Moog Prodigy Harmonic Shifting

Moog Prodigy

The Moog Prodigy has a nice sync feature that syncs both oscillators and frees up the pitch wheel to do something cool. The service manual says the sync switch locks the fundamental frequency of oscillator 2 to oscillator 1 and  “disconnects the pitch wheel from U11A (osc 1 & 2 pitch bend) and routes it directly to transistor Q7 of U3A (osc 2 freq mod). Therefore, the pitch wheel shifts the upper harmonics of oscillator 2”

I recorded the effect on a scope at high and low frequencies while adjusting the filter along the way. Apologies for the low quality.


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Olivetti Personal Computer M24

Anyone want to rescue these guys before they get trashed?


Posted in Surplus Electronics | 2 Comments

Hitachi CP-x445 Blue Washout Problem

After about 4-5 years of use in classrooms and as rolling stock we are seeing a blue and/or yellow washout effect with these projectors. We think the blue and/or yellow haze problem is because of several factors.

  • Dust buildup inside the optics .
  • Fading colour filters used in the internal optical process.
  • LCD image degradation.

Inside the projector the white light from the lamp is split into three distinct colours of  red, green and blue. Each colour illuminates their own monochrome LCD. Those LCDs are mounted on a prism that combines the separate images and displays the result you see via the lens.

The optical process to split the light up inside the projector is fairly complex and involves many light filters and mirrors to direct the light to the appropriate lcds. Those filters and lenses accumulate dust and also fade over time due to heat and other environmental factors.

Not sure if a fix is possible will post more info if any.



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NEC VT695 Projector Design Flaw

Found a defect with these NEC VT695 projectors. The projector fault is when the status light flashes red as if the lamp cover is off even if it isn’t. There is a design defect in which the tab (on the lamp cover) that closes the lamp cover switch is so fragile that it breaks over time. We are at about 2 years in with these guys and the plastic tab is so cheep that it’s snapping from the switch’s minimal pressure. Pictures coming soon.

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NEC MT850 Projector Problem

Believe it or not we still use these old ass projectors at my work. Why? Cause they still work well in most situations and we have lamps that need to get used up.  Noticed a strange problem with several units in which the green channel (G in RGB) was shifted to the left (or right depending on the software orientation) by about 6 pixels. This problem is manifesting itself across several units after about 7+ years of use. I pinpointed it down to IC3404 “3 Channel Video Amp” by Mitsubishi M52307SP which seems to be faulting. BIG GASSFACE to NEC for letting me know that a digital service manual exists but is not available because they no longer have parts available for projectors manufactured before 2007. Here’s to keeping these out of a landfill for a little while longer.

Posted in Electronics Repair | Tagged , , | 2 Comments