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Author Topic: Pentranic CH-288 chassis screen white out  (Read 282 times)

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lilshawn

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Pentranic CH-288 chassis screen white out
« on: August 15, 2017, 04:56:18 pm »
Have a pentranic monitor, the monitor worked in the shop... pushed it on the truck...drive to location 30 mins away...dead. (of course) Drag it back to the shop and find plenty of B+ but no switching of the HOT or flyback. search for broken traces but find none.

Traced to failed resistor R331 that feeds power into the HA11235 IC chip. replaced chip and resistor.

Monitor powers on, but now raster is whiting out the screen. can faintly see video. Brightness control does nothing. Screen control on flyback is still factory sealed so it hasn't been changed. checked the brightness pot...wiring... replaced switching transistor (Q108) and checked all the diodes and resistors in the area... all check out good. replaced neckboard with known good, same thing. Issue is deflection board.

B+ is 108v (within spec). "18v" is a little low at 15.8v but not so low as to consider it an issue.

At a Loss where to look from here.

grantspain

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Re: Pentranic CH-288 chassis screen white out
« Reply #1 on: August 16, 2017, 06:47:14 pm »
I don't have a schem but have you checked the video b+, should be around 180v

lilshawn

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Re: Pentranic CH-288 chassis screen white out
« Reply #2 on: August 16, 2017, 07:16:14 pm »
I have a service book for the Makvision version of the chassis (2425... it's a CH-288 chassis as well anyways...it goes under a pile of different names)

it does specify 108 +-0.5vDC for the B+.

schem is available here:

http://www.arcade-museum.com/manuals-monitors/Pentranic%20CH-288%20Switchable.pdf

ed12

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Re: Pentranic CH-288 chassis screen white out
« Reply #3 on: August 16, 2017, 08:17:11 pm »
chk on the cathode of d404 see what u get ?

ed
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grantspain

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Re: Pentranic CH-288 chassis screen white out
« Reply #4 on: August 17, 2017, 11:49:41 am »
I have a service book for the Makvision version of the chassis (2425... it's a CH-288 chassis as well anyways...it goes under a pile of different names)

it does specify 108 +-0.5vDC for the B+.

schem is available here:

http://www.arcade-museum.com/manuals-monitors/Pentranic%20CH-288%20Switchable.pdf

I was talking about the video b+, maybe you would call it video amp voltage-looks like it comes from pin 9 of the flyback.on a lot of chassis if this is missing then you get a bright white screen. I would check r409 and c407

lilshawn

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Re: Pentranic CH-288 chassis screen white out
« Reply #5 on: August 17, 2017, 07:08:57 pm »
I didn't get much of a chance today to look at this... had to run out of town and fix some other stuff. I did quickly check the voltage at D404 and got from 120VDC at startup down do 107 finally settling at 98 once the picture stabilized.

R409 is measuring kinda weird... It seems really high... I'll take it out and do some testing tomorrow

ed12

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Re: Pentranic CH-288 chassis screen white out
« Reply #6 on: August 17, 2017, 09:46:48 pm »
that's what I was thinking
ya 120 is low enough to cause that (g08)
so yes resistor then filter
and good measure says replace with new 1 no matter what

ed
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lilshawn

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Re: Pentranic CH-288 chassis screen white out
« Reply #7 on: August 18, 2017, 01:37:42 pm »
R409 was measuring 230k ohms instead of 3.3 ohms.

despite looking absolutely fine from the outside... no discoloring or damage at all.

Luckily I have like 5 chassis I can rob parts from. Change it out, seems to look okay now. just need to tweak some color settings on the neckboard since I swapped that off too just to be extra sure. NBD.

ed12

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Re: Pentranic CH-288 chassis screen white out
« Reply #8 on: August 18, 2017, 04:20:14 pm »
:)

ed
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