Davis Powerbeam V help needed

[qx2vu]

Hi

I am looking for a service manual (or just the schematic) of Davis Powerbeam V DLP projector. Picked up one of these from a 'junk' dealer - lamp and optics are fine. Video is OK but VGA RGB input does not work.

Any help will be appreciated.

Thanks,
Jay

[fredex]

I also need service info. Bulb strikes then goes out.
fredex

[pinkmouse]

Needs new lamp.

[TRIBB]

Did the service manual ever show up?

My projector lost its life in the last weeks - didnt like being at home alone ... weird!

Anyways - its totally dead - but everything was disabled so it cant be due to false powersettings or lightning ...

But service manual is needed

[terminills]

did you ever get the vga working... it looks like to me it won't work without the buffer cable.

[davewi11]

Just in case anyone here still wants to know, I have solved the mystery with the Buffer Cable.

As the projector can be mounted on the ceiling, a long VGA cable is needed, so the manufacturers had to add drivers to the cable as PC's can only drive the normal length of cable. Also it was preferable to maintain the facility of using an external monitor for the PC.

The Powerbeam has +12V output on pin 9, and -5V output on pin 15, so no doubt the drivers were powered by these. The RGB lines are loaded by 75 ohms in the Powerbeam as in a normal monitor, and probably the drivers had 75 ohms output impedance as well, like the PC does.

The problem is that the H and V sync lines are loaded by 150 ohms in the Powerbeam, and probably driven by 150 ohms at the drivers to match the cable. The sync outputs from the PC are only TTL, so can't drive 150 ohms directly, thus no sync.

I examined the video board to try and work out what voltage and polarity is required by the sync inputs on pins 13 & 14. Unfortunately the lines went to an IC with only an in-house number on it, but I did measure the supply pins and found them to be 0V and +5V, so it was probable that positive polarity sync was required.

I tried making a transistorised driver to drive the cable. This almost worked, but was prone to spurious instablity unless I kept my fingers on the components.

So I just unsoldered the two 150 ohm surface mounted load resistors on the video board, beside the VGA connector. Hooray! A standard VGA cable now worked.

By the way, I wanted to try a tungsten-halogen bulb in the projector instead of the mercury vapour lamp, because the colour rendition of it was bad, like my friend's modern projector also with a mercury lamp. These are notorious for having hardly any red. Deep yellow came out as almost green.

The tungsten bulb fixed the problem. Warm tones and decent reds and yellows. Admittedly the brightness is lower than the vapour lamp, but there you go. I was able to put a large toroidal transformer to drive the bulb in the space vacated by the Osram lamp drive unit. I have it on a separate lead so I can switch off the bulb but leave the fans on till the bulb is cold.

Thank you to the guys on this forum who found out the trick of adding a 330 ohm resistor between pins 3 & 4 of the 8 way connector (green and yellow wires) to kid the computer that its lamp is still there.