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Main => Monitor/Video Forum => Topic started by: shess on April 27, 2009, 09:40:23 pm

Title: Pentranic ch-288 with no horizontal deflection -- FIXED
Post by: shess on April 27, 2009, 09:40:23 pm: So I've got a thin vertical line on my screen and as the computer boots up I can see the colors change on the line, so I know it's getting a picture. I checked the board for broken traces and broken solder joints but found nothing obvious. The board was made in 2000 so I'm skeptical of doing a full cap kit. I looked at the schematic but wasn't really sure what to start with. Any ideas/advice?

Thanks,
Scott
Title: Re: Pentranic ch-288 with no horizontal deflection
Post by: qrz on April 27, 2009, 10:34:47 pm: usually, the loss of h deflection ( vert line) will detune the stage enough to destroy the h output xistor.

what u more likely have is a line extending l-r across the center of screen ( h line ) caused by the loss
of VERTICAL deflection.

schematic here: http://niemandisplays.com/nvd%20ch-288%20cga%20only.pdf
courtesy of Rickn

for starters,
check for B+ at pin 7 of ic3, higher than pin 7 vdc at pin 3
check c393,c398,r336

qrz
Title: Re: Pentranic ch-288 with no horizontal deflection
Post by: shess on April 28, 2009, 06:44:06 am: I checked out Bob Roberts page on monitor orientation and the line is on the shortest axis, so it is a loss of horizontal deflection, not vertical. Are those things you told me to check in the vertical path or horizontal?

Scott
Title: Re: Pentranic ch-288 with no horizontal deflection
Post by: qrz on April 28, 2009, 08:43:22 pm: that was for a more common loss of vert .

hv w/no h sweep should be relatively easy to spot. burn mark
i.e., a cold solder joint that has/is arcing . ( it is a 1200+Vpp signal ;) )

check c908,l902,

qrz
Title: Re: Pentranic ch-288 with no horizontal deflection
Post by: shess on April 28, 2009, 09:25:47 pm: dude, you are my hero. So there was a big hole burned underneath L902 and a resistor was soldered in on the underside. Well the person accidentally lifted the solder point off the PCB, so I just soldered a small wire from L902 to next component inline and now the picture is perfect, thanks again!!!

Scott
Title: Re: Pentranic ch-288 with no horizontal deflection -- FIXED
Post by: qrz on April 28, 2009, 10:24:34 pm: glad u got it going. good job !

the symptom u had described is infrequent compaired to vertical issues....,
and u might be surprised how many folks get confused on sweep direction. ;D

i
i
i no h sweep /hv ok ----------------------- no vert
i
i

for standard crt mount / reverse for 90 degree mount

qrz
Title: Re: Pentranic ch-288 with no horizontal deflection -- FIXED
Post by: shess on April 29, 2009, 09:45:11 am: It can be confusing...I've got another monitor with no vertical that I have to work on...but thankfully I have a flowchart for that one. Last question on the Pentranic...in addition to the hot/neutral wires I see another green wire soldered into ground...does that mean I don't need an isolation transformer for it? I couldn't find anything written on the chassis/tube to say one way or the other. The frame also looks powder coated versus the plain metal on older WG, G07, etc so can that even conduct electricity?

Thanks again,
Scott
Title: Re: Pentranic ch-288 with no horizontal deflection -- FIXED
Post by: qrz on April 29, 2009, 04:39:22 pm: IF the monitor has a SMPS ( switch mode pwr supply ) , the supply's xformer provides the isolation.
no additional iso needed . won't hurt anything to connect one - jus' redundant

qrz
Title: Re: Pentranic ch-288 with no horizontal deflection -- FIXED
Post by: shess on April 29, 2009, 04:41:13 pm: Hmm...the wires go right into the PCB just like my other monitors...so I'm just going to play it safe and use the iso transformer. Thanks.

Scott