68kMLA Classic Interface

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550 board. No sound after recap.

Posted by: MJ313 on 2016-06-10 15:22:54 So one of my 550 boards, after recap, has no sound. Caps check out OK, but I am wondering if it's a sound chip issue. Anyone know which chip is the sound chip? Or any common trace issues with this board re: sound? Thank you. Here's a pic of my good working board... if you can point me to the sound chip I will check it for goo.

Posted by: 360alaska on 2016-06-10 16:18:13 Sound before recap? Sound at the jack?

Posted by: MJ313 on 2016-06-10 17:11:25 Hey! Very good questions. No, no sound before recapping. And Yes! I just checked and there is sound out of the headphone jack. I suppose that rules out the sound chip.

Posted by: 360alaska on 2016-06-10 18:01:27 And the 550 puts out sound with another board?

Posted by: MJ313 on 2016-06-10 18:03:10 It's in my CC, but Yes, the sound works fine with my original CC board and my other 550 board.

Posted by: 360alaska on 2016-06-10 18:18:30 Well, since there is no wiring diagram that we have, your best bet would be to trace from the jack on... Or from the speaker back, On my LC III it had no speaker sound but did have sound at the jack and I just had to retouch a via.  I just traced out it... On the LC III the audio amp is an 8 Pin chip, Perhaps the 550 is similar?

Posted by: MJ313 on 2016-06-10 18:20:36 Yeahhh... this is where I run out of airspeed and altitude. I'll give it a shot though. 🙂

Posted by: MJ313 on 2016-06-11 04:10:23 It was the headphone jack. I'm glad it was that easy, but yeah, I feel like an idiot. After testing the jack last night and then removing the headphones this morning, the sound came right back and has been rock solid. Something must have crawled in there and died... then been pulverized when I did the jack test? These boards were pretty dirty and had been living exposed for quite some time. Should've checked that way back in the beginning. Live and learn.

Posted by: techknight on 2016-06-11 05:59:43 the reeds in the jack probably have corrosion/blackening of the metal. When you insert a jack, it will scrape away at the metal. Making contact again.

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