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Radio Shack TRC-499 Mic Mod

sunbulls

Sr. Member
Apr 25, 2017
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This is another compact I recently rescued. These are often seen on Ebay or at garage sales without the mic. Once the stock mic’s 6 pin RJ-11 module connection has been damaged, either on the radio or the mic plug, these radios are usually tossed or sold for parts. Buying a replacement mic with the same configuration is not a viable option. This proprietary mic is extremely rare. My solution is to convert these over to the Cobra 4 pin standard. The 4 pin Uniden BC645 electric condenser mic then becomes an ideal replacement. Other than the useless owner’s manual, you won’t find much on-line information about this radio. Consequently I decided to draw the following mic pin-out and provide other basic information along with a few photos.

Comparison.jpg
Radio Shack TRC-499 mic.jpg


TRC-499 RJ11 pinout.JPG

TRC-499 board.JPG


There’s still a little work to be done such as cap replacement and alignment. As you can see there’s glue on top of some those caps. Over time that glue can become corrosive. At least none of it is daubed under any of the caps where it can do the most damage.

They used a 10 pin LED readout instead of the usual 16, but most compacts opted for green and every since it has become my top color of choice for all readouts.

I’m not sure what they’re using for the driver transistor. The numbers are unreadable. They usually use something like a 2SC3214 in combo with the 2078, but this looks like a TO-92L (a little longer than a regular 92). There wasn’t any heat sink attached to it. This concerned me, but no heat was felt after a long key down.

No other model I worked on is quite the same as this one, but the layout is similar to some of the Cobra 19 DX series, Ultra, plus some of the other compacts from that time period. Most of the board has through hole mounted components, but it also has 4 vertical boards that contain mostly SMD components. I guess you could call it a highbred.

Without doing any alignment I was surprised to see about 3 ½ watts out. Modulation was a little over 50%. Adjusting the pot brought it up to 80% without distortion, that’s good enough for my purpose, at least for the time being. The receiver seems sensitive, but to make better judgment. I’ll wait until the caps and alignment is finished. I like the squelch action. For some reason these cheap compacts do remarkably better that many high end radios.

Final: 2SC2078
Audio IC: KIA7217AP
PLL: C5122A1P
RV2: Modulation
RV1: Squelch range
 

Bought one of these mics last week because in the back of my head I recalled a smart guy had a good use for one.

I don’t have a need for it this day, but, tomorrow is another day.

Thx
 

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