Re: Testing vectorbeam monitors.

This might be helpful for you!

http://www.outerworldarcade.com/arcade/cinematronics/manuals/cine_faq_v096.pdf

-Grant

On Fri, Feb 1, 2013 at 3:14 AM, John Robertson <pinball@telus.net> wrote:
> Being a bit annoyed that I have no test procedures, nor theory on how these
> Vectorbeam monitors work I started playing with one today that was giving me
> excessive current draw on the power lines. So I've been working on a test
> procedure using a few of my shop tools and thought others may be interested
> an can also expand on the process.
>
> 1) you can power up these monitors with the YOKE unplugged with little risk
> to damaging any output transistors - this static test allows you to service
> the VH section on the bench if you can provide the required +/-25VDC. I use
> a dual regulated power supply and limit the current to 0.2A per supply and
> get full HV output with a known to be good chassis.
>
> 2) the deflection circuits on these monitors are basically stereo
> differential transistor amplifiers so - if you unplug the LF13331 you can
> feed into the inputs of the two op-amps an audio signal of -50db or so @
> 1000hz and then be able to trace the audio signal through the two amp
> sections to find problems. I'm using a heathkit Audio Signal Generator for
> this, you can set the output signal from 0 to 100khz, and
> -50/40/30/20/10/0db adjustable.
>
> Need to test if the feedback resistor can be lifted and see what happens to
> the input differential pair, I suspect that will aid in following the audio
> path.
>
> Note too that if you use a current limiting power supply you can test the
> amps by unplugging both the 13331 AND the output transistors - with no input
> signal there is little risk (is any) of damaging the driver transistors, as
> long as you limit the current ot around 200ma max at +/- 25VDC.
>
> I'd love to find a service manual on this sort of audio amp, but hunting
> online today didn't lead to anything useful other than theory - and tha twas
> more time than I wanted to spend on troubleshooting these.
>
> I'll try and report more tomorrow as I dig further into this chassis which
> currently is pegging the am-meters on the -27 supply without any obviously
> shorted devices.
>
> 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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Received on Fri Feb 1 08:52:40 2013