SP50 Receive Audio

arlojanis · Post by **arlojanis** » Sat Dec 10, 2005 12:43 pm

I have a SP50 with very low receive audio on internal speaker or accessory speaker. I am feeding the radio with a signal generator and audio tone. I have the same scope level on input and the two outputs of the audio output IC ( measuring to ground). Measuring cross the outputs I have almost nothing. DC volts on the outputs are the same ( to ground). Note to other techs: pins 6 and 7 on the schematic are reversed ( numbers are reversed). Any ideas?

Bat2way · Post by **Bat2way** » Sat Dec 10, 2005 2:53 pm

When the internal and external speaker audio levels are low or nothing, usually found chip cap C481 cracked and/or just bad on earlier version boards. Scoping it will tell you immediately. If you touch a soldering iron to it's ends, it will normally break apart if cracked. Also check and touch up the solder on R481.

arlojanis · Post by **arlojanis** » Sat Dec 10, 2005 3:05 pm

Yes, I have checked those. They are before the volume control. The audio output IC seems to be the problem area.

Bat2way · Post by **Bat2way** » Sat Dec 10, 2005 8:07 pm

Ohm out coils L404 and L405 through external speaker-mic jack to speaker leads. I've found L404 may open up intermittenly with board flex. On the bottom side of the circuit board, you may have to heat up and insert a tiny soldered wire through the coil L404 (closest to the Volume On-Off switch) eyelets to make continuity. You will have to clean the eyelets carefully, and a tiny wire (such as 1 strand from 8 conductor flat phone type cable) will slip down in nicely. I'm presuming you have already shorted J403 pins 4 & 5 to eliminate the jack? Hope this helps.

arlojanis · Post by **arlojanis** » Wed Dec 21, 2005 6:39 am

The problem was the audio output IC. Here is a note: A good audio output IC gets very hot after 12 seconds of 1 kHz tone from signal generator. Voice does not cause a lot of heat.

ralphwarren · Post by **ralphwarren** » Mon Jan 16, 2006 10:49 pm

I had a similar problem and tried a diff vol pot off an scrap unit. Worked great.