Site hosted by Build your free website today!

Dave's Miscellaneous Stuff

I will NOT be held responsible for any info that is listed here

****** N9EWO's ICOM "Chinese" HM-36 SIMPLE Hand Microphone Modification ******

Newer Icom HM-36 hand microphones are made in China (as indicated on the rear of the mics case). Unlike the Japanese made versions which are fine (marked Japan or unmarked) , these later Chinese mics sound buzzy and have nasty excessive bass at least when used with HF transceivers. From my contact made with Icom America , it's the old story "we have never heard of this" . Many hams around the internet have covered this problem so this is not a one or two sample defect.

There are other HM-36 modification variations on the internet , but here is what I did to improve the poor microphone audio (passive).

I will NOT be held responsible for any info that is listed here

After removing the 3 case screws and separating the 2 parts, unplug the microphone from the PC board (see photo below)

Separate the PTT lever and PTT spring from the side with the PC board (taking note of placement). Remove the 4 screws holding the main PC board down. One is longer than the other 3 , the longer one passes through the PTT microswitch and a small plastic bracket . Separate the board from the case, slide the up-down buttons out at the same time. Flip the PC board over.

- REPLACED R3 resistor : from 22K to 2K (2.2K works too). The schematics you see around indicate a 2K here.
- Removed R1 resistor: 1K
- Removed C2 capacitor : 10 uf
- Removed the inch WHITE cotton "Plug" (or Gray Foam in later production) that sits in front of the mic element. It's located in the same black rubber holder with the mic element. This cotton or foam MUST be removed for this modification to work properly. See the pictures below.

Finished. Put it all back together and enjoy the improved mic audio.

Notes : I would NOT remove the small black flat felt disc that is in front of the rubber microphone holder . I tried this and it made no difference in my testing (after the modifications were made) . We found the stock C1 coupling capacitor , 0.22 uf @ 16v to work just fine.

I will admit , there is only so much that can be done with this simple "low cost" modification.
There are other options around the internet that will improve the microphone's audio greatly, but are more involved (not tested by me) . Of course with the IC-7600 the transmit audio EQ can be tweaked .

Dave N9EWO
ver 6.5

Icom's Chinese versions of the HM-36 Hand Microphone have serious issues with sound quality.
Here is a photo after modification that improved the audio as connected to a Icom IC-7200 HF transceiver.
You can see R1 and C2 were totally removed. We left C1 ( 0.22 uf ) alone.
(photo: N9EWO)

The inch WHITE cotton plug (or "gray foam" in later production) that must be pulled out in front of the mic element.
You may have to dig a bit to get it out. DO NOT pass up this part of the modification , as you will not get good results .
(left photo : N9EWO, right photo : Roar Dehli)

********** N9EWO tries the KK5DR Icom PS-125 Fan Modification **********

Matt KK5DR came up with a great and very simple modification to the tame down the noisy internal fan in the Icom PS-125 power supply. We tried it and I must say the fan is much more quiet and no excessive heat either with my phone ONLY operations. Not to say that it totally cures the noise (it dosen't) , but now I can actually put up with the PS-125 fan noise. Does not sound like a jet airplane taking off anymore. As usual, TRY THIS AT YOUR OWN RISK !! Click on the link above for more information. Hardest part is to take it apart (properly) !! Should work for the PS-126 as well (not tested) ?

KK5DR's Icom PS-125 Fan Modification
(click here for details) . Adds a resistor in the fan power lead.
In our case we used a 56 OHM "wirewound" 3 WATT resistor in heat shink tubing (fan power + side, red wire).
Used one wire zip-tie to help keep it from moving around (as shown above).
Even using a
3 WATT resistor it runs near "dead cold" in my testing (even without the fan air blowing on it ) ,
so you do not have to worry about "resistor" heat issues . Be sure and PROPERLY use heat shrink tubing (do not use black tape).
(N9EWO Photos)

I will NOT be held responsible for any info that is listed here.

Ten Tec RX-340 : Display quirk noticed in 2005 sample / Sync detector continues to be a joke

With a "brand new" 2005 sample I checked out in the summer of 2005, a couple of notes. Note: I do not personally own a RX-340.

The main (larger) display had a nasty to my eyes that was not acceptable. Segments were not evenly lit. The main display is made for Ten-Tec in Korea by Samsung. Being almost a $ 4300.00 receiver , I feel that Ten Tec should be rejecting these when they look this bad (picture below that I took of the actual "test sample" display). There is simply no excuse for this. A sample that I used in the summer of 2001 had none of this and looked fine.

One other side note is that the "Sync Detector" continues to be almost worthless. It simply cannot hold lock, it keeps popping in and out even on the strongest signals with no interference around. It makes for a real aural treat when it's working, but more times than not it does not cut it for my standards. Try again Ten-Tec !

Even with the WJ8711A's sync only being double sideband, it sure holds lock much better over the RX-340 any day (in my view).

See my full RX-340 review here.

Dave N9EWO

Kenwood R-1000 “39.545 Mhz” Display Repair

Download (N9EWO PDF) : Kenwood R-1000 "39.545 Mhz" Display Repair

After years of operation the Kenwood R-1000 can suffer a fixed 39.545 Mhz display and/or a dead radio/display (or it can just go wacky). First place is to check and re-solder solder joints at Q201 and Q203 on the small power supply / PLL board on the underside of the chassis. This is where connector # 12 is located. The two TO-220 devices mounted on the large heat sink and the PC board solder connections can work loose after many hot/cold cycles.

Just as important, be sure and touch up the solder joints involving connector # 12 and the four power rectifier diodes as well as these can cause for bad connections too. Especially so with pin one and two on connector # 12 as these are 5 volt pins closest to the heat sink. In extreme cases all electrolytic capacitors, Q201 and/or Q203 and/or the 4 power rectifiers may need to be replaced on this board. Beyond this, I cannot be of any additional help.

Dave N9EWO

Back to Main Page