K7000 Questions

[mcandrewsound]

I have some questions about the k7000 chasis..

1) I have one of the Zenith made boards..  If the flyback is toast, is this an oversize paperweight?

2)My other k7000 was blowing fuses. I replaced the HOT and Flyback.  Now, when I power up, I can hear the 15k squeal, but.. nothing on the screen, and it looks like the filament isnt lighting.  I verified 0 volts on at the neckboard for the filament.  I dont see any cracked traces or bad joints.  I measured the voltage at the big ceramic resistor on the side, and am getting 160v...  Is this a regulator failure? Is the HV shutdown engaged, therefore preventing the filament from energizing?  Should I still be hearing the squeal if the HV is shutdown?

3) Can a 13 or 25 chasis be used on a 19" tube?

Thanks!

Andrew

[mcandrewsound]

Some updates..

The K7000A appears to have a different HOT..??

The regular K7000 is back to blowing fuses, once I found the leg of the HOT I forgot to solder (lol) it did kind of a sratchy high pitched deal for about 15 sec, then popped the circuit breaker (thanks to Bob R!).. Im not sure it my new hot is still good or not... Resistance from center leg to any of the side legs is 200-300 ohms, outside legs is 80 ohms..  The whole monitor is a frankenstein deal, with a electrohome frame, who knows where the tube came from.. What resistance should the yokes have?  Is there somewhere I can find a yoke resistance spec?

Thanks,

Andrew

[lilshawn]

The fly back for standard Wells made k7000 (the 0528 fly back available from many suppliers) will not physically nor electrically work to repair the Zenith made chassis. nor vice versa. - paperweight


a better way to test the hot is to set your meter to Ohms Setting.

Ground the Black lead to the Chassis and touch the Red lead to the center leg or metal tab (Collector) or the Transistor.

Open or High resistance is GOOD.

Shorted when BAD

Test with the power off (obviously)

The HOT can be replaced with a HIGHER Amperage rated Transistor. This helps prevent shorting out when other parts blow. I use a D1398 as a replacement.

[mcandrewsound]

Another peice of info..

This chasis actually has D18 Soldered directly to the bottom of the PC board, with another ceramic cap soldered in the D18 holes (parallel to the diode). Is this normal?  Whats the value of this cap?  Its brown, but I cant read the ink..

Thanks,
Andrew

[lilshawn]

it's quite common to have little changes like that, i would check R213 on neck PCB...

[Ken Layton]

The Zenith flyback has been N.L.A. for at least 15 years. That chassis can now be a parts chassis. To make that monitor functional again will require a change of chassis. A Wei-ya model 1220-H replacement chassis will work and it also needs to be operated from an isolation transformer like the conventional k7000 and the Zenith K7000A.

[mcandrewsound]

Ok, Im going to focus my efforts on the origional k7000 I have.. I have replace pretty much all the diodes and caps (except c37) in the HV path, and I keep blowing fuses and HOTs.. The VR shows good resistance between the ground leg and other legs... I did fire up the chassis early on without the HOT and I didnt blow a fuse.. Will this blow the Flyback?  Im thinking of yanking it again, and making sure my 130v is correct.  Is this the correct approach to troubleshoot this? 

Thanks,
Andrew

[mcandrewsound]

I did a complete cap kit, c 37, another new HOT.  I found one cap was supposed to be 47 mf but was actually 100mf, another cap with a busted leg.. Still instantly blows the fuse.  Heres a dumb question.. for the flyback, the red and black wires..for the fly back I removed, red goes to a pin on the neckboard, and black goes to the neckboard socket.  On my other board (the zenith) the red goes to the neckboard socket, and a gray goes to the pin on the neckboard.. Am I correct in assuming black to neck board socket, and red to pin??

Thanks,
Andrew

[mcandrewsound]

Ive blown a couple more HOTs trying to fix this chassis..  Ive replaced dang near every cap, the voltage regulator, and d18..  Basically as soon as I attempt to fire it up, it blows the HOT and the 3a circuit breaker.  Can I test this chassis off of the tube?  Could the tube cause the flyback to die or short out?  Im running out of ideas. 

Thanks,
Andrew

[lilshawn]

i'm not sure how to isolate the power supply on this model perhaps someone else can shed some light.

basically what you do is disconnect the power supply from the rest of the board and substitute a 60 or 75 watt lightbulb for the load of the rest of the board (the power supply will not work without a load.)

PS : get yourself another light bulb and connect the bulb to both ends of a blown fuse...so the current flows through the bulb....if you have a dead short someplace it will come on bright and stay...otherwise it will settle down...this will also save parts you have replaced by limiting the current flow.

[Kevin Mullins]

I'd start by double checking the bridge rectifier diodes, the voltage regulator (IC4) and C36 for shorts.

[lilshawn]

also, parts can test okay while powered down, but perform poorly once under load.

diodes and HOT's are famous for that.