Pentax af560fgz underexposing

It was our grandaughters 3rd birthday today and we went around to the party - Grabbed the K20d and the 560fgz and fired some shots.
Turns out that the flash was only managing about 1 in 5 correct exposures - Seems to under-expose by two of three stops - I put in new batteries, changed the camera to all the different modes and even set the flash compensation up. I gave it some extra time in between frames but still the same. So i used the pop-up and it was perfect every time!
Now then - can this sort of thing be fixed if I take it in to be repaired? (I have a af360fgz to use if it can) Has anybody else suffered the same problem? The flash is a couple of years old so I'll have to get me wallet out anyway!
Any ideas!
Duncan.

Duncan, read this thread and see if it helps. Would you have been certain of getting the correct exposures with your 360?

Dan

Well, the flash doesn't work out the exposure

The camera body works it out! (In P-TTL flash metering mode)

There are several reasons why you may get underexposure. Typical examples are reflective subjects - the preflash fires and the camera sees the reflection, thinks "whoah! that doesn't need much illumination" and fires little flash for the main exposure.

So, watch out for mirrors, really shiny surfaces, and reflective strips on coats.

But, as Dan points out the thread (or my e-book) may help a lot!
Matt

Thanks for the help with this guys, after reading some of the massive amount of information on the subject on the forum i'm going to lean towards a more "manual" camera and flash combination!
I'll give it a bash this week.
Thinking back - I mostly used the af540fgz with the k20d set at 1100-1600 iso and had no problems - Last weekend however I took a lazy approach and stuck it in "point an shoot" and it seems the problems started because of this!

Many thanks again,
Duncan.

Duncan,
What I have found is this: if the non-flash meter reading is waaaay underexposed then the flash will likely be underexposed too.

Unfortunately, the metering usually doesn't help by choosing a low ISO when the flash is enabled

If you only set one thing - set the ISO to within two or three stops of ambient and the flash will generally be fine. In fact, with P-TTL flash you can just set the camera to fully manual: e.g. ISO1100, 1/30s, f/5.6 (ensuring it is still underexposed without the flash) and the P-TTL flash will do the rest

Have fun with the experimenting!
Matt