Recently acquired (as a gift) ICOM IC-207H delivered VHF output power problem.
Overall this is a piece of great rig, 2m and 70cm ham bands, very wide RX covering AM Air band, 300MHz, 500MHz and 800-900MHz bands after RX mod.
Unfortunately, in early stages of production ICOM screwed small important thing which sooner or later will lead to troubles on VHF, UHF or in catastrophic phase – both bands. The problem lies in thermal grease, huh, actually lack of even small piece of it under two Power amplifiers IC’s.
I suppose many of these rig’s suffering the same, or even ended in junk box as a parts donor, just because these IC’s are completely unobtainable.
No spare parts on the
market, makes this little great rig like a brick, or to be exact not cheap
receiver. There are some options and chances to replace original IC with some
Mitsubishi or NEC hybrid IC’s, but effects are not satisfying.
Let’s dig deeper into this IC.
I will focus on VHF one, as luckily UHF remains OK, and healthy. In very early stage of SC-1091 production these small tracks were just sprayed on ceramic base of IC, later Icom decided to add soldering along all of them.
Why? I suppose they observed MANY failures in these IC’s because of temperature stress of ceramic base and different thermal expansion between copper and ceramic. Well, that’s IT!
But what the heck, why they didn’t add any thermal grease between the base and chassis to spread out the heat…?
OK, let’s see the patient we will try to revive:
Nothing wrong seen at first look. Transistors look intact, no sign of magic smoke, no burned marks – nice and shiny piece of IC.
But after examining all tracks, I discovered something… Tracks looking good but no continuity from power supply PIN to first transistor… Reason ? Broken ceramic base, because of extensive heat condensation, probably at cooling stage.
Where? Let’s see.
No, not at all. All things described below are risky and need some skills and stuff to do.
I know what I’m doing, so this paper is only pointing You to help You revive your TRX – this failure is most popular failure of hybrid IC power amplifiers. Same thing happening in FT-847 VHF/UHF pre-drivers, method of repair is shown on my blogpage, under Yaesu tab.
Let’s do it.
First we have to slowly heat the base up to 60-70, up to 90 degrees C, to avoid thermal shock in the place of repair. For reconstruction I have used very thin 0,15mm tinned Kynar wire, but any copper wire ~0,1mm will do. After ~5 minutes of heating, using flat tip soldering iron we have to add very small pieces of wire along the broken tracks, and secure them with solder. Of course don’t forget about plenty of FLUX (any for SMT soldering will do) In my case these tracks were just “bias” feeding driver with proper voltage at LOW/MID-LO/MID and HI power stage, and two ground tracks – adding solder will not change anything in terms of impedance or anything. These tracks are not easy to solder, just because ceramic spreading the heat from soldering iron, that was also the reason for pre-heating the base. I was using small flat 5mm tip iron, temperature was set to 420C.
After couple of more gray hairs ;-) decided the work is done.
At this stage it was looking like this:
After checking all tracks, and cleaning the ceramic, it was shiny like new.
Job done. After adding good thermal paste, and assembling the radio tested output power confirmed that it was worth try.. 48,7W output measured at 50Ohm. If Your TRX suffering power loss on VHF or UHF – time to revive it.
GL !
