Toshiba 40RV52U TV has just started cycling off & on. Is this a problem with the power board?

Did you do a flashlight test?

Check and replace damaged component/s at its back-light inverter board, or replace this board as card basis. If you wish to get some details; check the site linked here. Surf the site with patience. Pull up older posts. It will be best to replace the inverter board as card basis.
http://electronicshelponline.blogspot.com/
In some models of LCD TVS; the backlight inverter and its T'Con board will be a part of the panel itself, and will be a built-in type inside the LCD panel. If so, they can't be replaced. In this case; a panel replacement is the only repair. For some other models, the backlight inverter section circuit will be a part of the main power supply regulator [SMPS]. To such sets, the power supply section circuit too should trouble shoot. Contact any service technician. The circuit will differ with models and versions.
Type in the brand name and type of your device, in the search box [at the top right] of the display window; to gather down all the posts related to your device brand. It will make surf easy.

Fault in the main power supply regulator board. Check and replace damaged component/s at its main power regulator [SMPS] section circuit. Contact any service technician. If you wish to get some details; check the site linked here. Surf the site with patience. Pull up older posts.
http://electronicshelponline.blogspot.com/
It will be best to replace the power supply regulator board as card basis rather than making "Surgery" to it; which usually will make loss for both money and time. Even though you can make it right, it will cost around an amount equal to the cost of a new board; including the cost of (spare parts + service charge) More to say, most of the spare parts to it will be difficult to get from open electronic spare part market. This is true to most of the flat panel TV power supply boards; irrespective of its brand and screen size.

Given the age of that unit, It may not be possible to get parts for the unit. The problem you are experiencing sounds like a poor connection on either the receiver for the remote or the main board power unit.

If just using one remote to try have it tested----many digital cameras in a dim light will react with a flash on the display screen when remote is pointed at them and buttons pressed.

Also try putting remote against remote receiver lens on front of set--if it reacts close up---the remote receiver in the set is bad---can be same if no reaction at all.

Either the remote or the receiver---one or the other.

A last thought here is some sets (read owner manual) have a feature to lock out the remote which can be engaged by accident.

You have failure/weakening in the vertical section , the retrace lines appear due to the change in the freq.
Check out small value capacitors in this section. confirm by shorting parallel with the right polarity. Unless you are familiar with electronics please do not attempt unless with help. the fault is not very serious and could be attended with low expense.

You may have bad T-CON board, try cooling it with small fan blowing on the vents of the TV.
If you are going to DIY and have proper tools and know safety precaution then please read on:
Please see my basic troubleshooting guide here:
http://www.fixya.com/support/r5093881-lcd_flat_panel_tv_troubleshooting_guide

http://s807.photobucket.com/home/budm/allalbums

http://en.wikipedia.org/wiki/Capacitor_plague

Parts: www.shopjimmy.com

color adjusting

If the tv does all those symptoms but after some seconds the tv works and stays doing the job. THen the tv has a slow microprocessor to recognice the different resolutions or video inputs.

But if the tv cannot do anything and stay aout of signal forever. send the tv to the waranty. (no waranty? you have to use the component input instead to have digital signal reproduced

am toshiba authorized servicer-have same model in shop for same problem-dvd board is defective-new board is about 290 from toshiba america parts-tv is actually made by orion with toshiba name stuck on outside-orion is junk-cost more than new set to fix-junk it and buy a panasonic-so far they still make their oun stuff