K7000a No Heater Voltage

mk3u2012

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Hello,
I have a K7000a Zenith built chassis that was dead. Blown fuse, shorted HOT, shorted voltage regulator. I replaced all and powered on momentarily to find that the flyback was indeed bad (arcing). That was expected. I had a donor k7000a chassis with the same flyback which I pulled and installed. The chassis was the 19" variety rather then the 25" yet the flyback part # is confirmed the same.

After installing I have high voltage (28k with HV probe) which seems proper for 25" tube. Fuse doesn't blow. HOT and voltage regulator both are good. B+ is at 130vdc tested at both the neck board P202 pin 3 and R301. According to the manual it says it should be 123vdc, but its not in shutdown. I have no heater voltage at the socket pins on the neck board. Therefor no neck glow and no picture on the tube.

Am I missing something? Power supply and horizontal circuits must be working for it to have HV. And I've tested the VR pins 1 and 4 are not shorted. HOT isn't shorted. I have not capped this monitor. Is it possible an electrolytic could be keeping this monitor from getting heater voltage? Is this just a cold solder joint or broken trace? Flow chart goes from No HV in one direction. To over 130vdc in the other direction. This is neither and after following the flow chart for no HV I've exhausted the normal culprits in which my tiny brain has the capacity to remember after 9pm on a Thursday evening.

Greater minds and fresher thoughts welcome.
Thanks
Blake
 
R213 on neckboard can cause no heater. it's not something I would expect on a K7000A though, I think they used those rivet things for all the resistors but I could be mistaken. I can't visualize the Zenith neckboard right now.

it's just a straight winding from flyback through R213, it's AC voltage you can measure at the 2 topmost pins on the neck socket 9 and 10.
 
R213 on neckboard can cause no heater. it's not something I would expect on a K7000A though, I think they used those rivet things for all the resistors but I could be mistaken. I can't visualize the Zenith neckboard right now.

it's just a straight winding from flyback through R213, it's AC voltage you can measure at the 2 topmost pins on the neck socket 9 and 10.
Already measured it and its completely dead. I'll test R213
 
I see R304 as a possible culprit too. Not sure if thats on the 25" chassis or not but its before R213 and on the main chassis.
 
I suppose check the white/blue wire plug, it's not extremely common but I've seen wires ripped off the plugs. also make sure you have 2 ground wires coming off the neckboard -- 1 goes to the heatsink wall on the deflection board, the other connects to CRT ground on the tube. if the heatsink ground wire is missing you'll have no working heater from my past haphazard experiences. those ground wires are prone to fraying and breaking off too, if they look real ratty I add solder, pull them off, remove old solder, cut and strip wires, resolder. I'm not in the business of repeat business.

r213.png
 
Yea I did inspect the blue and white wire harness. Tested directly off the pin to confirm. It has continuity. I'm thinking you may be onto something with the ground wire on the heat sink. I'll double check that. Here is the k7000a schematic showing R304. It differs from the k7000 schematic which you picture.
 

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The more I think about it (not in front of the chassis) I feel like I also haphazardly attached the ground that should go to the heat sink to the CRT ground strap. I recall there being a grey wire with single pin connector that plugged into the neck board and the only other wire coming from ground I would have instinctively put to CRT ground. Looking at pictures I see the original setup had that black wire going to the heat sink and then what looks like a jumper going towards the tube (CRT ground I assume). All speculation for now. I'll know for sure tonight. Thanks for the idea @mecha as I really believe this may be the issue.
 
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