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Author Topic: TMC VFO - how does it come apart?  (Read 5155 times)
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w3jn
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« on: February 11, 2007, 08:43:34 PM »
The VFO in my GPT-750 has an intermittent in the tuning cap - conveniently right at 3700-3750 KHz- plus, it's about 60 KC low at the high end of its range.  I tried taking it apart and the damn thing is like a matrushka doll - layer upon layer of shielding, insulation (asbestos  Shocked ), heater elements, repeated - then finally a cast aluminum box with no way in from the top.

Apparently I have to go in from the back, and this will require removing the whole assembly from the transmitter - disconnecting about 25 wires, removing a bunch of screws, and several knobs.  Before I go thru this I wanna make sure that's the right way and I'm not missing something.

Anyone had one of these bad boys apart?
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WA1GFZ
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« Reply #1 on: February 12, 2007, 08:24:43 AM »
John,
Could it be as simple as a dead spot on a wiper contact. Try running the tuning through the range a bunch of times. It could be a glob of hard grease of tarnish on a contact.  When was the last time the vfo went down that low??? lazy dumb idea
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w3jn
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« Reply #2 on: February 12, 2007, 11:48:24 AM »
Tried that, Frank, the problem is that the VFO is geared down so low it's about 5 KC per knob revolution.  It literally takes 5 minutes of knob spinnin' to get from the top (4 MC) down to 2 MC.
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WA1GFZ
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« Reply #3 on: February 12, 2007, 12:45:49 PM »
How about removing the knob and driving it with a variable speed drill.
Just go slow and be careful to stay away from any mechanical stops??
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WU2D
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« Reply #4 on: February 12, 2007, 03:25:10 PM »
John,

Before you go further, we may have to call in the EPA to remediate the Asbestos Superfund site which your shack has become.

Actually Frank's drill idea is interesting, but you had better set the torque to low or make a slip clutch, cause it may get messy at the end of travel.

How about suspending the entire unit in a bucket of deoxit while drilling. This arrangement would look like an electric ice cream maker.

Mike WU2D
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W2VW
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« Reply #5 on: February 12, 2007, 05:51:58 PM »
Box the rig up and send it back to the store Grin
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w3jn
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« Reply #6 on: February 12, 2007, 06:55:20 PM »
Cheez.... all the good advice I've given on this forum and this is what I get in return  Grin

Maybe it's time to dig out the ol' HP synthesizer.  Kind of a sacrilege to run the ol' girl on a solid state device, but it beats driving it with a ricebox I guess  Roll Eyes
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« Reply #7 on: February 12, 2007, 07:10:48 PM »
I feel your pain. Removed a bunch of screws from the one here to see what lives inside. Gave up after 2 hours. Rotso rock. No pun intended
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