• You can now help support WorldwideDX when you shop on Amazon at no additional cost to you! Simply follow this Shop on Amazon link first and a portion of any purchase is sent to WorldwideDX to help with site costs.
  • A Winner has been selected for the 2025 Radioddity Cyber Monday giveaway! Click Here to see who won!

Cobra 29ltd classic no transmit with DDS VFO

gcrcien

Member
May 12, 2023
3
6
13
34
Hello everyone, I'm new to the forum, I've been doing some modifications for friends, putting a homemade VFO on cobras and other radios, I've encountered some trouble with the cobra 29, I have installed the coax and applied the LO to the footprint of the vco, (16mhz at pin 3 on ic2-yd7310s) after aligning the VFO I can move along the band correctly.
The issue comes when I try to tx, I get nothing, I have programed the correct offset of +455khz to the Arduino and I can see the frequency change on the oscilloscope, however no tx.
Is there some pin/cable that has to be pulled down or apply 8v that I'm missing?
I have removed the channel selector and display, as well as the vco and pll
I can see the 10.240mhz oscillator but I'm not sure where to look at next. I should have noted that before the mod, the radio was working hahahaha. I'm also having issues getting the proper schematics and service manuals to work with
 

Attachments

  • IMG_20250925_193628187_HDR.jpg
    IMG_20250925_193628187_HDR.jpg
    1.5 MB · Views: 13
  • Like
Reactions: Crawdad

Can't remember if the out-of-lock detector is high or low when locked.

Pretty sure it's high. If you haven't pulled up that line coming from the original PLL the transmit will shut down as if the PLL were unlocked, even though your source of local-oscillator input to the mixers isn't coming from the PLL any more.

Just a hunch.

73
 

dxChat
Help Users
  • No one is chatting at the moment.