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Mitsubishi CS-35201: Intermittent Sound

 
 


TonyG
New User

Jan 28, 2005, 3:31 AM

Post #1 of 7 (1515 views)
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Mitsubishi CS-35201: Intermittent Sound Can't Post
Sound is intermittent (common to both channels) for both stereo and SAP. Sound will cut out and cut back in with no clear pattern or timing. Circuit cooler on all components has no effect. Reseated all connectors and delicately wiggled many components. However, sound always OK when using external amp with RCA outputs on back of set. Any thoughts?



mel
Veteran

Jan 29, 2005, 1:03 AM

Post #2 of 7 (1504 views)
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Re: [TonyG] Mitsubishi CS-35201: Intermittent Sound [In reply to] Can't Post
The only common component that I can see which would affect the speaker output but not the audio output jacks is the B+ to the sound output ICs. I would suspect a lose component (bad solder joint) or a marginal component (voltage regulator or zenor diode) in this area. The schematic that I have on a similar chassis shows these as Q751, D752, or R761. You might also want to check out www.FreeFlatScreens.com/?r=10948674 for an opportunity to earn a free replacement for this set with a little effort on your part.


TonyG
New User

Jan 30, 2005, 12:08 AM

Post #3 of 7 (1493 views)
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Re: [mel] Mitsubishi CS-35201: Intermittent Sound [In reply to] Can't Post
Hello Mel,
Thanks for the suggestions. There are two voltage test points in the audio section, 12VDC and 20VDC. Do you think one of those was B+? Both voltages are stable with or without sound. I tried resoldering any connection that looked less than perfect but the problem persists. I could only locate R761 and it's connections were good and the component did not look toasted. In addition to a step function cut out, the sound now occasionally gets raspy before dropping out, and sometimes comes back in at "half" volume and jumps to full volume for a few seconds before dropping out again. I feel blind without a schematic. Do you know where I could get a copy of the audio portion of this TV's schematic?
Thanks, Tony


mel
Veteran

Jan 30, 2005, 1:35 AM

Post #4 of 7 (1492 views)
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Re: [TonyG] Mitsubishi CS-35201: Intermittent Sound [In reply to] Can't Post
Your last post may have narrowed it down some. Is your audio out IC an LA4270 labeled IC3A2 and is there a transistor nearby labeled Q3AO (it may be on the bottom side of the board)? If so, one of these components may be bad without showing any visible signs. I am working from a SAMs Photofact 2992 which is an entirely different model but may have the same circuitry.


TonyG
New User

Jan 30, 2005, 4:37 PM

Post #5 of 7 (1483 views)
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Re: [mel] Mitsubishi CS-35201: Intermittent Sound [In reply to] Can't Post
I located LA4270/IC3A2 as you describe. Its nearby neighbor is labeled IC3A0. Both are standing vertically relative to the main board and mechanically mounted to a vertically standing 3-walled aluminum heatsink (picture the heatsink as three walls of a room using the main board as the floor). Also in close proximity to IC3A2 and mounted on the main board are R3C0, R3C4 and C3C5. Thanks.


(This post was edited by TonyG on Jan 30, 2005, 4:50 PM)


mel
Veteran

Jan 30, 2005, 11:50 PM

Post #6 of 7 (1466 views)
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Re: [TonyG] Mitsubishi CS-35201: Intermittent Sound [In reply to] Can't Post
It sounds like the same chassis that I am looking at. Unfortunately, with an intermittent condition such as yours, if there is not a bad connection somewhere in this area, you probably have a marginal component and about the only way to be sure is to change it. If need be, you can download the SAMs E-Fact from www.samswebsite.com for $20.


TonyG
New User

Feb 2, 2005, 4:20 AM

Post #7 of 7 (1460 views)
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Re: [mel] Mitsubishi CS-35201: Intermittent Sound [In reply to] Can't Post
Thanks for helping me out on this problem. I'll pursue the schematics and try some parts-replacement troubleshooting. It'll probably be a few weeks away but I'll try to get back to you to let you know how I made out.
Tony

 
 
 


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