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Author Topic: replacing the USB and LSB xtals in a Galaxy GT-550  (Read 3671 times)

Posts: 33

« on: April 18, 2013, 11:22:44 PM »

I bought a new set of xtals from ICM as I couldn't get the old ones to adjust on freq (apparently a common problem with tyhe GT-550). If you are familar with this rig, you will understand this next question. How do you get your soldering iron in there to unsolder the old xtals and solder new ones in place? I wouldn't be very difficult if the bandswitch shaft was removable but it isn't. If you know the trick I'd love to hear it. tnx & 73 - Bill

Posts: 2483

« Reply #1 on: April 19, 2013, 07:00:10 AM »

Bill I have 3 Glaxy GT-550A transceivers.  I wanted to have a properly working one in my boat anchor collection.  Unfortunately I ran into the same problem(s) that you did.  Of course this rig was completely hand wired.   It looks like Galaxy built this rig in layers under the chassis without much thought to future access for repairs.

In each of mine the B+ resistors on most of the tubes had gone very high in value due to 40 years of age and / or heat.  Getting to them is a night mare because so many other components were installed on top of them.  While trying I broke off phenolic and wax paper formed coils and ruined the rigs.  I do not consider myself to be a klutz.

After trying to return 3 different GT-550A rigs to original working specs (mainly replacing defective resistors), all I have left are 3 nice parts rigs because I broke critical (un-obtainable) parts while trying to replace defective parts..  

Unless I find a mint working GT-550A, one of these won't be in my collection.

Good Luck!

Dick  AD4U  
« Last Edit: April 19, 2013, 07:50:25 AM by AD4U » Logged

Posts: 5688

« Reply #2 on: April 19, 2013, 07:23:07 AM »

When encountering repairs of this type, I first like to just sit there and STUDY the situation, making visual inspections, using magnifier if needed, and coming up with the best course of action in order to effect a good repair. 

*Sometimes it is necessary to lift a PCB off of its mountings in order to get to the other side, rather than tackling removal of things such as a bandswitch as cited here. 

*Sometimes necessary to *disconnect* wires in order to get to the place.  This should be done and documented, in the old days that meant taking notes with pencil and paper, making drawings, today I use the digital camera (or cellphone cam, same thing) to document wire placements, colors, etc. plus hardware assembly as it originally appeared as well as at various steps during the disassembly, such that there will be a guide to follow when reassembling. 

*Above all, I TAKE MY TIME on a project such as this one, often setting it aside until I feel reasonably certain that I will have both the time and the energies to devote to slowly and carefully working on the thing.  Use of that camera allows for putting the project to the side if necessary to relieve strained mental and physical facilities, picking it back up again at a later time when revived and able. 

If all else fails, and since these are xtals, I *might* resort to the old "top of the board" replacement techniques, ugly, perhaps, but functional.  Consider that most xtals of that vintage are made of cans that are soldered to the base.  Desoldering the can reveals the inner crystal plus its leads.  Careful disassembly from the top side until there is nothing left but the two leads sticking up through the board yields to places to solder in the new xtal.  A dab of non-acidic RTV or a glob of hot glue to physically "mount" the new crystal case to the board and you have a fast bug ugly way to effect the repair.


Posts: 2085

« Reply #3 on: April 19, 2013, 12:24:51 PM »

old RCA broadcast manuals advised the engineers at stations to clip the leads as close to the part as you could, solder on the new part to those leads, and minimize downtime.  sounds like a starting point on these rigs.

Posts: 322

« Reply #4 on: April 20, 2013, 05:22:36 AM »

I agree with another post. Take your time. BE PATIENT.
Also, grab your digital camera and take pictures from various angles. Make sure you download them to your PC for viewing and that they are clear.

Look the situation over carefully. Come up with a list of steps that you think are required to get the job done.

If you get frustrated, walk away from it for a day.

Be very careful working on the bandswitch. If you break a wafer, or break a lug off the wafer, you're in trouble.

Clipping the lead near the attachment point is a good idea. It will improve visibility as well as remove thermal mass, making desoldering and clean up easier.

Make sure your soldering iron is up to the task - clean with the correct size tip.

Finally, have a good place to work where you can leave the radio if you need to walk away for a spell

You Can Do It

Vy 73

Posts: 33

« Reply #5 on: April 22, 2013, 11:49:52 PM »

My thanks to all who commented. The xtals are mounted with their leads facing the top of the chassis inside a confined area. There is no room to get a soldering iron in there.  I was considering cutting the bandswitch shaft and rejoining it later with a brass shaft coupler. A few of your comments made me rethink my paradigm that the xtals had to be mounted with the leads facing the top. My solution was that I could mount the xtals with the leads facing the bottom of the chassis giving me room to solder. I used a right angle cutter to cut out the old xtals. I attached short wires to the old leads along with some clear tubing and soldered in the new xtals. I took photos if anyone is interested. Its now up and running and receiving on both sidebands tweaking the xtal caps by sound. Next I'll do the formal alignment. Thanks & 73!
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