Intermittant PTT on Icom HM-133 microphone

[rex.vk3pk]

I recently found that my HM-133 PTT microphone was intermittant, requiring considereable force to make it
key the TX. Sometimes during an over it would drop out of TX. I know that others have had this problem and have solved(?) the problem with packing the PTT switch with a small circular shim of cardboard.

I found that the tactile switch clicked OK, but would often not go to TX as described. However, testing with a multimeter accross the switch contacts, I found that I had continuity across the contacts everytime, suggesting a dry joint on the PCB.

I reflowed the solder on the contacts(adding a small amount of conventional solder).

Since then, the switch has worked flawless without requiring me to have white knuckles during contacts.

73, Lee

 

[Ham4CW]

Hiya Lee

Some of the Kenwood handheld transceivers suffer the same problem.

All of the newer radios use lead free solder (makes sign of cross and utters suitable incantation), which is a pile of rubbish!

The new lead free solders, normally consisting of a mix of copper & tin, take a lot more heat to melt, and the flux used is very critical of temperature. At one point I was responsible for a production facility that used lead-tin solder paste (originally), and then had to swap over to using copper-tin paste. We all ended up spending most of out time looking for dry solder joints, and re-flowing PCBs by hand. Copper-tin solder just does not flow like lead-tin solder.

Also, copper-tin solder is much less flexible and tends to break away from components making the mean time between failures much shorter.

I know that copper-tin solder was created to please the hippies out there, but I see much more wastage due to premature failure of electronic goods than I ever did when lead-tin solder was the main stay of the industry. So in a round about sort of way they have shot themselves in the foot!

Once lead-tin solder became outlawed for general sale here in the UK I spent about two weeks buying up every roll of lead-tin solder I could lay my hands on!

Anyway, back to PTT switches. Something that has been occurring for a while now is the use of subminiature 'tactile' switches in the role of PTTs, but as us Hams like BIG buttons to press manufactures tend to 'dress up' teeny tiny switches with large plastic over-covers or levers. So the operator 'sees' a BIG button, but in reality it's still a teeny weeny tactile switch, destined to break the first time the operator gets over excited or 'ham fisted' (no pun intended!).

The Kenwood TH-F7E is a prime example of a dressed up switch. A great looking handheld, with a very sturdy feel to it, but the PTT is again a tiny tactile switch held in place by four (of the top of my head) tiny pads of solder. One 'good' press and the switch breaks away from the board, taking the PCB tacks and lands with it.

I guess that's why I prefer CW, at least you get a choice of 'switches', and very sturdy they are too!

73, Mark.

 

[rex.vk3pk]

Hi Mark,
I agree with your sentiments. Wave soldering + Lead free solder = Trouble
In particular switches & connectors that are subject to mechanical force and/or higher currents will almost certainly fail and therefore should be looked at early in fault finding. The Silicon is many times more reliable then the solder that they are held down with.

I have made many repairs on PC power connectors(high current & mechanical forces), PC audio connectors(high mechanical forces) and SCR/TRIAC/POWER TRANSISTORS(high currents/heat).

This may be of help to those who have these types of failures. Don't be afraid to have a go at repairing them.

73 Lee

 

[Ham4CW]

Yup, lead free solder is a waste of space!

Only the other day I had an FT-1000MP MkV that had a problem with the Class-A biasing.

The radio would hold the output power at 25 watts as it should when in class-a mode, but the PA standing current just did not increase.

After a good deal of head scratching and testing the fault turned out to be a dry joint on one pin of a six pin device about the size of a match head!

Amateur Radio equipment is not the only area where lead free solder is taking its toll. The vast number of Play-Station 3s that are suffering from the dreaded "yellow light of death" syndrome are all mainly due to failed solder joints. The folks that make them say that there are no issues with this unit, yet, they have a full blown exchange system in operation!

73, Mark.