G05-801 Deflection Board question

The Deflection board in my G05-801 (def board is type 02-160005-01) has on
it, in locations Q604 and Q704, a transistor that has written on it 913
(and a large M that I guess is for Motorola), and under that is JE253.

Now, according to the schematics, these locations should have an MPSU57 -
is this JE253 package being used as a replacement does anyone think? It's
certainly not a *direct* replacement whatever it is as the readings I take
with the diode tester on my multimeter are very different to that of the
MPSU57's on the board.

If required, would it be okay to replace these JE253 transistors (or
whatever you call them) with MPSU57's or equivalents?

I hope not to have to replace them but am currently testing all transistors
as the monitor won't display any graphics, just a 'glow' taking up most of
the screen that slightly varies in intensity when things are moving about,
especially evident when the ship fires (the game is Asteroids). I know the
main game board is fine. From reading on the Vectorlist this 'glow' problem
invariably points to either a bad transistor OR a problem with the two
large black 10W resistors at R620 and R720. These two resistors get
EXTREMELY hot when the monitor is switched on. In situ their resistance
checks out as it should (5.1 ohms for one, 4.5 for the other) - I would
test them out of circuit but they don't want to come off the PCB. They
seems to have extra casings around the legs and will not de-solder.

The four accompanying wirewound green resistors near them also get pretty hot.

Curiously enough, both the two black resistors (supposed to be black, not
scorched! :-) AND the four green ones, if tested with the continuity
tester, all show as a short - or is this 'normal' for these type of resistors?

I removed one of the green ones and the resistance was again fine, but
still showed as a short with the continuity tester.

I'm puzzled - can anyone help please?

Thanks,
Phil

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Received on Sat Jan 5 16:27:22 2002