CurtPalme.com Home Theater Forum

[1031]

[draganm]

[Nashou66]

[1031]

Ok here is one mod that is quite easy to do. Every Marquee owner know´s and have heard horror stories what happens if filament voltage rises too high and many has done that "P14 mod" to Lvps. Ok there is many Marquees still that has not have proper mod done and there is risk that tubes can damage due too high filament voltage. So i designed very simple circuit that cuts P14 supply from tubes if filament voltage rises too high. I wanted simple system and tested how accurate is basic 5V relay.
So idea is to use relay that has 5V coil and use series resistor to adjust "cut out point" I tested vith lab supply and I noticed that it is accurate enought to cut out overvoltages. That cut out point is near 6.6-6.8Volts and it seems to be best compromise so that relay doesent cut out too early (near that 6.3v)

To find out value of series resistor to relay, i used 470 ohm multiturn trimmer and adjusted it so that 6,6v is point that relay cut´s
It was little under 160 ohm, so then i replaced that trimmer with solid resistor (150+8,2 ohm) and tested "cut out point" again, it was again near that 6,6vdc.

So simple 5V relay + series resistor can be used as overvoltage protector.
If there is voltege that exceeds that 6,6v then relay cut´s supply and then picture just fades away.. to get picture back projector must disconnected from mains for while. ( but if that happens best thing to do is do that P14 mod to Lvps)

Ok more..

Noise..yeah, there is lot of it at P14 line.
Filamets are inside of tube catode and cathode signal is good to have no noise in it. Filament is so close to cathode that noise can modulate actual video drive that cathode gets.
Also filament lines goes through VNB´s and near video OP-amp´s, so noise there can "jump" to video signal..

Here are some pictures from "proto" that i made just for this post.. It is ugly, but i made that one just for scope picture´s + detais

i have used similar filter +ovp on my marquee about 2 years with no problems and i made one to marquee owner here in Finland and he reportet that there was noticeably difference at dark parts of picture (unmoddet LVPS, old cap´s ..)
On mine marquee there was smaller improvements (recapped LVPS+ VNB mods)

First part after relay (at + side) is inductor that is rated between 2-5 amp (low resistance for lowest voltage drop) it´s inductance can be between 47uH (micro henry)-100uH.
After that there is 1,5uF 50v plastic cap between + and gnd, after those there are two ferritebeas (one at+ line one at gnd line) after those 10nF cap and between outputleads there is small (size1206) smd cap 10pF
That 100uH+1.5uF part is quite effective to lower noise and those bead´s + 10nF+10pf are there just to take "residues" away

It is easy to connect-> just use proper connector´s and put it between P14 connector and motherboard.



Edit/ part details: Inductor that i used -> http://fi.farnell.com/murata-power-solutions/1468362c/inductor-68uh-6-2a/dp/1077059?Ntt=1468362c

Relay (JQX68F)-> http://www.relcon.de/produkte/detail.php?produkteID=193

Ferrite bead-> manifacture: Kitagawa
Type: RI-3,5-4-1,2 30/51 Ω @ 25/100 MHz

Rest is pretty much basic stuff

[Nashou66]

Nice jarmo, I was looking at the schematic, if you do not want the relay section for the filter can you just eliminate the resistor and the relay and just leave in the inductors ,caps and ferrite beads.?

Athanasios

[1031]

[1031]

I forget to mention..
P14 adjust must done again (with filter in place) there is small voltage drop due resistance of inductor, so connect volt meter to p14 connector or to motherboard pins and adjust LVPS P14 trimmer and adjust P14 voltage back to 6.3Vdc

[draganm]

nice, It might also be good to have a molex connector on the board that only accepts the plug one way. I know on the MB you can't reverse it.

[Nashou66]

I could make up a PCB board for this if there is enough interest with the Relay for those who have the know how and the ability to test the shut down point and then other version where you could bypass the relay section with a jumper. Drag if you want to split cost on getting some of these made up you could populate them and sell them with your mods or I could populate them and send them out to you. I think i could make a small enough PCB boar with a plug in connector
that would fit into the existing Marquee p14 socket and then have a vertical socket coming off the board for the P14 plug from the LVPS to go to.
It be some time before I even begin to use the eagle software, its been awhile since i looked at it. But last time I made up 10 Gamma boards it was about 100 bucks not populated, just the PCB's.

taking it a step further there is a company that makes super clean power regulators any size you want, i cant remember who or where i saw them but they make replacement modules for audio components, i bet they could make a 6.35v super clean power output to replace the LVPS.s I bet it could be fed the power form the existing power supply, we just crank up the voltage to where it would be enough to power the new supply. But then again this could be just alot of overkill where the simple filter above will work just fine, i was just think aloud again !!
Athanasios

[1031]

[David_Web]

Interesting idea.

Looks like I was right about the PSU being noisy. Despite it being regulated(lm317 IIRC). I wonder how bad the rest of the rails are.
839.8mV P-P noise is a LOT!
Shielded cables for power might be a good idea.

So external PSU do seems like a good idea.
If nothing else, think about the geek factor. =)


As I asked in the other thread, any idea bout power draw for the different parts? Maybe someone can measure it, and measure the noise at the same time.


Any harm leaving power on VIM and other places (for a little while) when the rest of the system is powered off. Or should it be triggered with a relay? Or will that damage too? (as some circuits don't like to be disconnected at the wrong side of the PSU).

[dturco]

I think I'll give this a try. I'll get a soldering iron, a magnifying glass, a few rectifiers,diodes, tants, caps, and ......







A chain to hook to my new boat anchor.

Don't worry guys it will never happen I won't use a soldering iron.

[Nashou66]

David, The other place that there is lots of noise from what i have heard form others is the main 385 VDC line going to the HVPS. This goes right under the tubes and by other power supply rectifies in the LVPS. there are things you can do here to prevent jumping of the noise. maybe I'll look into it myself. But the VBim and other Boards would benefit from cleaning it up right on the board and not before, jus ask Mike Parker, he does this on the VIM, VNB's and now the FCM/FGM boards. I plan to test htis also on the CVA and VDM.

And Dave you stay away from your marquee!! your only allowed to touch the remote!!!

Athanasios

[dturco]

What, I already bought welding gloves.

[1031]

[David_Web]

Unfortunately it will be a while before I get to play with my Marquee. Lots of things has to be done before that.
But if I still need it when the time comes Ill send a PM.
Although I think I have most parts needed to make one.
If you really want me to test I could. But it might take some time.

Would putting ferrite cores around cables help with anything? I have a bunch from when my dad worked at IBM.
Shielded twinax cables might be useful too. Lots of RG-62 coax as well. Got to be some more fun stuff laying around.

Any idea where the noise is coming from?
Is it from the PSU or the working parts. Or both. Or EMI pickup.

"David, The other place that there is lots of noise from what i have heard form others is the main 385 VDC line going to the HVPS. This goes right under the tubes and by other power supply rectifies in the LVPS. there are things you can do here to prevent jumping of the noise. maybe I'll look into it myself. But the VBim and other Boards would benefit from cleaning it up right on the board and not before, jus ask Mike Parker, he does this on the VIM, VNB's and now the FCM/FGM boards. I plan to test htis also on the CVA and VDM. "

I'm not sure how much benefit vs hazard that would be. Some passive components and shielding maybe but Ill hold of making a PSU or putting anything directly in the power path.

I guess it would be cumbersome and not really doable for Mike to make external PSU or the like. So he does what he can with the tools available. Preventing noise pickup should be doable in both ends. Then the caps on the board can deal with the local back EMF generated by ICs and whatnot.

I'm not sure how much improvement one has to gain, especially with an 8" Marquee. But Ill give it a chance anyway. If I see a lot of improvement it can be easily migrated to the bigger brother. After all the only thing 9" have is light output and resolving power.
And at this time I want to get rid of some noise. And offload the LVPS.

[Nashou66]

I still think its amazing how much noise you can clean up on this heater voltages:

Before Jarmos Filter



After the Filter Mod



Athanasios

[WTS]

Do you have a schematic of this filter? What does the Marquee use for regulation on the filaments?

[Nashou66]

[WTS]

Odd that the regulator puts out that much noise.