I wanted to point out something...
(Don't worry, It's ok - I'm Punning myself here - Don't Panic!)
Think of this as a "How to Interpret Handy Andy's Run-On-Sentences..."
Check to make sure the TX and RX stuff does work, there are several spots I see in the schematic that use Electrolytics and if they've expired will kill SSB and AM too - so If you have AM but not SSB in RX mode, it is my thoughts that the DC switch that should be constant 8V to the Clarifier in the Mic HANDSET is not followed thru - or wire opened up - killing the supply to keep the SSB OSC side working...
This has gotten me into trouble before, but I wanted to show you a way to know how I think...
In the above "paragraph" I'm running thru a process of how I would look at a problem. This doesn't mean it's a fix, but a route to a possible solution.
1st, I'd check the RX/TX functions - in the JCP - it usually has some type of TX light which would indicate that your "On The Air" - so the poster does, so we can move on from there?
To a point yes, but RX voltage fails come from some different sources, one obviously is the RX/TX switching, another would be the buss feeder lines that power other parts of the radio that don't toggle on or off, but the Receiver gets power from these sub-sections along the way.
So, does the Meter light work? Does the lamp stay pretty much constant brightness?
Does adjusting the knobs, operating the Noise Blanker ANL - cause changes in brightness - these could indicate a power supply feeder line is "weighted" down by something pulling more current than usual.
Squelch controls and CB/PA switches can be intermittent - does the speaker "thunk" when you turn it on?
Squelch can "Stay on" killing your receiver because the AGC section treats SSB signals differently in RX mode - it's padded delay so you don't set your squelch too hard onto the noise floor and chop off the vowels despite the consonants.
Microphone wired up ok? I mean that? Yes! it can be the one you just used 3 months ago, well that doesn't mean the DPDT contacts always "stay contacted" with their respective terminals. Many of you may remember how the Grants and Cobra 148's used 2 types of Ground, one for speaker and another for the Mic element return - if one or the other failed you got quirky intermittent operation. So if the Mic cord is old or been overly stretched - well, we may be onto something of a broken wire onto internal break in the coiled cord.
Another portion of the Paragraph I mention Electrolytic, failure of these seems to be a CHRONIC problem these days - a quality issue. IF a cap fails, they may not show up until they're needed to absorb some type of spike or keep power supply filtration in tolerable ranges. Can put the radio asleep if they pull down the RX voltage lines to a point where Squelch "triggers" dues to the imbalance. SEE: SSB SQ adjust...
DC Switching - if you have AM but not SSB, does the receive send or route voltages properly in SSB mode?
It pays to know your history on a radio - for did the radio arrive working or was it used? Now sold, you got it, now this condition exists...Well, it could be something as simple as a mis-wired MODE switch. Someone wanted constant 8V to power the Clarifier but got lost when they wanted to deconvert it. Or worse, they removed an Echo board and didn't re-solder the power wires properly when they removed it...See MIC wiring and the Handset.
As you can see, with the complexity of radios and their component counts, the problems become exponential as to routes of simple failure turn onto a Freeway full of symptoms looking for the exit to the cascade of events - caused by age or previous work that was not completely done.
Ok, a quick Cliff - Notes Guide as to how I think...I just forget that others don't think like I do, so they get lost trying to figure out what I meant.
I was just trying to save bandwidth by not having to type all of the above and bore the reader...
All the best!
:+> Andy <+:
