How To Repair the ICOM HM-133 PTT Switch

HM-133 Front View

When the Push To Talk (PTT) switch on an ICOM HM-133 microphone wears out, the switch can be replaced instead of buying an entire new microphone.  Replacing the switch is easy and will save a great deal of money. Below are the part numbers and a step by step guide to walk you through repairing the HM-133 microphone PTT switch.

When the PTT in my HM-133 stopped working, I was initially able to squeeze the PTT key harder to make it work. This made the switch work better, but it would wear out my hands during a long conversation.  Squeezing the PTT harder only helped for a few weeks.  I tried cutting paper into small squares and using the pieces as shims. The shims went between the key you press and the switch inside to push it a little farther.  Eventually the PTT switch stopped working altogether, rendering my HM-133 and its IC-208H as useless.

I was going to pick up a replacement at the local Ham Radio Outlet, but the HM-133 was about $80.  No disrespect to the guys at HRO, but I suspected I could fix it more cost effectively.  As it turned out, I was able to fix my microphone for $0.29 by simply replacing the switch instead.  The difficult part was figuring out an exact replacement switch that would fit the microphone circuit board.  After a time-consuming search, I found an exact replacement switch for the HM-133.

PTT Switch Part Number

I found the following switch part number fits my HM-133:

  • C&K PTS645VK39-2 LFS (manufacturer’s part number)
  • Digikey CKN10053-ND (I purchased mine from Digikey)

Fixing the HM-133

Assuming you know how to solder, replacing the PTT switch inside the HM-133 is easy. All you need a small Philips screwdriver and the appropriate soldering equipment.

Remove Cable from HM-133Push the tab in to release the cable from the bottom of the microphone. Side it out to remove the cable.
Remove the screws from the HM-133A small screwdriver removes the two screws from the back of the microphone.
HM-133 Microphone Rear OpenOnce removed, the back of the microphone comes off easily, exposing the circuit board inside.
HM-133 with Key RemovedRemove the key from the side of the microphone by lifting the plastic key out of the frame carefully. It should come out easily. If the rubbery piece pops off, it can easily be put back later. Notice there are three Philips head screws labeled 1, 2, and 3. Use the screwdriver to remove these three screws.
HM-133 DisassembledWith the three screws removed, the printed circuit board is lifted from the microphone body by lifting on the connector. The board should lift out easily.
HM-133 PTT SwitchThe original PTT and the replacement C&K switch purchased from Digikey are shown here. The replacement is upside down, but the are identical in every aspect, right down to the color of the actuator.
HM-133 PCB (Keyboard Side)With the PCB removed from the microphone, it is turned upside down, exposing the keyboard and LED side. The four PTT switch pins are visible in the middle of this picture. Desoldering these four pins allows the switch to be carefully removed from the circuit board. The holes can be cleaned, and the new C&K switch inserts easily. Solder the new switch to the circuit board and the repair is complete.
HM-133 Microphone ReassemblyAssemble the HM-133 in the reverse order.

  1. Align and insert circuit board into microphone body. It should easily go into place.
  2. Insert and tighten the small screws into the holes labeled 1, 2, and 3. Do not over tighten the screws.
  3. If the gray rubbery piece came off earlier, put it back in place now.
  4. Insert the plastic key back into the body. Its axle must go into the hole at the bottom and the key portion should cradle the gray rubbery piece. I did this by performing a twisting operation on the PTT key as I rocked the axle into the pivot hole.
  5. The back of the HM-133 microphone has a catch that forms a hinge. Align the two halves at the top and close the microphone in a clam-shell motion as shown in the picture.
  6. Insert and tighten the two screws that hold the body together. Do not over tighten the screws.
  7. Align and insert the cable into the bottom of the microphone.

Fixing the ICOM HM-133 microphone is an inexpensive, straight forward repair that can be completed in about a half an hour once you receive the new switch. For me, it was difficult finding the correct replacement switch part numbers. Now that I have published the part numbers, the task should not only be easy, but economical too.