Viking VFO 122

[KX5JT]

This VFO is driving me NUTZOID.  It just stopped working a few weeks ago.  Now it had been sitting in storage for 3 years after my A/C furnace fire along with all the boat anchors.  But I pulled out the Viking II with the VFO a few weeks ago and brought them up slowly on my new variac.  Everything was awesome.  Then I went to turn it on a couple weekends ago and no more signal from the VFO. 

So I tore into last night.  I took all it's clothes off, down to just the chassis.  The workmanship was pretty bad, very long leads and globs of solder on some of the joints, so I cleaned up some of the long leads and reworked quite a bit of the solder joints.  The filament lights on the 6au6 (but it was lighting before).  The O2A gives a beautiful purple when the knob is switched from off to the first band setting.  Out of the blue.... it started working..... I barely touched it and boom, the oscillator indicator dipped and I could find a signal on the receiver.  Awesome!! I kinda moved it a bit, thumped it and everything worked well, couldn't get it to fail.   

Put it all back together with it's bezels and outer cases and front panels.... plugged it in ..... nothing.

Frustrating. 

[w4bfs]

hiyajohn .... still sounds like the dreaded cold solder joint ... a very likely place being the octal power plug ... pop the cover and give each wire a good tug ... when you resolder, make sure a little bit of the wire sticks out the end

[KX5JT]

I will do that!!! And if that doesn't do it, I'm seriously considering stripping it down and rebuilding it.

[KB2WIG]

J,

You could try the quick and dirty reheat all solder joints.........

You only have two full weekends left.

klc

[Pete, WA2CWA]

I will do that!!! And if that doesn't do it, I'm seriously considering stripping it down and rebuilding it.

Anyone poking around a chassis looking for intermittent needs to have a plastic or wooden diddle stick. A very valuable tool that can save hours of hair pulling, excess smoking, and heavy drinking.

[Jim, W5JO]

Sitting for a long time can cause trouble for the tube socket.  It doesn't take much corrosion on the grip pin to stop oscillation.  I have had similar problems that required changing the tube socket, I just couldn't get the pins clean.  Washes and the Deoxit stuff only lasts for a while.  Sometimes switch contacts can be the culprit.

[kb2vxa]

Maybe a stupid question, but if it worked naked and not with its clothes on, could some clothing be touching something it shouldn't? It wouldn't be the first time there was a bit of tape stuck on the inside of a case for a reason.

[WD8BIL]

Could be a screw going in too far.

[KX5JT]

I don't think it's a screw.  The case is designed such that it's very difficult for an outer case screw to reach anything near the chassis.  In fact, if I recall, the 1/4" key jack on the back is about the only thing besides the two front knob shafts that hold the chassis to the outer case parts, they seem to just screw into each other more or less.  

Besides, when it was 'naked', it did not work when first powered up until I picked it up to look at something.  Suddenly the oscillator dipped and it was working.  It's most likely a bad (cold) solder joint.  I'm going to tackle it this weekend again.  I might just rebuild most of it.  We'll see how it goes.  

I'll check the tube sockets too Jim!  Thanks for that tip!

Kevin, I know time is ticking, I also have the backup plan in progress.  I will build a coupler to pick off some flea power from the TS-570 and run it through a step attenuator and see what that looks like on the scope for about 20 volts peak.  The trick will be keying my rig, I might just have to key it up then the Viking.  Can't leave it running or it will blank out the receive.

Plan C is to stay rock-bound... I will lose 20 and 15 meters if I do that.

John

[K9PNP]

Had to clean up the power/band switch on mine a number of years ago.  Almost same issue, but I luckily [pure luck] found it with a wooden stick probe.  Believe it was originally part of a Tinker-Toy set.  As said above, a handy item.

[KX5JT]

With all these great tips, I know I should have this sorted out soon!! Thanks everyone!  I'll keep this thread updated as I go along.

[KA0HCP]

"Chop Sticks"...free with every order!