'74 Chromacolor II Overload

[Spinning Head]

I've got a '74 or so 19" Chromacolor II E line chassis (19EC45) that I got a from a great aunt's estate about 40 years ago. It was daily driver for awhile but hasn't been powered up for probably 20 years. When powered now, line current is approximately 3.6A and circuit breaker pops after a minute or so. Listed line current is 1.4A. So not a dead short and no obvious shorted diodes or horiz. out. I initially thought a leaky run cap in the ferro-resonant transformer. But same condition after disconnecting the cap. All of the DC power supply voltages are only at about 10%. 130V = 13V; 230V = 23V, 24V = 2.8V, +35 = 2.8V; -35V = -2.5V. I disconnected the yoke to break the 130V and also tried removing the vertical module to try to isolate the overload, but haven't been able to isolate it yet. This set has the instant on, with a separate filament transformer. With power off there's no current draw and no glowing filament, yet DC resistance measures the expected 145 Ohms. So this may be a clue. Any thoughts as to how to isolate the overload?

[BeamT]

Always wanted one of these, or even better a 19" 4 Tube Hybrid.

Is this set equipped with a remote control? Simple power switch? The set was running when it was last powered off?

I'm sure some of the others will comment...and I don't have a 19EC schematic...but here is my swipe at it...

You have already ruled out the run cap, I would have voted for that first. It doesn't seem like your 130v supply is ever getting off the ground.

I believe the Chroma module is the first in the module daisy chain for the 130v supply. Pull that one, or the first one if you can determine which one is first. This should separate the 130v B+ rail from the set at its earliest point without pulling a wire. The modules are just an interlock. Still popping the breaker?

Troubleshoot the 130v supply-
Check the DC resistance to ground from the 130v filters, check the 130v rectifier diode. After setting so long, maybe one of the filter capacitors is bad.

Troubleshoot the 24v Regulated supply-
Check the 24v rectifier diodes for shorts. Check the regulator transister for shorted conditon and the reference zener diode. Check the DC resistance to ground from the 24v filter capacitor.

You could try pulling the regulator transister to isolate the 24V supply. I think the regulator gets its bias from the 130v rail, so with that isolated, the regulator is out of the picture?

Is there a glass fuse that protects the filament secondary xfmer stand-by circuit? Is it open?

On down the road, have the safety capacitors in the horiz output been updated?

[BeamT]

Well,,,,I'm not much help. Disregard what I said above, it's what you get from trying to remember instead of looking at an actual schematic. Isolating the loads IMO is a good strategy. I found a partial schematic of the power supply. I see 4 DC supplies to account for. I can't see much about the loads.

I'm not sure the module interlock is present in the 19EC45?

The yoke plug and the vert circuit fuse I believe you have accounted for.

On the load side-

Where does the Horiz Output/Transformer get its supply? With the screws removed from the Horiz Output Transistor, what is the DC resistance to ground in the collector circuit? Probe behind the heatsink or through the screw hole. Could the Safety Capacitor/s be shorted to ground? Especially if they are the original white capacitors mounted on the Horiz Output Transformer. Damper diode could be shorted. Tripler could be bad. I believe you already checked the Horiz Output Transistor? All high failure parts.

I see the glass fuse that protects the filament xfmer secondary. Its located on the bottom center of the chassis behind the vertical upright portion, near where all the DC supply diodes are located. Is that fuse open?

Sorry for the distraction...

[zeno]

First there are 2 versions of the ##EC45 Look for the run ## inked on chassis.

Under run 401 they used 5 identical caps ( part ## 22-5001) from the HOT
C to E. NEVER run set with them unhooked. They could open or short. If
they are white they HAVE to go. Orange Sprague ones are good.

Run ##401 and higher. The 5 caps are gone & replaced with the infamous
4 lead cap. Kit part ## 800-860. Again white ones MUST go, orange
are OK.

Usually a dead 130 V short gives a loud hum & breaker pop in seconds.
An overload gives less hum & a slow breaker pop. Usually its the trippler.
Just unhook the input to test.

Last thing is the motor cap. They are going left & right now. Usually the sets been restored but it shorts in a few days. To test lift one end & try it.

gotta go cook.
good luck Zeno
LFOD !

[Spinning Head]

Finally got some time back on this and found a shorted 4700pF ceramic disc before the diode for the 130V. Since the shorted cap was in parallel with the winding, it took awhile to find. I was getting concerned there was a problem with the power xfmr. I've put 325Vac across the 'motor' cap with a current meter in series, and the current is right where it should be. This set has got seven of the Zenith special 22-5001 white caps. I believe these are 0.015uF, but not sure what voltage. I'm assuming at least 2kV. Any thoughts?

[BeamT]

I've had good luck with Panasonic ECW series for this capacitor .0018uf @ 1.6kv.

Mouser Part # 667-ECW-HA3C182H4 Panasonic .0018uf (1800pf) 1.6kv 3%
or
Mouser Part 667-ECW-H16182RJV Panasonic .0018uf (1800pf) 1.6kv 5%

Digikey has also carried these in the past.