sorry cant ready the model number but its about 7" diagonal B&W rotary tuners guessing late 70's.

Pic brightness all the way up, get a barely decent pic completely cuts off at anything less than about 1/4 turn on the brightness.

Beside a weak CRT (which I have not checked yet) I assume I will need to check CRT voltages for bias settings. Anything else come to mind?

Check the CRT and CRT voltages. The CRT voltages need to be very close to what's on the schematic or you may have problems.

here is it, the model number tag is rubbed clean

There's a Sony 5.5" CRT on eBay now, don't know if it's correct for your set or not.

http://www.ebay.com/itm/Vintage-Sony-5-5-B-W-picture-tube-/330757155658?pt=Vintage_Electronics_R2&hash=item4d02a9ab4a

And a 9"
http://www.ebay.com/itm/SONY-9-CRT-UNIT-R-90APW1-/190354078033?pt=US_Rear_Projection_TV_Lamps&hash=item2c51fcb951

Whoops, I see you said it's about 7", well I'll keep looking.

http://www.ebay.com/itm/Rare-Vintage-Sony-Black-White-Portable-CRT-TV-AC-DC-Power-Collectible-LOOK-/230793631136?pt=Vintage_Electronics_R2&hash=item35bc5f55a0

here is is for sale, interesting the CRT looks about as bright as mine.

I can't even see how to take the darn thing apart to check the CRT...

model TV-770

Im going to email you the sams on it, its going to blow your mind:D:banana::ntwrthy:
The filament IS the cathode and it uses a little isolation transformer that looks like it may apply the horz/vert blanking too.
I see a 1uf boost filter cap that could cause low boost/low G2

It is a unique design thats for sure. There are disassembly instructions in here.

looking at the schematic now, I also see a coupling cap on the base of the video out transistor that if leaky could f up the bias.

I rescanned it at 300dpi, the first one sucked.
Would you have figure out how to get that apart??? Be honest....:smoke:

another odd thing the contrast pot does not do much except at the extreme end so I will look at the 100uf emitter bypass cap as well. I also see a voltage divider used for the base bias, if that 9100 ohm resistor went high then the bias would be fouled up as well. think I will check C501/C503 and the C505/C508 (boost filter on the brightness you mentioned). Will also get voltage readings on that transistor and the CRT pin 1 and the anode.

I prob would have missed the ones referenced to by removing the smoked screen cover of the CRT.. :yes:

Just to note so everyone doesnt think were too crazy here....the crt is kinda like a 5U4, The filament is the cathode so they use an isolation transformer much like you would to save a crt with a heater to cathode short. The isolation transformer is driven by the flyback.

I have a feeling this is one of those deals where they crt never goes bad or is always the problem. No way to test it.