Sony KV-32XBR400 has audio but no raster. CRT fil. is lit

[[email protected]]

I havent opened this set up yet. We're trying to decide if it might be
worthwhile to attempt to chase this down in the home or if we should
take it to the shop. Its just such a heavy sucker. I don't have a
schematic for it yet either. Apparently it was working when the raster
just suddenly quit. Sound is OK and thee filament is lit. I know I'm
not providing very much information here but since I can see the
filament through the vent holes would that suggest that perhaps the HV
and horizontal circuits are working fine? I havent seen a CRT filament
powered by anything besides flyback scan derived for years now so I'm
assuming this, but I don't know. Actually I thought these sets usually
just shut down and blink if ANYTHING goes wrong with them but this one
is not doing that. Are there any common problems that are associated
with the above symptoms that anyone knows about? Thanks very much,
Lenny Stein, Barlen Electronics.

 

[Leonard Caillouet]

Lenny,

email me privately. There are several issues with these that you need to be
aware of.

Leonard
use first initial followed by first 6 letters of last name at devoynet dot
com

 

[RonKZ650]

Probably lost vertical sweep, or the old weak picture tube trick.

 

[[email protected]]

Turn up the G2/screen voltage slowly and look at the face of the tube.
If the picture suddenly comes back on, troubleshoot the picture tube
and AKB circuits. Lots of prior postings regarding Sony AKB here.

If it appears you have a slight halo effect at the top of bottom of the
screen, IMMEDIATELY turn the G2/Screen control back down to where you
marked it before turning it up. You have a loss of vertical and the
vertical ic still has one of its DC sources +15 or -15v still going to
the yoke. This will deflect the beam into the neck of the tube and
break the tube if you leave it on with the G2 up for too long.

Final test is to try and adjust the volume, if that works then you know
that the clock and data lines are not the cause of the problem.

David

 

[Leonard Caillouet]

This is a pretty new set. Sony is no longer blanking the pix when the AKB
circuit cannot balance the return pulse. I don't recall for sure but I
think this is one of the chassis that will keep the video active.

Leonard

 

[Leonard Caillouet]

What was the problem?

Leonard

 

[[email protected]]

Yes and no. It will not blank due to an imbalance of the return pulse.
It will blank due to a problem on the AKB line, like railed at zero
volts or full voltage. Same thing I thought until I ran into the AKB
causing blanking due to a problem in the circuit on one of the newer
sets. The troubleshooting steps still applied, looking and verifying
the three AKB pulses coming up as the tube warms up. In my case the
AKB return pulses were never visible at all.

 

[[email protected]]

As I recall the final AKB buffer was leaky-shorted. Measured good on
diode test, but when in circuit did not buffer and pass the signal, the
dc voltages were all wrong.

I am sure in the past you remember that Japanese 2sa???? that use to
commonly do that, as well as Q5104 in the corner of some Zenith crt
boards on the G1 line that also exhibit similar problems.

No matter how many times I see a leaky transistor, I wonder how they
actually fail that way internally.