You are here:

TV/VCR/Stereo Troubleshooting/vertical output: Mitsubishi CS 27407


QUESTION: I have the Mitsubishi model 27407 which until recently worked well. Then it began to 'click' with an associated dimming of the picture slightly, then I noticed the raster lines at the top of the image were spreading apart slightly, and finally vertical display went out with just a bright horizontal line on the screen remaining. Otherwise no other issues.
I assume this may be due to the failure of vertical output integrated circuit. I have a Sams 3064 for the CS 2725 which I suspect has the same vertical output circuit which centers on the LA7838 so I ordered one of those and awaiting its arrival. I haven't opened it up to verify that I am correct. If you happen to have the wiring diagram for the 27407 would you verify that IC number for me?
Second, I notice that there are a number of electrolytic caps associated with that circuit. Would you advised replacing all of them at the same time, or just verify that each is working with an ohmmeter?
Lastly, is that IC soldered in or is there a socket for it? If the former, to remove it should I begin by cutting the wires and then heat and remove each of the wire ends from the circuit board?
Thanks for you help in keeping this nice TV set going.
PS I am an Allexpert in the Auto Repair section for Chrysler and Dodge vehicles.

ANSWER: If you have lost the raster I suspect the horizontal deflection amplifier has gone bad.  The horizontal output connects to the flyback transformer which produces the high voltage for the raster.  So, you could have horizontal, vertical and flyback troubles.

And, yes, in sets this old it is entirely likely that one or more of the caps in the power supply has shorted down and killed off one or more of the voltage lines to the various circuitry. You should examine the caps visually to see if there is any bloating or swelling or electrolyte leakage coming out of where the wires connect.  Replace those that look suspicious.  That would be the first step; if that brings up the voltage it may be the only cure necessary.

Sorry, I don't have schematics or manuals.  And, looking online I didn't find much either. The set is old enough that factory support has probably ended  (which is usually 5 to 7 years age of the product.

So, take alook at the power supply and then let me know if you need a next step.

---------- FOLLOW-UP ----------

QUESTION: Thanks for the leads as to where to look. I have now opened up the CS 27407 set in question and have found that it is laid out quite differently from the 2725 for which I have the wiring diagrams (although the cabinet and internal structural aspects are identical, the actual circuit board components are quite different such that I couldn't locate the flyback transformer or associated components.
I want to be sure that I understand that you believe that a picture that has a bright horizontal line in the middle of it suggests indeed that the vertical output section of the deflection board is the area to focus upon. The diagrams that I have for the 2725 don't actually id the flyback, but does suggest the area of the vertical output section of the deflection board. I assume that if I were to buy the SAMS Photo Fact that it would point me to the vertical output area of its deflection board where I would look at the caps.
The SAMS that is available is for the CS 27401 rather then my 407 so assume it may be close enough in its shown layout. SAMS wants $22 for the Photo Fact. Given all this, do you believe I have a chance at fixing this if I buy the Photo Fact?
Thanks for your impression about this situation.

As with all electronics fixing is a matter of bang for the buck and effort.  Often the repair is too expensive making it a bad investment of time, effort, hassle and cost.

As electronic components age they become more prone to failure.  Electrolytic caps are often the first to go with other capacitors later on.  Statistically when a set first fails due to some component failure it is the start of other failures to come soon thereafter.

The problem, often, especially with tvs, is that the first failure is often followed by another failure soon thereafter.  When the repairs start to add up with time lost and frustration one wishes the set was just replaced at the beginning.

So, I am not a fan of thinking a repair will put the set back to normal for the long term. A typical set of this genre has over 3,000 components and the failure rate of the many components coming from parts suppliers means they are all of the same life expectancy and leaving you with a set that is probably designed by the engineers who specify the component parts a life expectancy of the set to be about 5 to 7 years.  Why?  Market study after market study has shown that the average tv set buyer replaces older sets in that time frame; they want to upgrade to new or better products and they just don't keep them around any longer; thus, the manufacturer specifies accordingly.  Professional equipment and big RPTV are designed for life expectancy of 12 to 15 years because they are costly and not replaced so frequently.

Therefore, I would not advise paying such a handsome fee for the manual.  Experienced troubleshooter hardly ever use manuals; their experience leads them to know where to look and how to test and make the judgment on what to do to get it going again.

What did the lytics in the power supply look like?  If you have a voltmeter you should be able to tell if the dc voltage at the caps looks normal or not.  If not then you must find out why the voltage is down.  Sometimes just lifting the connection to the suspect cap will let the dc voltage go back up to the expected level and that tells you the cap needs replacing.

And, if the power supply is not suspect after checking a few of the dc voltages you next should look at the voltages in the vertical section; checking for a large voltage at the output of the vertical amp stage.  You don't have to have a schematic for this level of testing - you can guesstimate what stage you are looking at.  If all the voltages around the vertical amp were very low than you know there is either a power supply problem or a shorted condition within the  vertical circuitry.

Maybe these ideas will give you something more to go on.  

TV/VCR/Stereo Troubleshooting

All Answers

Answers by Expert:

Ask Experts




Consumer Electronics of all kinds. Audio, esoteric audio systems and components, video, tv. Digital equipment for consumer use. Ham radio and automotive electronics. Note: I give advice on tv repair based on general consumer electronics engineering experience but I am not engaged in actual repair of sets. MAKE SURE YOU GIVE THE MAKE AND MODEL NUMBER AND AGE OF THE SET. BE SURE TO CHECK YOUR EMAIL FOR THE RETURN ANSWER DURING THE NEXT 24 HOURS AS I TRY TO REPLY TO ALL QUESTIONS WITHIN THE SAME DAY IF NOT THE SAME HOUR.


Electrical Engineering; recording, broadcasting, design, international standards, tv and radio theory and practice.

FELLOW of AES (Audio Engineering Society)
Senior Life Member of IEEE (Institute of Electronic and Electrical Engineers)
International Consulting Organization

IEEE Spectrum
Various Consumer Electronic publications


Awards and Honors
Famous Engineer for Digital Audio

©2017 All rights reserved.