Replacing Icom IC-703 Output Transistors with RD15HFV1

My IC-703 came with one working output transistor. Good enough to sell the rig as "working" but not much more. I tried replacing the RD07MVS1 but they are a bitch to replace.

Granted, by now the PCB had been reworked at least twice (the finals I got were not the original finals) so things were a bit iffy.

photograph of output transistors

layout of output transistors from Service Manual

C1650.1C2012 JB 1C 104K-T2012 (0805)
R1602k2ERJ3GEYJ 222 V (2.2k)0603
R20633MCR10EZHJ 33R (330)2012 (0805)
C2010.1C2012 JB 1C 104K-T2012 (0805)
C1550.1C2012 JB 1C 104K-T2012 (0805)
R211220ERJ1TYJ 221U (220R)(2512)
C21339pGRM31M2C2H390JV01L(1206)
C20539pGRM31M2C2H390JV01L(1206)
R210220ERJ1TYJ 221U (220R)(2512)
C1500.1C2012 JB 1C 104K-T2012 (0805)
C2000.1C2012 JB 1C 104K-T2012 (0805)
R20533MCR10EZHJ 33R (330)2012 (0805)
R1632k2ERJ3GEYJ 222 V (2.2k)0603
C1610.1C2012 JB 1C 104K-T2012 (0805)

Output transistor schematic

Then in a fit of not double-checking I assumed (never assume) that the current to the finals goes through the fuse right there next to them on the board, so that's where I inserted the multimeter to set the idle current. Don't do that. RD07MVS1s can and do catch fire.

So much for that then. Something had to be done.

Enter Bubba with his Dremel

Bubba was here with his Dremel

I should have been a bit more conservative, I think. But I wouldn't have been able to save those two traces, so I'll just have to add wires. One trace runs from R300/R305 to R306, the other is the T8 line between R100 and R250/R301.

RD15HFV1 pinouts

RD15HFV1 bolted down

Some very rough CAD

New transistors installed

It's ugly, but I'm back on the air again. With cheaper, more robust finals. I'll call it a win.


[Image] Hit Count hits since 2017-04-26.

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