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Troubleshooting a WG 25k7191 no picture blowing fuse
joej85a:
--- Quote from: grantspain on March 20, 2020, 04:22:56 am ---any one of the poly caps and the diode around the deflection header will cause the fuse to blow immediately
using this method will prove your b+ supply is correct and there is no issue in the regulation circuit
its the first thing i do on 7000 series chassis when they come in for repair
make sure you use a anti surge fuse also
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Thanks so much for this. Where is the easiest place to isolate the b+? Just pull a leg on the VR?
joej85a:
--- Quote from: princess prin prin on March 20, 2020, 10:14:16 am ---1) Suck solder off pin 2 of the flyback and make sure the pin is no longer touching the pad around it.
2) Measure resistance across pin 1 and 3 of the flyback. Zero ohm/short? If so go to 3.
3) Suck solder off middle pin (COL) of the HOT and here too make sure the pin is no longer touching the pad around it.
4) Measure resistance across pin 1 and 3 of the flyback. Zero ohm/short? If so go to 5.
5) Desolder C36.
6) Measure resistance across pin 1 and 3 of the flyback. Zero ohm/short? If so go to 7.
7) Desolder D18 and C69 and test them out of circuit.
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Prin, thanks for this awesome walk through. Currently my VR (IC4) and the HOT are out of circuit. Do I need to reinstall them for the above test?
Thanks all!!!
princess prin prin:
The B+ is isolated by sucking solder off pin 2 of the flyback (well it still goes to the neckboard but not relevant). For a bulb test you can connect the bulb to the small pad near pin 2 of the flyback and to a ground point (big heat sink for instance). To do the things I said it doesn't matter if IC4 is in or out. For the bulb test it needs to be in. The HOT can stay out for these tests.
joej85a:
great, thank you for the clarification. I will try the bulb trick and see what I get.
With both the IC4 and the HOT out of the board, I do NOT get a short between pins 1 and 3 of the flyback. I did verify that leg 2 is indeed isolated.
So... No short there, anything else to check before moving to the bulb test?
Thanks again everyone for the expertise.
joej85a:
Gentlemen!
I feel like some progress was made today. At your suggestion I did the bulb test, here are the details.
1. Isolated pin 2 of the Flyback, verified it was isolated.
2. Re-installed the VR (IC4)
3. Put in a new fuse
4. Did NOT reinstall the HOT
5. Attached the positive of the bulb lead to the small pad beside the leg 2 pad of the isolated Flyback
6. Attached the negative of the bulb lead to the ground plain
Installed in the machine, hooked everything up except the degausing lead, and powered it up. The bulb came ON nice and bright, and it did NOT blow the fuse. So with that result, I can verify the VR is working and I am getting High Voltage to the flyback correct? Suggestions on where to go now? Re-install the HOT and do the bulb test again? Thanks all for the help so far, I am excited.