Yaesu FT-100D Repair [2], SRF7043 Crack


The FT-100D which I bought last week “for parts or repair” has some issues. I documented those issues in the last post. I have sone some work and have halfway fixed one problem. There was a short which was drawing around 8 amps continuously, all signs pointed to a problem with one of the final transistors. There was a part which had been soldered to the ground plane near the SRF7043 VHF/UHF final amplifier. When I desoldered it, I could see the surface of the SRF7043. After a little cleaning I noticed the dreaded cracking which has happened to a lot of FT-100D radios. I researched and asked in a FT-100 owners group about this and decided to remove the SRF7043. Once I had removed the final amplifier I put power back to the unit and now I no longer have a continuous 8 amp draw. There are no more SRF7043s easily available as replacements. There is a guide by VK3BKC on replacing the SRF7043 with the MRF1570N. The MRF1570N is not a drop in replacement the width of the device is about the same, the thickness about the same but the solder tabs are different. The MRF1570N has 8 tabs / pins, and 1 pad on the bottom, 5 Sources, 2 Gates, 2 Drains. The Sources are all common, or connected.  The biggest issue is the distance between the screw down points. The distance between centers for the SRF7043 is 18.42 mm. The distance between centers for the MRF1570N is 20.57mm. The radcomm VK3KBC guide suggests grinding the inside diameter of the package to work the distance between centers to fit. I would hopefully like to find a workaround for this. I am thinking of some kind of milled aluminum or copper blocks with perhaps better heat sinking. 

 


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