Search found 432 matches

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: 5043

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: 7010

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: 5043

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: 7010

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: 20202

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: 2097

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: 2671

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: 2671

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: 6076

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: 6076

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: 4208

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: 6226

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: 6076

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: 6226

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: 10000

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: 5690

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: 11141

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: 4121

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: 6076

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: 11141

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: 6226

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: 2142

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: 47438

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: 47438

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.

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