I get the OSD and audio but no video signal from the main tuner just a blank raster. Screen voltage is OK. I get video in the PIP window but when I swap pictures the main screen stays blank and only the audio changes. The jumper bewtween pins 7 & 8 of the fly is good. Thanks for any help. Mark Affordable TV Repair
Was the old fly arcing ? If so it probably damaged the video circuit. The way PIP is accomplished in alot of sets makes it immune to ABL, which is the path by which the fly can do any damage. Even more common is the OSD not being affected by ABL.
With a print you're looking for the pin of the fly at the bottom end of the high voltage secondary. Without a print you're looking for a pin on the fly with a cutout in the PC board to isolate it. This is so if the fly secondary arcs it won't cause a carbon track on the PCB and it also lessens the possibility of fire. There should usually be a reasonable positive DC voltage there. Some older sets would have the B+ on that pin and be resistored down for control of the video, but newer sets use dynamic ABL that is not clamped in normal operation. If you see 0V or a negative voltage there you are very close to the problem.
Once you run it down and get your video back, view a high contrast fast moving scene with the picture cranked. You might even want to temporarily crank up the sub contrast, which you of course return to the old setting when you're done.
What you are looking for then is compression and rarification of the raster lines. This dynamic ABL is used for sweep correction. On a direct view it usually goes to the vertical and video. Some projection sets also send it to the E-W pincushion as well and sometimes the integration network is a bit complex.
If you lack a print, get the datasheet for the jungle (LA7612 ?) and work back from there as well. While you might have a shorted cap near the fly (in the circuit) it is also possible it zapped something that either amplifies or buffs the ABL line. The first check I would do is the resistance from the ABL pin to ground. If it's shorted start unsoldering stuff from it, or if you happen to have a low ohms meter you can find it that way.
In a nutshell, I'd say it's a 99% chance or better that the problem is in the ABL somewhere. I'd go there unless you don't have sync. In case you don't know how to test for sync, the OSD will move if you remove the input signal. Just FYI if you don't have any OSD you turn up the G2 so you can see retrace lines and watch their behaviour when you apply or remove a valid video signal. You might not have to even bother, if the PIP image is stable you got sync usually.
I hope I pointed you in the right direction, good luck.
JURB
PS ; I gotta try to help you save this beast, have you seen the new shit they're building ? What a nightmare.
JURB
ElectronDepot website is not affiliated with any of the manufacturers or service providers discussed here. All logos and trade names are the property of their respective owners.