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

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.

Reply to
captainvideo462002
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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

Reply to
Leonard Caillouet

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

Reply to
RonKZ650

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

snipped-for-privacy@yahoo.com wrote:

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Reply to
dkuhajda

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

Reply to
Leonard Caillouet

What was the problem?

Leonard

Reply to
Leonard Caillouet

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.

Reply to
dkuhajda

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.

Reply to
dkuhajda

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