eHam Forums => Mods And Repairs => Topic started by: KD5RPU on August 10, 2002, 11:00:51 PM

Title: Icom IC-27A
Post by: KD5RPU on August 10, 2002, 11:00:51 PM
I have an Icom IC-27A.  When turned on the only thing that lights up is the VFO light and the decimal point on the frequency display.  I have turned the squelch all the way down and tried to tune around, there is no audio and it is unknown if its transmitting. I can hear the telltale bump in the speaker when the unit is turned on, so I assume the speaker is working.  I opened it up and could not see any visible damage or problem (thats the extent of my capability).  Has anyone had this same problem or any suggestions? Thanks, KD5RPU (JR).    

Title: Icom IC-27A
Post by: N4EOE on August 24, 2002, 02:01:42 PM
Sorry I can't help with your problem. Can you help with mine? I need to know the pin assigment (signal names) of the Icom-27A microphone. I recently got one, but without a microphone. What is the model number of your mic?


Title: Icom IC-27A
Post by: KD5RPU on August 24, 2002, 02:59:10 PM
My mic is a HM-23. I'm sorry I don't have a manual yet, but will send you the diagram as soon as I get one.  Can you tell me what the white wire on the power connection goes to.  Is this another ground wire or a power wire for accessories?
Thanks, KD5RPU (JR)

Title: Icom IC-27A
Post by: NG1P on April 13, 2003, 10:09:08 PM
I know this is late. I just picked up a IC-27A and it worked for about 30 minutes. Looks like I have the same problem you do. Take off the top cover of your rig and look at the front right and look for R67 and R68. Mine where black discolored to the point you cant read them. Im trying to figure out the value and then replace them. I think this will fix your problem.

Title: Icom IC-27A
Post by: KD5RPU on April 29, 2003, 01:10:04 PM
Well I finally found the manual online it's at
It does not have a schematic attached but does have the microphone wiring diagram.  My resistors were burnt as well, the ceramic on the larger one was almost completely gone.  The smaller (sorry can't remember the position R67?) measured at 120ohms.  I think the markings were brown-red-brown with the multiplier gold. For the larger it measured at 28ohms but I don't know how correct that was as it was broken open. The only visible bands were red on far left and gold on far right (gold being closest to the outer edge of the radio). If I find out anything new I'll post it, thanks.
KD5RPU (Jim)

Title: Icom IC-27A
Post by: KD5RPU on April 30, 2003, 11:27:51 AM
I also noticed that there is a red led light under the red cover and it is lit when I power up the radio.  Does this mean anything?

Title: RE: Icom IC-27A
Post by: KAF4931 on March 08, 2013, 05:01:05 PM
The two resistor color bands that you are requiring are R67 (front) is red, violet, black, gold
The second R68 (back) is Brown, red, violet, gold....
Mine aren't as burnt up so I could see them  easily.... Enjoy

Title: RE: Icom IC-27A
Post by: KA4POL on March 09, 2013, 08:50:45 AM
In my schematic the resistor values are given as follows: R67=1.8k and R68=220 Ohms. They should have color bands brown, grey, red and red, red, brown. The gold or silver bands are the tolerance, gold being 5%.
If these resistors are burnt up it does not make much sense to just replace them. R 68 is the emitter resistor of Q 8, a 2SC1571. R 67 goes from base to ground. So this would seem to indicate the transistor is fried. The connection to the microphone is decoupled from DC by a capacitor. If the capacitor is good I am wondering how a 1.8k resistor should burn up. Also the 220 Ohm resistor could only get 6 V through R 65, 100 Ohms.So just 19 mA would be flowing. That does not burn a resistor if it can take .2W. If it is 27 Ohm as just described This is a different story in contradiction to my schematic. Also brown red violet would mean 120 MOhm. Should be very strange for this circuit.
Sorry I can't help with the original problem, just trying to clarify a few things.

Title: RE: Icom IC-27A
Post by: N5VTU on March 09, 2013, 07:03:12 PM
Nothing like reviving a 10 year old thread!