Megger MIT230 Mosfet details?

[Mad Axeman]

Hi Folks

I've got a Megger MIT230 1kV insulation tester apart in front of me. At some time it's decided to take up drinking. I've given it a good clean and it's fired up into life but it's got problems. The res range seems fine but all IR ranges are showing 15 - 16M with probes open. After a good check with an eye glass (yes, I'm an old fart who's eyesight isn't what it should be) I've found a mosfet with a lump! It doesn't look well at all. Unfortunately I can't read the full number on it due to the 'lump'. All I can make out is FQT13N??L. Anyone out there have a schematic and can tell me what mosfet it is? Not sure if it's the cause of the problem but it can't be helping. Sorry about the picture quality. Phones are not meant to take close up shots

[jonpaul]

We have bought several UK made professional insulation testers at flea markets for €5..20!
Link to the original manufacturer and model, no idea who or what his is.

Pix are fine, but I Suggest that you trace out PCB for schematic

Blown up FET or transistors will usually require many other damaged parts to be found and replaced, often the driver IC.

I would suspect the root cause is breakdown in the poorly designed pot core HV transformer or HV caps, diodes.

Bon chance

Jon

[fzabkar]

https://search.datasheetcatalog.net/key/FQT13N

[factory]

...snip...

I would suspect the root cause is breakdown in the poorly designed pot core HV transformer or HV caps, diodes.

Bon chance

Jon

I doubt you can blame the design for the corrosion on the PCB, the OP mentioned it had "taken up drinking", either it's got wet from drink/water, or maybe it's another victim of leaking batteries, pretty hard to tell from the picture.

The FET is probably FQT13N06L, as used in the MIT320 mentioned here: https://www.vintage-radio.net/forum/showthread.php?t=112071

David

[Mad Axeman]

Thanks for the replies. I'm not sure what had been tipped into the unit. It was a bit sticky so probably some type of fizzy drink. A toothbrush and isopropylene alcohol (okay, can't spell it!) has sorted the mess out. It is a FQT13N06L. A few hours after my post I got thinking (dangerous thing to do!) and thought 'I've got a working one in my van' so went out, pulled it apart and got the number. Why I didn't think of that earlier I just don't know. Anyway, 5 of them (minimum order) are now on order from RS. The only ones RS had in stock are in France so not due for a couple of days. I'll let you all know how I get on.

I have to admit, considering it's made by Megger the switch quality is pretty poor.