AF280T Problem

I have got an interesting problem on one of my 2 AF280T flasguns. With a fesh set of batteries it appears to charge normally. If you press the test button on the back, it fires normally. Put it on a dedicated camera and all the indications like flash ready and shuter speed are normal. However, press the shutter and nothing happens. My thought was maybe the flash contact. However, if I use a piece of wire between the central contact and ground, the flash fires. the problem of not fdiring occurs on all my Pentax's from SPII to P50 and AF bodies.

I spoke to Harrow Technical who, although very helpful, said it was a problem new to them. My intention is to have a look at it myself. If I completely mess it up, the cost of a replacement from Ebay is not likely to be anymore than a repair with post 2 ways. I could just throw it away and get a replacement but that's not very green.

So has anyone come across this problem before or does anyone have any suggestions?

Many thanks
Kim