[TechAssist] jvc c13210s vertical? la78xx circuit
- From: "Wayne Vanaman" <Wayne@xxxxxxxxxxxxxxxxxxxxx>
- To: <techassist@xxxxxxxxxxxxx>
- Date: Thu, 12 Aug 2004 13:06:14 -0500
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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