[Boatanchors] Boatanchors Digest, Vol 114, Issue 6

[Bill Cromwell]

On 07/04/2013 05:57 PM, bonddaleena at aol.com wrote:
> Hi guys. I did subscribe to the Swan Group on Yahoo yesterday.... Of course, the first looong posting I tried bounced... Ah, well.
>
> Here's what I think is the root of my problem, please bear with me:
>
> I have 2 nice Swan 250Cs (I know, I know). Both receive excellent, and exactly the same, when using my HP 606A SG. One has NO xmit output. I have discovered this is a common problem with these radios.
>
> Not being an x-spurt on xtal filters, I measured the in-circuit resistance of the xtal filters.
> The 'good' radio measures 300K ohms. The 'bad' radio measures 36M ohms. I got to this point by 'scoping the signal. Very little carrier balance seen on the scope. The manual is very cryptic on xmitter alignment.
>
> Since the local Radio Shack is out of Swan IF Filters...... I just can't understand why both receivers are exactly the same, but no xmit. The block diagram shows a signal path through the IF Filter???? Yeah, I can swap them, but I need to understand the problem......
>
> Strange, indeed........
>
> thank you,
>
> ron
> N4UE
>
Well Golly!

The schematic in the BAMA manual has bits n pieces cropped out by the 
scanner. Some of the missing info is the interconnections of the bias to 
the TX mixer, V2. I hope you have a better manual to look at. I am 
assuming that you do not hear the dead TX's low level stages at the 
operating frequency in the other or another six meter receiver at a 
distance of four inches. I would be looking at the relays that apply and 
remove the blocking bias. Pin one of V2 should have the full negative 
bias during receive - about negative 110 volts and will not operate at 
all with that bias. It's not supposed to in receive. In the TX mode the 
voltage chart says 0 (zero) volts on that pin. Should be something close 
and ceratinly not negative 100 volts. If the blocking bias doesn't go 
away in the TX mode you'll have to find out why. Look at the relays and 
their wiring.

More tomorrow (maybe). I printed the comic book but the stuff is 
incomplete. Why couldn't they have cropped the danged dial light instead 
of the relay and bias wiring?

73,

Bill  KU8H