WG K7500 27" blown resistor, maybe more

[kayoteq]

Not a big priority, but would like to get this working again. A monster 27" with a Hitachi tube.
Powers up okay, no odd noises, but..

here's a composite of the factory photo showing it's current state.. width pot will adjust my 'line'.


Resistor R402 is a crispy critter. Had to get the schematic before I even knew what resistor it was.. the label's burnt away.

Figure on getting in a cap kit, reflowing everything, and fixing that resistor, but there's always the issue of 'what made the resistor toast?'
is the failed section responsible for the current minimalist display, or a indication of one of the common failures?

Thanks.. I do read the recommendations here, but this was dirt cheap. Best to learn on your own stuff before a client's..

[lenub]

I have a wg 7801 13" with the same issue. Do you know what resistor on this board would cause the same issue. I waiting on a cap kit and will reflow what looks bad but i had a feeling that the cap kit wasn't going to fix my problem
   thanx

[grantspain]

vertical frame collapse
most likely culprit is the vertical frame ic
http://www.wellsgardner.com/pdf/repair/K7500.pdf

this shows all the likely problems

[lenub]

had a spare ic3  ic vert output and changed it out and no help same thin line
 is there a cap that would cause this?
 

[kayoteq]

"NO VERTICAL SCAN  D302, R402, U601, U701, R303,T700, D603 R627, C610, C603    HORIZONTAL LINE CENTER OFSCREEN"
No mention of the chip.. but yeah, figured it was the common problem. Guess that's why the PO went for a complete replacement.

Me and my friend were joking about the 'you may have.. vertical frame collapse'..
"but doc.. can it be cured?"

All WG mentions on-line is the flyback. the monitor is 'obsolete'. That's 99% of my collection.

And also, sorry for not searching the forum adequately, once I searched 'vertical IC' it came up all sorts (unfortunately)
rather than my specific model. Doh! I see why the complaints. It's two pages of results.


That's a real chronic issue. At least Apple extended their warranty on their monitors that had flyback issues. (got mine fixed twice, then had an accident that
busted the neck- being a packrat techie, I still have the case/chassis..)

Again, not a high priority, nor a big investment. But hate to have all that display technology sitting around when it could be used to make a giant cab.. scale up a Pac-Man to
a 8-foot tall monster

Ah! found the chip (maybe, will have to dig out the schematic again)
at  American Gaming: 086X0366-001     $32.10     
Alternate (read: cheaper) sources available? May just do an old-fashioned solder tweak on the thing and cross fingers.

Back in the box it goes till parts are gotten.. Makes a great (big) piece of furniture.

[grantspain]

u601=tda1771  vertical deflection ic,it should be a few dollars

@lenub , you may find a safety resistor or cap on the voltage feed for that ic.
just go through all the suggestions in that repair guide
i would look for a problem with the +25v,there is a cap but i can't make out the number too well on the schem maybe its C608 0.1uf 100v,you should meter around there to see if you have the +25v present
also check +25 at tp 205
also check your remote board for broken vert size pots or bad solder

[sarge]

First off you need to check your 25VDC flyback derived supply that powers the vertical ic.  You can check this at TP205.  Since R402 is already burnt, there probably will not be nothing there.  More than likely you have a bad U601 (vert output ic) and/or a bad D603 (which is right behind the vertical IC) that more than likely went bad due to failed electrolytics in your vertical section.  My suggestion is to replace R402 and BRIEFLY power on and off the monitor and see if the resistor gets hot to the touch.  If it does then change U601 (TDA1771), check and replace, if necessary, D603, and replace, at least, all the 600 series electrolytic capacitors.  If it doesn't get hot then check your vertical supply voltage.  If it's not there, check D302 and R303 which are near the flyback.  If you have to replace either of these items, you'll want to do the quick power on test to see if R402 gets hot again or you may end up replacing them again.

[kayoteq]

(much relief) yes, yes.. that chip runs $2.21. Don't know what that thing is at the AG site..  Coolness. I don't want to pay a lot for this muffler.
That and the cap kit will triple my investment. Back in the box it goes, get the parts together, tackle it later..

Thanks for the translation from WG parts-speak. (U601?)- I'm thinking okay, D=diode, R=Resistor, U="Flux capacitor, rating 1.21 jiggawatts?"
I should just go ahead and print those PDF schematics out and put it in the box for when the parts are ordered/come in..

 Now on to the dead digital one. Based on my cache of searched WG threads, I'm already got a guess before I even get it out of the box...
Edit: I was wrong.. Not dead, not eprom crazy. some convergence issues, some blobs of discoloration, but it powered up,
PC video displays..just needs some tweaking. Happy camper. 4 bucks well spent.