Vectorlist Archives: Re: identical G05-802 problem with 2 differ

From: COLIN DAVIES <colin.w.davies_at_btopenworld.com>
Date: Mon Nov 30 2009 - 08:09:19 EST

I know you said you checked for shorts on the looms.... but I saw no mention of the chassis... So....

Are any of the Chassis Transistors (body or leads) shorted to the chassis iself ?... ( The Screws should be insulated and you need to use a mica insualtor if it were misssing... That would be sure to cause trouble....

Regards, Colin Davies

--- On Mon, 30/11/09, Colin O'Brien <colin@onepointzero.com> wrote:

From: Colin O'Brien <colin@onepointzero.com>
Subject: Re: VECTOR: identical G05-802 problem with 2 different deflection PCBs
To: vectorlist@vectorlist.org
Date: Monday, 30 November, 2009, 11:42

I did in the beginning, but since then I've only re-metered the sections that connect directly to the deflection PCB side without finding anything.
I'll give it another thorough going through just to be sure.

Colin

On 30 Nov 2009, at 11:06, Pinx wrote:

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