good ol' k7000

[lilshawn]

been a while since i've worked on one. This one plays dead. fuse is good.

I couldn't hear any of that annoying 15k whine from the deflection. one cap was swelled up good (C57) cool, i'll just cap this bugger and get it going again. I took the chassis into the warehouse and replaced a number of the larger caps (basically all 470uF and up. and the 160 volt 'lytics.)

Take the chassis back and throw it in. could hear some deflection though, but no picture...screen is still blank. i crank up the flyback it shows a green looking horizontal line.

Great no vertical deflection.  this should be IC3? What kind of voltage should i be looking at? or am i barking up the wrong tree?

in the mean time, i'm going to dig up a tube so i can test this in the warehouse.

[ed12]

u have a knock down chain here that takes 135vdc down to the vert supply
2 zeners and 2 transistors and a sneaky coule of resisters
180 ohm and 330k
if the 330k is open chk the trans and zener >11v<
and the >5v< biasing..

ed

[lilshawn]

went ahead and replaced the LA7833. checked the power supply resistors and found R91 to be cooked. was reading in the megaohms instead of 1.2 ohms. replaced with new one. (2 watt)

diode D25 seems okay but D13 didn't read right. I read it in circuit so i'm going to pop out one side and re-check it. i'll have to check c41 too. make sure it's not shorted and caused the resistor to go bonk...

EDIT:

yep, d13 was shorted. stole one out of a parts chassis. I'll hook up this bastard tomorrow and see if it works.

[lcmgadgets]

Oh, it's a monitor!  I had to google it to b sure.

...boy, so often here I find myself reminded just how much more so many of u guys know about this stuff than I do.

...but I'm not giving up on my white elephant.

[lilshawn]

burned it in for a few days and it's good to go. 

I'll "explain like I'm 5" this for the future, this chassis numbering system is a real clusterf- so i'll decribe where the items are so you don't spend 2 hours searching for the parts.

the circuit goes like this... if you have no vertical deflection (thin horizontal line means you are getting horizontal deflection, but no vertical) there is an issue with the voltage running the chip that does the actual deflection or the chip itself.

the raw voltage off a flyback coil flows through R91 and then through D13 to drop the voltage down. it's ripple and sag filtered by C40 (2200uf 35 volt). there is a high frequency filter cap (C41 0.001 uf) to cut down on noise some more in the power. Check diode  and resistor (1.2 ohms 2 watt). cap c41 should read open not shorted. all these items are jammed between the flyback and the large aluminum heatsink. It's probably a good idea to go ahead and just replace C40 since it's jammed in there getting nice and hot so it's probably toast anyways.

Then the voltage runs across the board through D25 to lower the voltage a little further. (behind heatsink for IC3) Its ripple and sag filtered through C48 (100uf 35v, just to the front right of IC3) to run IC3.

if your diodes and resistor are good, go ahead and replace IC3. it's likely your issue. if any of the diodes are shorted, replace it AND IC3, it's toasted by the high voltage getting through the shorted diode(s).