KV2782/2785

[John Wright]

Hi. I write this immediately after I just read a post on here from a
regular, admitting that he spends his time here telling people to "forget
about fixing it", so I know pretty well what I'm going to get in response to
this...

However...

The basic question is -- does the 135V power supply in a Sony KV-2782R need
to be isolated at all? From the AC line and from the power supplies to the
audio section?, and how much current am I expecting to see there?

If strange crackhead ideas will discourage you from answering that, then
don't read any further. I am not interested in being told how stupid my
intended idea is, nor am I interested in being told to scrap it..

Since you're still reading...

I have these two Trinitron TVs - a KV-2782R and a KV-2785R. I'm pretty sure
the GA board from the 2785 works and the GB board from the 2782 is very
close to working, so I think I can get one of the two sets to work -
probably the 2785 as the 2782 also has some other problems on the mainboard.

For the other set, I'm aiming to simply replace the power supply with
something a great deal simpler. The audio section is simple - from following
the bottom of the GB board around, it appears that the audio board gets two
supplies isolated from each other - one being 16V and the other being 15. At
this point I suspect that the 15V supply is not isolated from 135V, but I'd
like to know for sure.

I intend to recreate the 135V supply using one of the Sanken STR hybrid
regulators, with a pass resistor to reduce its dissipation. In order to
figure the correct value for the resistor, I need to know how much current
will be passing through here. (yes, I am aware that it will vary, and that
the resistance needs to be computed for the LEAST value so as to prevent
overvoltage).

I also need to know if isolation is necessary at this point.

 

[BWL]

Unless it's different from every other Sony I've ever worked on, the 135v is
isolated from the AC lines via the SMPS transformer. If you don't isolate the
AC from the chassis, you'll have to make sure ALL external connections (RF,
A/V) are isolated from the chassis. Failure to do this will result in brief but
spectacular fireworks when the unit is connected to cable or another piece of
equipment.