FT- Tips and Tricks

[N8YX]

Starting this thread as a gathering place for assorted repair info, tips, tricks and gotchas for older Yaesu equipment. Say, everything from the early 70s through the mid 80s. Parts sources, modifications (both factory and community derived) and servicing procedures can be found here. (If enough interest, I'll sticky it - and create similar for Kenwood, Drake, what have you.)

[N8YX]

Tip #1 and 2 - FT-980 VCO/PLL Boards

I have several of these (very underappreciated) rigs in my collection, each in various stages of functional restoration and cosmetic refurbishing. There is a commonly known problem with the VCO which derives the BFO frequencies; occasionally a user will comment "...won't decode sideband...". This condition is almost always caused by TC4001, a 3pF trimmer capacitor inside a shielded can at the upper right of the assembly. They go intermittent and won't allow the reference oscillator to be tuned to a point where the loop control voltage can stabilize the circuit.

TIP 1: The capacitor can be replaced by removing the PLL/VCO Assembly from the rig, removing the snap-on metal covers, unsoldering and disassembling two shield enclosures (top and bottom of boards) then removing and replacing the part. Here's one possible source: http://www.surplussales.com/Variables/Ceramic/CerCap2.html

My PLL/VCO Assembly also appeared to exhibit a very slight warbling (so-called 'PLL dead-banding') when tuned across a signal. It's usually caused by a bad loop filter capacitor. Given the fact I wanted to check the condition with a "known good example" installed, I got hold of a surplus PLL/VCO Assembly. Ostensibly working, of course.

Except in my rig, it didn't. This caused a bit of hair-pulling until I closely studied the circuit and the Assembly itself for possible causes.

Tip 2: There are two SIP connectors in the shielded compartment immediately adjacent to the BFO section of the Assembly. A print on the PCB indicates the direction the connector barriers are to be installed. Both of mine were installed backwards, thus preventing control and reference signals from making it to required points on the board. When I checked those connectors from the foil side of the board in preparation for removal, I found the solder to be OEM - no one had removed and reoriented them at some past point. This also means there were two different wiring orientations for the mating plugs as used in the '980's main wiring harness.

Lesson learned - check your boards before swapping them. AFAIK, this change was never documented in any of the Yaesu-published FT-980 technical materials.

[N8YX]

Tip 3: Build your own control shafts.

This is a long Tip, and we'll play on a bit of German history to coin a term: "Shipping Shaft". This is what happens when a Clueless Seller packages a heavy piece of equipment so that - while in transit - control knobs strike the packing material and shear off the end of the shaft. This is more common with a serrated shaft end (which uses press-on knobs) than it is with solid shafts.

One of my FT-980s (which was obtained for the proverbial song) had this sort of damage prior to me acquiring it and the previous owner never got around to finding a replacement. I looked high and low and couldn't locate a suitable replacement, but one day I was rummaging through a pile of spare hardware and happened to come across the piece I needed to fabricate my own shaft.

First, a pic of an undamaged '980 shaft alongside its broken counterpart.

15303

[N8YX]

The Yaesu shaft diameter is 6mm. A 1/4" shaft (common in the U.S.) won't fit Japanese couplers, nor will it clear the hole in the rig's front panel through which it passes. 6mm aluminum control shafts in 6" and above lengths are difficult to find, and almost impossible to find in a serrated/split-end format. We can, however, readily source brass tubing in a variety of diameters. The other piece to the puzzle is the serrated "end". My junk box yielded such a shaft; it probably came from the tuning mechanism of an analog AM/FM radio. Whatever the source, I've had the thing for YEARS.

A trip to a local hardware store yielded no 6mm brass tubing but I found some 7/32" (5.5mm) into which a 3/16" brass rod slides smoothly. The tuning shaft I had on-hand wouldn't fit into the tube, and the tube was a little loose inside the Yaesu coupler - so it needed to be enlarged. We do this with a set of numerical drill bits, a tapered punch (to flare the tubing end slightly), a striking block and an anvil. The striking block is a piece of hardwood, drilled slightly larger than the largest OD bit we'll use to form the tubing; we'll call this the "end bit". Use a caliper to measure the tuning shaft at the widest point it'll be inserted, then locate a bit of that diameter. Next, locate a bit which will just slip into the tubing. The next larger bit is your "start bit". Bits in between the diameters of the start and end bits are "intermediates". In my case, the start was a #12, intermediates were #11 and #10 and the end bit was a #9.

(Or course, most of this forming can be eliminated by using a 6mm OD tube - but where's the fun in THAT?)

Here are all the pieces shown together.

15305

The tube is placed in an anvil (plastic block with a hole drilled in it) and a tapered drift used to alternatively flare each end just enough that the Start Bit can be inserted, shank end first. We're only looking to stretch the metal a tiny amount per pass. Thoroughly lube the bit and tube with spray oil then place the shank of the Start bit into the opening. Place the driver block over the pointed end of the bit and gently tap it an inch or so into the tubing. Then use the solid brass rod and a hammer to drive the bit back out, and repeat the swaging process for the other end of the tube. Repeat with the next larger bit in the series...until you get to the End bit. Check the fit as you go. By now, your tube should be swaged to 6mm (or thereabouts) at each end and the tuning shaft should fit snugly into its end:

15306

[N8YX]

When the tubing is prepped, thoroughly clean all the metals. I wire-brushed the tuning shaft with a Dremel tool to remove excess dirt. Use a brass brush (not steel) for this. Then, clean with alcohol. Place the tuning shaft in a heat-proof holder and apply some paste flux to the end which will go into the tubing, then heat it up with a propane torch and tin it with solid-core lead/tin solder.

15307

Flux the end of the tube, insert the tuning shaft into it then place it in a suitable holder. Heat the assembly with the torch and apply a little solder to the shaft/tubing interface. Take care to not get any in the splines.

15308

[N8YX]

Insert the brass rod into the tube, flux the un-soldered end then put in fixture and solder.

15309

When cool, cut the rod even with the end of the tubing. Then sand down the area so all high spots are removed. Lastly, chamfer the end.

Check the fit. The part shown is a tight 6mm diameter, and is a replacement sprocket made by Greg, NR6C. Lightly sand the shaft if needed.

15310

Similarly, check the fit where the shaft will pass through the panel. Sand as needed, but don't remove too much material:

15311

Then check to see if the knob presses on fully:

15312

[WØTKX]

(To be continued)

I kinna hepmyself. :mrgreen:


https://www.youtube.com/watch?v=PfK-UzQ48JE

[N8YX]

"Measure twice, cut once" is a good rule to live by. So...what if we used the OEM shaft as a reference and our part came up too short? This is a simple fix.

Remember the piece of rod you cut off the assembly earlier? Dig it out of the trash, clean it off. Grind a tenon onto the end of the assembled shaft, as shown in the picture. Cut a piece of tubing to the length you need then use the tapered punch to flare the ends. Clean tubing and shaft, assemble and flux everything then place in fixture and solder.

15313

[N8YX]

When cool, sand the newly formed end into its final diameter. If necessary, use a jeweler's file to touch up any high spots.

Here's a comparison of the OEM and the replacement shafts:

15314

And the new shaft in the FT-980. The yellow arrow shows where the shaft passes through the front panel. I put a piece of heat shrink tubing on the shaft to act as a bushing. The resultant assembly "feels" more solid than OEM.

15315

A couple more thoughts:

You can get the serrated shaft from any number of junked stereo receivers (low and high end alike) but I wouldn't pay eBay prices for a tuning shaft for 'Classic Receiver X'. You may also choose to leave the assembly hollow and only install a small stub (~1") of tubing into the non-serrated end. This will make the finished shaft a bit lighter.

Flatted shafts can be made by constructing the assembly with a stub at both ends, then milling (preferred) or grinding flats onto the shaft. I'd use the correct OD tubing for this (measure your coupler or knob with a caliper to verify) so you'll get a proper fit.

[WØTKX]

I repaired the shaft on a Dentron Supertuner using a Delrin rod of the correct diameter

It held the set screw for the knob better than metal after drilling a small hole for the screw

[N8YX]

I repaired the shaft on a Dentron Supertuner using a Delrin rod of the correct diameter

It held the set screw for the knob better than metal after drilling a small hole for the screw
Remind me to tell you how often I cussed those tuner shafts when I had one in the shack.

[WØTKX]

Yea, suckage. i fixed it, and sold it. :)

[N8YX]

Tip #4 - always check the simple things first

While diagnosing a problem with the TX Clar(ifier) LED in an FT-980, I carefully pored over the circuit diagrams in the Technical Reference, took my best stab at the source of the trouble (a faulty output driver; SN74LS373N) and proceeded to disassemble the rig, desolder the chip from the CPU board, fit a socketed replacement, reassemble the radio...and watch the problem persist.

The LED in question is used to indicate that the "Clarifier" function is active on Transmit. Note that the '980 doesn't feature an RIT/Clarifier knob - that function is implemented in the manner which Ten-Tec did it on the Paragon and Omni V. You press a button for the desired incremental tuning mode (receive, transmit or both) then use the VFO knob to adjust the frequency.

This LED was stuck "on", even though the TX Clar could be turned on and off via the front panel button. A little digging around on the CPU Board (and the specific pins of the '373N) showed the output to be held Low. The wiring harness was removed from its CPU Board connector and checked for shorts - and in fact, the conductor which controls the TX Clar LED was shorted to ground. Next, the lead in question was desoldered from the Keyboard unit (which contains the LED). Short still preset. This implied disassembly of the harness. So...I removed some hardware to allow the rig's front panel to be tilted down for servicing - and after a little bit of tracing the wire, found the problem: It had become wedged between the sheet metal which comprises the main chassis and the front panel carrier bracket.

A little snipping/rework followed by proper harness dress fixed everything. This bears consideration in any rig whose front panel is capable of being swung down for service and which has bundles of wiring near the structure intersection points. Make sure the harnesses aren't capable of being guillotined when the assembles are swung closed.