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Author Topic: WG K7191 issues  (Read 2316 times)

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retrocat

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WG K7191 issues
« on: March 18, 2021, 08:55:37 pm »
i have a wg 25" k7191 i bought that was blowing fuses.

what i've done:
replaced electrolytic capacitors (cap kit), diodes (d19-d22), flyback, HOT, VR

i got it running but the screen had horizontal collapse.
i checked the yoke and it seemed okay, and resoldered the joints on the horizontal width coil.

my board (P538) has these metal film caps on the bottom that look pretty bad, could these be the cause of the problem? i can't seem to find any images online of a board with 2 caps on the bottom like this, but from researching i suspect they are C36 and C69? the markings on one of them are all but gone so i cant figure out the value.

retrocat

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Re: WG K7191 issues
« Reply #1 on: March 18, 2021, 09:56:55 pm »
also looking at this closer it appears to be a broken trace? there is no continuity between the 2 points marked with yellow

retrocat

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Re: WG K7191 issues
« Reply #2 on: March 18, 2021, 10:57:02 pm »
after looking at a bunch of stuff online i think i've figured it out.

i think the cap in the top of the photo is c69 and the bottom one is c36.
whoever put the c36 cap on also left the original 4 legged one on the top side of the board. so i think i need to remove them both and replace that one the proper way.
when i fixed the broken trace the fuse blew again.
i then found c37 is shorted which i think is the cause of the blowing fuse. i am going to replace it, c36, c69, and c38 while im at it.

grantspain

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Re: WG K7191 issues
« Reply #3 on: March 19, 2021, 02:40:20 am »
the 4 legged cap needs to stay in as long as it reads ok, that looks like a factory mod
you should replace c37 if its bad and check d18

Zebidee

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Re: WG K7191 issues
« Reply #4 on: March 19, 2021, 03:08:21 am »
It is quite common for those brownie caps to be added to a chassis to adjust horizontal width in particular. Capacitors in parallel add capacitance, and an easy way to add a cap is to put it under the board. If not added in the factory, it might be that someone has changed the CRT at some point and modded those caps to tweak the horizontal width.

So, I wouldn't remove them yet unless they test bad. Follow Grantspain's advice first.
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retrocat

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Re: WG K7191 issues
« Reply #5 on: March 19, 2021, 02:46:15 pm »
good info.
 i'll pull the c36 and check if its ok. what should i do if its bad? replace it like this http://www.thegleek.com/bobroberts/csc.html and keep the one on the bottom as well?

Zebidee

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Re: WG K7191 issues
« Reply #6 on: March 21, 2021, 12:24:16 am »
Brownie caps don't fail often like electro caps do. If it is bad you can replace with a single cap of the same type and same combined value (you'd need to read and interpret the cap codes, add the values, replace with cap of that total value or as close as possible - there should be a little wiggle room).
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retrocat

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Re: WG K7191 issues
« Reply #7 on: March 27, 2021, 12:17:20 am »
i got it!
replaced the voltage regulator, c37 and c38, all tested bad.
c36 and c69 tested ok so i left them alone.

now i have a new issue, i cant get the vertical position right. it doesnt want to take up the whole screen, and its getting squished at the bottom as well if i move it down too far.

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Re: WG K7191 issues
« Reply #8 on: March 27, 2021, 02:12:09 am »
Well done!

Check pots (vertical of course). May as well check your B+, as you've changed that voltage regulator. Also check voltage to your vertical deflection IC. If it is wrong then you might have a failed or failing support components (resistors, caps) nearby.
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grantspain

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Re: WG K7191 issues
« Reply #9 on: March 27, 2021, 02:59:25 am »
and give the 50/60hz pot a little tweek

retrocat

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Re: WG K7191 issues
« Reply #10 on: April 11, 2021, 05:49:13 pm »
Well done!

Check pots (vertical of course). May as well check your B+, as you've changed that voltage regulator. Also check voltage to your vertical deflection IC. If it is wrong then you might have a failed or failing support components (resistors, caps) nearby.

how do i check voltage to the vertical deflection IC?