When I sow the bottom of the heatsinks were almost touching the board I removed just a piece 1-2mm of the heatsinks. Just to be sure they could not touch the board.
Il 24/ago/2018 05:01, "Adrian Waiblinger" <
vk5zbr@...> ha scritto:
The standard heat sink is to small. To make it worse there is no heat sink paste on them to transfer the heat to start with. ?those poor Fets ?get cooked.? If you can¡¯t leave your fingers ?on them it¡¯s to hot. ??
Remember the 12volt rail is on them as well so have a inline fuse 3amps to protect your pcb.
On 24 Aug 2018, at 11:40 am, jfein2000 via Groups.Io <
jfein2000@...> wrote:
My uBITX was working for cw and ssb but the irf510s were running too hot.? All output dropped to zero, no smoke or dramas and I was sure the IRF510s were fried and I just happened to have four more around so replaced them.? No joy.? Changed them over suspecting one of them might have been defective.? With the new ones in the Ubitx powered up fine and I started the bias adjustment.? It was showing about 450 ma initially and I tried to bring it up the 100 ma over that, current draw shot up to over 5 amps and this time there was smoke.? The trace from the positive 12 volt on board 3 pin connector was burned and I jumped it, replaced the irf510s and tested them before putting them in.? The seemed to be switching ok.? I checked all the toroids for continuity and they look good. ? So now I can get the 450 ma and can adjust the bias up ok but I am getting no output.? If I plug in the key the power seems to short and there is a strange hissing noise.? None of the wiring has been altered since the unit was working and all connections look good.? Speaking into the mike doesn't budge the current draw as it should so I am thinking something else has burned out.? Any suggestions would be appreciated if anyone has experienced a similar event? Thanks Jeff
