TV screen went black, sound OK

without a surge protector could have spiked the
Tvs circuity boards

without the TV having any defaults or life from the screen

doubt if a digital desk top unit to tune it would help

Do you have or are you using the original Mitsubishi remote for this?

SD TECH

Ordenalo en esta direccion

http://www.hbelects.com/shop/product_info.php?products_id=2693

Espero le sea util.

check your power board, most likely that's the part that is causing the problem.

that is a common problem with that model you will need the v26 power pwb repair kit and the V26 FMT pwb repair kit. You can get both kits at the following link which includes the replacement capacitors and instructions on where the capacitors are located. Heres the link.
http://servicemanuals.vstore.ca/

Maybe the audio amplifier IC of the tv are damaged

Mitsubishi has offices in Brazil. Apparently, they are out of the consumer TV and consumer entertainment business for a number of years now.

With the phasing out of CRT television sets, I have my doubts you will find a flyback unless you can find a scrap TV of the same model as yours. You can also try eBay or others like that to see if you can find this part.

Jerry G.

I realized that there is a 90 day warrantee on parts and a 30 day limited warrantee on labor for the  repairs that were done. As I stated, the original problem was the picture shrinking after a few minutes of the set being on. The repair firm took my control board with them. When they came back to install the repaired control board in my set there was a load spark during the installation, after which I had a black screen and no sound.  The repair firm took my set them and installed a "CAP Kit", a STRM6511, and a "D1881". The set worked perfectly until two days ago.
I called the repair firm an they are coming out this Thursday to check out my TV.   I am hoping the problem is related to the failure of one of the parts installed to fix a similar problem which occurred after the sparking incident.
 

there are bad solder connections on the vertical deflection IC resolder them and you will be fine

It seems your set has a loose conection in the high voltage circuits,in fact by now it should have many loose conections in different areas like the power supply and the horizontal deflection circuits,if you are familiar with tv service you can use the information as the first step to take,some of the loose conections are hard to see even for the trained technician but the one giving you this problem should not be hard to see,if you are not too familiar with tv service be safe and call for assistance from a servicer a least for an estimate.