SS360FM mk II . FM receive just isn't right.

[cb4ever104]

Hi All .

I've been working on this 360FM for most of the week. Changed the 2SA1012. Used Nick's mod (thanks !) to convert it to 5 bands. Changed the band switch to a 5 way one. Changed the led , +10khz , and the beep. So it's kept me pretty busy.

So I'm more or less finished with it. However. The FM receive just doesn't sound right. There's no "crunch" to it. It's more like a mild hiss. It's maybe as if there's a tiny signal coming in (there isn't) that's cancelling out the usual FM white noise. I changed the discriminator just in case , but it's still the same. L6 does vary the received audio , but it's still not right. Before I really jump in I was just wondering if there were any other common known issues that might cause this ?

The radio works fine apart from this.

Thanks in advance for any information.

Sammy

[14CS06]

Hello Sammy

If L6 does not react it must be replaced



@+
Claude

[astradyne]

I'd go with Claude on this one Sammy. If L6 isn't adjusting correctly then that would be my first port of call for repair. Hopefully this will be the issue and an easy fix.

[cb4ever104]

Hi.

Sorry. Maybe I should have been a bit clearer. L6 is fine. That's what I was saying. I changed it anyway just to be sure. I'm still getting just a hissing noise on FM. I'll start doing some more tests around the discriminator. Won't be able to continue with it till June, but I'll post back with any findings.

Cheers

Sammy

[13EL121]

Hi Sammy, maybe a dry capacitor in the audio stage? Check the 330uf near the audio chip. Had the same issue. Are there the grey YEC caps inside?

[cb4ever104]

Hi Ralf .

Could be , although the other modes seem fine . I don't have the radio at the moment , but I've been looking at the schematic . I'm thinking maybe a filter issue , but I'll need to do some more testing . I'll post back once I've had another chance to look at it .

Cheers

Sammy