You wrote
<<
>I have a recently purchased OM-1n with a flash problem. The flash will
>only fire when "FP" is selected on the sync knob. I use a Sunpak 555,
>but it is the same with any flash I've tried. Does anyone know why this
>is? What will be the result of shooting with the sync select set to
>"FP" rather than "X"? Thanks.
>>
The following may help you diagnose your problem, especially if you know a
bit about electronics!
Background:
I don't have the official OM1N schematic but assuming it is
similar to the the OM2N in so far as the flash is concerned then the OM1N has
two sets of sync switches one for FP and one for X. The FP switch circuit and
coaxial flash connector is isolated by a commonly available 1N400(6?) series
diode from the X sync circuit. The X/FP selector either connects the X and FP
trigger switch contacts in series (X mode) or shorts one end of the FP switch
to ground (FP mode) It ony operates on the coaxial connector ** unlike the
OM1**.
Here are 6 things that could cause this to fail:
1) If the X sync polarity of the flash is negative on the trigger pin rather
than the positive required. (depends on flash see below for more)
2) If the diode is broken.
3) The X sync trigger contacts are shorted.
4) The Xsync trigger contacts are dirty and fail to connect.
5) the hotshoe screw connector on the pentaprism is shorted (commoner on OM2
than on OM2N where they changed the design to reduce the incidence) Don't
know if the design changed on OM1N vs OM1.
(6) The coaxial connector is not making good contact.
Check for (1) with a digital voltmeter by checking the polarity on the
coaxial flash connector of the flash. With the positive voltmeter lead to the
centre pin and the negative to the collar the meter should read a
**positive** voltage.
Check for (2) by switching the sync switch to FP and selecting the diode test
range on the digital voltmeter (marked with a diode arrow like symbol). With
NO FLASH CONNECTED hook up the meter to the hotshoe sync pin (the most
central pin) and hotshoe ground (or camera metal base). Swap the leads (to
reverse the lead polarity ) and try again. The meter should show no reading
in one direction and a lowish reading in the other direction (often reads
about 650 on many meters). If there is no reading in both directions the
diode is broken also if it reads a number in both directions it may be leaky
(bad). This assumes the OM1N is the same as the OM2N on its flash
connectors, quite likely as the OM2 and OM1 are the same. To replace the
diode requires removing the top plate and getting at the circuit board near
the on/off switch. The diode is near the front. Removing the top panel
requires a fair bit of skill not to damage anything.
Checking for (4) you can get at the X sync contacts as well as thw WX
contacts in the base of the camera by removing the base plate. Both sets of
contacts must work for X sync to work. The contacts are towards the RHS when
viewing the camera from the back. Removing the base plate is not too
difficult but don't lose the screws and remember the MD locating hole does
not have a screw so don't try to put one back when you reassemble.
Check for (5) with an ohmmeter. Connect from centre pin on the hotshoe to the
camera metal base or hotshoe ground. There should be an open open circuit or
tens of Mega Ohms. If there is a short remove the hot shoe turn the camera
upside down and with a pin try to scrape out any metal slivers from the
inside of the shoe screw. Olympus calls the improvement on the OM2N screw,
the "ant-shortcircuit shoe screw".
Checking for (6) is possible with an ohmeter. Check continuity using an
ohmmeter (with the connector plugged into the camera). Test continuity from
the plug going to the flash to the camera metal base. This tests the outer
connector.
More on Flash polarity:
The Tseries flashes which are deigned for the OM1N have a positive trigger
voltage (about 5V for the T20 for eample) with respect to camera chassis.
Thus only flashes which have the coaxial trigger pin of the connector
positive with respect to the collar will work on X sync with the OM1N because
of the isolating diode. In some flashes it is possible to connect it either
way, if the connector on the flash body is a blade type connector and can be
plugged in either way round. Try it both ways to test. (it does no harm if it
is wrong, it only does not trigger). My Sunpaks with blade connectors can
only go one way round. I also have a Sunpak 544 similar to the 555 and it
has the correct polarity (+ve) as does the 611 so your 555 probably has the
correct polarity.
If the polarity is wrong you can cut the cable and hook it up reversed if
you have moderate soldering skills. There are flash cable vendors who will
make custom cables for moderate (?) charges who have the special long Sunpak
flash connectors. (a regular audio connector does not fit).
Regards,
Tim Hughes
Hi100@xxxxxxx
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