Are these things I should consider bad

[Username1]

If that 125v is too high, look at c248 in the power supply.... 3.5mfd off the 235v leg on the transformer....

128v at the diode there just before the filters and choke.

Also q212 voltage regulator.... Take a test of the 23v source on the scope, and dmm, that voltage should be spot on, and across that zener diode, should be 24v spot on....
good test for your dmm and scope for dc....

[TinCanAlley]

Originally Posted by Username1

If that 125v is too high, look at c248 in the power supply.... 3.5mfd off the 235v leg on the transformer....

128v at the diode there just before the filters and choke.

Also q212 voltage regulator.... Take a test of the 23v source on the scope, and dmm, that voltage should be spot on, and across that zener diode, should be 24v spot on....
good test for your dmm and scope for dc....

I'll do these next. I've been going over the 125V sources and they all show up as 129V. The DMM and scope are in agreement there. I also checked the 125VAC and did the math. The DMM showed 128V and the scope had 126V after doing the calculation given me for RMS.

I'll let you know the voltages asked for.

[jr_tech]

Originally Posted by Username1

If that 125v is too high, look at c248 in the power supply.... 3.5mfd off the 235v leg on the transformer....

I have been looking at the schematic and scratching my head over that cap... what does it do? Is the transformer somehow set up to be a constant voltage device?
jr

[Findm-Keepm]

Originally Posted by jr_tech

I have been looking at the schematic and scratching my head over that cap... what does it do? Is the transformer somehow set up to be a constant voltage device?
jr

That transformer supply is ferroresonant - an L-C tank, and causes the transformer to provide some level of regulation itself. If the 440V cap goes bad, you'd know it, with a dead set, or really low voltages. If you get B+ and other transformer secondary voltages, move on, as the ferroresonant circuit is working. Zenith stressed this after seeing a spike in folks ordering the cap. Reliability testing showed the cap had a 40+ year life, and shops that didn't understand the circuit would order and replace the cap to eliminate that as the cause of whatever problem they had. I've only seen one go bad- and a dead set was the result, with the blown input fuse as well.

We always kept the caps from the sets we junked, and I used one two summers ago as a makeshift run capacitor in my HVAC Gaspack to keep the AC going in July 2011. Date code on the cap is 1979....

Cheers,

[TinCanAlley]

Originally Posted by Username1

If that 125v is too high, look at c248 in the power supply.... 3.5mfd off the 235v leg on the transformer....

128v at the diode there just before the filters and choke.

Also q212 voltage regulator.... Take a test of the 23v source on the scope, and dmm, that voltage should be spot on, and across that zener diode, should be 24v spot on....
good test for your dmm and scope for dc....

The voltage to and from the regulator (Q212) is correct. I get 23.4V and 24V. Each is only off by .2, but that's most likely my DMM. The scope also showed the proper divisions from baseline for DC.

I thought that 3.5uf canister wasn't soldered in, but it is. It's also 440V. What size resistor will I need to discharge it?

[TinCanAlley]

Originally Posted by Username1

128v at the diode there just before the filters and choke.

Okay, on the AC side of the diode I get 131VAC and on the other side I get 131VDC. According to the schematics, the Red-Blk is supposed to be 100VAC. So if I test directly to where the Red-Blk connects, I shouldn't seem much more than 100VAC, right?

Here's a pic of the red-blk connection and the 3.5uf 440V cap. If you think this cap needs to be checked, let me know. I'll have to unsolder one of the leads.