Re: Testing vectorbeam monitors.

John Robertson wrote:
> John Robertson wrote:
>> John Robertson wrote:
>>> Grant Thienemann wrote:
>>>> This might be helpful for you!
>>>>
>>>> http://www.outerworldarcade.com/arcade/cinematronics/manuals/cine_faq_v096.pdf
>>>>
>>>> -Grant
>>>>
>>>
>>> Yes, however there is little on troubleshooting the actual amplifier
>>> when the problem is not the output transistors! At the moment I have
>>> amplifiers that appear to be unbalanced and I don't (as yet) know
>>> why. What I am trying to do is set up a process for troubleshooting
>>> the X & Y differential amps that is fairly easy, and by treating
>>> them as audio amps I think this will do the job. I don't do a lot of
>>> analog amp work these days and am getting rusty...usually these
>>> deflection boards are a snap to fix.
>>>
>>> Today I will be taking typical voltages on the various transistors
>>> with a zero volt input - this should produce a zero volt deflection
>>> and work from there.
>>>
>>> The annoying thing is this amp is almost identical to one that was
>>> published back in the late 60s in an electronics magazine (I'm
>>> pretty sure it was Popular Electronics Brute 70) as a high power
>>> transistorized stereo amplifier - I built the darn thing back then
>>> for a family friend, but can't find pdfs of the article(s) (two
>>> issues?) as I seem to recall that they covered troubleshooting the
>>> differential amp...more google searching I guess is in store for me.
>>>
>>> Similar amps:
>>>
>>> http://www.hilberink.nl/amps/amps4.htm
>>>
>>> http://michaelgellis.tripod.com/audioamp.html
>>>
>>> John :-#)#
>>>> 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 :-#)#
>>>>>
>>>>>
>>
>> As a followup found an interesting book on transistor theory:
>> Fundamentals of Linear Electronics: Integrated and Discrete
>> By James F. Cox (2001) by the following search terms in google
>> "troubleshooting the differential amp transistor". Reading pages 216
>> to 221 (missing pg 281 - darn!) is very helpful - rounds out the
>> explanation in the theory section of the vector pdf discussed above.
>>
>> The book is running $85 used, so I don't think I'm going to treat
>> myself just yet with a copy (new is $220!)...and no library near me
>> has a copy:
>>
>> http://www.worldcat.org/title/fundamentals-of-linear-electronics-integrated-and-discrete/oclc/247983125
>>
>> John :-#)#
>> --
>
> More info on servicing Vectorbeam monitor deflection PCBs:
>
> 1) check the pots for corrosion (would have saved me an hour or so of
> time). In fact, replace the suckers when working on this chassis, the
> parts are available from Digi-Key (etc.) for around $1.25 each. Bornes
> type 3325 if I'm not mistaken, 100R and 5KR horizontal. Replace IC
> sockets at the same time if originals.
>
> 2) if pots are good, then check for the following DC voltages across
> the parts with no input (remove LF13331 & short pins 2 & 15 to ground)
> and having added two 100R 5W resistors across the yoke outputs to act
> as a light load, note these measurements were taken from a
> known-to-be-good deflection board:
>
> R112: 0.9V
> R114: 51.6V
> R115: ~0.33V
> R118: 0.6V
> R115: 0.2V
> and across diode string D109/D110/D111: 2.02V (easiest to simply check
> this voltage across the collector/metal case of Q104 & Q105).
>
> Part reference numbers are from:
> http://www.outerworldarcade.com/arcade/cinematronics/manuals/cine_faq_v096.pdf
>
>
> Is Tom McClintock still around as it needs editing/updating? Haven't
> seen a post from him since 2011...
>
> I'll report the voltages across the two 100R 5W resistors the next
> time I set this up, waiting for some pots to come in (Monday).
>
> John :-#)#

Problem turned out to be a bad 2N5322 and the clue should have been that
the center voltage was always negative instead of around 0V.

The last problem I was having was brightness...not thinking that the
problem could be the monitor I was using I went into a bit of trouble
trying to track down what could be the problem including rejuvenating
the picture tube.

As part of the process I decided I needed to get the original chassis
working for this tube (22VATP4), and in doing so discovered that the
voltages for this tube are higher than used in the 19". Should have
remembered this, but - well - forgot to take it into consideration. The
19" schematic shows the cathode B+ to be around 80 - 85V whereas the 21"
tube needs about 95V to work properly. The HV transformer is all that is
different between the two chassis - the 18KV one is number HV18 and I
assume the 25KV one is supposed to be HV25.

The short point is, when testing a chassis make sure you have the
correct picture tube even in the B&W games otherwise the drive voltages
will give you trouble...

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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