Colecovision No Sound Problem. Help?

[Niki]

I have a Colecovision with a no sound problem. The video is perfect, it just doesn't have any sound. Occasionally, I will get a buzzing static-y sound, not with any particular game. I have tested it on multiple TVs all of which work with my friend's colecovision and I have verified that all my cables work. One odd thing is that I have the expansion module to play Atari games on it and the sound works perfectly on the Atari games I put in there. (Not sure if the expansion module has it's own sound chip...?)

 

My first instinct is that it is the sound chip, SN76489AN, but I would like additional feedback from anyone who might have more experience with this kind of issue before tracking down obsolete parts from china that I may not need. I have soldering/desoldering experience and some general electronics knowledge, but not a whole lot.

 

Any help would be greatly appreciated. Thank you.

[+nanochess]

It's easy to check if the sound chip works, use small headphones in pin 7 of SN76489AN.

 

http://es.wikipedia.org/wiki/Texas_Instruments_SN76489

 

Also with a logic tester check if pin 6 and 5 goes active to low and if there is clock in pin 14.

[Niki]

Thank you for the response.

 

I attempted to use some small headphones on pin 7 and I did not get anything. The Logic tester goes active to high on both pin 5 and 6, Pin 14 goes to low. So, does that mean the the chip is bad or are there other things I should check first before ordering parts?

Edited July 13, 2013 by Niki

[+nanochess]

Thank you for the response.

 

I attempted to use some small headphones on pin 7 and I did not get anything. The Logic tester goes active to high on both pin 5 and 6, Pin 14 goes to low. So, does that mean the the chip is bad or are there other things I should check first before ordering parts?

When you put a game and the music is playing, the pins 5 and 6 should be ticking to low (74LS138 generating selection) and pin 14 should be changing continuosly (you can measure a frequency of 3.58 mhz here)

 

Of course, you need a logic tester that can detect pulses.

 

In any case if everything else is working fine then it's 90% sure that the chip is bad.

 

By the way, the schematics http://www.atarihq.com/danb/files/colecovision.pdf

[Niki]

Thank you so much for all of your help! I'll order the part right away.

[+nanochess]

Thank you so much for all of your help! I'll order the part right away.

I'm glad of being able to help you.

[channelmaniac]

I have a couple of tubes of these chips, just don't have them up on the website yet... but, good luck ordering from China. Too many counterfeits...