Replacing the relays in the Yaesu FT-480R (FT-280)

tl:dr:

Figure 1:
The front panel of my "FT-280R" all-mode 2 meter
transceiver including paper labels showing the "new"
modes.
Click on the image for a larger version.

If you have a Yaesu FT-480R that doesn't work, it's probably the relay(s)!

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Back in 1994 I picked up an FT-280R at a local swap meet for a good price - particularly for an all-mode 2 meter transceiver.

Except, of course, there was never such a thing as an "FT-280R":  This radio had clearly been modified, a previous owner attaching pieces of self-adhesive paper with "R" written on it after the model number, and similar "+" and "-" labels added to the MODE switch.

A look under the hood shed some light on this mystery:  It had likely been sent back to Yaesu at some point as an FT-280 - an uncommon radio (perhaps sold only in the Japanese domestic market?) that did not have repeater offsets - and modified to the otherwise-identical FT-480R which did "know" about repeater offset.

At some point I acquired the manual for the FT-480R (I don't recall if I got it from Yaesu, or if it came with the radio) which the elements of a service manual - including schematics, locations of semiconductors and adjustment/test point and alignment procedures - but it was clear that this radio wasn't exactly like an FT-480R, either, as it contained an additional board with a pair of relays on it that the manual didn't show.

Figure 2:
The "unobtanium" 221D012 relays used in the FT-480.
These relays use a different from factor from modern/
available relays requiring a bit of "adaptation".
Click on the image for a larger version.

It quit working!

As this radio was probably made in 1980 or 1981, it's long in the tooth and about a dozen years ago, it gradually became too unreliable to be useful, requiring more frequent "percussive repairs" to make it transmit or receive and the problem was traced to three relays used to steer important things like the transmit and receive voltages to their respective circuits.  A bit of "cleaning" (piece of paper between contacts, contact enhancer, etc.) would help initially, but even that stopped working.

These relays were Fujitsu 221D012 - low-current, DIP-style DPDT units, but a quick check revealed that their form factor (pin-out, pin spacing, etc.) was not in common with anything else that was in current production.  I did find new-old stock units that some were available - some on EvilBay (who knows what they really are?) and others from RF Parts - but they were quite expensive, on the order of $20 each from RF Parts.

Figure 3:
One of the control boards with two of these relays.  This
board seems unique to the "upgraded" FT-280 as it doesn't
match what is in the FT-480 manual.
Click on the image for a larger version.

Since there were three relays that had gone intermittent, I didn't relish spending $60 (plus shipping) for relays that were likely 40+ years old - and since these were un-sealed, they would likely have (or soon have) the same oxidation issues that made the original relays so unreliable.

"Substitute" relays

As no drop-in relays were available, I found some similar-sized, 12 volt DPDT relays - using a now-common pin-out (I used Hui Ke HK19F-DC12V-SHG relays - but many others share the same pin-out and could have been used) - and set about making a "carrier" board to accommodate them.  While I could have made a PC board to adapt their pin-outs to those of the original Fujitsu, I decided that with just three relays in question, doing so wouldn't be worth the effort.

Figure 4:
Carrier board with relay mounted to it.  The clearance on the
board shown in Figure 3 allowed the relay's position to be
slightly shifted, simplifying construction as the new relay's
pins offset from the original relays'.
Click on the image for a larger version.

Instead, I used a small piece of phenolic prototype board.  For the undocumented board with the two relays, I had a bit of extra space available on either side which allowed them to be offset from the original pins:  Short pieces of wire (26 AWG) were soldered to the proto-board in the locations of the original relays' pins and short wire jumpers were run from there to the locations of the corresponding pins on the new relays.

To "ruggedize" this assembly, the jumper wires were covered with UV-cured resin before the new relays were soldered into place and then each relay assembly was soldered into place on the board.

The third relay - next to the carrier oscillator, on the main RF board - was a different matter:  It was surrounded by components which meant that there wasn't enough room to offset it from the homebrew carrier board, so the new relay had to be placed directly atop the original pins.

Figure 5:
Carrier board and relay used near the FM oscillator on the
main board.  Unlike that in figures 3/4, this relay couldn't
be offset so the pins were folded over and wires used to
connect the relay to the carrier board so that it could sit
directly atop the original location.
Click on the image for a larger version

To accommodate this, wires were soldered through the homebrew carrier board like before, but the pins on the new relay were laid onto their sides and short pieces of 30 AWG wire-wrap wire were used to connect to the proper locations.  Again, this was flooded with some UV-cured resin for both mechanical stability and to prevent the relay's pins from touching the wires on the carrier.  A bit more resin was then used to adhere the new relay to the carrier board, making a solid unit.

With the leads straightened,  they were carefully aligned and pushed through the main PCB and soldered into place.  As it turns out, although the "new" relay sits slightly higher than the original, it just clears the bracket for the switches on the bottom panel of the radio.

Testing the radio

With radios of this vintage - with individual wires going everywhere - the bane of the service technician is wires breaking off their soldered connections on switches and/or board.  If caught early, the "bend" of the wire will keep the broken-off end very close to where it should be attached - but too often, one spends a lot of time reverse-engineering:  While the schematic is (mostly?) complete, neither it or the parts layout diagrams detail where every wire and connection go - particularly on the front-panel switches.

Figure 6:
A look on the main RF board on the underside
of the radio's chassis.  The two "new" relays are
along the top edge while other relay below and
to the left of center, just above the metal box
with the black label (the FM modulator).
Click on the image for a larger version

The broken wires fixed, the radio worked the first time it was powered up - more or less:  Going through the (somewhat incomplete and ambiguous) alignment procedure in the manual brought the radio back to usable condition - but one "semi-major" problem remains:  None of the top-row buttons (the yellow-brown) work reliably.  A bit of testing revealed that shorting the terminals on the back of the board resulted in their functions working, but a check with an Ohmmeter showed that they had all gone to high resistance despite having been injected with several flavors of "DeOxit":  The button switches themselves will have to be replaced, but I'll have to get with a friend with a 3D printer to come up with a means of mechanically coupling the front-panel buttons with the "new" switches.  Fortunately, the radio is perfectly usable - particularly when using SSB - even if none of these buttons work.

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This page stolen from ka7oei.blogspot.com

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