Re: Trouble with Space Wars Monitor

On Wed, 11 Aug 1999 10:38:52 -0400, you wrote:

>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.

For a little while, then you will start noticing smoke coming from
R118, R119, R218, R219 and possibly Q108, Q109, Q208, Q209, as these
parts try their best to drive the yoke alone.

Running the monitor without the yoke plugged in, and the power
transistors NOT plugged will eventually lead to monitor damage.

>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.

If you are running the monitor without the power transistors then the
burning out of R219 would be expected, you might want to recheck the
above list of parts for possible damage.

If the power transistors are plugged in and R219 is burning out you
most likely have a problem with Q211, a bad transistor, a short to the
heatsink, a bad connector (either at the socket or on the main board),
etc.

>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.

R119 would indicate a problem with Q111 (see above list of possible
problems), most likely your replacement was bad.

>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.)

The newer schematics show it as a 2N2102. I don't have any transistor
specs here in front of me, but I would guess that the 2N2102 is a
little beefier than the 2N3904. (Though it might have just been
cheaper.)

Q107 might have been your original problem.

>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.)

If you're not sure, check again, and always check after replacing a
transistor and BEFORE turning on the monitor.

It sounds like you need to re-verify the power transistors

-Zonn
Received on Thu Aug 12 13:51:12 1999