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post #31 of 48 Old 09-27-2010, 07:58 AM
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Hi,

Your HDM is overheating and causing the IGBT's(output drivers) to Oscillate. Try this- reduce your horizantal size by about 20% and run the unit. If you do not see the issue, the HDM is the cause. The problem usually only happens at higher scan rates( Are you running it above 960P?). check the rev. on HDM ( ie 07P, 08P, 09P 10P). There are certin revs that will not work with versions of machine code on the DPB( u7 ).

I hope this helps!
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post #32 of 48 Old 09-27-2010, 08:11 AM
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Have you re-soldered any of the drivers solder joints? I go through and reflow all solder for the output drivers and the width coils. Also check C50. That cap should be replaced with a new 220uf 160v cap.

Athanasios
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post #33 of 48 Old 09-27-2010, 09:05 AM
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Thanks projspecialist and Athanasios

I have touched up all of the solder joints on the HDM. I did swap and try another HDM and had the same problem.

projspecialist - yes, it seems to only happen at the higher scan rates. my board is a 08P rev. when the HDM is the hottest, by decreasing the hsize 25-30%, the problem goes away - the amount of hsize change is directly related to heat.

Athanasios - I'll have to check c50, but it may have been changed already

where are the IGBTs/output drivers located on the board? towards the heat sink side?

for 1080p, what's the typical hsize and retrace setting used? my settings let me get the most image on screen (but obviously are taxing the HDM)

thanks!

Brent
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post #34 of 48 Old 09-27-2010, 09:16 AM
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swapping VIM's, HDM's, CLM's, etc. has proven to be a dead end and it has taken up a lot of time too. I've never seen a bad MOBO in 7 years either.

from a wise EE
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Never underestimate what a flaky power supply can do. I learned long ago to always check the power supply. I'd be surprised if it isn't one of those three things.

the other 2 are DPB and HDM, both checked, re-checked, swapped,re-capped, you name it. The LVPS is all that's left.

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post #35 of 48 Old 09-27-2010, 09:18 AM
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Quote:
Originally Posted by brente View Post

Thanks projspecialist and Athanasios

I have touched up all of the solder joints on the HDM. I did swap and try another HDM and had the same problem.

projspecialist - yes, it seems to only happen at the higher scan rates. my board is a 08P rev. when the HDM is the hottest, by decreasing the hsize 25-30%, the problem goes away - the amount of hsize change is directly related to heat.

Athanasios - I'll have to check c50, but it may have been changed already

where are the IGBTs/output drivers located on the board? towards the heat sink side?

for 1080p, what's the typical hsize and retrace setting used? my settings let me get the most image on screen (but obviously are taxing the HDM)

thanks!

Brent


Hi Brent, the output drivers are clamped right to the heat sink. The heat sink is screwed tot he PCB. I would remove the heat sink and clean the insulator and then clean the backs of each output driver. Apply new Thermal heat sink compound and put them back on.

Also inspect the heat sink insulator to make sure there is no cracks or brakes on it where the IGBT's come into contact.

Having a better contact surface area to the insulator will help heat transfer better to the heat sink. You'll now for sue if the old compound was dried out.

Athnaasios
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post #36 of 48 Old 09-27-2010, 09:31 AM
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what is your retrace setting? Press" pic" on remote- option 8. It should be set to "short" for your setting of 1080P. Also, what version of u7 do you have? It will read 5.x...

This is a very common problem when the 08P board is pushed to it's size limits for horz deflection at higher scen rates. My guess is that both "08P "boards you have are somewhat damaged. There is an interaction between the DPB board and the deflection boards. The DPB board is pretty much the "heart" of this projector. It sends deflection signals to the larger HDM and Vertical deflection boards.
U7 is critical to some of this as there where issues with revs 5.4, and 5.5. Ideally, 5.6 is what you want to be using for home theater applications.There are newer versions, but the machine code for the revs above 5.6 are programmed for specific clients- mainly gov. and simulation work.
Your issue could either have been caused by issues on the DPB or a weak/ failing HDM- I have seen both cases.
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post #37 of 48 Old 09-27-2010, 09:41 AM
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Quote:
Originally Posted by projspecialist View Post

This is a very common problem when the 08P board is pushed to it's size limits for horz deflection at higher scen rates. My guess is that both "08P "boards you have are somewhat damaged.

one HDM is 08P and the other 07P. both behave the exact same way and the problem only occurs on short retrace and at operating temperature. at cold start (up to 2 hours normal run) or long retrace problem does not occur.

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post #38 of 48 Old 10-03-2010, 05:45 PM
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I just had this problem too. It was the daughter board on the HDM revision 07. I cleaned the daughter board, put it back on and now all is fine. I have an 08 board that did work but now doesn't also.

my .02
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post #39 of 48 Old 10-03-2010, 06:35 PM
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the only thing i can think of is the belly fans, i would try replacing them.
look for fans that have at least the same airflow and the voltage must be the same.
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post #40 of 48 Old 07-01-2012, 12:31 PM
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so finally got around to doing / testing the larger heatsink on the HMD for those cases where the horizontal deflection starts to Oscillate. I wanted to see how much of an improvement there was in temp. reduction. I never did figure out what went wrong with my Cree FET modified HDM or why it failed during testing, but this was something I always intended to do since this issue popped up on AVS for Ralpharch. Since then it has been posted by at least 3 or 4 other people.

It always seems to crop up in situations where 2 or more of the following situations exist

1) ceiling mounted configuration
2) high scan rates
3) picture set to "short retrace".
4) warm ambient temps (summer-time viewing)

What I did, and what i'm pretty sure VDC did as well, was to modify the focus amp sink and swap it over to the HDM. One of the 5 small fins needed to be milled off to clear some board top components. However the increase in overall surface area is significant and more importantly, the new fins are directly in the air-flow of the belly fan ( like they are on the FCM). I also applied new insulating tape since the tape needs to actually make a 90 degree turn at the top and go horizontally over the perpendicular fin for 3 or 4mm. This is because the tall FET's on the HDM actually touch the top of the factory heatsink and the FCM sink didn't have the tape extend as far.

I used Silicone coated KApton tape with a dielectric rupture strength of 7000 volts+ Dielectric Silicone paste as an added thermal conductor and electrical insulator. Here are the before /after temp's in different room conditions 64Khz horizontal sweep.

1) original 07P HDM factory heat-sink
start (ambient) 79F / Finish 148F = + 69 degree's

2) with new larger heat-sink
test 1
ambient 86F / Finish 134F = + 48 degrees
test 2
ambient 79 / finish 126 = + 47 degree's

So according to my calc's the new heatsink is shedding heat faster and reaching a steady state temp. that is 32% cooler than the original Electrohome factory version. the only issue I see with this modification is
a) you need a milling machine to modify the FCM sink
and
b) you need a bad FCM or maybe an old m8000 FCM donor board ot cannibalize the heat sink from. I'm sure the correct extrusion could be sourced as "new" but there would be a minimum order. Probably a 10 foot section is what most places want to sell + oversize shipping rates. however if your seeing this issue you have an option now
450

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post #41 of 48 Old 07-19-2012, 11:28 PM
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To me this kind of wonky oscillatory behavior would make me want to look for defective and/or overheated op-amp (or some component in the feedback portion of the op-amp circuit) or an open somewhere in the path.

Here's the thing I notice about your pic: the oscillations aren't centered on top of where the lines normally appear (sans-oscillation.) It's like your keystone adjustment dies when oscillations start. (See pic below.) Also, even though your h-scan is obviously messed up, except for the oscillations the horizontal scanning seems perfectly normal. Thus, I'd want to trace the keystone circuit and blame whatever it consists of...



It occurred after writing this that it's easy to know if this is the part of the circuit that's giving you problems. (...so here I am inserting this line.) Turn on the PJ, wait for this problem to hit, and try adjusting your keystone setting. Does the keystone still work? (Obviously there will be oscillations, but you should still be able to see obvious keystoning adjustment if it is still working properly.) If so, I'm almost certainly wrong and you can forget this post. If not, your problem is here... read on!

Acording to the service manual, the keystone signal is actually controlled by the VDM. (Page HDM-5). This signal is common to all three tubes, so that feature is consistent.

The keystone and pincushion signals are sourced at DAC U8 and get summed on the VDM using op-amp U701. (00-263330-02P.pdf) One possibility is that this op-amp is defective. Another is that the connection between the OP-AMP and DAC is bad leaving an input to the op-amp floating.

The signal then leaves via pin KEY-PIN on PA13/PC13 pin 13 to the Upper Mother Board and travels to the HDM via pin JC12/JA12 pin 15 (00-260358-02P.pdf)

On the HDM, JC12/JA12 become PC12/PA12 pin 15 and appears as KEY&PIN instead of KEY-PIN.

It is fed through multiplier U18 and summed with other signals using the 4 amps in U17. Again, U17 could be bad or have a floating input.

After that it is summed with H-DRIVE using U6, and as I've already said, your overall H-pattern seems fine, so my guess is the problem is not in U6 or beyond. A situation where a component superimposes an oscillation on top of an otherwise good signal seems unlikely to me, and, as you pointed out, it has to be somewhere in the signal chain that effects all three tubes in the same way. This whole chain ends with the generation of the B- supply, common to all three tubes; after that, I don't think there's anything common between them.

What's more, the multiplier RC4200 could be the cause of the oscillation amplitude decreasing as the scan goes down the screen. (I don't know what B-FDBK looks like, but if it's a ramp from top to bottom and KEY&PIN is oscillating, the output you are getting would make sense.)

If this is the problem, I'd start by cleaning and reseat the VDM harness. (I don't know if a floating KEY-PIN could lead to oscillations, but it's worth a shot.)

If I had swap boards available, I'd swap the VDM to be certain the board wasn't feeding the bad signal via KEY-PIN in addition to the obvious HDM swap.

If I didn't have swap boards available, I'd scope the KEY-PIN output from the VDM as it's accessible without an extension board. Without a scope and with no possibility of swap boards, I'd resolder VDM U8 and U701 and U18 on the HDM. If that didn't do it, I'd replace U701 on the VDM and U18 on the HDM.

Trickier is to check the intermittent connectivity issues between the VDM harness and JC12/JA12 pin 15. You'd have to scope the HDM KEY&PIN line with the PJ on. Not sure how I'd go about this, frankly... probably solder a shielded wire to the line and run it outside the PJ to scope it.

Hmm. Quick calculation. C93 is 47 uF. It looks like there are about 10 lines per oscillation. If your horizontal scanrate is 45 khz (720p), that's an oscillation frequency of about 4.5 khz or about 28k rad/sec. 28000 = sqrt(1/LC)... 1/(28000^2) = LC, if C = 47uf, L = .00003H, or 30uH. That's seems high, like you'd need about 30 meters of wire for the VDM harness to get that. Then again, I did just pull about 4 numbers out of my butt. So...

A pure SWAG would one of the two op-amps is defective. It doesn't seem like the inductance would be high enough for a loose connection to form the right frequency oscillation with a 47uF cap. I don't know for sure. I'm just sloshing numbers around to see if I hit anything interesting.

One way to solve this is to go looking through the relevant circuit sections looking for something that could reasonably form a time constant of about 30k rad per second, but I don't think that's less work than what I've already outlined.

Out of pure curiosity I'd love to know what the source horizontal rate in the picture you took is and how many scan lines per oscillation it is so I can accurately compute the frequency of oscillation. Of course, I'm a geek that way.

ugh OMG I just realized you bumped a two year old thread.

Chiem

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Hey, what's this silly piece for? Eh, we don't need that. *ZAAAAP!*
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post #42 of 48 Old 07-22-2012, 07:10 AM
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Are you absolutely sure that all three belly fans are spinning. Even if the one under the focus board stops, it can cause this.

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post #43 of 48 Old 07-26-2012, 09:28 AM
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Chiem, lots of good info there but out of the half-dozen or more people who had this problem not one mentioned a KEystone problem. I have not been able to reporduce it on my bench so still some things kind of hanging out there.
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Are you absolutely sure that all three belly fans are spinning. Even if the one under the focus board stops, it can cause this.
Curt the belly fans have been covered to death. smile.gif yes, they were all spinning in all cases.
i'm still waiting for the results from the larger heat-sink but I had another customer with a heat issue (non-osciallting but just running hot) who reversed the direction of the belly fans on his ceiling mounted Marquee. They blow up now instead of down, and he's reported excellent results AFA how hot the machine gets.
I think it's obvious the marquee was really designed primarily as a "wheeled cart" presentation and fans blowing up from the bottom, so reversing the fans with a ceiling mounted app makes sense. AAMOF I'm surprised they didn't tie in a simple fan-reversal circuit to the scan-reversal feature.

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post #44 of 48 Old 07-28-2012, 10:39 PM
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I was using the projector for a number of hours tonight and the oscillations started to occur. I did try the keystone adustment and, sure enough, when I was within a keystone setting from 15-19 (my setting is at 18), the oscillations occurred. If I went above or below that range, the oscillations went away...

Chiem - to answer your question about scan rate, my guess is that the video source was 1080p with horizontal scan rate of 67.5kHz
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post #45 of 48 Old 10-22-2012, 01:58 PM
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some bad news. Despite the drop in operating temperature I recorded the larger heat-sink I installed did not in fact cure the problem for this particular case. I had explained that there was a good chance the problem would be fixed but there was no way to guarantee this and it would have to be a "try it and see" type arrangement. Still, I'm really bummed out, hate to fail
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I have only put about 5 hours on the projector since I received everything back. Im very happy with your work, thanks.
>
> The problem is not resolved. The first few hours were perfect, and I thought it had gone away, but it hasn't unfortunately.
>
> I haven't had a chance to do some digging on the issue yet.
Since Brent has shown the Keystone is in fact an issue here (way to go Chiem), then I wonder if something can be done to that circuit to mitigate the issue.

Although I suspect the real issue is a bunching of scan lines in the keystoned area , there by placing more load on the deflection circuit similar to short retrace, as opposed to an actual problem in the keystone circuit itself.

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post #46 of 48 Old 10-23-2012, 12:28 PM
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Should start doing g90 mods...
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post #47 of 48 Old 10-23-2012, 06:47 PM
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I wonder what the software on his CLM/DPB is and if matches the HDM's software since some Marquees should
have matching software like my Longbows. If i put in a different Ultra CLM with non LB software I get weird results.

Wish we had a list of matching CLM/DP to HDM software versions.

Athanasios
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post #48 of 48 Old 10-24-2012, 02:35 PM
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this is an issue with the big power FET's Nash, of that I have little doubt. Dennis had this exact same problem and his Cree FET modification cured it completely. Unfortunately it causes uneven screen brightness, so while it's a really cool modification all in all it doesn't appear to be an ideal solution.
Now there might be a way to do something with the Key circuit and reduce the load on the FET's, don't know just throwing out idea's.
Has anyone looked at a more robust direct replacement FET? So instead of modifying the entire circuit just dropping in a higher duty rated part?

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