ANOTHER Ground/signal issue - comments anyone?

[Humphry]

Any and all thoughts on this appreciated. This thread started as something else, so please scroll down to the latest post.

[absolom7691]

Sounds like one projector is single-ended and the other is differential.

[Humphry]

Hi Absolom,

Thanks so much for your response. The signal wires going into the drivers on the both projectors are very definitely single ended as there is only +'ve and ground. HOWEVER there is a "DMX board" in the Lightspace projector that processes all the ILDA pins. Also just to mention that the Pangolin FB3 ties R-,G-B- to pin 25 which I confirmed with my multi meter. So even if one of the -'ve colour channels is sending signal, it's directly ties to pin 25 and therefore would be "negated" I think. Am I missing something? Any tests I can do?

UDATE: Even when FB3 is unplugged from IDLA cable the problem persists.

Sounds like one projector is single-ended and the other is differential.

[catalanjo]

.....@ "So even if one of the -'ve colour channels is sending signal, it's directly ties to pin 25 and therefore would be "negated" " ... IMHO ... this may well have the effect of converting the zero volt line to +5v
Check continuity between any zero volt line and pin 25 ... if there isn't any then try connecting them ...possible that a pullup/down resistor somewhere might get a bit warm when you do this!
Cheers
Don't have intimate experience with Lightspace projector but if ILDA through connection is buffered on the DMX board, the resulting signal will have definite -5vdc on all neg colour lines, if these are tied to a floating pin 25 connected anywhere to DC ground then any supposedly zero volt DC line will be transformed into +5vdc .... hope that makes sense to U

[Humphry]

Hey Catalanjo,

Thanks for your time. I followed your advice and connected (pin 25) with (R-), (G-), (B-) and it solved the issue for red and blue channel. Now the static beam on the new projector only projects green. I was able to replicate this on both my old projectors. I noticed the wire I used to connect them start to get slightly warm - so I am 80% sure there is lots of current flowing through the -'ve signal wires to ground.

When I measure with a multimeter I get +7v on the +Green (pin 17) and ILDA gnd (pin 25) when there is no signal. But when I measure from chassis AC ground I get +12v between (pin 17) and (AC Ground), yikes!

I still have no idea what the problem is. Anyone got any ideas?

[catalanjo]

I am still not at all clear how, or more to the point where, your signals are connected to !

If you can post a diagram, a block diagram, (or even a list) it would make it much easier to pinpoint your problem !

If wires are getting hot then first of all .....STOP!

I have tried to re-read the thread but it is still somewhat abstruse to say the least ..........
It is beginning to sound as tho an op amp somewhere is "up to rail" on it's output (DMX card most likely).

Usually with this kind of thing the problem/solution is blindingly obvious to anyone, EXCEPT, ... the poor sod who is actually confronted by it!

Cheers

[absolom7691]

My advice would be to ditch the DMX card. If I had to guess, it's a PT-ITrust board. Problematic at best. If you're not using DMX to control your projector, there is no need to keep it.

[polishedball]

Buy a DZ splitter.

More than likely an input impedance driver issue when mixing drivers in a daisy chain.

[Humphry]

Hi guys thanks for all the advice. I sorted out the symptom, but I don't know what the cause was!

@Absolom I bypassed the built in PT-itrust board (connected ILDA directly to laser drivers) and hallelujah, it works
Anyone got any thoughts about what the actual problem was? I am just concerned that the wiring in my old projector is wrong and caused this, so perhaps you could have a look a the below?

@Catalanjo, could you perhaps have a look at my wiring scheme below, is there anything wrong with it? The two ground options presented on Pangolin's wiring article are:

(AC Ground)+(DC Ground) together ---------- (ILDA 25) separate
OR
(ILDA 25)+(DC Ground) together ----------- (AC Ground) separate

As you can see from the diagram I *tried* to follow the first option when I wired these a few years back. But it seems impossible to separate (pin 25) from DC ground as all the drivers seem to connect them together natively on the board, is this standard for drivers? I measured a spare 532nm Laserwave driver and it definitely connects G- with 0V DC of its power supply. And therefore AC Ground because I have linked it to DC Ground. Now it just looks like all 3 were tied together the whole time.
Do all modern day lasers totally prevent phantom ground possibilities, and therefore I should rather isolate AC ground from the central grounding scheme? Very confused about this. FYI I am using CNI and laserwave units.

[Bbe]

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