K3 Speaker Amp - sub side inop
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Hi Don,
I was wiring up a switch box for dual-sourcing hifi speakers, and looks like I had a short on the Sub (right) side circuit. This may have damaged the speaker amp, U1 on the DSP board (sh 3 of 9 from 6/2010 schematics). Symptoms: If only the main RX is operating, output is roughly equal from both speakers. BTW, the Sub AF is set to Balance. If the sub RX is also enabled in diversity with balance set full CW, I hear nothing. If the control is set full CCW, I hear the main RX. If I use the headphone jack with sub RX enabled, I get the two signals as expected. -- This seems to point to U1, the speaker amp on the DSP since the headphone output is OK for both channels. Is there some way to confirm U1 is bad? I will be running a sig gen into the main and aux antenna inputs to drive the two channels separately and try to isolate the problem. Any ideas are welcome. Meanwhile, is the LM4950TS stereo amp available as a component from Elecraft, and is it user-repairable? Many Thanks! matt W6NIA K3 #24, K2 #2810 ______________________________________________________________ Elecraft mailing list Home: http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/mmfaq.htm Post: mailto:[hidden email] This list hosted by: http://www.qsl.net Please help support this email list: http://www.qsl.net/donate.html |
Re: K3 Speaker Amp - sub side inop
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Matt,
Yes it sounds like you have blown the right channel of the speaker audio amp. The headphone amp is a different chip. I don't know how to confirm that is what failed other than to devise a connection means for a 'scope at the input and output of each channel. 73, Don W3FPR On 8/27/2010 2:48 PM, Matt Zilmer wrote: > Hi Don, > > I was wiring up a switch box for dual-sourcing hifi speakers, and > looks like I had a short on the Sub (right) side circuit. This may > have damaged the speaker amp, U1 on the DSP board (sh 3 of 9 from > 6/2010 schematics). > > Symptoms: > > If only the main RX is operating, output is roughly equal from both > speakers. BTW, the Sub AF is set to Balance. > > If the sub RX is also enabled in diversity with balance set full CW, I > hear nothing. If the control is set full CCW, I hear the main RX. > > If I use the headphone jack with sub RX enabled, I get the two signals > as expected. > > -- > > This seems to point to U1, the speaker amp on the DSP since the > headphone output is OK for both channels. > > Is there some way to confirm U1 is bad? I will be running a sig gen > into the main and aux antenna inputs to drive the two channels > separately and try to isolate the problem. > > Any ideas are welcome. Meanwhile, is the LM4950TS stereo amp > available as a component from Elecraft, and is it user-repairable? > > Many Thanks! > matt W6NIA > K3 #24, K2 #2810 > Elecraft mailing list Home: http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/mmfaq.htm Post: mailto:[hidden email] This list hosted by: http://www.qsl.net Please help support this email list: http://www.qsl.net/donate.html |
Re: K3 Speaker Amp - sub side inop
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>> Any ideas are welcome. Meanwhile, is the LM4950TS stereo amp
>> available as a component from Elecraft, and is it >> user-repairable? That chip is fragile. I've blown it twice, just with excessively loud audio. (AGC OFF) I'm a fairly good solderer, and I bought a replacement IC here: http://search.digikey.com/scripts/DkSearch/dksus.dll?Detail&name=LM4950TS-ND I was able to remove the old chip by cutting all the leads, and removing them one by one, but when I looked at the tiny pads on the circuit board, I chickened out. I couldn't see any way to solder those pins to the pads without shorting them to each other. They are EXTREMELY close together. I ended up sending the DSP Board back to Elecraft for repair. Dave Hachadorian, K6LL Big Bear Lake, CA . ______________________________________________________________ Elecraft mailing list Home: http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/mmfaq.htm Post: mailto:[hidden email] This list hosted by: http://www.qsl.net Please help support this email list: http://www.qsl.net/donate.html |
Re: K3 Speaker Amp - sub side inop
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Dave,
There is a way to solder those small pitch ICs - just run a bead of solder over all the pins, and then use solder wick to remove the excess. Only caution, all the leads must contact the pads at once for this to work - remove ALL the solder from the pads first, and make certain none of the leads on the new IC are bent. If you can manage a 3rd hand, a bit of pressure on the chip while doing the solder wick "mop up" will help assure you do not wick solder that is between the pad and the lead. 73, Don W3FPR On 8/27/2010 3:47 PM, Dave Hachadorian wrote: > > I was able to remove the old chip by cutting all the leads, and > removing them one by one, but when I looked at the tiny pads on > the circuit board, I chickened out. I couldn't see any way to > solder those pins to the pads without shorting them to each > other. They are EXTREMELY close together. > > I ended up sending the DSP Board back to Elecraft for repair. > ______________________________________________________________ Elecraft mailing list Home: http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/mmfaq.htm Post: mailto:[hidden email] This list hosted by: http://www.qsl.net Please help support this email list: http://www.qsl.net/donate.html |
Re: K3 Speaker Amp - sub side inop
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In reply to this post by Dave Hachadorian
Some of the SMT tutorials on the Internet show ways of using fine-gauge
rosin solder or solder paste to solder these ICs - essentially, they tell you to rely on surface tension and the natural bond of the solder to the pads, literally pulling the solder away from a shorted condition to pool on the individual pads. In fact, one tutorial I viewed shows actually laying down a "worm" of solder paste bridging all the terminals on one side of a chip and then applying heat with an embosssing gun - a scaled-down heat gun. As soon as the solder goes liquid it draws back to the pads. Might be worth trying, though I admit I chickened out when it came to trying to replace the RS-232 transceiver on my KIO3. 73, Pete N4ZR The World Contest Station Database, updated daily at www.conteststations.com The Reverse Beacon Network at http://reversebeacon.net, blog at reversebeacon.blogspot.com, spots at telnet.reversebeacon.net, port 7000 On 8/27/2010 3:47 PM, Dave Hachadorian wrote: >>> Any ideas are welcome. Meanwhile, is the LM4950TS stereo amp >>> available as a component from Elecraft, and is it >>> user-repairable? >>> > That chip is fragile. I've blown it twice, just with excessively > loud audio. (AGC OFF) > > I'm a fairly good solderer, and I bought a replacement IC here: > http://search.digikey.com/scripts/DkSearch/dksus.dll?Detail&name=LM4950TS-ND > > I was able to remove the old chip by cutting all the leads, and > removing them one by one, but when I looked at the tiny pads on > the circuit board, I chickened out. I couldn't see any way to > solder those pins to the pads without shorting them to each > other. They are EXTREMELY close together. > > I ended up sending the DSP Board back to Elecraft for repair. > > Dave Hachadorian, K6LL > Big Bear Lake, CA > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > . > > ______________________________________________________________ > Elecraft mailing list > Home: http://mailman.qth.net/mailman/listinfo/elecraft > Help: http://mailman.qth.net/mmfaq.htm > Post: mailto:[hidden email] > > This list hosted by: http://www.qsl.net > Please help support this email list: http://www.qsl.net/donate.html > > > Elecraft mailing list Home: http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/mmfaq.htm Post: mailto:[hidden email] This list hosted by: http://www.qsl.net Please help support this email list: http://www.qsl.net/donate.html |
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In reply to this post by Don Wilhelm-4
A video is worth 1000 words: http://www.youtube.com/watch?v=jlwoOetHAkU The LM4950 pins have a pitch of 0.38mm. The video guy said his pins were ~0.4mm. His procedure is exactly what Don described above. I've soldered an AD9834 in KD1JV's ATS-3 transceiver pin by pin but those are wider at 0.65mm. Using the above technique is definitely the way to go for very fine pitches. 73, Bill |
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