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Troubleshooting a WG 25k7191 no picture blowing fuse
princess prin prin:
When you do a bulb test you should also check the voltage. I suggest to check it on R101: on one leg it should be 130V and on the other 12V. Also, before putting the HOT back in circuit test it with the multimeter in diode setting. A good HOT will give readings as in the picture below (they don't have to be exactly the same but in that range). Reversing the leads (e.g. red on collector, black on base) will give OL (or whatever it displays when the leads don't touch anything). Across base and emitter you only read 40-50 ohm.
joej85a:
--- Quote from: princess prin prin on March 21, 2020, 05:08:11 pm ---When you do a bulb test you should also check the voltage. I suggest to check it on R101: on one leg it should be 130V and on the other 12V. Also, before putting the HOT back in circuit test it with the multimeter in diode setting. A good HOT will give readings as in the picture below (they don't have to be exactly the same but in that range). Reversing the leads (e.g. red on collector, black on base) will give OL (or whatever it displays when the leads don't touch anything). Across base and emitter you only read 40-50 ohm.
--- End quote ---
Thanks Pin, I will check the voltage and report back. Also, I am checking my HOT as suggested and using 2 different meters I get "566" from B to C, and "594" from C to E, OL when reversing the leads, and 53 ohms across B to E. There is no decimal before the numbers but I am wondering if the meters just dont have decimal or it is measuring in millivolts?
I tested the replacement HOT I ordered and get "564 from B to C, then "586" from C to E, OL reversed, and 43 ohms across B to E.
Lastly, I noticed on my schematic of the 7191, the factory VR is a STR30123. When I got the board, it had a STR30130 in it, so that is what I replaced it with. Curious if that could be causing issues.
Again I will test the voltage and report back! Thanks!!
joej85a:
Okay, back with the results, I am definitely having some kind of High Voltage issue.
I hooked everything up, powered it up, light bulb came back on, and I tested voltage on both sides of R101. I have 12.4v on one side and 154.8v on the other. From the schematics it looks like it should not be more than 130v. I am assuming this is one of the issues I am having. Could this be due to the 30130 instead of the 30123? This is a new VR.
Also, as I was testing, something started smoking, it looked like it was coming from either R99 or R96, but the bulb did not go out. I immediately unplugged the power.
Visual check of R99 there may be some staining or oil on the side, hard to tell what its from. R96 looks fine visually.
Thoughts?
grantspain:
if you have a str30130 its a 25" chassis
in any case b+ should be 130vdc with that ic, if you loaded the b+ line correctly then your regulator ic is bad
joej85a:
--- Quote from: grantspain on March 21, 2020, 09:24:57 pm ---if you have a str30130 its a 25" chassis
in any case b+ should be 130vdc with that ic, if you loaded the b+ line correctly then your regulator ic is bad
--- End quote ---
Thanks for the info. Aggravating as it is a brand new one, but my guess is that there is something else going on, that must have killed the new one. I suppose the best next step is to order a new one, install and then do the bulb test again.
Along those lines, to do the Bulb Test, is it okay to just hook power up (from the isolation transformer) to the chassis board to do the test, or does it need to be hooked to the yoke and grounded to the screen ground, etc, etc?