ICOM IC-7410 Tech Notes

Loss of RX and TX:

A fault in this 5-volt regulator circuit can cause loss of receive. And although the rig will still transmit, it will not be connected to either antenna ports.

The 5V regulator circuit on the CTRL board has a single diode (D802) in series with the input of the regulator chip (IC801). The KDS4148U diode is only rated for 450mA maximum peak current. And the TA7805F regulator is rated for 1A.

There’s a vacant slot on the board for another diode to be installed in parallel, doubling the current-handling capacity. But for whatever reason, the factory only installed one diode. The single diode seems rather “wimpy” for the job, and I’ve seen it fail.

There are a few options:

  • Replace the single diode with an original type, and hope it doesn’t fail again.
  • Install two original type diodes, which may be less likely to fail.
  • Or replace the original diode with one that is rated for the same current as the regulator chip, such as a 1N4000-series diode.

It is worth noting the IC-7600 has basically the same circuit, using the same single diode and regulator chip. But it has a 15-ohm resistor in series with the diode, which the IC-7410 does not.

This circuit does not seem to be an issue with the IC-7600, which may be due to the current-limiting resistor. So one could add a resistor to the IC-7410. But nevertheless, I think installing a 1-amp diode is best. Besides, the TA7805F chip has internal over-current and over-heating protection. So using an over-rated diode wouldn’t be an issue.

The original diode and vacant slot are circled in red:

A 1N4004 diode soldered in place:

Special note about removing the bottom cover:

There’s a thick thermal pad placed between the bottom cover and two of the toroidal coils, L11 and L101 on the CTRL board. See the pictures below:

The pad shown stuck to the two coils:

The pad shown stuck to the bottom cover:

NOTE: If you don’t have the skills or equipment to work with static-sensitive surface-mount components, please leave it to an experienced technician.

Mike Nadeau – N1EQ
www.n1eq.com

April 3, 2018