Re: Testing vectorbeam monitors.

Grant:

If you look in the introductory pages, you will see John's name
mentioned in the acknowledgements. I think he also hosts this manual on
his site.

Pat

On 2/1/2013 7:52 AM, Grant Thienemann wrote:
> 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"
>>
>> ---------------------------------------------------------------------------
>> ** Unsubscribe, subscribe, or view the archives at http://www.vectorlist.org
>> ** Please direct other questions, comments, or problems to chris@westnet.com
> ---------------------------------------------------------------------------
> ** Unsubscribe, subscribe, or view the archives at http://www.vectorlist.org
> ** Please direct other questions, comments, or problems to chris@westnet.com
>

---------------------------------------------------------------------------
** Unsubscribe, subscribe, or view the archives at http://www.vectorlist.org
** Please direct other questions, comments, or problems to chris@westnet.com
Received on Fri Feb 1 12:22:59 2013