Re: Problem with a new driver board

Helmut Wabnig

On Sat, 25 Apr 2020 11:05:06 -0700, you wrote:

I have a question for the group. A while back I put in a new driver board  for the icom 7000. I had just learned about it from another ham. When I got it back, I was testing the radio on 10 m. I have it connected to an ldg at 100 pro antenna tuner. I forgot to tune it up before I transmitted. I thought the tuner would tune the antenna while transmitting. Also I thought the radio would reduce power if the swr was high. Well, after a few seconds smoke was coming out of the radio. No power out. I shut it off right away. I sent it back in and was told that Q1 had burned out. It is now working again. Does anyone know what could have happened? I also have heard of some having problems with the finals burning out and in fact mine had weak finals on 2m and 440. I do not operate it much on 2 and 440. Also, after I had just had the driver board installed, I thought it would help the radio tolerate more heat. I am not sure what happened except that I should have tuned it on low power before I
transmitted on 10 . I am using an off center fed dipole which is not that off on swr on 10. I also thought the radio should have protected itself by reducing power. I also sent the ldg tuner in and had it checked. They re calibrated it.

Also, I understand the radio cannot tolerate long key downs on fm or other heavy duty modes.

Thanks for the feedback

Two minutes full power is at least approved by my experiments.
Usually we work either SSB with 30% average power
or we use SSTV and FT8 with 50% duty cycle.
I always add the fan mod, a 470 Ohm potentiometer from the 12 Volt
to the red wire of the fan. This mod keeps the unit cool during
receive and creates a heat reservoir within the metal mass
of the casing.

I would not rely on a transceiver reducing power with bad VSWR.
All ICOMs have that 4 pole flat connector for driving the tuner
with 10% reduced power automatically.

From my repair work I remember having seen bad PA cooling pads.
I always flattem then by stoning and apply a better cooling transfer
paste as we have them in the PC CPU coolers.
The silver paste is better than the white.

Adding the gate resistor with the preamp FET is obligatory.


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