[MRCA] mystery diode solved! I was the problem.

[B. Smith]

That work bench is entirely too neat.
Z


On 9/17/2025 9:40 PM, Ray Fantini via MRCA wrote:
> After spending a couple days trying to sort the discriminator that’s 
> used to drive the tuning meter on the AN/PRC-74 I have discovered that 
> the problem is the meter itself, and not the discriminator in the 
> power amplifier! Would like to think that I am not a complete moron 
> and when I saw the tuning meter was not working one of the first tests 
> was to read across the meter with the VOM in low power mode and the 
> meter went full scale. But not a bit of movement when in tune or 
> transmit. Tonight after reinstalling the PA assembly for the tenth 
> time, I decided to take the discriminator output directly from the PA 
> just to see if I was getting anything at all and discovered that I get 
> good swing and readings up to 1.0 mA on an external meter. For some 
> strange reason the tuning meter works at five or six mA but not below 
> one mA where it's supposed to, no sign of any movement at all but good 
> meter action using an external zero to one mA meter. Don’t have any 
> idea how it can fail like that, but it has. I did end up replacing 
> CR-15 with a 1N914 and that works but the new problem will be where to 
> come up with a miniature zero to one mA meter to replace M201?
> You can see the radio in the attached picture and everything works 
> great except that meter will in no way fit in that radio.
> Thanks for all the help with the diode, although in the end I was the 
> problem, still the first time I have ever seen a meter fail like this.
>
> Ray F/KA3EKH
>
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