[TechAssist] Re: JVC TV model AV27CM3- top half of screen stretched with foldover [SECOND POST]
- From: "Jim Myers" <jr.myers@xxxxxxxxxxx>
- To: <techassist@xxxxxxxxxxxxx>
- Date: Mon, 7 Oct 2002 15:44:49 -0500
Gary, I have the 27CM4.pdf if you want to give it a try, it uses LA7837 but
I think the pinout is the same. I can "beam" it to you if you want.
Jim Myers
Since 1972
Telrad Electronic Services Co.
Fort Wayne, IN 46815
jr.myers@xxxxxxxxxxx
260-432-4486 Fax and Voice
Fax is always on
----- Original Message -----
From: "Gary McCartney" <number63@xxxxxxxxxxxxx>
To: <techassist@xxxxxxxxxxxxx>
Sent: Monday, October 07, 2002 2:19 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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