Re: Speaking of Vectorbeam/Cinematronics...

John Huie wrote:
> I've sworn off working on this one but I'm curious what those "in the
> know" think.
>
> I've got a Cine monitor that works but is missing the vertical
> deflection. I tested the deflection transistors on the heat sinks and
> two of them were bad. Upon replacing them, it behaved exactly the
> same way but one of those previously bad transistors heats up veeery
> quickly. So hot that you don't want to touch it.
>
> If this were your monitor, what would you suspect as the cause for
> overheating one of those transistors? I've double checked to be sure
> it's not grounded out. I'm thinking the thing should just be sent off
> to someone who has more background than myself but it is interesting
> to me to hear your thoughts anyway.
>
> John
>
Hi John,

Try my voltage checks that I have just posted earlier today (Tech Tips -
Vectorbeam...). Remember to unplug the yoke for doing these tests to
avoid damaging components.

Do you understand what the Diode Test is? Rather simple - most modern
digital multimeters have a diode test built in. The switch position
shows a diode... The negative lead is often the anode (banded end of a
diode) and the positive lead is then the cathode (other end) - if you
put the meter leads across a good diode you should see something like
0.3xx (Germanium ) to 0.8xx volts (Silicon diodes) when the leads are
one way and open when the leads are reversed.

Power OFF!!

Now if you take the leads and check a transistor you will find that if
the leads are across the Emitter and Collector of a transistor you
should have roughly 0.7xx V or higher (open is often the case - a meter
reading being blank or whatever the meter shows for not connected),
anything around 0.0xx is likely a shorted transistor. Now find the Base
of the transistor and put the leads between the Base and Collector
(reverse leads if no reading) - should be around 0.7xx V, and repeat for
the Base and Emitter (roughly the same 0.7xx voltage). Sometimes you
will have a lower reading and you may have to remove the transistor to
see if the rest of the circuit is causing anomalous readings (small
value resistor for example) - if it checks OK out of circuit then it is
/probably/ OK and can be put back.

Check ALL transistors and diodes for shorts or weird readings - with
these monitors the readings should be similar between the two channels
(X &Y deflection) comparable transistor/diodes.

Or you can send the chassis off to someone to fix - I'm sure there may
be someone close to you (I'm in Canada) that can help.

John :-#)#

-- 
John's Jukes Ltd. 2343 Main St., Vancouver, BC, Canada V5T 3C9 
Call (604)872-5757 or Fax 872-2010 (Pinballs, Jukes, VideoGames)
                 www.flippers.com 
"Old pinballers never die, they just flip out"
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