Icom IC-7200

Rugged HF/50MHz

Background

This is my 2nd IC-7200. I foolishly sold my original one and very quickly regretted it.
From the Silent Key equipment of Peter GM0CXQ
Obtained 01/06/23

The current HM-36 microphone supplied with IC-7200 is poorly designed and problems are well documented on the internet.
I carried out the “K1RF/PY3SS Modification” documented here : k1rf_modified_py3ss_hm-36_mic_mod_reva.pdf
The newly modified HM-36 now functions “correctly” with adequate drive for the radio, and a better frequency response.
It is now possible to set Mic Gain < 20 and Compression = 4 and obtain adequate ALC and full power out and a reasonable degree of compression without the need to “Close Talk” the microphone.
It is also now possible to obtain full power out, and some ALC deflection, without use of Compression, by adjusting the Mic Gain accordingly. This was difficult/impossible with the stock HM-36

I found that on a long (> 1 hour) Olivia QSO at 50W that the rear panel/heatsink reaches 60°C, and even the side-handles reach 43°C
The fans initially turn on with the PTT and run for a few seconds after dropping back to RX
As the temperature increases the fans switch to medium, and then fast speeds while running during TX and also remain running for longer at the switch back to RX
One mod suggests adding a small resistor across the fan switching transistor to keep the fans running slowly at all times, so that duing RX they might remove even more heat before the next period of TX
The mod is here ic_7200_fan_mod.pdf
I carried out the mod, with a 120 ohm resistor and then had a similar long Olivia QSO to compare the temperatures of the rear heatsink and side handles.
Despite the continuous running fan I found that the rear panel still reached 60°C and the handles reached at least 40°C during the TX phase.
They probably cooled down a little more on RX, but not significantly, and not enough that the temperature on TX was noticeably lowered.
There seems no major benefit in the mod, as the thermal design of the radio seems able to cope without it.
There may be a downside though, the fans will now run continuously whenever the radio is turned on, which will cause them to prematurely wear out, or become noisy.
After one night's use I removed the modification and restored the fan control to normal.

— John Pumford-Green 02/06/23 08:04