Testing 130V voltage regulator

[Reece]

Resurrecting this thread: I had to let the set sit for a while due to other demands on my time. The set works fine, great picture and sound. But I have a couple of questions before closing it up.

1. I had to replace Q501 the horizontal driver with the suggested equivalent NTE 399. Per Sams, the collector should be 33 volts but I get 52. My guess is it's because the replacement is close to the original NAP part but not exactly?
2. The HOT Q502 I replaced with the suggested NTE 2353. Per Sams, the collector should be 127 volts (pin 4 out of the 130 volt regulator is the correct 130 volts) but I can't get a readng: the DVM just shows random tenths of a volt. My guess is because the signal on the line is fooling the DVM? How to measure this voltage?

[Zenith26kc20]

The horizontal pulse will keep the meter from working properly. It will also kill it (the meter, that is) as the pulse is around 1500 volts. Most DVM units are rated 600 DC volts. The horizontal driver can confuse the meter as well. The older VTVM, if rated high enough voltage can read the voltage. I use an older Conar that can go to 1200 volts DC on the highest range. On those sets, if they don't get scrambled at lower brightness levels the regulator is working fine. Also, check the electrolytic capacitors around the vertical IC.

[zeno]

OK a few tips. The meter issue has been well covered.

Measure the HOT collector indirectly by measuring one of the
scan derived voltages off the FBT. If off you have problems.

Usually there is a low ohm resistor or coil in series with the low ohm
FBT winding to the HOT so if you got 130V you almost have to have 130V at the HOT. ( along with BIG pulses ).

When you change a HOT especially to non OEM run it say 5 seconds then feel it, must be cool. Keep on doing that at longer intervals being sure it doesnt get so hot to burn you. Should be comfortably warm. If you have a Power Rite or an equivalent monitor the current the set draws. Should be abt .75 amps with a normal pix. If you got hoz out troubles the
current will slowly rise often before any symptoms. Of course some
troubles will short an HOT instantly but thats for another show.........

73 Zeno

[Reece]

Thanks for the info. I have a VTVM but don't know the highest range and will have to go look. I've run the set for 20 minutes or so at a time and all the heat-sinked devices including the HOT remained OK to touch. Within the next two days I hope to be able to check it all out.