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VM1000 backlighting dimming

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dean.psiropoulos(at)veriz
Guest

Posted: Wed Jan 05, 2011 10:59 pm Post subject: VM1000 backlighting dimming

A question for both Bob and VM1000 owners with the original (black and

white) LCD display:



Situation:  I bought the VM1000 system in 2002 but it wasn't operating in

the airplane until 2008. Flying at dusk I notice that the LCD screen

backlighting works but is not bright enough for me to read the display.  The

VM1000 manual says the backlighting power is generated by a 0-80 volt AC

inverter inside the VM1000 CPU box and that the inverter output is

proportional to the DC voltage on the dimming input of the CPU connector.

The manual notes that full brightness will be achieved when close to full

battery voltage is input at the dimming connection.  Unfortunately it does

NOT say exactly what value of "close to full battery voltage" is required to

get full brightness.  



Bob:



I installed a B&C dimmer (DIM 5-14, half amp output max) on the dimming

input of the VM1000 CPU connector. I got to talking with someone about the

output of this device and a question came up as to exactly how close to bus

voltage is output when the control is set to full output. I can't recall, is

the output pulse width modulated, and if so, does the device ever achieve a

full bus level output voltage?  Or, if the LM317 is a linear device, is the

DIM 5-14 circuit designed to achieve a full bus level output voltage when

the pot is set to full output? If not what percentage of full bus voltage

can I expect?  Also, if the DIM 5-14 output is too low can I remove the

circuit board from the equation and just connect the potentiometer (that is

supplied with the DIM 5-14) between the Essential bus and the VM1000 dimming

input to achieve full voltage at the VM1000 dimming input (in other words,

is the potentiometer robust enough for this task or will I burn it up)?  Any

other words of wisdom you care to pass on?  

VM1000 Owners:



Have any of you come up against this issue?  What did you do to solve it?

Were you using a B&C dimmer or some other device?  Being the original

designer/owner of Vision Microsystems sold the company and disappeared, does

anyone know exactly what percent of battery voltage is required to get full

output on the display? What failure modes does the display backlighting

system exhibit (i.e. if the backlight works is it just insufficient dimming

input voltage that makes the brightness too low or does the inverter circuit

have failure modes that set the backlighting to some intermediate

brightness)? If so what are those failure modes and can the circuit be

repaired to restore output to full brightness. 



Thanks everyone



Dean Psiropoulos

RV-6A  N197DM

2 years of flying fun

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recapen(at)earthlink.net
Guest

Posted: Thu Jan 06, 2011 5:41 am Post subject: VM1000 backlighting dimming

Dean,



I replaced my original VM1000 shortly after Vision Microsystems was sold.

If I recall correctly, Mr. Turk (I think that was his name) was still available through the company that purchased Vision Microsystems.  You might try contacting him through the new company.



I don't know if I have enough components remaining to cobble it back together to answer your question as I have been parting out the remnants of mine in hopes of keeping as many of the old systems alive as possible.



Let us know how this pans out as there are a number of us in the curious mode....



Ralph

--

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nuckolls.bob(at)aeroelect
Guest

Posted: Thu Jan 06, 2011 7:45 am Post subject: VM1000 backlighting dimming

Bob:



I installed a B&C dimmer (DIM 5-14, half amp output max) on the dimming

input of the VM1000 CPU connector. I got to talking with someone about the

output of this device and a question came up as to exactly how close to bus

voltage is output when the control is set to full output. I can't recall, is

the output pulse width modulated, and if so, does the device ever achieve a

full bus level output voltage?  Or, if the LM317 is a linear device, is the

DIM 5-14 circuit designed to achieve a full bus level output voltage when

the pot is set to full output? If not what percentage of full bus voltage

can I expect?  Also, if the DIM 5-14 output is too low can I remove the

circuit board from the equation and just connect the potentiometer (that is

supplied with the DIM 5-14) between the Essential bus and the VM1000 dimming

input to achieve full voltage at the VM1000 dimming input (in other words,

is the potentiometer robust enough for this task or will I burn it up)?  Any

other words of wisdom you care to pass on?



    The B&C linear dimmers are based on the

    LM317 style 3-terminal regulators. They

    were intended to service incandescent lighting

    where 99% of operating time calls for an

    output on the order of 4-5 volts (just

    visible in the dark cockpit). These devices

    have about a 1.2 volt drop in the max bright

    condition. Suggest you wire a spdt switch

    to bypass the dimmer and apply full battery

    voltage to the VM1000 in the BRIGHT position

    and route to the dimmer in the DIM position.



    Does this dimmer have any control tasks other

    than to control the VM1000?



   Bob . . .

   Bob . . .

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nuckolls.bob(at)aeroelect
Guest

Posted: Fri Jan 07, 2011 5:15 am Post subject: VM1000 backlighting dimming

I've got the exact same problem with my older VM-1000 using a B&C 

dimmer. I rarely fly at night, so fixing the problem has not been a 

priority. It seems that when I first installed the devices, it worked 

as advertised with plenty of night lighting. On a recent night 

flight, however, the VM 1000 was too dim to use. At some point, I 

added another device to the dimmer that supports the VM-1000. I have 

supposed that the additional current draw caused the problem, but as 

stated, I haven't taken any steps to correct.



   The first thing to do is get MEASUREMENTS

   as to how much voltage is being applied to

   the VM1000 dimming input. Combine this with

   an experiment to bypass any existing dimmer

   and apply full bus voltage.



Up until recently, the VM-1000 has been supported by an outfit here 

in San Antonio (Boerne Stage Airport.) Thanks to my weak memory, I 

can't remember the name of the new outfit or the new owner, but I 

remember their exact location and I still have their phone number. 

They were very helpful a couple of years back when I first flew and 

helped me get a different CPU chip for the higher fuel pressure 

reading my AFP fuel injection required. I haven't talked to them in a 

couple of years, but assume they are still in operation. Their phone 

number is (was) 1-830-755-6330. I'll check further to see if they are 

still in operation and if they have any suggestions for the dimming problem.



   They should suggest the same sort of

   investigation and experiments to determine

   if there is a VM1000 problem or and externally

   induced power supply issue.



   When we did the DIM series devices now sold

   by B&C, the design goals concentrated on how

   a dimmer is used the vast majority of the

   time.



   When flying in a max dark adjusted condition,

   one's visual acuity for seeing things outside

   was best if lights inside were just barely

   bright enough to read the instruments. Typically

   4 or 5 volts on 12 v incandescent lamps. The

   short interval that the lamps could use a

   full-bright voltage supply was during twilight.



   The only time pilots wished such lights were

   brighter might be during thunderstorms. The B-52s

   I worked on in '61 had "thunderstorm lights." Sealed

   beam lamps above the pilot's heads on both

   sides. Lightning flashes tended to blind the

   crew so it was then useful to have some really

   robust flood lighting! I tend to stay away from

   thunderstorms . . . they're too loud.



   Do the homework to see if the lighting problem

   with the VM1000 is internal or externally

   caused.



   Bob . . .

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