Remember to bolt down your chassis

MKplayer1start

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capped a K4900 for a buddy tonight and as I was testing it with a 60-1 vertical pcb I decided to rotate the monitor and guess who forgot to bolt down the chassis? ya awesome. there was a flash and then monitor dead.

replaced voltage reg since it had continuity between the outside legs, now I'm looking at replacing the hot. fuse is still good. what else should I be looking at after shorting a chassis out to the frame?
 
yup all 6 of them the two in the degauss circuit as well. D 501-506

your two vertical transistors also. Q 302-303

and the big wite resister in the corner that sticks straight up. R313

and the other wite resister one along that line. R363

and R355 and R506.


Peace
Buffett
 
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Ok I got it out of HV Shutdown. I replaced R313, R363, R506, R355 and I got this image:

f5c0a79d.jpg


i then started adjusting the Horizontal hold pot and the screen went black. Monitor is still on, but I lost image

Thoughts?
 
looks like one of your vertical transistors is fried.

you will have to measure them to find out.

Q302-303

Peace
Buffett
 
Just to be safe I replaced Q302 & Q303 even though they tested good. Not that I really know what they're supposed to measure lol but there's no continuity between any legs, and they measure 9.+ one way and 5.+ the other way. The ones I swapped out measured the same.

Still the same

I definately have HV, you can hear the monitor is on, there's neck glow, and there's a good pop on discharge, but I notice there's no static at the front of the tube.

Sucks I had an image and when I adjusted horizontal hold it cleared up and I could see the game, and then black screen.
 
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What's your B+ voltage?

If this is where you test B+

09f660b6.jpg


then it's 0 :(

Negative on the metal frame, and positive lead on either blue or purple connections I get 0.

I must not be checking it right cause I just checked a working chassis and it also reads 0.

Should I have the DMM set to DC?
 
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yes, set the meter to DC

I just tested 5 different chassis, and I can't get a reading on any of them. I just get 0. Must be doing it wrong

You put the black lead on the metal wall and the red lead is used to check both legs of the resistor where the wires are soldered to?

Seems so simple but I just get 0 on every thing

DMM set to DC 200 range, I got another DMM with Auto range and both give me nothing
 
black lead to the frame that holds the tube.

red lead to the big resister leg's hanging on the wall of the chassis.

Peace
Buffett
 
black lead to the frame that holds the tube.

red lead to the big resister leg's hanging on the wall of the chassis.

Peace
Buffett

I'm an idiot. I guess it has to be checked while the monitor is on LOL

I got 168.4 on one side, and 169.4 on the other.

Is this too high? Or is this right?
 
you will get it eventually;)

that is two high.
you are in HV shutdown.

check the trace from the center leg of R313 to the #2 leg of the VR to see if you have continuity.

then so we can see where you are at.

realist/summarize all of the things you have checked and replaced since the time of the accident.
and what the readings are.

Peace
Buffett
 
you will get it eventually;)

that is two high.
you are in HV shutdown.

check the trace from the center leg of R313 to the #2 leg of the VR to see if you have continuity.

then so we can see where you are at.

realist/summarize all of the things you have checked and replaced since the time of the accident.
and what the readings are.

Peace
Buffett

R313 has 2 legs, did you mean R363? R363 has a middle leg

From the 2nd leg of the voltage reg to the middle leg of R363 I have continuity.

From the 2nd leg of the voltage reg to one of the legs on 313 I have continuity

Is this good or bad?
 
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no i said R313.

it is the tall wite resister.

the center leg of it that is closest to the board is the furthest point of the circuit of the 130v rail.
measure between it and the #2 leg of the VR to see if you have continuity.

if you don't then you need to find out why.
mabye a jumper is bad or got blown apart when it came in contact with the frame.

Peace
Buffett
 
no i said R313.

it is the tall wite resister.

the center leg of it that is closest to the board is the furthest point of the circuit of the 130v rail.
measure between it and the #2 leg of the VR to see if you have continuity.

if you don't then you need to find out why.
mabye a jumper is bad or got blown apart when it came in contact with the frame.

Peace
Buffett

K I got it. There is continuity.
 
OK good your 130v rail is good.

next couple questions.

do you have continuity across.

TH501 test in circuit.
C501 test in circuit.



test theses diodes

D501-506 test in circuit.
D302-303 test in circuit.
D306 test in circuit.


test theses resistors out of circuit lift one leg.

R310-315
R503-506

some of those parts are in the power supply section and some of them are in the vertical section of the chassis.


Peace
Buffett
 
OK good your 130v rail is good.

next couple questions.

do you have continuity across.

TH501 test in circuit.
C501 test in circuit.



test theses diodes

D501-506 test in circuit.
D302-303 test in circuit.
D306 test in circuit.


test theses resistors out of circuit lift one leg.

R310-315
R503-506

some of those parts are in the power supply section and some of them are in the vertical section of the chassis.


Peace
Buffett

Tomorrow Morning I'm all over this. Best time to work on this stuff is when the wife and kids are sleeping!

Thanks for all your help Buffett.
 
no prob:)

let's hope one or more of theses parts is the culprit.
if not then it gets a little more involved in tracking down the issue.

if any of the parts show out of tolerance by more than say 10% i would possibly replace them.

if any of the big wite resisters are off more than 1ohm to 1.5ohm's then the chassis will not work.

also check for cracks in them as well.

Peace
Buffett
 
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