is it repairable ?

[surefm]

20250822_170938.jpg

So I have reversed polarity my 100w amplifier from Dutchshop and sadly is not working, it powers up but no amplification. is it repairable and can it be checked just by using a multimeter as I am not technically minded I'm afraid, Does any one know if Dutchshop do a repair service or is it one for the Bin ?

Thanks Mick

[King Croccy]

I don't know exactly but it's probably shagged the mosfet, which is the black transistor (mrf101an). You could try changing it.

The first thing I would do is check to see if there is a voltage on the gate of the mosfet (with supply connected and dummy load), if not it probably means it is shorted inside. Take the mosfet out and re-check for voltage on the board terminals (it may come back with device removed).

There is a way also to test mosfets with a multimeter on diode test. Check this video...

[jvok]

Schematic is here https://cdn.shopify.com/s/files/1/0719/ ... 1689931102

Only thing to go wrong really is the FET. The voltage regulator is protected by the zener diode so will have survived. I guess you could have killed the 100u cap but given its still on the board and not shot halfway across the room its probably fine too

[surefm]

Thank you for both replies, i will look at it tomorrow when i get off work, thanks again
Mick

[Albert H]

Remember - the FET is 90% of the price of that board!

If you're going to replace the FET, be certain the get exactly the same part number (and letters). Those devices are available as "mirror-image" parts, for making paired, balanced amplifiers. In a balanced amp, the two devices are legs towards each other, and bolted to the same heatsink, so you have to get mirrored parts!.

[Bazz]

Change the MRF101AN

120Watt VHF Amp & Adjustment of BIAS - 87-108 Mhz -

[surefm]

thank you for the replies, i shall look into costings and see if it would be more cost efficient and buy a new board
Thanks again
mick

[Unknown]

100% you've blown the fet. Just replaced with an mrf101an. Not B.