WOW...Ok, when the probable has been checked, only thing left is the improbable...
Ok...Ahemn...
You did change/swap out the channel selector - did you change the wiring header too? Or just plug in the new one to check against the old using the original harness.
There are checks I was trying to perform on a spare 33 over here a customer brought in for a look see. I can't take pictures of customer work without permission so - I'm left looking...
I was trying to do up a "truth chart" about the Band switch and channel selector.
You ran out of time - so did I - so I went home and did some more research.
I never did know if you "swapped" the header harness too or just plugged in a new one.
Why is that so important - if one of the wires is broken or the traces are bad to the PLL - the PLL may get the "notion" that something changed and so it "seeks" new programming.
The previous graphic shows ground traces in various areas, including one that is by IC6 and IC7 - if that trace is bad, you would not know it - because ohmic DC readings are fine - but on the LOGIC level - they are pretty dirty because you now have a noisy ground plane adding to the problem.
Its when you changed the band HI-LO switch, did the jump occur. So that means even though the channel selector shows the same channel - meaning the wiring in that board assembly is correct - there is a difference in sensing between the channel and Band switches. Something is triggering the PLL to re-look at states and change the frequency. Why? Well, ground loops and noisy grounds can force logic levels to get "Jittery" at times - this is true in any PC - a bad filter cap can do this - because the power supply feed may be ok, but the GROUND to it may not.
This may not be at the channel selector - it is prolly back that the BANDSWITCH header with the poor noisy stuff.
I noticed there was also TWO versions of this channel selector - one uses BLACK as ground wire - all harness pins are used too...
You may need to "scope" the ground wire and B+ wire from the switch on the Main PCB - for noises. I'm thinking you have one or several things wrong - poor ground case or front panel (shield ground from chassis) or you have a failed cap or poor filtering cap that using a bad ground that opened up or has gone noisy...or worse - a ground that floats at whatever is present locally. Again - a popped trace can do this...
Also, when the thing jumps, it's not a "HUGE" channel bump - it's rather small - it's why I brought up the resistor arrays - because if the CARRY on one is not terminated right - the chip can emit a "chirp" when the carry "blip" is not terminated - its' a noise issue - and why I brought it up - the carry goes from IC7 chip "B" pin 9 to IC6 chip "A" pin 14 (carry in) and it's pin 9 needs to show 47K to ground...termination point. The PLL sees the noise and then goes to what it thinks is right.
Remember the channel selector uses a different spot for voltage source that goes to the PLL - so if those pins change a lot or show noise - you have an injection point to make the PLL think you're changing channels and when the noise stops - it halts any activity because the PINS and CHANNEL are not the same as it once was.
An audio tracer can spot noise right away - so this may be a big area you have to check - even the jumpers that jump ground from one section to another are culprits too. You'll hear it as clicks and chirps if it's really noisy.
:+> Andy <+:
.
