Re: A few WG6100 tips and tricks

Oh, Oh... I know this one. There is a 10 ohm resistor at the top of the
pre driver stage that is open. I don't have a schematic so I can't tell
you the part number. It's going to be connected to the MPSU transistors
that feed the output stage. Ultimately, the pre driver stage is broken.

So here's what happening... one side of the pre driver stage is open, so
the output stage is biased to one side. This pushes the vectors off to one
side and makes one of the the 1.5 ohm resistors really hot.

Using a DVM, measure the voltage across each of the 1.5 ohm resistors in
both AC and DC mode. you should see 5-30 volts of AC across either 1.5
resistor, but you should see very little DC voltage across the 1.5
resistors. On your 6100, one of the DC measurements will probably read
greater than one volt in DC mode. Check all the resistors in the
pre-driver stage (the MPSU transistors). In my case, all the transistors
were fine, but one of the resistors was open.

-Scott

PS The 6100 amp is a classic transcondunctance amp (Vin, Iout), so it's
very simple to analyze. Or in the classic textbook terms: Current
sampling, voltage mixing. :-) Extra credit: what's the correct Rload for
testing without a yoke?

-S

At 09:45 PM 4/12/2004 -0400, you wrote:
>Thanks for the tips. I happen to be juggling three repairs right now.
>Here's a weird one for you:
>
>Installed both of Bob's kits (caps, transistors, extra parts) and the
>LV2000. Turn game on, fires up, hear deflection chatter, but the spot
>killer is on. All voltages are good. When I turn up the brightness, I get
>a bright "rainbow" pattern on the lower half of the screen. Not vectors,
>mind you. Just a bright horizontal rainbow effect.
>
>I've gone threw the FAQ and checked everything listed there. I've gone
>over the deflection board for bad solder joints, checked and
>quadruple-checked the chassis transistors for any kind of shorting (mind
>you, I didn't check their output voltage), and checked all of the
>connector/transistor socket connections for continuity.
>
>Any suggestions as to what I should next? Thanks for any help offered.
>
>Brian
>http://www.orubin.com
>
>*********** REPLY SEPARATOR ***********
>
>On 4/12/2004 at 6:34 PM Joe wrote:
>
> >Just got done fixing several 6100's this week... and here's a few tips
> >for everyone.
> >
> >1. Don't use NTE 10 watt 1.5 ohm resistors. You need audio grade or non
> >inductive ones. One of these was on a board I got in and it was making
> >wavy lines on the bottom half of the screen after all else was repaired.
> >
> >2. Replace ZD902 with 2 75v 1 watt zener diodes end to end. (Positive of
> >one to negative of the other.) This will make a teepee sticking out of
> >your board... But, guess what, NTE 150v one watt zener is several dollars.
> >My fix will cost you under $.25 and last forever. The NTE part WILL fail.
> >This fix was told to me by Rick Schieve. I can't take the credit.
> >
> >3. Use MPSU57 and MPSU07's in place of the MPSA56 and MPSA06
> >(respectively) in the LV section. I HIGHLY recommend using the CEN-U07 and
> >CEN-U57 parts. They hold up just excellent - much better than the uniwatt
> >packages! If you do this, again, the LV section will be bullet proof. This
> >fix will cost you just a few $$$. The other upside of this is that when a
> >deflection transistor fails and begins to draw too much current through
> >the LV section, it will only blow the 15 ohm resistor. If you have an LV2k
> >in there, I hope you have surface mount soldering equipment. If you order
> >the transistors from me, I will throw in some free 15 ohm resistors, if
> >you ask.
> >
> >4. Run your game a little bit smaller than full screen. By doing this, the
> >deflection transistors won't need to work as hard. This means less heat
> >and longer life.
> >
> >If you have anything to add, please do.
> >
> >JB
> >
> >
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Received on Thu Apr 15 16:32:29 2004