View Full Version : Sony KV-20M20 - HV but no picture, curiosity


RetroHacker
10-08-2017, 09:06 AM
Recent find, a Sony KV-20M20. This set has *clearly* seen a ton of use, the tube has heavy QuickDraw burn-in. When I grabbed it I didn't notice this, but it was immediately apparent when I got it home. This was likely on 24/7 for a very long time, and has no hope of ever producing a usable picture again. But, I figured I'd fire it up and see just how bad it was. But, the screen is blank. Completely and totally. I'm getting HV, sound, everything appears to be fine. But no picture. This model doesn't have a standby light - I'm used to some Sony sets that would flash the standby light in a error code, one of which could be that the tube had such low emissions it wasn't switching on the video. I haven't opened it up yet to try cranking up the G2. What I can't remember is in this situation, can entering the service mode bring up the display regardless of the feedback it's getting from the tube? I tried the usual Display/5/Vol+, and Display/5/Vol- that I remembered with no effect. It's been a while since I worked on one of these.

I could be mis-remembering a lot of this. This set might not be that smart, and it's just a failure of cathode drive voltage or something. I CAN see the filament glowing in through the side of the casing, so there's that.

Really just curious here - with this much screen burn it's basically scrap, but it would be interesting to see just what kind of a picture it can still produce.

-Ian

zeno
10-08-2017, 11:02 AM
Most Sonys used AKB = Auto Kine Bias. Sony throws in a curve
ball. If any guns are weak the video shuts down. There is no known
way around it. Turning up G-2 will give a raster with retrace but
no video. There is a trick to prove what gun(s) is causing it &
prove its that & not the IC etc but I never had one that wasnt
the CRT. Rejuvination is a waste of time. Sony color tubes
will look better for a day at best.

73 Zeno:smoke:
LFOD !

Ed in Tx
10-08-2017, 04:26 PM
I have a little KV-9PT60 and it's getting really slow to show a pic, and when it does it looks magenta, like the green is weak. After about 20-30 min it finally has a decent gray balance. A TV tech at work about 10 years ago used a trick he came up with to clear some leakage between elements using a 40 kV stun gun of all things, when it originally developed a problem with blue and was all yellow and green, and it worked fine up until recently. That set's 20 years old.

Then there's my 22 year old KV-27V10 which looks and displays a picture just like it did in 1995 when I bought it at Circuit City. Never a problem with that set. It gets used daily for a few hours.

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