Help needed for Cobra 148 NW ST

[CTStallion]

Glad you got it all working!

Got a question tho, are you planning on using this mobile or for a base? If you're using it on the base, the large transformer/choke (I think it can/might be labeled as T1) can be jumped and bypassed and that will help with the warble on SSB. Also, on some of the 148 NW/ST's, the C1969 final in some of the later production radios are NOT genuine, they are fakes, and will also cause a warble issue.

If the radio is used mobile, you can still bypass this transformer/choke, but you might get a little bit of whine or noise, you can build your own choke with heavier wire and retrofit that inline with your positive power wire on the power cord.

The diodes for the RX mod is a great idea, but for TR14, it's best to sub in a C1730L instead of a C2999. Then use a C1674 for TR19, that combination yields the bests results that I have seen so far in testing.


~Cheers~

Will do, THANKS!

 

[Robb]

Bought one of these radios - used - a couple of years ago and see what it was like. Aligned it and did a standard clarifier unlock. It worked OK (no SSB warble) so long as the ALC was kept at 12w. Then the final blew.
Bummer.

So I found a 2sc2312 transistor to replace the 2sc1969 - online from a reputable retailer - and put it in and it worked for a week. Then for some unknown reason the PLL became unlocked. My best troubleshooting guess was that the VCO chip was toast. Couldn't find a replacement part cheap enough. Put it in a box and forgot about it for almost two years. Destined to be a parts radio - so I thought.
Bummer.

Then I read this thread, dragged that radio out, cleaned it off, pulled it apart, and replaced the bad resistor (R130).
Radio works now.
Cool.

1) I've replaced one of the caps in the audio circuit (C172) with a 2200uf/25v and it did help some with SSB warble. Very little. So I'm going to replace the other cap (C181) mentioned with a 2200uf/25v.

2) Still questioning the quality of the part at D35; might pull a veractor out of another junk radio and see if it helps.

3) Don't think it would be wise to bypass the choke/xformer because it would be too noisy to use in mixed applications.

4) Guess I will set the ALC for 12w and the DK for 3w and put it together.

5) Never saw the voltage reg lose voltage in SSB/TX mode.

6) Needs to have the ST adjusted too.

7) Will put in a set of schottky diodes and leave the receive TR alone.


Thanks to all who contributed to this thread. This radio suffers from a well deserved bad reputation and I think that some of the more common problems it has - have been answered here.
At least some of the stink has been let out of this stinker.
Much appreciated to all y'all!

 

[BayouRadioAmplifier]

months ago, I was given a Cobra 148GTL "D"
( made in China version )
and told it has problems and does not work. so got it working, but in SSB mode
it had frequency FMing, the "Voice Lock" was squirrely.
.
so a few days ago it went out completely. could not change
frequency. I quickly determined that the PLL was bad,
having a low voltage (3.2 VDC) on pin 9 of the PLL chip IC1.
(it should be 8 VDC)
The VCO was working, being able to tune its' inductor L19.

I have the schematic, and this radio has that extra reset board.
(not it my schematic diagram)

so did a google search on all this, and it directed me to this thread,
and I read all the posts. thanks!!!!

I found that 10 ohm resistor R130 on the blue wire, at the main circuit board,
hidden down there, that was bad. replaced it with a 10 ohm half watt.
now 8 volts to IC1, adjusted VCO tuning L19. TP9 VCO tuning voltage
now goes from 4.1 to 5.2 VDC from ch 1 to ch 40.

All OK now. SSB sounds good now.
the RIT "Voice Lock" works good.

so have the radio up loud, listening to all the madness on
ch 38 LSB.

this post really saved me time. thanks again.

.....