Re: identical G05-802 problem with 2 different deflection PCBs

Have you meter'd all your looms for dead shorts ?

Pinx
----- Original Message -----
From: "Colin O'Brien" <colin@onepointzero.com>
To: <vectorlist@vectorlist.org>
Sent: Sunday, November 29, 2009 11:18 PM
Subject: VECTOR: identical G05-802 problem with 2 different deflection PCBs

>
> Hello,
>
> I've been a lurker here for a while, quietly absorbing the insight but
> I've hit a problem that has me (and my limited knowledge) baffled.
>
> I have a working asteroids game board (2 actually), with which I can play
> fine on the scope (also when grabbing the signal from P100 instead of the
> test points)
>
> When I initially got the machine, I had problems with the monitor
> (G05-802) having no horizontal deflection and the spot killer being
> active. After checking the PCB, I replaced a couple of transistors on the
> board a well as the Q708 & 709 chassis transistors.
>
> Upon powering up, I would lose the 2 chassis transistors in question and
> sometimes the F700 fuse. I practically inspected every single component
> on the board, but found no extra faults. I looked for shorts, tested
> voltages (95V at P500, 30-35 VAC coming in at P100 pins 7 & 10, 12kV for
> HV etc) but found nothing that looked suspicious to me.
>
> I recently got a new known working/tested deflection PCB as a
> comparison/reference point, hoping that would help me see what was wrong
> or, at the worst, serve as a working board. Well, no luck there, when I
> plugged it in the spot killer was on and I had no horizontal deflection.
> I guess I can deduce from this that my problem is outside the PCB itself?
>
> Powering it up a second time to take some readings, the spot killer was
> still on but I'd lost the picture, turning brightness/contrast up only
> produced a faint haze towards the top of the screen.
>
> Inspection of the PCB revealed R713 was burnt to a crisp as well as its
> neighbours Q705 and Q706 both being shorted. I checked the chassis
> transistors, they were fine, I looked for shorts in the sockets, plugs
> and cables leading to them but found nothing wrong either.
>
> I replaced the dead components but powering it up now blows F700 when I'm
> lucky or the chassis transistors. I'm weary of powering it up again as I
> don't feel like destroying components for the fun of it.
>
> I'm at a loss now, not sure where to look outside the PCB. Could the yoke
> be at fault? I'm in unknown territory here and would appreciate any
> pointers I can get.
>
> Thanks!
> Colin
>
>
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Received on Mon Nov 30 05:06:54 2009