CurtPalme.com Home Theater Forum

[Nashou66]

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Interesting to say the least. I bet Scott would have an answer .How does the 1:1 pixel pattern look on each half of the screen? Do both sides resolve them equally?


Athanasios

[draganm]

My cree FET modified HDM didn't run long enough to see this problem ................just teasing you Dennis This board has kicked my ass so many times I don't really have anything intelligent to add

Could possibly be related to the fact that the original circuit used multiple HV Mylar caps in conjunction with the big power FET's and switched them in and out depending on frequency.
With one of the 3 FET's gone, those extra caps are no longer there and could very well be affecting the sweep / re-trace time? I don't know, I guess the easy thing to try is change the Cap value's higher and see if the problem is affected by that?

[dvh99]

yes it does affect retrace time but this shouldn`t cause this aomaly as the voltage required to sweep was about 1700v and far within the 2400v max of the 2 fets, remember those fets (3 of them) were put in series to cope with the high voltage.

i should read the documentation thoroughly to understand what exactly is going on.

[dvh99]

mmmmm, no ideas by you guys yet.

will increase the value of the gate resistor to 10 ohms and see what happens.

[dvh99]

??

any ideas???

please... scott wo bist du, ich bitte dich.

[tse]

Can you post a pic of a full white field? That might help to find what is wrong. Also a linearity pattern. Is the left side stretched out and the right side compressed?

Scott

[dvh99]

hi scott, the batteries of the camera are dead so i cannot post a pic at the moment but the pic i posted on page 49 is from a "white field", the linearity is ok btw.

[dvh99]

maybe this will work?

[tse]

Before you do any changes to the HDM I recommend using a means of extending the card out of the projector so you can get to what you need to get to. Disable the HV to save your tubes if disaster happens. The HDM provides a way to externally connect a variable DC power supply so gradual powering of the circuit while monitoring the results can be had. Making mods and just turning the projector on can be dangerous to the circuits and the tubes.

The below site has some good info on deflection circuits. It is not totally correct because the HV tansformer is not driven by the defelction circuits in projectors.

http://repairfaq.ece.drexel.edu/sam/deflfaq.htm

Scott

[dvh99]

thanks scott, that link is full of info.

[mutantaction]

Sorry to be demanding and stuff:) is there any way to get the pictures back in the thread?:

Thanks

[htguy1]

[htguy1]

One more thing, as winter approaches I am looking for new mods to make my pq better and lower video noise. I would like to buy the mosfets the caps I need to decouple the EL5166 and opa134 opamps on my neck cards and VIM (WHat are the best values/types to use? I'm a little rusty, as I have been out of the mod hobby for a while) How about power filtering for the various boards? ANy suggestions on parts to buy?

Thanks. I am looking forward to seeing the pq improve this winter.

God bless...
Mark

[Nashou66]

Those Parts are fine for the focus board. You might also need to change out the drivers for those, Q1,Q3, and Q5 that are 2N7000's.

Certain Bandwidths will put the resonant caps that the IRF520's control in or out of the circuit. You can see for sure if one or more of the IRF's are out by going into the internal frequency menu and trying all resolutions and see which ones are in focus across the
screen. If one resolution in sharp then that IRF is ok. When you find out what frequency is out then you now which IRF is bad or its corresponding driver. Another way you can test is to short the drain to source( I think that is what Scott told me I lost his email ) of the bad IRF. if the grids come into focus then you know its bad or the driver is. I never figured out what part was bad as I changed the driver and the IRF. The only thing i never thought to look at was the Zener diode that limits the Driver to I think 9 volts to open and close the gate of the Mosfet.

For de coupling the Op Amps there are several approaches. Some like to Stack a series of Surface mount caps on top of each other in a series of progressive increase in value. Starting for examle with a 100pf, 1nf, 10nf and then a 100nf. etc testing different values of that type of progression is how some do it. What Chris Stevens did was take two COG type 1uf caps(http://www.digikey.com/product-detail/en/CK06BX105K/1001-2031-MIL/2397510) twisted together and place them in parallel to the already existing 100nf SMT ceramic cap's used on the +/- 5 volt rails. Now I would also add a 22uf OsCon cap over the top of the Amps from + to - Pin's. I found OsCons are excellent for this . And this adding of the OsCons on most of the amps on all other boards really help. But it can get expensive so try to find deals on Ebay for the OsCons. I found some from a seller in China I think it was Jade electronics or something like that.

Hope this helps. I haven't been doing any work On PJ's lately and I do want to eventually get these pics back up once I host them somewhere.

Athanasios

[CxTurbo]

Nash,

Would 22uf 20v OSCON be ok for this purpose? I do no see any on the bay in a higher voltage.

For my own knowledge and making sure that I understand perfectly by stating +/- you are talking the power rails correct?
I am used to 12vdc automotive stuff and sometimes get confused with AC 8) getting better though.

My LVPS and HVPS are all done and working well thanks to you guys. Now on to the other boards. I will not be touching the CLM myself though. Still trying to find someone willing to do all the stuff you describe for me.


James

[dvh99]

i think he is talking about putting a oscon on top of the opamps.

i would exchange the opamps on the focus board for the tle2074 for instance or another low noise amp.

http://nl.mouser.com/ProductDetail/Texas-Instruments/TLE2074CN/?qs=sGAEpiMZZMtCHixnSjNA6CumnoLUElGjtkQTPuP%252bT7A%3d

[CxTurbo]

Yep, I understood the opamp part.

Maybe I worded it wrong. Is the cap placed across VCC- and VCC+ pins of the tle2071 or whatever opamp is used?

Adding the VCC- in there messes me up as I am used to 12vdc and only a + or - with - being ground. I am working on it though 8)

James

[Nashou66]

Hi James, For the 22uf 20v OsCon you would go from pin to pin on the opAmp, Don't put them on each coupling caps already there( the 100nf caps). So one 22uf cap for each Video OpAmp, the AD435 or 435 power rails and then the final Video OpAmp depending on what version VIM your working on. Also using those on all op amps and some other chips especially on the CLM, the CMM, and the Stig amp board help.

Athanasios

[CxTurbo]

Great Nash, Thanks for the clarification.

I looked again and could find 16v and 20v 22uf in large quantity. I have not looked at the volatge on the VCC- and VCC+ pins. I would think that the 16v would be a smaller size and the leads would work better on the opamp pins. Would there be issue with the 16v or should I just stick to 20v? Either way I will grab up all that I can to do all of the boards. I think I am going to tackle the VNB's and boards on the back sink next.

James

[htguy1]