Re: Singin' the G08 blues. Blown deflection transistors.

----- Original Message -----
From: "Sean McLachlan" <sean@lithoflexo.com>
To: <vectorlist@vectorlist.org>
Sent: Wednesday, November 03, 2004 2:10 PM
Subject: VECTOR: 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.

Yeah, those fuses are great aren't they? Probably the most reliable part on
those boards.

> 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.

No, you shouldn't have :-).

> 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.

Saying you heard deflection chatter is (was) a good sign, but after such a
catestrophic failure, I don't think diagnosising where you were will help at
this point. Once you get the replacement transistors, you'll need to start
debugging again from square one.

> 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).

Hmm, my copy shows those correctly:
Q201; Q251 2N3904 Current Limiting Board
Q202; Q252 2N3906 Current Limiting Board

Q201 and Q202 are one on board, Q251 and Q252 are on the other. If yours
doesn't match, maybe it's time to me to
repost the FAQ.

> It also lists the
> voltage for pin 8 on the HV header as 6.3v, and the schems say 63v.

I think either the schems are wrong or you just aren't seeing the period. I
believe 6.3V is a pretty typical heater fillament voltage.

> 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.

Special thanks to Tom McClintock for his work on the document; adding
tables, formatting, additional references, information, and prodding me to
put more effort into it (shouldn't have said anything about the prodding;
now he'll probably want me to finish that Cinematronics monitor document),
and generally making it a coherent document.

You're welcome and good luck on your G08.

> Sean McLachlan Salt Lake City, Utah
> rgvac@classi-find.net Video Game n00b since 2/2001
>
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Received on Thu Nov 4 13:52:42 2004