Singin' the G08 blues. Blown deflection transistors.

This is a very long read, but I'm trying to be complete. Sorry.

My back ordered 2N6259's (deflection transistors) come in at RaElCo today.
I plug them in, along with some other misc parts that were missing or bad
when I got the monitor. As recommended by the G08 FAQ, I leave the yoke
unplugged so as not to blow stuff before I can check a few things. I power
it up and measure the X and Y voltage at the yoke plug and things look good.
I'm getting values fluctuating around on both axis's indicating deflection
is happening. Nothing blows. I plug in the yoke, hold my breath and turn
it on. I hear deflection chatter; soft but it's there. But no heater glow
and no picture. Drat. No HV. So I measure the voltages at the 10 pin HV
header, and get .7v on pin 2. It's the X axis pin and it should be about
3.5v. Pin 8 is also .7v, it's the heater voltage and should be at 63v, so
that explains the no glow in the neck. Pin 10 is at 26.5v, which sounds
good till you realize it should be 400v. The other pins have the proper
voltage. I had the monitor powered up for about 30 seconds at a time 4 or 5
times with no signs of trouble.

About this time I notice that the width adjuster pot R702 has the middle leg
busted off. "Hey, that's on the X circuit, maybe that's the problem." I
solder a wire to what's left of the middle leg and put everything back
together. I power it up and within 3 seconds I see flame. Whoo hoo! My
first G08 fire; today I am a man. My hand is still on the switch so I get
it shut off fast. On inspection, R252 and R253 on the vertical Y axis
current limiter boards are roasted. No fuses blew. I check the other
diodes and transistors on that board and they are OK. However, both Y
deflection transistors and one of the X deflection transistors are blown.
That was a fast 18 bucks. And I only ordered 2 spares. ARGHGHGHGH.
Shouldn't have plugged the yoke in.

So, as soon as I get another 2N6529 I can give it another shot. In the
meantime, anyone have any insight as to what happened here? I'm crawling
the archives, but would appreciate anyone's educated guess.

I should say that when I got the monitor, the X vertical limiter board had
both R202 and R203 resistors shot, a blown diode and a popped 2N3904
transistor. The Y limiter board was OK.
I don't know if I busted the leg off the width pot or not. It's right next
to a plug and I might have snapped it trying to pull the plug out.
One of the 4 power rectifier diodes was missing, and I replaced it with a
higher rated part because I couldn't get the original. I also put in 250v,
5A fuses instead of 125v 5A fuses because I didn't have the 125's. I have
re-soldered every header pin on all the boards, and fixed several bad
connections.

And since I am on the subject, the G08 FAQ lists incorrect parts for the
Horizontal and Vertical current limiter boards. Instead of 2 2N3904's, it
should have one 2N3904 (NPN) and one 2N3906 (PNP). It also lists the
voltage for pin 8 on the HV header as 6.3v, and the schems say 63v. I
figure anyone who read this far is probably working on a G08 and might need
that info. And a HUGE thank you to Mark Jenison for compiling the FAQ and
for anyone who contributed to it. It's invaluable.

Sean McLachlan Salt Lake City, Utah
rgvac@classi-find.net Video Game n00b since 2/2001

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Received on Wed Nov 3 14:12:13 2004