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

4558 was bad. ssb tx shows a substantial increase in average power, pep power remains the same.

Working on a dx959...the mic amp chip (4558) output is noisy when cold...better when hot, but not good. 4558 on order, will post results.

Roger beep...beeps on key-up and un-key.
When radio is hot: in ssb mode...100 watt carrier, no tx audio/AM mode 100 watts, no tx audio.
Anyone?

pic of mod

This is a modification I came up with as I was unhappy with narrow receiver bandwidth in the President Washington operating AM mode. I have successfully used this simple mod on several radios with this circuit board. I would like to see some other ideas or comments on improving AM mode operation for...

I adjust the ALC while monitoring the output waveform on an oscilloscope. Turning the ALC up too much will result in distortion. Are you useing a PEP watt meter?

The 148 GTL series are all similar. 3 pin regulator or otherwise. I also had 2 in. One had a bad 8.3 volt rx switch, TR44 and a shorted audio amp TR41. No rx and poor am tx audio. the other was no rx...cold solder at c175. This one also suffered form poor quality construction requiring reinstallatio...

This alignment procedure fits the 148 D china radio

The service manual is on cbtricks.com...Look for :cobra_148_gtl_sm_pg01_pg15.doc

your green rx led is lit?

Voltage on collector of TR44 should be 8.3 volts during receive. This is a receive only voltage.

Good luck with the radio.
Maybe there are some others out here with some better input.
Later.

148 D Schematic...It's labled 148 F on the top. They said the 148 E is exported to Mexico, and the 148 D is the Domestic version...Don't know what the 148 F model is. This is What Cobra sent me when I asked them for the 148 D, china radio.

Sorry, about that...I posted too soon...so disreguard. I was thinking about a different radio. Some radios use a seperate local oscilator for am. I'll look into getting that file to you.

I recently worked on the same radio, "148 D"
I have the schematic of that radio.
Cobra sent it to me a few months ago.
If you need a copy, let me know how I can get it to you.

Is the no rx symtom on ssb and am?
If no am only rx, 7.345 LO?

Replace 10 meter band local oscillator crystals?

When adjusting channels or "scanning the band" with my Cobra 19 Plus, the receive will mute briefly per one press of a channel button, or stay muted when holding a channel button down. Removing D6 will disable this muting feature and allow "scanning the band" without waiting for ...

So, Dodgem250, what are the reasons a mosfet final in a cobra 29 won't work?

I reprogrammed the pins on the 858 chip to give the 5 kHz channel increments. On frequencies below CB channel 1, 26.965, in the 5 kHz mode, there is a 2500 Hz tone on both TX and RX. The amplitude is less than 1% audio. The other frequencies do not have this. The 5 kHz channels above 40 are fine. Ha...

No luck on those sites Rick. Jim, I am looking for about 10 new ones.
Still looking. Thanks!

I am looking for replacement relays for the 858 PLL chassis like the President Washington.