wednesday 3rd Dec 2008, 22:58
Forum: CB Radio Repair and Troubleshooting
Topic: Test your knowledge Uniden (President) Grant PC-409
Replies: 43
Views: 115396

Test your knowledge Uniden (President) Grant PC-409

timrim:
The 11MHz signal at TR29 is clean.

================
euhara:
L17 tests OK.
by The Defpom
Wednesday 3rd Dec 2008, 22:27
Forum: CB Radio Repair and Troubleshooting
Topic: Test your knowledge Uniden (President) Grant PC-409
Replies: 43
Views: 115396

Test your knowledge Uniden (President) Grant PC-409

timrim:
There is no noise at the crystal.

=============
Rick:
There is still noise at TP10 when injecting 3V at TP9.

C79, C80 and C81 test OK.
by The Defpom
Wednesday 3rd Dec 2008, 12:19
Forum: CB Radio Repair and Troubleshooting
Topic: Test your knowledge Uniden (President) Grant PC-409
Replies: 43
Views: 115396

Test your knowledge Uniden (President) Grant PC-409

eurhara: There is noise at pins 5 and 10 of IC2, pin 8 is clean. C80,81,90, and 92 are OK There is no noise on pin 7 of IC3 ====================== James Unit 198: I do not know if the VCO has failed, you have to tell me what is wrong by troubleshooting the radio. TR20 tests OK. C84 tests OK (the one...