Trouble with Space Wars Monitor

I'll try to sum up my problem as clearly as possible, this is my first X-Y
monitor game, so I'm new at this:

Currently, the monitor only displays the upper left quadrant on the screen.
All of the power transistors (Q110, Q111, Q210, Q211) check out OK when
tested with a diode tester. If I run the monitor with the power transistors
disconnected, I get a nice little rectangle in the middle of the screen. If
I run the monitor with the vertical power transistors disconnected and the
horizontal power transistors connected, I get a longer rectangle centered
horizontally from the middle to the left edge of the screen. If I run the
monitor with the horizontal PT's disconnected and the vertical PT's
connected, I only get the small rectangle in the middle of the screen (I
expected to get a narrow rectangle, centered vertically, from the middle to
the top edge?) Also, R219 keeps burning out.

Here's a history of my assorted repairs from the past:
It started with a vertical deflection problem where the monitor was only
displaying the top half of the screen. I replaced Q111 (with a used 2N5876)
and powered the game up. Shortly after powering the game up (about 10
seconds) R119 burned out.

I then decided to check / replace most of the transistors. I replaced Q110,
Q111, Q210, Q211 (using NTE219 as replacements for 2N5876), and checked out
the following transistors using the diode tester: Q108, Q109, Q106, Q107*,
Q104, Q105, and Q208, Q209, Q206**, Q207, Q204, Q205. * I replace Q107, it
was bad. ** I replaced Q206 with the correct transistor (it was a 2N2102
and the schematic shows it as a 2N3904.)

I've also checked the following: the bank of 5 diodes on both the horizontal
and vertical circuits, R116 and R216, R124 through R129, R224 through 229,
the +/- 25 VDC, and checked to see that I had 30 Volts DC across pins 7 and
4 of one of the TL081's. Oh, one more thing, I checked to make sure that
the power transistors were isolated from the heat sinks (I though I might
have accidentally grounded one when I replaced them.)

I'm sure there's something really basic I'm failing to do or check, but I'm
sort of at my limit here.

Any support, suggestions, or condolences would be greatly appreciated.

Thank you,
Chris Marlowe
cmarlowe@comcastpc.com
Received on Wed Aug 11 09:38:16 1999