Reverse-engineering Vivitar 3700

[JMG]

Hi,

I know this isn't 100% on-topic, but I figure that it could help with
compatibility in the long run, so it might be of interest to this
group.

I just got a Vivitar 3700 flash. These units are modular, in that they
have a unit which clips on to the bottom which could communicate with
different types of cameras TTL to control the flash automatically.
There is no manual power adjustment What I'd like to do is similar to
what you're doing with your controller, only without the wireless: use
the quench pin to make it fully manually adjustable.

I'm trying to reverse-engineer the pins on the base unit so that I can
program an Atmel chip to do the timing (unless I can figure out an
easier, analog way to do it, but I'm much handier with digital
circuits). The problem is, I have no fancy equipment - no scope and no
logic probe - so my testing is fairly rudimentary. The module is
largely too complicated for me to figure out the circuits, so other
than tracing which connections pass-through from the hot-shoe, I'm
just testing the pins directly on the flash and seeing what I can see.

The base unit, without any modules, has 10 pins. Only six of these
pins are used to make contact with the TTL module that I have, so I've
only been looking at these six. Pin 2 passes through the module
directly to the center pin on the hotshoe and Pin 6 passes through to
the ground. Pin 1 also appears to be a ground, and Pin 5 appears to be
Vcc. The voltage on 5 stays at around 4.25V relative to ground,
although it drops a bit immediately after the flash is fired. Pin 3
appears to be a status pin - its voltage is equal to pin 5 when the
flash is ready to fire and zero when it is recharging. This leaves pin
4 as the quelch pin; it's normally at the same level as pins 1 and 6.

With no connections made, firing the flash goes at full power. If I
short pin 4, my suspected quelch pin, to pin 1, it fires very briefly.
Shorting to pin 6, though, seems to fire at full-strength, which
implies to me that pin 1 isn't a "true" ground, but perhaps pulses
immediately after firing, and I just can't see it on my little
multimeter. Either that, or my connections are bad. Shorting pin 4 to
pin 5 and firing fires at full-strength, but the flash does not
recharge at all; I can hear something happening, but it never gets to
full strength. The only way to get it to charge again that I've found
is to turn it off and on again.

So, in summary:
Pin 1 - Possible ground
Pin 2 - Fire (pass through to hot-shoe centre pin)
Pin 3 - Status (High when ready, low when charging)
Pin 4 - Quench?
Pin 5 - Vcc?
Pin 6 - Ground (pass through to hot-shoe ground)

If anyone has any ideas on how to test this, or about what might be
going on, I'd appreciate it. My next step, I think, will be to program
an ATTiny to fire the flash and then pulse the quench pin after a
certain delay and see what happens.

Thanks!

Jonathan