Recent content by Night Stalker10

That's good news, thanks for the update. I assumed that the L19 voltage effected all the channels, not just a few. I learned something new again.

That's good info. I had a guy bring me his Cobra 29 with a no receive issue. A slight adjustment on L19 brought the radio back to life. Just another thing to keep in mind, or add to the little black repair book.

Okay, so If ch36 isn't transmitting, just do the same frequency test in transmit mode on IC3. Pins 6, 7, and 8 should show 27.365mhz for ch36. I'm not sure why it is showing 13.1mhz on pin 6 when you checked it on ch34 &ch35. Pin 4 should show 10.240mhz on all the channels in receive mode. Also...

Spivey, when you get a chance to look at the radio again. A real quick test would be to put your scopes probe (try X10) on R63 just behind L20. On ch34 key the mic and see if you are getting a signal on the scope, and also check the frequency which should read 27.345mhz. If you can't verify the...

I assumed he had receive on channels 35 - 40, just no transmit. That's why I thought it would be good to check things out with the IC3 TX mixer, PLL and VCO first. If everything checks out okay in those circuits, then the next thing that might could cause this problem would probably be something...

That's an interesting problem. Have you checked the voltages and frequencies in the IC3 TA7310p TX mixer? Pin 1 gets its 16-17 mhz reference signal from TR20 (osc) which should be 16.649mhz while on ch 34, and 16.659mhz on ch 35 in RX mode. Notice the 10khz difference in freq, are they changing...

At least it's decent looking on the inside for its age. These were real audio monsters with a Johnson base power mic. I believe there was a mod you had to do inside to open up the audio.

That's a great point, I didn't think of that. On a Cobra 29, L22 is the balance coil for ch1 and ch40, and it comes off of the 1/2 Ref Osc pin 10 of the PLL. ON this 858 PLL it would be pin 8, but it's not used in this radio. I assume that's why it wasn't in the synthesizer alignment section...

It sure surprised me when the tone came through my speaker. I'm not sure what to tell you, but I have 37.880mhz at TP6 and the collector of TR17 is around 2.6v and the pll pin 1 is in lock mode. I guess I will wait awhile before I put the covers on just to be sure.

I'm currently injecting a -114dbm signal and I hear it on channel 1 and 40. Currently on ch 19 the -114 signal is around 11db sinad.

Yes

The 1khz signal came through the speaker shortly after applying the 5 volts as I was adjusting L20 and the frequency was I think around 36mhz or somewhere in there.

I've spent a lot of time on this radio over the last couple of months, and I can't thank you Brandon and Nomad enough. I've learned a lot about the VCO 10 pin sip modual. I have no idea what part was effected by jumping the 5 volts and adjusting L20 and seeing the frequency increase, but it...

With my dc meter on TP5, I can turn the voltage down using L20 to .07V and the frequency reads 31.5xxxxmhz on pin 10 of ic5. Turning the core on L20 to the top of the can, raises the voltage to 4.77v which is the Vcc voltage. At 4.77v the frequency moves up to 32.2xxxxmhz. Now when I jumpered...

TP1 does show 10.240Mhz, and pin 11 of the upd858c shows 1.4xxxxMhz.