[TechAssist] Re: JVC TV model AV27CM3- top half of screen stretchedwith foldover [SECOND POST]
- From: al <al@xxxxxxxxxxxxxxxxxxxx>
- To: techassist@xxxxxxxxxxxxx
- Date: Mon, 07 Oct 2002 15:34:57 -0400
gARY,
I have a close schematic(?)Does yours use a LA7837?HTHAY? al
Al Leatherman
alleathe@xxxxxxxxxxxxx
973-361-5796
Mine Hill, NJ. 07803
http://WWW.ALS-TV.NET
----- Original Message -----
From: "Gary McCartney" <number63@xxxxxxxxxxxxx>
To: <techassist@xxxxxxxxxxxxx>
Sent: Monday, October 07, 2002 3:19 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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- » [TechAssist] Re: JVC TV model AV27CM3- top half of screen stretchedwith foldover [SECOND POST]
