Panasonic PVC-2021 Vertical Deflection

[Krankshaft]

Re: Panasonic PVC-2021 Vertical Deflection

I agree for critical regulation like the vertical IC this approach was sloppy. An IC based regulator would have been better.

The last Panasonic I worked on used linear IC regulators and none of this zener crap.

I could have adjusted the height but it would feel weird to do this service mode value shouldn't drift unless something had changed since calibration.

It's against my nature to tweak service mode adjustments unless a critcal part replaced requires it. I certainly didn't want to mask a real problem like a failing vertical IC.

All in all I think it's because of the iffy temperature stablity of the core of the regulator circuit the zener diode it's right next to the regulator transistor like 2/16 of an inch away as it generates heat (and believe me it gets quite toasty) it heats the diode. Maybe this was intentional to heat up the diode and stabilize it thermally? Maybe not.

Thanks for all the help on this guys.

[Toasty]

Re: Panasonic PVC-2021 Vertical Deflection

>>i really dunno why they bothered...why not just put 7812 and be done with it...<<

Because the 7812 would still need this circuit as it is the on/off control. You'd need this plus the 7812. The zener was cheaper.

[Krankshaft]

Re: Panasonic PVC-2021 Vertical Deflection

The zener was cheaper.

I honestly think that this was the core consideration of this circuit design.

I considered scrapping the zener and using an LM317T to get the 11 volts but the end result would look a little hacked due to the resistors to set the output.

Well hopefully I won't have to deal with a weird circuit like this again.

Hear that Panasonic! Keep your kinky circuits to yourself .

[Toasty]

Re: Panasonic PVC-2021 Vertical Deflection

The cat foretells more Panasonics in your future...

[PlainBill]

Re: Panasonic PVC-2021 Vertical Deflection

I agree for critical regulation like the vertical IC this approach was sloppy. An IC based regulator would have been better.

The last Panasonic I worked on used linear IC regulators and none of this zener crap.

I could have adjusted the height but it would feel weird to do this service mode value shouldn't drift unless something had changed since calibration.

It's against my nature to tweak service mode adjustments unless a critcal part replaced requires it. I certainly didn't want to mask a real problem like a failing vertical IC.

All in all I think it's because of the iffy temperature stablity of the core of the regulator circuit the zener diode it's right next to the regulator transistor like 2/16 of an inch away as it generates heat (and believe me it gets quite toasty) it heats the diode. Maybe this was intentional to heat up the diode and stabilize it thermally? Maybe not.

Thanks for all the help on this guys.

I'm surprised the vertical deflection was that sensitive to voltage. Of course, TVs have always had plenty of vertical overscan. It's been a fact of life from the days TV CRTs were round. Rather than using a regulator IC for the +12 supply, it should have been incorporated into the vertical deflection IC. Essentially a no cost improvement.

And who says parts don't drift as they age? Yes, carbon film resistors are more stable than carbon composition, still care to bet some of the resistors haven't drifted in value? Caps change, too.

PlainBill