K7500, I'm really at my wits end with this one..

local413

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Ok, so here goes:

Got this K7500 and another from a dual Crusin USA.. First one had a blown, I mean exploded flyback.. Capped and replaced the fly, all good. Now the second chassis has been a problem.

First time I fired it up a resistor in the center of the chassis smoked.. Ok, replaced that. I then capped it, replaced the flyback, and reflowed solder where it needed it. Fired it up, horizontal line across the screen.

So, I follow the Wells Gardener repair guide and test each component that is listed.. Hell, I even replaced everyone of them.. I also pulled both ICs and replaced with known working ones in sockets.. Replaced U601 too..

Fired it up, horizontal line across the screen..

Ok, great.. Maybe the new flyback is the problem.. Swapped in the old one.. Same issue.. Ok, maybe one of the "known working" parts I swapped in was bad.. Replaced one at a time, same issue. I even tested the yoke (ohm reading for horzontal and vert) .08/1 and 7.2/7.5 so the yoke is good.

So.. I'm about to smash this thing.. What am I missing here?
 
Wish I could be some help so at least I can give you a free bump.

I'm sure you reflowed the neck board when you did your reflowing. (just figured i'd ask)
 
Thanks man, and yes.. Heh, I reflowed the neck board.. Actually replaced the (3) trannies and added larger heatsinks to each one.

Just bummed out with this one.. As I really went the extra mile, by socketing the ICs, capping, new fly, nos remote pcb, etc..

Anyone know if the tranny that's attached to the frame could possibly do this? I tested it and it looks ok.. Just wondering what would happen if I fired it up with the tranny disconnected..

Wish I could be some help so at least I can give you a free bump.

I'm sure you reflowed the neck board when you did your reflowing. (just figured i'd ask)
 
Do you know what that transistor does (Q710)? The answer is in the 7500 schematic from wells gardner along with the vertical and horzontal circuit breakdown and voltages.
 
Do you know what that transistor does (Q710)? The answer is in the 7500 schematic from wells gardner along with the vertical and horzontal circuit breakdown and voltages.

pincushion i think
 
I think there's a Bi Polar cap on that chassis, make sure you (or someone else) didn't switch it with a polarized cap
 
check your resistors just to the right of the flyback.....they are around 1.2 ohms. One of the resistors is either open, or the trace has lost continuity from here to the rest of the chassis.
 
List the parts that you replaced.

The most common causes of vertical collapse are:

- bad U601
- shorted D302
- open R303
- bad U701
- reversed or bad cap in the 600's
- cold solder/crack in the chassis in the 600's
- bad vertical yoke
 
check your resistors just to the right of the flyback.....they are around 1.2 ohms. One of the resistors is either open, or the trace has lost continuity from here to the rest of the chassis.

Bumping this old one that seems to have the same problem as mine.
Guess I will check continuity from r303 outward.



Edit on this one. The post I quoted seems to be virtually irrelevant. The resistors to the right of the flyback lead to one additional point on the chassis, not throughout the chassis.
 
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