[TechAssist] Re: jvc c13210s vertical? la78xx circuit
- From: "tvservice" <tvservice@xxxxxxxxxxxxx>
- To: <techassist@xxxxxxxxxxxxx>
- Date: Thu, 12 Aug 2004 14:16:21 -0500
Does this set have D422 75volt zener
if so replace it
Robert
tvservice@xxxxxxxxxxxxx
H & H Electronics Inc
----- Original Message -----
From: "Wayne Vanaman" <Wayne@xxxxxxxxxxxxxxxxxxxxx>
To: <techassist@xxxxxxxxxxxxx>
Sent: Thursday, August 12, 2004 1:06 PM
Subject: [TechAssist] jvc c13210s vertical? la78xx circuit
> I am baffled:
> JVC TV C13210s, no vertical?
>
> Unit turns on, then about 4 seconds later turns off.
> Turning up the screen control showed no vertical deflection.
>
> Replaced IC421 LA7830 with JVC original, D422 75v zener, c424 100uf, c423
> 1000uf. No vertical.
> Changed D421, R423 (V return resistor).
>
> Voltages and waveforms for ic421
> pin 1=0v, ground
> pin 2=8v. This is the output pin, should be 14 volt with 40v vertical
> drive. I have a pulse of about 20v, but instead of the ramp there are H
> pulses about 5vpk.
> pin 3=24v, no pulse, flat DC
> pin 4=.9v drive, negative pulse???
> pin 5=1.2v instead of .6
> pin 6=24v
> pin 7=0v instead of 8.7, no pulses.
>
> Changed jungle ic201 ta1242n, no help.
>
> Micro:
> pin 1 Hsync cals for 3.9v, has about 4v "DC" with H pulses
> pin 2 V-sync, 0v, no pulses
> pin 3, Neck calls for/has 4.7v DC.
>
> The V yoke rings 13 times with the Sencore LC102.
> Applying 100v H pulses to the H side of the yoke shows about 6v 45KHz
> ringing on the V side of the yoke. I tried this on a JVC 27" TV yoke and
> saw the same thing.
>
> I drove the yoke with the vertical from the Sencore TV92 thru the plug to
> see if the connections/yoke were breaking down under load. 40V V drive
from
> the TV92 thru an ampmeter showed 500mA current.
>
> Put 24VDC on the vertical IC and gave it drive-Vertical output. Realized
> that the drive from the Jungle was a negative pulse...went looking for the
> power supplies for the Jungle.
> Pin 9=9V (pif vcc 8.6vdc)
> Pin 13, ground, ohms good.
> Pin 18=3.3v (3.2)
> Pin 26=8.9v (8.8)
> Pin 42=4.5v (dc ref 4.5)
> Pin 46=9v (vcc 8.7)
> Pin 48=9v (sif vcc)
>
> Removed and tested c401 and c402 off of jungle pins 23 and 24.
>
> What in the world am I overlooking?
> This is the basic vertical deflection circuit for TVs using the LA78xx
ICs.
>
> Wayne Vanaman
> Omega Electronics
> 6904 W Fairfield Dr
> Pensacola, Fl. 32506-3310
>
> Wayne@xxxxxxxxxxxxxxxxxxxxx
> WWW.PensacolaTVRepair.Com
>
> 850-456-5995 voice
> 850-458-6369 fax
>
>
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