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Figured I'd tickle the list a bit to keep it active.

Pulled one of two FT-980s currently inline out of line in preparation for replacement of TC4001 and all the electrolytics on that particular assembly. The other I'm using for my FT8 position - which works great under computer control but after warmup, the main tuning encoder won't change operating frequency when tuned downward. I have a game plan for both of these.

The third '980 I own - in the queue for some time now - needs some updates (filters, the Gen TX kit installed) and will become a backup to the other two when done. #4 needs its front panel replaced and ultimately will become a guinea pig for other mods I have planned...including deciphering the Aux Band ROM programming.

A TS-930S replaced the first '980. An FL-7000 was connected to the Yaesu and I'll cable the Kenwood up to it as soon as the amp cable I ordered arrives. (Would usually build this stuff but Ye Olde Junque Box is fresh out of 7 pin DIN males.) It's nice to let the rig control the amp for band and tuner changes but I guess I'll live with manual operation for the time being. The '930 was modded pretty extensively a few years ago and I'm pleasantly surprised how well it works on the crowded low bands. Alas, its internal tuner is less than optimal for rapid QSY - which is why an FT-980/FC-757AT replaced it for FT8 duties.

Hopefully, the G0 with a '980 problem (on a QRZ thread) shows up here and we can all assist with keeping another one on the air.

73 all - Fred, N8YX

Which filters did you use, Wald?

I may be interested in them.

73 - Fred, N8YX

Let me have a look at my filter stash and see if I have enough to filter all of mine up. If not I'll be in touch off-list. May also grab these for my FT-726Rs.

Thanks!

73 - Fred, N8YX

Hi Wald,

Would it be feasible to add a 6-dB or so amp just prior to the filter (I think most 6-pole xtal filters run about 9dB loss for CW ?)? That should compensate enough for the loss before the 3rd IF Amp.?

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-Mat Breton, N8TW

For all who have repaired the VCO/PLL unit:

Did you replace the electrolytic capacitors when you had the unit out of the radio? I just replaced TC01 on the first of two boards and so far it seems to be working. Any value in swapping these out?

73 - Fred, N8YX

These groups need a "Belay that..." button due to what happened next.

As soon as I hit "send" on my previous message I went to check on the rig, and the misbehavior which prompted me to replace TC01 was back. Hmmmph. Since I had a production line set up at my rework area I changed the trimmer on every loose PLL/VCO Unit I had and tried each in the rig - along with one from another radio in the repair queue. Apparently, the issue wasn't with that assembly - sounds like random noise modulating the VCO and eventually it drifts out of lock.

I swapped a spare BFO Unit in and that cured it. Question for Matt/Wald and whomever else has repaired this assembly: When the RF transformer went bad (open), what were the symptoms? I think this may be what's going on here.

A second rig in the queue appeared as deaf as a post. Its RF Unit was swapped into a working rig for test purposes and is fine. Next, the IF Unit was swapped...problem follows the board. That one's now headed into my "test mule" for additional troubleshooting. I've a couple things to do WRT RF Unit testing (evaluating a spare board) and installing filters but two of the rigs are coming along nicely.

Wants:

If anyone has a spare Inrad 2110.1 (2.4KHz B/W; 8.9875MHz center) filter or its Fox Tango/Seiwa equivalent, I'm interested in buying it.

Will post more as I solder.

73 - Fred, N8YX

Progress on two of three, and insight to problems with the third.

I installed an AM and a narrow CW (250Hz B/W; 8.9MHz CF) filter in one of the queued-up '980s today and used that radio to test my repairs to the various PLL/VCO Units I have on hand. It still has some warm-up drift which I think will be cured with a master reference oscillator crystal swap. FWIW, Yaesu was still stocking these as of a few years ago (thanks Jose!) but I'm going to look into modifying one of my spare BFO Units to use a garden variety 30.0000MHz computer timebase crystal.

After the RX sections were working, I turned to Ye Olde Junque Box and retrieved one of what is probably the last unused Gen TX kits in existence. It went into the first of the rigs, though it looks like a TX parameter-set procedure is in order. Good power below 14MHz; not so much above. There's adjustments for that.? I had another Gen TX kit on what now appears to be a defunct RF Unit; it was bought for parts regardless and after I removed the kit the board was cycled back into the spares collection. That kit was put in radio #2, which also needs a bit of alignment. Part of this evening was spent setting IF stage gains and getting S meters to accurately track the generator output.

The deaf-as-a-post repair mule got a little more bench attention. It faintly hears a .01uV signal but the AGC doesn't appear to be very effective between On and Off, and I cannot adjust the S meter. Thoughts are that the AGC Detector/Amp section is wonky. Of course, this discovery was made after I bought another IF Unit from the action site...but spares are nice to have, I suppose.

That rig also suffer from the same tuning problem as another rig (still in line) does, and which I detailed in a thread earlier this year. I think what's going on is the MC14093B on the Dial Unit, which receives pulses from the photointerruptors and conditions them. CMOS of the period occasionally goes bad from "tin whiskers". I have another Dial Unit to swap into Radio #3 (due to come out of line when the ones I'm working on go back in service) and have a bunch on 14093Bs inbound too.

One of our members posted an ALC mod which shortens the response. I think both of the rigs currently on the bench sorely need it, based on observations of how the rig controls TX power. There appears to be a positive feedback loop in place due to the long action time - this causes a power rise. One more thing to investigate.

Have a few more mods up my sleeve once everything is up and running. Chief among these are auxiliary cooling fans.

73 - Fred, N8YX

Got numbers 1 and 2 ready to go as soon as your filters arrive, Wald. The other things I need to do to these are to put a new battery backup harness in one and replace the FSK Unit in another. Seems it doesn't want to produce any output - the faulty unit joins a growing collection of modules destined for troubleshooting and repair in the "mule".

Those TCXOs look interesting, particularly in light of the fact they allow for external adjustment. One of my other favorite lines of gear is JRC. Their NRD-525 uses a 12.8MHz TCXO as its reference oscillator. A neat mod involves fitting an adjustable unit then making circuit changes which will allow the BFO control to tune it over a narrow range. (Normally, the control is only operative in CW mode.) This allows for "poor man's ECSS detection" - which is kinda funny as I lucked into a -525 with an Edvis PLAM board already installed.

I seem to recall a similar keyer design for the FT-90x...the several '980s and 901/902s I have which aren't equipped with keyers can benefit from the addition. Happen to have a source of these or a link to the design?

73 - Fred, N8YX

Hi Fred!

"Question for Matt/Wald and whomever else has repaired this assembly: When the RF transformer went bad (open), what were the symptoms? I think this may be what's going on here."

I was very lucky in two respects:
1. The transformer that went bad was the BFO mixer, and therefore easy to locate. This transformer is actually in the first stage of the AF board.
2. I was able to repair the transformer (vs trying to reverse engineer and fine a similar one)

1. The symptoms for mine were obvious: I had great audio for FM, AM-N, AM-W ... and no audio for RTTY, CW-N, CW-W, USB, LSB (even with strong RX signals injectected). A look at the signal flow in the Technical Supplment guide showed that the common circuits would be either the BFO, or the BFO Mixer. After verifying the BFO was working, I was left with the mixer circuit.

2. Inside the transformer, one wire had broken off right where it was soldered to a pin. While the wire was too short to directly connect, I was able to "extend" the pin with a piece of thicker wire, and then attach the broken wire to that.

On the downside, the broken wire was intermittent, and it took me several attempts to track it down. Just rotating the rig would sometimes make it work/non-work. Temperature would cause it to occur or "fix itself". Pushing on the AF PCB in different spots would do things, misleading me to thinking it was a solder joint or trace issue.

But ... once found and fixed the rig has performed flawlessly since.

--
-Mat Breton, N8TW

On Thu, Dec 23, 2021 at 11:20 AM, Wald N4PL wrote:

I also thought of the TXCO solutions. It looks like Seiko has an interesting part in the pipeline, available next year from Mouser:

Hi Wald,

I've also considered installing a TXCO. I actually had to change the pulling trim capacitor (larger value) in the existing circuit to extend the adjustment range ... it has drifted beyond what the original trimmer could compensate for.

I think the "poor man's" xtal heater in these rigs is tough on the xtals (worse than normal aging drift). And even with the heater working properly there is still some amount of drift as the fan turns on/off, room temperature changes, etc.

One thought I've had is the effect a CMOS square wave or clipped sine wave might have if not filtered. The tank circuit on T11 (VFO board) does a great job of cleaning up the existing oscillator ... so maybe we could inject the signal ahead of that stage? The output of T11 is supposed to be around 1.5Vp-p (nominal) I believe.
?
--
-Mat Breton, N8TW

Happiness is 3 working '980s and a 4th well on the way (test-bench mules are never done).

Got an FSK Unit in the mail, swapped into the radio w/ no FSK output...and full output. Aligned the transmitter sections of #1 and #2, put the covers on and pulled #3 (my FT8/PSK rig) out of line for troubleshooting. It had a wonky tuning problem wherein after it warmed up the dial wouldn't move the frequency (as I noted earlier in thread). A spare Dial Unit fixed it and I now have MC14093Bs for the defective one. This rig also had a transmitter/receiver alignment performed.

I get ~105w out on 160-30, 120 on 20, 140 on 17-12 and 100 on 10. This is uniform across all three radios and far below the max rating of the PA transistors. Full power is achieved at the 9 o'clock setting of the Drive control. I may tack a resistor across the "mule's" Drive pot when I get that one on the air and see if the spread can be made more linear, a la the FT-90x's Carrier control mod.

While I had the radios apart I changed some of the indicator LEDs, using different colors. Yaesu loved yellow for these; Kenwood, red. I like to see status-at-a-glance and chose mine based on operating parameters and warning level. A pic of the result is in the Files area. Should anyone want more details I'll create a separate thread on the mod.

Also got Wald's XF-455MC filters installed in two of the rigs. These have narrow(er) filters at 8.9MHz, so I swapped the CW-W and CW-N lines of J01 on the IF Unit. Dave ('JRB) pointed out that the Yaesu Gang recommended using the 455KHz/600Hz B/W filter in combination with the APF function. My observations are that it'll work well for everything but the most demanding contest operation, so it's nice to have both options.

Next project...I'm weighing two options for the auxiliary cooling fan arrangement. One is a mounting bracket made from aluminum angle; the other is a flat plate w/ cutouts for air flow. If I go with the latter I'll design a plate on my CAD terminal then post the DXF file into our Mods area. Members who want them can go to one of the online laser-cutting outfits and submit the file. FWIW, I'm going to use a pair of 70mm 24v computer fans so the mounting holes will be dimension-ed accordingly.

73 - Fred, N8YX

Bumping this one again...

Tuning problem resurfaced yesterday. Looks like I'll be soldering ICs. Will update the group as soon as the covers are back on the rig and it has some run-time. Hopefully the 14093 fixes things else I'll be diving further into the Dial Units - and after that the CPU Unit.

73 - Fred, N8YX