[TechAssist] Re: JVC TV model AV27CM3- top half of screen stretched with foldover [SECOND POST]
- From: "LeRoy Westlund" <llw@xxxxxxxxxx>
- To: <techassist@xxxxxxxxxxxxx>
- Date: Tue, 8 Oct 2002 09:58:19 -0600
Not much chance of that, Gary.
This set is famus for bad connections at the Vert. IC,(even though they look
good),...so you may want to double check for a broken trace at that point.
LLW
LeRoy Westlund
Westlund TV & Electronics " It's such a pretty world
93 North Main today !....
Centerfield, UT 84622-0087 Look at the Sunshine. "
Ph./Fax 435-528-3822 :-)
mailto:LLW@xxxxxxxxxx
-----Original Message-----
From: Gary McCartney <number63@xxxxxxxxxxxxx>
To: techassist@xxxxxxxxxxxxx <techassist@xxxxxxxxxxxxx>
Date: Tuesday, October 08, 2002 7:26 AM
Subject: [TechAssist] Re: JVC TV model AV27CM3- top half of screen stretched
with foldover [SECOND POST]
>
>Leroy, thanks for researching that for me. Unfortunately it didn't solve
>it. Someone sent me a partial schematic for a similar model, so
>hopefully that will help me notice something. The waveforms I measured
>seem to check out against the print, so thats good, except for the blip
>on my output waveform. Do you think there is any chance that my brand
>new generic LA7838 could be causing the exact same symptom as the
>original IC?
>
>
>Gary
>
>
>
>
>LeRoy Westlund wrote:
>>
>> Gary,
>> I see that you didn't list C422 as one you have checked.
>> It is a 1ufd. @ 35 volts (Tentanilum).
>> Worth a try, maybe ?
>>
>> HTH,
>> LLW
>>
>> LeRoy Westlund
>> Westlund TV & Electronics " It's such a pretty world
>> 93 North Main today !....
>> Centerfield, UT 84622-0087 Look at the Sunshine. "
>> Ph./Fax 435-528-3822 :-)
>> mailto:LLW@xxxxxxxxxx
>>
>> -----Original Message-----
>> From: Gary McCartney <number63@xxxxxxxxxxxxx>
>> To: techassist@xxxxxxxxxxxxx <techassist@xxxxxxxxxxxxx>
>> Date: Monday, October 07, 2002 1:17 PM
>> Subject: [TechAssist] JVC TV model AV27CM3- top half of screen stretched
>> with foldover [SECOND POST]
>>
>> >
>> >I still haven't solved this set.
>> >
>> >Measured B+ to vertical chip. I get 28.7V with 1.5 V p-p of ripple.
>> >Replaced D534 rectifier and C534 filter cap but no change in ripple.
>> >Also measured output of 12 V regulator I changed earlier. Measured
>> >11.94V, with no noticable ripple. Scoped input pulse to vert. chip at
>> >pin 2 and got nice clean square wave at 8V p-p and very high duty cycle,
>> >maybe 95%. I don't have waveforms or schematic in print to verify my
>> >measurements to be correct. Scoped vertical output waveform on pin 12
>> >and get 55V p-p pulse with a blip in the slope which doesn't look
>> >normal. I drew a picture of this and posted it for you to view:
>> >
>> >
>> >http://www.number63.ca/waveform.jpg
>> >
>> >
>> >
>> >Also replaced yoke. I found one in my stock which appears to be the
>> >exact same yoke only out of a Philips set and the connectors were a bit
>> >different. I switched the connectors from the JVC yoke and tried it. No
>> >change in problem. If anyone is interested, here are the yoke numbers
>> >(from the stickers on the yokes). Sorry I don't have record of the
>> >Philips TV model.
>> >
>> >Original JVC yoke: CE20240-AOA
>> >Philips yoke: 362075-7
>> >
>> >
>> >Changed a few more small caps and resistors in the vertical section.
>> >Problem has not improved. Any help appreciated.
>> >
>> >
>> >
>> >Gary McCartney
>> >
>> >McCartney Electronics
>> >7134 Fife Rd, RR 7
>> >Guelph Ontario Canada N1H 6J4
>> >Fax: (519)821-1530
>> >email: number63 (at) inetsonic.com
>> >
>> >
>> >
>> >
>> >
>> >My original message:
>> >
>> >
>> >This is a 27" JVC tV model AV27CM3. No Sams listed but there is one for
>> >model AV27CM4, # 3379.
>> >
>> >The vertical linearity is off all the way from the bottom but once it
>> >hits the center of the screen, it starts stretching so bad that there is
>> >about 3" of foldover.
>> >
>> >Working without a schematic. I have replaced:
>> >
>> >IC421, LA7838
>> >IC422, 12V regulator
>> >ZD425, 75V 1W
>> >C425
>> >C426
>> >C430
>> >C421
>> >C536
>> >C530
>> >
>> >I removed D421 and checked it but I don't know what it is. marking on it
>> >is 3N. It looks like a glass 1W zener but symbol on board shows it as a
>> >regular diode. Checks ok anyways.
>> >
>> >Does anyone have a schematic of the vertical circuit plus hopefully
>> >waveforms?
>> >
>> >Thanks for any help.
>> >--
>> >
>> >
>> >
>> >Gary McCartney
>> >
>> >McCartney Electronics
>> >7134 Fife Rd, RR 7
>> >Guelph Ontario Canada N1H 6J4
>> >Fax: (519)821-1530
>> >email: number63 (at) inetsonic.com
>> >
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>--
>
>
>
>Gary McCartney
>
>McCartney Electronics
>7134 Fife Rd, RR 7
>Guelph Ontario Canada N1H 6J4
>Fax: (519)821-1530
>email: number63 (at) inetsonic.com
>
>
>
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