G05-802 Monitor keeps blowing F600

Cmiller

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I am struggling to repair my G05 on my Asteroids game and would appreciate some advice. I just installed a cap kit and replaced the following additional components:
D607 & D708
Q605 & Q606
Q705 & Q706

I tested every other part (mostly in circuit) and they all seemed OK as far as I could tell. The sad part was that it worked for a while. I was feeling pretty good that I got it working after all of component testing and research. I played a few games and ran it for about 45 minutes without issue. I even had shut it on/off a few times during that period. On the last time, I opened the coin door to go into test mode. As expected, the interlock killed the power. So, I pulled it out the interlock and got into test mode just fine. I exited test mode and things continued to work. Then I shut the door. Upon doing so, the game restarted (as expected), but the monitor never came back on. I checked and found F600 was blown and the spot killer was on. Hoping it was a fluke, I replaced F600 and it immediately blew again. FYI: The game plays fine if I plug it into my V2000.

This is the symptom (F600 blowing) that caused me to recap and check for other components. So, I'm back to square one. Any suggestions on what to try next?

I read something in the B&W vector guide about testing the voltages from the frame to F600 and F700 without the yoke and XY inputs connected. It says it's supposed to be zero or less than 10 volts...if not Q706 may is shorted. I just replaced Q706. I'll pull the chassis (again) and see if Q706 is shorted. If so, what could be causing that? I don't want to give up, but after testing every component and having it actually work for a while, I'm pretty disheartened at the moment. I thought I'd be moving the game to my basement tomorrow. Now, it's still broken in the garage :-(.

Thanks, Chris.
 
Test all of the small signal transistors (there are four per axis, with the TO-92 packages). Then the two that are bolted to the heatsinks (for the axis in question). Then the frame transistors (bottlecaps). Chances are you just missed one of them.

Make sure you have good mica (or better yet silicone rubber/silpad) insulators on the bottlecaps.
 
Thanks. I will look at those as you recommended and update this post.

I forgot to mention I did replace all of the bottle cap frame mounted transistors as well and make sure they were not shorted to the frame. I'll test them again anyway.

This does still leave wondering why it worked for a short while. If there is a bad transistor I missed, wouldn't the F600 have blown from the beginning? How could that happen?

Depending on what I find (or don't) I may be sending this chassis your way. I'm worried I'll find one of the ones I replaced is bad again.

Thanks for sharing your expertise and time.
Chris.
 
Is this a new game to you? (i.e., did it ever work?)

Another possibility if you got it form someome else is that potentially someone did a prior repair and put wrong value parts in it. I see this every so often. Check any other previously replaced parts, to make sure they're correct.

But yeah, if you want to send it in, let me know.
 
The game is somewhat new. Had it for several months. The monitor worked when I got it, but then failed last month.

I'll check the parts. If any of the parts I replaced test bad or I see anything else unusual, I'll Be sending it to you.

Thanks.
 
I finally got some time to test the transistors you suggested. It turns out some of them are bad (even the ones I replaced). It's time to throw in the towel and send it to you (look for the PM soon). It's frustrating that it worked for a short while and now the parts I replaced are testing bad. Thanks again for the guidance. Maybe I'll have better luck on my next chassis.
 
One last post on this...

Is it possible the PCB is sending to many volts to the monitor and creating this problem? What would the normal range of AC volts I should expect to see from the XY Output section of the PCB? I'm just curious as I believe I've read another post about the PCB being the root cause.

PM sent regarding repair

Thanks.
 
I finally got some time to test the transistors you suggested. It turns out some of them are bad (even the ones I replaced). It's time to throw in the towel and send it to you (look for the PM soon). It's frustrating that it worked for a short while and now the parts I replaced are testing bad. Thanks again for the guidance. Maybe I'll have better luck on my next chassis.


One of the tricky things about these monitors is that the parts that are blown are often secondary failures (i.e., symptoms of the actual failure), and not the root cause.

So people try to fix them, replace the parts they measure as bad, fire them up, and they work again briefly until the replaced parts fail again. So it's necessary to find and fix the actual root cause (which is usually something small and hard to find), and also everything secondary, else you'll chase your tail if you miss any one thing.

It's unlikely you're getting overvoltage from the brick. You can test the DC output of the rectifier, which should be between 35 and 40V (I forget which exactly, as the v2000 and G05 are different), and you should get -35 or -40V on the negative side as well. But you may find one of them is off, if things are blowing (again, it's hard to tell what is causing the issue, and what is a result of the issue.)

But yes, I can fix it. I'll reply to your PM with my info.
 
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