K7401 - Bad Capacitor?

Brosiedon

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Pulled and checked several components on my k7401 today (HV shutdown clicking and no B+, lightbulb test failed, 0v at B+ test point). Hot tested good, diodes per Fromms book good, U101 unsure, R108 was high. Ran into three caps in the Horizontal Output region to check per Fromm's book that read open both directions out of circuit.

Does this mean they are all toast?

Also, I am trying to identify what the attached one even is. I haven't been able to decypher the top line. Thanks a bunch for any help!
 

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You need the power supply working first!

If theres a short on the B+ trace to the HOT, the power supply will

tick, remove the short first then use a bulb to see if the PS is regulating correctly.

a bulb is used for over voltage or over current, you need voltage there first!

you need to test the B+trace for any low ohms then lift one end of each suspect.

or jumper between a trace to isolate the low ohms to ground, that's if you have a short.

a simple resistance check to ground on the B+ will tell the story.

It will point you straight to the suspect then you take it out of circuit and test

the trace again if high ohms the you have the bad part in your hand.

You don't need a HOT or flyback to see if the power supply works.

If no shorts on the B+ then you don't look at the HOT or any high voltage part

you fix the power supply.
 
You need the power supply working first!

If theres a short on the B+ trace to the HOT, the power supply will

tick, remove the short first then use a bulb to see if the PS is regulating correctly.

a bulb is used for over voltage or over current, you need voltage there first!

you need to test the B+trace for any low ohms then lift one end of each suspect.

or jumper between a trace to isolate the low ohms to ground, that's if you have a short.

a simple resistance check to ground on the B+ will tell the story.

It will point you straight to the suspect then you take it out of circuit and test

the trace again if high ohms the you have the bad part in your hand.

You don't need a HOT or flyback to see if the power supply works.

If no shorts on the B+ then you don't look at the HOT or any high voltage part

you fix the power supply.

Thank you very much for the help!

Alright, so either I just don't know what I am doing (likely) or I am too dumb to understand. Do you mind if I walk myself through this here and you confirm I have this right?

-Bulb test means nothing until you havevoltage at your B+
-To find my power supply issue I need to measure the resistance from my B+ trace (so TP202 for B+ should work) to ground. I am expecting a small ohm reading, I just got an open circuit from that test.
-Had I gotten a low ohm reading I should have pulled each leg of other components on that trace one at a time and retested. Once I receive a high ohm reading I know which component is shorted.

Is this correct? Or do I specifically need to do the same thing to the three traces touching the HOT?
 
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yes you need B+ at the bulb to verify the PS works on the chassis.

you will be able to adjust your B+ using the bulb.

pull the J12 jumper end closest to the flyback and put your red lead on it for measuring the B+, the black can be attached to the vertical IC heatsink.

once you have that you can reconnect the PS back up and see if your chassis ticks or comes to life.

if it still ticks, you either have a short in the Horizontal section or the startup circuit has issues.

you can have both issues, but it does not happen often.

if you need parts i have them.

if you hit a brick wall and need it fixed, your welcome to send it in.

Peace
Buffett
 
yes you need B+ at the bulb to verify the PS works on the chassis.

you will be able to adjust your B+ using the bulb.

pull the J12 jumper end closest to the flyback and put your red lead on it for measuring the B+, the black can be attached to the vertical IC heatsink.

once you have that you can reconnect the PS back up and see if your chassis ticks or comes to life.

if it still ticks, you either have a short in the Horizontal section or the startup circuit has issues.

you can have both issues, but it does not happen often.

if you need parts i have them.

if you hit a brick wall and need it fixed, your welcome to send it in.

Peace
Buffett

Thank you Buffett! I believe I see what I did wrong here. I tried this test some time back, but I pulled the jumper and proceeded to test my B+ from the test point again. Obviously I wouldn't get anything from there. I will put stuff back in and try it again!

A question on testing these boards with out a tube, for increased access. I've read on these forums that for safety, or I assume to mimic the glass of the tube that it is worthwhile to place the anode cap in a glass jar to isolate it. Can this be just any mason jar? Or does it need to be on the thicker side? I assume discharging it will be required before removing the anode back out of it?

Thank you again!
 
I would remove the monitor unless its in a arcade.

At shop or home I would pull the monitor out

lay it on its side to access the bottom if you like it won't hurt anything.

or remove chassis fix and re-install it and test it good before

putting back in game.

being lazy will make you put the chassis in and out a few times.

and could create more problems.

Using any other to trouble shoot chassis requires a good experinced skillset.

the yoke needs to be connected at all times and if your next to the yoke

you don't need to remove the hv cup.

the 5 watt resistor on the left side gets bad connection and could be the only reason

which just needs re-soldering.

if you have no B+ if no shorts on the B+ trace.

I said if the B+ has low ohms then remove the HOT or any suspect on that trace

and recheck the B+ trace again. to confirm you have removed a short

from the B+ if high ohms then there is no short on the B+

and you should have voltage if none then you need to fix the power supply first!!
 
Thank you guys! I will see if I can get a bit further on this tonight!
 
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