Re: LF13331 Symptoms

On Tue, 14 Oct 1997 11:29:19 -0500 (CDT), <jwelser@ccwf.cc.utexas.edu>
wrote:

>
>Hey all,
>
> I posted about a week back about my Rip Off losing the
>negative Y deflection. FIguring this was just the output deflection
>transistor, I replaced it, but no dice.
>
> I replaced the 3 transistors listed in the manual, swapped
>the 2 DACs, and touched up all the solder joints in the vertical
>deflection section of the board, but still the same thing. I checked
>those 5 diodes in a row and all were OK, and I measured the resistance
>across the tantalium capacitor, and it was also OK (it was the same
>as the one on the horiz. deflection section was, and it wasn't shorted
>or opened.)
>
> Now, I'm not exactly getting a half picture -- I'm getting like
>a little over a half picture. I re-read the vectorlist postings from
>a couple of months ago, and Zonn mentioned that the LF13331 was on his
>"Most Likely To Die" list. So, what exactly are the symptoms of an
>LF13331 going out? All the manual mentions is that they are, indeed,
>likely to die.

It could be the LF13331 but it sounds unlikely. Weird because it really
sounds like an output transistor. Did you do a doide check on all the
pre-driver transistors? Making sure they all had decent Base-Emitter
and Base-Collector readings and no shorts?

Another thing you might try is to make sure the power resistors are all
reading the proper value. Cinematronics does have short circuit
protection built in, if one of these resistor values changed to a higher
value (or opened up), the output would go into short circuit protection
mode and cut off your picture.

A note on the LF13331, there was a problem where if the negative power
supply came up before the positive supply it would blow out this chip.

There should be a diode connected between pin 4 and 5 (I believe) I
can't remember the direction but check some of the newer schematics
(Solar Quest: www.sipes.com ) as they added this diode to the schematic.

Also if your monitor is old enough it won't have the neon bulbs
connected from the wiper of the "brightness" control to ground, if
they're not there, you should add them. Simply connect two NE-2 neon
lamps in series and place them between the Brightness control wiper and
ground (See the same schematic as above). This bleeds off any voltages
above 180v that can be there during power ups/downs (from high voltage
static discharges).

-Zonn
Received on Tue Oct 14 10:36:41 1997