>From Gene Poon on Yahoo group.
Sincerely,
C. Brendemuehl
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> The Vivitar 550FD M/P/O (Minolta/Pentax/Olympus) is a medium power
> bounce-head flash with TTL capability, for use with all Pentax
> cameras with or without flash programming. It has its own sensor for
> autoflash, so it can be used with the screw mount models, the K
> series and the MX/ME, with the user setting X-sync shutter speed and
> aperture. It has the simple flash program for the ME Super, MV,
> etc., where the camera will automatically set the X-sync shutter
> speed when receiving a "ready" signal from the flash and the user
> sets aperture. On the Super Program, LX, etc., it will do TTL flash
> with auto aperture select and auto shutter speed select using the
> camera's internal sensor and Pentax's ANALOG communications link
> between camera and flash. On the autofocus Pentax cameras, it is
> SUPPOSED to be able to do full TTL programmed flash with auto
> aperture select and auto shutter speed select via Analog
> communications, but on most of them, one of the pins used for
> dedication to Minolta or Olympus cameras causes spurious signals to
> be introduced to the autofocus Pentax body via the digital contact in
> the hotshoe. This interferes with the control circuitry of the
> autofocus Pentax. Depending on the camera model, the effect may be
> improper exposure; an unstable shutter speed, switching at will
> between X-sync and ambient; or a lockup of the camera's circuitry
> until the battery is removed (if you are lucky, there may be no
> effect at all, but that's not what I normally see).
>
> This is a shame; the Vivitar 550FD M/P/O is a lightweight and
> reliable flash unit; if it didn't have this anomaly with the
> autofocus bodies, it would be usable with both manual and autofocus
> Pentax, and could be considered to be an "almost AF280T" lacking only
> a rotating flash head and viewfinder "Sufficient Flash" indication;
> and that function is included, on the rear panel of the flash,
> instead of in the viewfinder. It's inexpensive in the used market;
> while the Pentax AF280T is a current Pentax model generally selling
> in used condition for $50 and up on Internet auctions, the Vivitar
> 550FD M/P/O can generally be had cheaply.
>
> It is easy to modify the Vivitar 550FD M/P/O internally to eliminate
> this interference with the circuitry of the Pentax autofocus bodies.
> Yes, one could tape off the offending contacts, but the sharp tips on
> the pins will wear through the tape in short order. NOTE: this
> modification involves minor disassembly, and work with some small
> wires inside the bottom of the flash. If you feel you may have
> difficulty doing it safely, refer the job to someone who is skilled
> in this kind of work.
>
> First, for safety's sake, you MUST discharge the storage capacitor by
> switching the flash "ON" and to the "M" mode, and then discharging
> the flash using the "READY/TEST" button, switching it off IMMEDIATELY
> without any delay. Remove the batteries and let the flash sit for
> 24-48 hours, which should bleed off the residual voltage on the
> storage capacitor.
>
> Remove the mounting foot by unscrewing four screws. Be careful not
> to lose the screws; if you do, don't use anything longer as a
> replacement since there is circuitry inside the bottom of the flash
> and you don't want a longer screw touching it. Gently pull the
> mounting foot away, and notice the wiring on the inside of the foot,
> to the numbered terminals. Do NOT touch the visible circuit board,
> but note the wires connected to the pins marked "1" and "2". On
> mine, the wire to "1" was purple, the one to "2" was white. Cut them
> off the pins with a nail clipper or small wire cutting pliers; I
> recommend leaving a small bit of the color coded insulation on the
> terminal so you can reconnect correctly later on if you want to.
> Using a small piece of tape, insulate the wires you cut, so they
> won't touch each other or anything else. Put back the mounting foot
> and the four screws. Put a small piece of tape inside the battery
> door, marked "PENTAX ONLY" because the flash dedication won't work
> with Minolta or Olympus any more unless you put the wires back.
>
> That's it. Now the Vivitar 550FD M/P/O will work with the Pentax
> autofocus bodies, at least up to the MZ/ZX series (I have not tried
> it with the *ist series, film or digital). Since I use both the PZ-1
> and LX, the 550FD is now ideal as a lightweight flash that can be
> used in TTL automation with both bodies.
>
> NOTE: This only applies to the Vivitar 550FD in its M/P/O version;
> the C/R and N versions do not have Pentax circuitry in them at all.
> Also, the same modification works on the Vivitar Series One 600
> M/P/O, which is the same basic flash as the 550FD M/P/O but with a
> rotating zoom head.
-Gene Poon
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