50 " Phillips Plasma tv. Screen is black, blinking red light.

If you wish to get some details; check the site linked here. Pull up older posts.
http://electronicshelponline.blogspot.com/
faults & possible causes to LCD & Plasma screen are given with illustrations. You can get an idea about the fault to an extent. Faults to all LCD & Plasma screen are similar, irrespective of its brand and screen size.
Search the site by type in the "brand name" to your device; (Exclude the model number), in the "Search box at the top right of the display window of the Homepage" to get gathered related posts.

It sounds that the Y-Sustain or its driver sections has the fault. Visit this site for more details. Faults with Panasonic Plasma TVs are described in detail there. Blinking indications and faulty boards will be almost same to most of the Plasma TVs. Check this link, and select the site. Pull up older posts there. Sometimes, ads related to each post might help you to get details of availability of spare board.

7 blinks Driver SOS 2 SU / SD / SS Boards
(SC floating voltage area)
This is the fault indication meant by 7 blinks of standby light. Just visit this site 'Electro-help' Faults with plasma TVs are described in detail. Check this link and select the site. Pull up older posts there.

HI:
This is a plasma unit and philips plasma's are nortorious for bad power supplys, your problem may very well be the power suppy in the television, it is possible you blew a low B+ fuse on the power supply. There is also a issue with the Y-sustain board failing in this model, If you open the back and looking at the unit from the rear the y board is on the left side of the unit and the PS is in the center. disconnect the Y-sustain power plug from the power supply and turn on the unit if the unit stays on with no red light then the y board is bad. it does the same then replace the Power Supply.

There three common boards (Powers supply, Y-SUSTAIN, Z-SUSTAIN) that go out, since you have two TV to try out, you should check the Z and Y sustain boards.
What is the model number?
Try looking here for free service manuals:
www.elektrotanya.com

You can read anyon of the PLASMA TV training manual to get basic understanding how PLASMA TV works since they all have the same basic function blocks.
http://www.fixya.com/support/r7406380-tv_training_manuals

Basic LCD monitor and TV troubleshooting guide:
http://www.fixya.com/support/r6150077-basic_lcd_monitors_troubleshooting
http://www.fixya.com/support/r5093881-lcd_flat_panel_tv_troubleshooting_guide
http://www.fixya.com/support/r7406380-tv_training_manuals
Failed TV and Monitors: http://s807.photobucket.com/albums/yy352/budm/
Learn about bad caps: http://en.wikipedia.org/wiki/Capacitor_plague

i would say a power supply issue or maybe the Y SUSTAIN board, Check for swollen capacitors in the power supply, Test the voltages on the VA AND VS lines are there if so its more than likely your Y Sustain board.
Hope this helps

After all the research I found out that the IC on the Z board is bad and new board was ordered and replaced. The plasma work fine after that and picture is excellent with the new board. This forum is great, without this I couldn't fix it myself. Thank you.

replace the sustainer boards should correct this problem. New sustainer boards may cause red and green pixilation. If this happen, replace control board and TV is as good as new.

Your sustainer board is probably bad. You need to get the Y & Z sustainer boards replace then it should be okay.

I have a Phillips 50 inch Plasma. About two months out of warranty the top half of the screen would go black. Sometimes when we tapped on the back behind the upper right hand corner the picture would return. I did some research online and found that there is a Main Y sustain board (much like a mother board in a computer) and connected to that board is a upper Y Buffer board and a Lower Y buffer board. According to my research these boards seem to be the source of the problem. I am assuming that the upper buffer controls the top half of my screen and the lower controls the bottom. I removed the back of my TV (about 50 small screws) and searched for these parts by part number. Surprisingly all of the parts in my Phillips are made by Samsung. I found the parts on ebay at shopjimmy.com. I decided to try replacing the upper Y buffer first. I ordered it from shopjimmy for about 100.00. When I received the part I started to remove my upper Y buffer and realized that the new part was slightly different. The part number was the same but the REV. number was slightly different. The new part was missing a small white connector that connects the upper buffer to the lower buffer. I sent it back for an exchange for the right part with no problem. Ok so here is the interesting piece of this little adventure. When I started to remove my upper Y buffer I removed the screws and started to pull on it to loosen it. When I noticed that I had the wrong part I pushed it back into place and put the screws back . My TV has worked perfectly since I did that, with my original part. It has only been about two months, but if you are in the same situation it might be worth a try.