[TechAssist] Re: jvc c13210s vertical? la78xx circuit
- From: Gary McCartney <gary@xxxxxxxxxxx>
- To: techassist@xxxxxxxxxxxxx
- Date: Thu, 12 Aug 2004 14:57:52 -0400
Wayne, I seem to recall either JVC or Panasonic (can't remember which)
had white paint on the pcb around the vertical IC pins, leaving very
little area on the solder pads to make connection. If it is JVC I'm
thinking of, try scraping some of the white paint off the board so you
get better connections to the IC pins.
Gary McCartney
McCartney Electronics
Guelph Ontario Canada
Est. 1984
email: gary (at) number63.ca
Wayne Vanaman wrote:
> 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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