Bugger.

I've been having a fairly minor issue with my XG-751, where the Red BIAS (black) level starts out too low and rises as the projector warms up. I've swapped out all the relevant boards - neckboard, Gain and Video Out, but no change. With AKB one it's fine, it only does it when it's off.

Anyway, the last piece in the puzzle is the HV board which has the G2 amps on it.

So I held my breath, set my Contrast at 25% Amplitude at -50%, and swapped the board for another HV board.

New HV board works fine, except 25% contrast is like 80% with the old board. Focus is shot to hell, and amplitude was wider.

So I ran it long enough to verify that the HV board is not causing my red drift (beginning to suspect the tube itself actually).


But when I put my original HV board in, it shuts down with a Fd error (HV protect). ARRGH!!

Put the spare back again and it works. The spare has it's HV adjust and protect pots exposed. And adjusting the HV so the focus is good sets off one of the protect circuits. Kinda weird actually - the amplitude is too wide like the HV is low. Focus gets better along with the amplitude decreasing as I increase HV, but the contrast is already through the roof at 25%, and the protect trips.



I can mimic the problem with the original board on the spare board by turning the HV up a tiny bit until the HV protect kicks in with an Fd. Starting the PJ in this state chucks an Fd before the HV fires up, just like the original board.


So I think there is 2 possibilities with the original board:

1. The removal/installation process damaged it. Gees I was careful though. Let it sit for a while before I removed it, treated it with kid gloves.

2. The protect circuit is hyper-sensitive and I've disturbed things enough to trigger it. Removing the covers over the HV adjust and turning the HV down a bit might let it fire up. Then I need to do the HV PWB replacement procedure in the service manual.

If that doesn't work I need to do the replacement procedure on the spare board. Anyone have any idea why the HV behaviour with this board seems to be Low HV (wide amplitude), but contrast is really high?

Either way, I need a HV probe now..



Any help (Doug? Curt? Sweetchuck? Russ? Anyone?) would be appreciated.

Yes, I should have left the damn thing alone...but I am learning. After this I will have done just about every setup procedure in the manual (except Focus Balance, I have NFI what that does).

Mark

You're not asking for my opinion but I'll give it anyways...:)

Varying HV, even by a few Kv will change width, height, focus and G2 levels. Check for bad solder joints all over the HV board, re and re-ing the board can cause bad ones to act up. I've had lots of bad joints on those boards.

As for the shifting black level, it could be the tube, that's a new one on me though. Have never had that problem before, sorry!

I can send you a HV probe , it's not mine so you will have to be quick , email me.

The protect pots are super sensitive , By the way if you set it as per the manual with everything cranked right up with a full white pattern at 32KV with the protect pot set right it will trip out and cause an error FD . This is it's purpose , to protect the tubes.

You're not asking for my opinion but I'll give it anyways...:)

Varying HV, even by a few Kv will change width, height, focus and G2 levels. Check for bad solder joints all over the HV board, re and re-ing the board can cause bad ones to act up. I've had lots of bad joints on those boards.

As for the shifting black level, it could be the tube, that's a new one on me though. Have never had that problem before, sorry!


Yes I did! :) But I did add you as a quick edit - I didn't put you in at the start as I know you need to keep a few things to yourself to protect your livelyhood.

I can send you a HV probe , it's not mine so you will have to be quick , email me.

The protect pots are super sensitive , By the way if you set it as per the manual with everything cranked right up with a full white pattern at 32KV with the protect pot set right it will trip out and cause an error FD . This is it's purpose , to protect the tubes.


Thanks - I'll try work for one, and if they don't have one I'll take you up on that offer.

They plug into a regular DMM right? A pair of Banana plugs for COM and Pos and an Alligator lead to ground to the chassis?

Did you try my suggestion of Freeze spray to isolate caps with Thermal coefficients ?

Try to keep your original board in as setting up HV and protect 1 & 2 is a major PITA . I agree with curt on bad solder joints .

Thanks - I'll try work for one, and if they don't have one I'll take you up on that offer.

They plug into a regular DMM right? A pair of Banana plugs for COM and Pos and an Alligator lead to ground to the chassis?


No this is a complete unit with a analog gauge , it will be setup for the XG already , dead easy to use, just use the insulation I provide or you will arc everywhere and have the smell of ozone in you nostrils all day :)

Yeah, I'll get the iron out.

You do stress the hell out of the board getting those big plugs to the HV supply on and off.


(Red rising issue: I didn't try the Freeze spray yet - I'm trying to isolate which board it is, before I do that. Once I get this HV issue sorted I'll start replacing boards I've already done once before...)

No this is a complete unit with a analog gauge , it will be setup for the XG already , dead easy to use, just use the insulation I provide or you will arc everywhere and have the smell of ozone in you nostrils all day :)

Thanks!!

I was planning on using an old HV lead on the splitter and connecting the probe to the other end of that - well away from the chassis (like 0.5m).

I'll let you guys know how I go with a bad solder joint first.

Probe goes down into hv block and insulation sleeve slides over it , use rubber gloves when attaching as residual charge lurks


http://i122.photobucket.com/albums/o255/sweetchuckzx/DSCF0035.jpg

Ouch....looks nasty...like something a cross between a Proctologist and Dr Frankenstein would use... :)

Bump, to see if Doug is around - see if he's had any trouble with removing and replacing a HV board, then getting an Fd error.

I'm going to resolder every joint on the board - I can't find any bad looking ones to the naked eye.

Then I'll change out a few of the tiny little transistors - there's a couple that fail.

Then I'll shorgun the lot and change all the little transistors.

Then I'll get an EE mate to take a look.

During the meanwhilst (python term) I'll try and recalibrate the spare HV board with Sweetchuck's alien anal probe ;)

Anything else I could try? Rain dance? Wait...don't want rain while playing with HV..

Mark,
Kinda sucks when your trying to isolate a problem and create another when theres no apparent reason for it.
Having one fail from removing and re installing I havent had but it is possible if you break a trace or connection. It does take some pressure to get the HK HL connectors on and off. I have installed a few and missed the HD connector under the wire loom and it didnt fire and I had two new defects.

When you put the board in you want to have a couple of screws in place to keep the traces from hitting the frame.

I dont reuse pots that have been sealed, I tried that before and destroyed them (at least on the PGs) maybe on the XG but in the past had them available. The HV pot is a different value then the protects 1-2. This procedure needs to be done exact noting the pre conditions for setting the voltages, IE: switches, test pattern and contrast values and reading the meter right. These boards are not intended to be swapped without being adjusted to the chassis itself. For newbies have this done for you.

The wave board focus pot adjustments with the existing HV board should fall in line if nothing has changed on that board. Will PM. Doug

Thanks Doug, got your PM and E-mail.

I didn't miss a connection, but yes it takes some effort to get the HK/HL connectors off - that's a possibility. I don't *think* I've broken a trace. I was very careful.

I've been checking for a leaky transistor, but in circuit it's kinda difficult.


Found a difference is some of the resistors for the beam current switch between a 751 and 1101/1351. Might explain my odd HV behaviour with the spare board (1101 board).

Thank heaps

Mark

Sweet :)

I'm up and running with the spare board.

I displayed an all-white image, and set the anode/beam current mode to the high. Well, the beam mode switch setting for high wasn't the highest. I have NFI what is going on there.

So I set the switches so my all white image was highest output, cranked up B and C and set the HV protects to 0.15v. It tripped out on me a lot, but I got them out of trouble.

Then I eeked up the HV until the focus snapped in, and checked the pots again. The HV protect is really touchy.

When I get the HV probe I'll do it properly again.

Doug, do you think there is any reason why they specify a NTSC all white pattern? Would that matter? (It's a pain compared to a PC test pattern at my normal res).


And I found an interesting difference between an XG 751 and the LC 1101/1351 in the schematic. 2 resistors in the anode/beam current circuit are different. I think they drive the LC models harder. So this may explain why my contrast was much higher for a given setting with this board. I'm going to pull the spare HV board and swap the resistors for the 751 values - as my whole G2/white balance settings are based on a 751 board.

Phew. Fun and games...oh well, I'm learning more about the chassis.

Good stuff , I,ll send my anal probe off Monday , just give it a quick clean after you have used it :D

I'll bet you a carton of Tooheys one of the small transistors in your board are stuffed , may have even been the start of you original symptoms .

Tooheys??? I'm supposed to respond with something about Victoria Bitter being a better beer...but it's swill so I won't ;)

I've measured a few in circuit and haven't found any shorted ones yet. I'll keep measuring..

How did you get the pot covers off? Did you unsolder them first, then start cutting around the pot?

Still have this niggling feeling that there's nothing actually wrong and it's just tripping out the protects. Maybe stressing the board to remove those big plugs moved the HV pot or protect pot despite the silicone. They seem really touchy...

Anyway I'll keep looking. I'd like my old board working again.

You think a transistor on the way out could cause red bias drift? I'll take a look at the circuit (I only get the gist of them, I'm not an EE/tech, I'm mech eng).

Thanks

Mark

The transistors wont be shorted they have integral resistors , as such can't be measured using the diode juction method of finding a .6v voltage drop with a DMM
.
Faulty resistors have a habit of slowly increasing resistance until pop they are open ,they are never short. Disturbing the board may have been the last straw for the faulty transistor , I'll bet you a carton of VB then :)
Just change them all , very impossible to troubleshoot these .

Oh yeah , also I did remove the pots first and cut around with stanley.
But why do this to your setup board , when you find the fault it will be cool :cool:

YAY!!

Got my old board working. Resoldered the pins for the big cables. Changed a couple of transistors, as sweetchuck sent me spares, and it works. Dunno what fixed it...don't care really.

Now I'm off to mod my spare 1101LC HV board, to set the anode current resistors the same as the 751 board.
I'll still swap that in and calibrate it with a HV probe - so I have a functional working spare.

Then I'll continue trying to track down my red bias drifting issue..fun eh?

Thanks for the help guys!

Mark

Glad you got that sorted, Mark! I felt bad giggling every time I saw your thread title -- yes, indeed, your XG *was* Fd after the board swap... :D

Transistors fixed it , Tooheys will be fine thanks :D

Do you still have the red bias drift problem ??


YAY!!

Got my old board working. Resoldered the pins for the big cables. Changed a couple of transistors, as sweetchuck sent me spares, and it works. Dunno what fixed it...don't care really.

Now I'm off to mod my spare 1101LC HV board, to set the anode current resistors the same as the 751 board.
I'll still swap that in and calibrate it with a HV probe - so I have a functional working spare.

Then I'll continue trying to track down my red bias drifting issue..fun eh?

Thanks for the help guys!

Mark

Ok, I successfully calibrated the spare HV board, after changing the 2 resistors near the Anode current switches to make it the same as the original board.

Turns out the HV level, which I set by looking for best focus, was EXACTLY 32kv - within 0.1kv, or about as good as it could get given the resolution of the HV meter.
Didn't even touch the HV pot, just checked it and set the protects. So if you have a known good starting point, you don't *have* to have a HV probe to swap HV boards. Just adjust it for best focus (and correct amplitude) and you're there.

But yes, my Red bias drifted high as the projector warmed up. However I let it warm and stored the AKB setting so I'll see how it behaves tomorrow. Everything is a tiny bit different with this HV board.

All this opening and closing and swapping boards has knocked the edge off my setup....trashed it completely really. Convergence and Focus both need work. Think I might do it over again, get the guys around if they are keen.

I gave an EE mate of mine (Xtra owner) a neckboard and Video Out and Gain boards, he's going to take a look - he helped me tonight as you need 4 hands to do this on the ceiling.

And I will also check the G2 test points and see if they move as it warms. Anyway, the red bias issue is an annoyance, it's not that bad.

I'll get your probe back shortly Sweetchuck, thanks heaps.

Mark

Hmm...I was watching it, then shut it down and took the cover off - to check G2 testpoints.

Fired it up and got Fd...consarnit..

Mucked around, turned the protect and HV pots all the way down...nup.

Unplugged and replugged the connections to the flyback and G2.....yep, fired up. I think I have a bad connection in the flyback leads.

So I redid the protects and HV adjust.....all over again.

Now I'm checking the G2 values in TEST and NORMAL to see if they move as the red level rises during warmup.

I think I will have to admit defeat on the red bias issue, and just get used to letting it warm up for 15 mins. All my Xtras have been rock solid, both convergence and colours, from turn on - no warm up needed, I've been spoiled.

In the last week I've changed:

- Video Out
- Gain
- HV board

And I had previously changed the neckboard. I'm psyching myself up to change it back to the original neckboard again, but with little hope, as that's why I changed it in the firstplace. I hate dropping the card cage on the ceiling.

There are no other boards in the video path, other than the motherboard, which is basically passive.

I guess it must be the tube...which is a new-old-stock NEC original tube with 120 hours on it.

Oh well, I've learned a lot. Aint nothing about an XG which scares me now :)

Mark,
If you keep it in the test position does the red oddity still happen? It could be the tube but I have only seen one do that on a blue from a Plus. I had one splitter go flakey after 10 minutes also. Doug

Can't tell.

In test mode, or with AKB enabled, it behaves itself. It's only with AKB off that red starts low and rises to normal in 15-20mins.

If I hit brightness to turn on AKB briefly at startup, it looks good for a little while, then red rises too far. I have to leave it be till it's warm.

G2 voltages don't change at all, in test or normal, AKB on or off.

For sanity sake you can remove the red tube and slide in a burned dud and see if it does the same, make sure its grounded. Dont have to drop the cage for that but still a PITB. Doug

On the Blue I had it did the same. Actually the SM says not to attempt the white balance until its ran for 20 minutes but something is going on. AKB should not take that long.

I only have spare AC tubes.

And I really don't want to disturb the setup. A lot of work, both mine and Russ's went in to that. If it is the tube, I'd still keep using it. It's too good to let a 15min warmup worry me *that* much.


The last thing I will try is putting the fans back to stock. I currently have the side fans reversed and extraction through the baseplate. All the temps are good (4 probes).
I will put it back as NEC intended. It might actually warm up quicker.

You can use the AC tube to test. Actually the SM says not to attempt the white balance until its ran for 20 minutes but something is going on. AKB should not take that long. Try a hair dryer to warm it. Doug

Im curious, was the red a 08?

Actually I could load up an AC red with magnetics - I have spare everything. Other than toe in, and flapping, I could get the LC tube back pretty close...

Retube on the ceiling..oh what fun..

I think I'll put the fans back to stock and try the hairdryer first!

Thanks Doug

Well, I had a couple of wins tonight :)

Figured out which lead was causing my intermittent Fd error - little one to the def board was stressed. Rerouting it seems to have fixed that up.

And swapping the fans back to NEC stock has almost eliminated the Red Bias drift. Now it gets to normal in about 6 mins, and only I would notice it at startup.

So to all those reversing fans and fitting plenum extraction - if you have colour warmup issues, this may be exacerbating the issue.

I also noticed how much the Def board fan contributes to the noise - it's a SHOCKER. I'm going to do something about that one - have to go and see what Kenny did. LOL, fiddling with the fans has caused me no end of grief, but here I am, contemplating it again. :)

Now to put my original scoped Video Out and Gain boards back in.

Mark